Steven Shoelson | Harvard Medical School (original) (raw)

Papers by Steven Shoelson

Research paper thumbnail of The Impact of Salsalate Treatment on Serum Levels of Advanced Glycation End Products in Type 2 Diabetes

Diabetes Care, 2014

OBJECTIVE Salsalate is a nonacetylated salicylate that lowers glucose levels in people with type ... more OBJECTIVE Salsalate is a nonacetylated salicylate that lowers glucose levels in people with type 2 diabetes (T2D). Here we examined whether salsalate also lowered serum-protein-bound levels of early and advanced glycation end products (AGEs) that have been implicated in diabetic vascular complications. RESEARCH DESIGN AND METHODS Participants were from the Targeting Inflammation Using Salsalate for Type 2 Diabetes (TINSAL-T2D) study, which examined the impact of salsalate treatment on hemoglobin A1c (HbA1c) and a wide variety of other parameters. One hundred eighteen participants received salsalate, 3.5 g/day for 48 weeks, and 109 received placebo. Early glycation product levels (HbA1c and fructoselysine [measured as furosine]) and AGE levels (glyoxal and methylglyoxal hydroimidazolones [G-(1)H, MG-(1)H], carboxymethyllysine [CML], carboxyethyllysine [CEL], pentosidine) were measured in patient serum samples. RESULTS Forty-eight weeks of salsalate treatment lowered levels of HbA1c and serum furosine (P < 0.001) and CML compared with placebo. The AGEs CEL and G-(1)H and MG-(1)H levels were unchanged, whereas pentosidine levels increased more than twofold (P < 0.001). Among salsalate users, increases in adiponectin levels were associated with lower HbA1c levels during follow-up (P < 0.001). Changes in renal and inflammation factor levels were not associated with changes in levels of early or late glycation factors. Pentosidine level changes were unrelated to changes in levels of renal function, inflammation, or cytokines. CONCLUSIONS Salsalate therapy was associated with a reduction in early but not late glycation end products. There was a paradoxical increase in serum pentosidine levels suggestive of an increase in oxidative stress or decreased clearance of pentosidine precursor.

Research paper thumbnail of P408 LIVER-SPECIFIC IKK-β ACTIVATION SEVERELY AGGRAVATES ATHEROSCLEROSIS DEVELOPMENT IN APOE*3-LEIDEN MICE

Atherosclerosis Supplements, 2010

Research paper thumbnail of Evidence for the presence of somatostatin 28 in plasma

Research paper thumbnail of The Insulin Receptor Juxtamembrane Region Contains Two Independent Tyrosine/#Turn Internalization Signals

We have investigated the role of tyrosine residues in the insulin receptor cytoplasmic juxtamem- ... more We have investigated the role of tyrosine residues in the insulin receptor cytoplasmic juxtamem- brahe region (Tyr953 and Tyro) during endocytosis. Analysis of the secondary structure of the juxtarnem- brahe region by the Chou-Fasman algorithms predicts that both the sequences GPLY953 and NPEY~ form tyrosine-containing E-turns. Similarly, analysis of model peptides by 1-D and 2-D NMR show that these sequences

Research paper thumbnail of Substitution of the insulin receptor transmembrane domain with the c-neu/erbB2 transmembrane domain constitutively activates the insulin receptor kinase in vitro

The Journal of biological chemistry, Jan 25, 1992

To examine the role of the transmembrane domain (TM) of the insulin receptor in insulin-induced r... more To examine the role of the transmembrane domain (TM) of the insulin receptor in insulin-induced receptor kinase activation, we prepared four mutated insulin receptors: 1) a Val938----Asp substitution (IR/TMv----D), 2) insertion of a 3-amino acid repeat (Val938-Phe939-Leu940) (IR/TM+3), or the entire TM was replaced by the corresponding domain of either the 3) platelet-derived growth factor (PDGF) receptor (IR/TMPDGFR) or 4) c-neu/erbB2 proto-oncogene product (IR/TMc-neu). Each mutant receptor was stably expressed in Chinese hamster ovary cells, assessed by fluorescence-activated cell sorting, insulin binding, and biosynthetic labeling. All mutant receptors exhibited normal affinity for insulin. Pulse-chase experiments showed that each proreceptor was processed into alpha- and beta-subunits, although the rate of IR/TMV----D conversion was reduced approximately 3-fold. With IR/TMPDGFR, IR/TMV----D, and IR/TM+3 basal and insulin-stimulated levels of autophosphorylation and tyrosine kin...

Research paper thumbnail of Cellular effects of phosphotyrosine-binding domain inhibitors on insulin receptor signaling and trafficking

Molecular and cellular biology, 1997

Shc and insulin receptor substrate 1 (IRS-1) are cytoplasmic substrates of tyrosine kinase recept... more Shc and insulin receptor substrate 1 (IRS-1) are cytoplasmic substrates of tyrosine kinase receptors that engage, localize, and activate downstream SH2 enzymes. Each contains a phosphotyrosine-binding (PTB) domain that is structurally unrelated to SH2 domains. We have designed high-affinity, cellular inhibitors of the Shc PTB domain by incorporating nonnatural, phosphatase-resistant amino acids into short peptides. None of the inhibitors bind the IRS-1 PTB domain, consistent with distinct specificities for domains. The best inhibitor of the Shc domain was introduced by electroporation into Rat1 fibroblasts that express human insulin receptors. Insulin-stimulated phosphorylation of Shc was inhibited, with no effect on IRS-1, and downstream effects on mitogen-activated protein kinase and DNA synthesis were both inhibited. The PTB domain inhibitor had less influence on epidermal growth factor-induced effects and essentially no impact on serum- or phorbol ester-induced effects. The inhi...

Research paper thumbnail of Tyrosine-phosphorylated Cbl binds to Crk after T cell activation

Journal of immunology (Baltimore, Md. : 1950), 1996

Crk is a Src homology 2 (SH2)/Src homology 3 (SH3)-containing adapter protein that has been impli... more Crk is a Src homology 2 (SH2)/Src homology 3 (SH3)-containing adapter protein that has been implicated in intracellular signaling in fibroblasts and PC12 pheochromocytoma cells. Crk has been shown to bind to a tyrosine-phosphorylated protein of 116 kDa after TCR-mediated T cell activation. Here we demonstrate that the Crk-associated p116 phosphoprotein is not the Crk-associated substrate (Cas) but, rather, is a protein product of the c-cbl proto-oncogene. Whereas Cas was not tyrosine-phosphorylated after T cell activation, Cbl became highly phosphorylated. Crk immunoprecipitates from activated T cell lysates contain tyrosine-phosphorylated Cbl. This association is mediated by the SH2 domain of Crk, as evidenced by the interaction between Cbl and the fusion protein product of a glutathione S-transferase (GST) expression construct encoding the Crk-SH2 domain in vitro. Furthermore, phosphopeptide-binding studies revealed that the GST-Crk SH2 domain binds to a tyrosine-phosphorylated pe...

Research paper thumbnail of Structural basis for IL-4 receptor phosphopeptide recognition by the IRS-1 PTB domain

Nature structural biology, 1996

We present the NMR structure of the PTB domain of insulin receptor substrate-1 (IRS-1) complexed ... more We present the NMR structure of the PTB domain of insulin receptor substrate-1 (IRS-1) complexed to a tyrosine-phosphorylated peptide derived from the IL-4 receptor. Despite the lack of sequence homology and different binding specificity, the overall fold of the protein is similar to that of the Shc PTB domain and closely resembles that of PH domains. However, the PTB domain of IRS-1 is smaller than that of Shc (110 versus 170 residues) and binds to phosphopeptides in a distinct manner. We explain the phosphopeptide binding specificity based on the structure of the complex and results of site-directed mutagenesis experiments.

Research paper thumbnail of Crystal structure of the PI 3-kinase p85 amino-terminal SH2 domain and its phosphopeptide complexes

Nature structural biology, 1996

Crystal structures of the amino-terminal SH2 domain of the p85alpha subunit of phosphatidylinosit... more Crystal structures of the amino-terminal SH2 domain of the p85alpha subunit of phosphatidylinositol (PI) 3-kinase, alone and in complex with phosphopeptides bearing pTyr-Met/Val-Xaa-Met motifs, show that phosphopeptides bind in the two-pronged manner seen in high-affinity Lck and Src SH2 complexes, with conserved interactions between the domain and the peptide segment from phosphotyrosine to Met+3. Peptide binding requires the rearrangement of a tyrosyl side chain in the BG loop to create the hydrophobic Met+3 binding pocket. The structures suggest a mechanism for the biological specificity exhibited by PI 3-kinase in its interactions with phosphoprotein partners.

Research paper thumbnail of Insulin receptor autophosphorylation occurs asymmetrically

The Journal of biological chemistry, Jan 25, 1993

The unoccupied insulin receptor is a structurally symmetric, disulfide-linked dimer, comprising t... more The unoccupied insulin receptor is a structurally symmetric, disulfide-linked dimer, comprising two alpha beta halves, each with a potential insulin binding alpha subunit and a kinase active beta subunit. In the accompanying paper (Shoelson, S. E., Lee, J., Lynch, C. S., Backer, J. M., and Pilch, P. F. (1993) J. Biol. Chem. 268, 4085-4091), we described the utility of a novel insulin analogue, L-benzoylphenylalanineB25,B29 epsilon-biotin insulin (BBpa insulin)1 as a probe for receptor behavior, and we determined that binding and cross-linking of one BBpa insulin molecule could fully stimulate insulin receptor autophosphorylation. Here we use this analogue to determine the symmetry of the autophosphorylation reaction. The alpha beta half-receptor that does not covalently couple to BBpa insulin incorporates 50% more orthophosphate than the alpha beta half that becomes coupled to the insulin analogue. Phosphopeptide mapping of each receptor half shows minimal differences in the phospho...

Research paper thumbnail of Phosphoinositide 3-kinase is activated by phosphopeptides that bind to the SH2 domains of the 85-kDa subunit

The Journal of biological chemistry, Jan 5, 1993

Tyrosine-phosphorylated peptides based on the regions of polyoma virus middle t antigen and the p... more Tyrosine-phosphorylated peptides based on the regions of polyoma virus middle t antigen and the platelet-derived growth factor receptor that bind phosphoinositide 3-kinase are shown to activate this enzyme 2-3-fold in vitro. The concentrations of the peptides required to activate the enzyme are at least 10-1000-fold higher than the dissociation constants of these peptides for the individual SH2 domains of the 85-kDa subunit (KD < 100 nM). Doubly phosphorylated peptides are more effective than singly phosphorylated peptides. The results suggest that a fraction of the cellular phosphoinositide 3-kinase has SH2 domains with relatively low affinity for phosphopeptides and that binding of phosphopeptides to these enzymes causes activation. Thus, SH2 domains may be involved not only in recruiting the enzyme but also in regulating activity.

Research paper thumbnail of A photoaffinity scan maps regions of the p85 SH2 domain involved in phosphoprotein binding

The Journal of biological chemistry, Jan 15, 1993

Src homology 2 (SH2) domains are modular phosphotyrosine binding pockets found within a wide vari... more Src homology 2 (SH2) domains are modular phosphotyrosine binding pockets found within a wide variety of cytoplasmic signaling molecules. Here we develop a new approach to analyzing protein-protein interfaces termed photoaffinity scanning, and apply the method to map regions of the phosphatidylinositol 3-kinase p85 SH2 domain that participate in phospho-protein binding. Each residue except phosphotyrosine (pY) within a tightly binding, IRS-1-derived phosphopeptide (GNGDpYMPMSPKS) was substituted with the photoactive amino acid, benzoylphenylalanine (Bpa). Whereas most substitutions had little effect on binding affinity, Bpa substitution of either Met (+1 and +3 with respect to pY) reduced affinity 50-100-fold to confirm their importance in the pYMXM recognition motif. In three cases photolysis of SH2 domain/Bpa phosphopeptide complexes led to cross-linking of > 50% of the SH2 domain; cross-link positions were identified by microsequence, amino acid composition, and electrospray ma...

Research paper thumbnail of Structure of the regulatory domains of the Src-family tyrosine kinase Lck

Nature, Jan 21, 1994

The kinase p56lck (Lck) is a T-lymphocyte-specific member of the Src family of non-receptor tyros... more The kinase p56lck (Lck) is a T-lymphocyte-specific member of the Src family of non-receptor tyrosine kinases. Members of the Src family each contain unique amino-terminal regions, followed by Src-homology domains SH3 and SH2, and a tyrosine kinase domain. SH3 and SH2 domains mediate critical protein interactions in many signal-transducing pathways. They are small, independently folded modules of about 60 and 100 residues, respectively, and they are often but not always found together in the same molecule. Like all nine Src-family kinases (reviewed in ref. 3), Lck is regulated by phosphorylation of a tyrosine in the short C-terminal tail of its catalytic domain. There is evidence that binding of the phosphorylated tail to the SH2 domain inhibits catalytic activity of the kinase domain and that the SH3 and SH2 domains may act together to effect this regulation. Here we report the crystal structures for a fragment of Lck bearing its SH3 and SH2 domains, alone and in complex with a phos...

Research paper thumbnail of Polyoma virus middle T antigen-pp60c-src complex associates with purified phosphatidylinositol 3-kinase in vitro

The Journal of biological chemistry, Jan 15, 1992

Reconstitution of the polyoma virus middle T antigen (mT)-pp60-src complex and phosphatidylinosit... more Reconstitution of the polyoma virus middle T antigen (mT)-pp60-src complex and phosphatidylinositol 3-kinase (PtdIns 3-kinase) has been accomplished in vitro with immunopurified baculovirus-expressed mT-pp60c-src and PtdIns 3-kinase purified from rat liver. Both the 110- and 85-kDa subunits of the PtdIns 3-kinase associated with the mT-pp60c-src complex. The association of PtdIns 3-kinase with the mT-pp60c-src complex was dependent on the protein-tyrosine kinase activity of pp60c-src as a kinase-inactive mutant (pp60(295c-src)) still complexed with mT, but the mT-pp60(295c-src)) complex was unable to bind PtdIns 3-kinase. The mT-pp60c-src complex phosphorylated both subunits of PtdIns 3-kinase on tyrosine residues. The immunopurified mT-pp60c-src complex also associated with PtdIns 3-kinase activity from whole cell lysates, and this association was dependent upon the protein-tyrosine kinase activity of pp60c-src. Comparison of 35S-labeled proteins from whole cell lysates which assoc...

Research paper thumbnail of Regulation of diet-induced adipose tissue and systemic inflammation by salicylates and pioglitazone

PloS one, 2013

It is increasingly accepted that chronic inflammation participates in obesity-induced insulin res... more It is increasingly accepted that chronic inflammation participates in obesity-induced insulin resistance and type 2 diabetes (T2D). Salicylates and thiazolidinediones (TZDs) both have anti-inflammatory and anti-hyperglycemic properties. The present study compared the effects of these drugs on obesity-induced inflammation in adipose tissue (AT) and AT macrophages (ATMs), as well as the metabolic and immunological phenotypes of the animal models. Both drugs improved high fat diet (HFD)-induced insulin resistance. However, salicylates did not affect AT and ATM inflammation, whereas Pioglitazone improved these parameters. Interestingly, HFD and the drug treatments all modulated systemic inflammation as assessed by changes in circulating immune cell numbers and activation states. HFD increased the numbers of circulating white blood cells, neutrophils, and a pro-inflammatory monocyte subpopulation (Ly6C(hi)), whereas salicylates and Pioglitazone normalized these cell numbers. The drug tre...

Research paper thumbnail of Insulin biosynthesis, processing, and chemistry

Research paper thumbnail of Shf, a Shb-like adapter protein, is involved in PDGF-α-receptor regulation of apoptosis

Research paper thumbnail of Circulating forms of somatostatinlike immunoreactivity in human plasma

Circulating forms of somatostatinlike immunoreactivity (SLI) in humans were characterized using s... more Circulating forms of somatostatinlike immunoreactivity (SLI) in humans were characterized using several chromatographic techniques. After gelfiltration chromatography on Bio-Gel P-6 columns greater than 90% of circulating SLI was of high molecular weight (MW) and eluted in the void volume. When plasma samples were passed through protein A-Sepharose columns, more than 85% of the high MW SLI was removed, indicating that this form of plasma SLI is mainly due to cross-reacting immunoglobulins. Extraction of 10-ml plasma samples from normal subjects on octadecyl silyl silica cartridges eliminated the high MW material. In addition, this extraction technique concentrated the two lower MW forms of SLI, which coelute on gel filtration chromatography with somatostatin-28 (S-28) and the tetradecapeptide form of somatostatin (S-14), respectively. Extracted plasma SLI was further analyzed by high-pressure liquid chromatography (HPLC). The results confirmed the identity of S-28 and demonstrated that S-14 is converted, in part, to Des-Alasomatostatin (S-13) following secretion into the circulation. At least four forms of SLI are thus present in human plasma: cross-reacting immunoglobulins, S-28, S-14, and S-13. Concentrations of SLI forms in the plasma of normal controls and patients with renal failure or cirrhosis were measured to assess the role of circulating somatostatin in health and disease. High MW SLI was elevated above normal in the plasma of patients with cirrhosis, but was not significantly elevated in patients with chronic renal failure. On the other hand, concentrations of plasma S-28 and S-13/14 (total concentrations of S-13 plus S-14) were elevated in patients with either chronic renal failure or cirrhosis.

Research paper thumbnail of Solid-phase synthesis of nonhydrolyzable phosphotyrosyl peptide analogues with N α-Fmoc-(O, O-di-t-butyl) phosphono-p-methylphenylalanine

Research paper thumbnail of Nonphosphorylatable substrate analogs selectively block autophosphorylation and activation of the insulin receptor, epidermal growth factor receptor, and pp60v-src kinases

The receptors for insulin and epidermal growth factor undergo tyrosine autophosphorylation in res... more The receptors for insulin and epidermal growth factor undergo tyrosine autophosphorylation in response to ligand stimulation, while pp60v-src is an unregulated tyrosine kinase. In this report we show that each of the kinases phosphorylates an exogenous peptide that corresponds to the insulin proreceptor sequence 1142-1153. When the kinases were pre-phosphorylated, saturable Michaelis-Menten kinetics were observed. However, when the kinases had not been pre-phosphorylated biphasic kinetics were observed; at progressively higher substrate concentrations (greater than Km) less substrate phosphorylation was seen. Furthermore, when the kinases had not been pre-phosphorylated kinase autophosphorylation was inhibited at high substrate concentrations. On this basis we postulated that the substrate inhibition of substrate phosphorylation resulted directly from substrate inhibition of kinase autophosphorylation. To test this we designed additional peptides to function specifically as inhibitors of the kinases. Each of the 3 tyrosine residues within the substrate sequence were replaced either by 4-methoxyphenylalanine or phenylalanine, residues structurally similar to tyrosine but unable to accept phosphoryl transfer. Both analogs inhibited insulin and epidermal growth factor receptor autophosphorylation, whereas only the Phe-substituted analog inhibited pp60v-src phosphorylation. These data suggest that autophosphorylation of tyrosine residues near the kinase active site is a generalized mechanism for tyrosine kinase activation and that activation can be selectively blocked by substrates and nonphosphorylatable analogs.

Research paper thumbnail of The Impact of Salsalate Treatment on Serum Levels of Advanced Glycation End Products in Type 2 Diabetes

Diabetes Care, 2014

OBJECTIVE Salsalate is a nonacetylated salicylate that lowers glucose levels in people with type ... more OBJECTIVE Salsalate is a nonacetylated salicylate that lowers glucose levels in people with type 2 diabetes (T2D). Here we examined whether salsalate also lowered serum-protein-bound levels of early and advanced glycation end products (AGEs) that have been implicated in diabetic vascular complications. RESEARCH DESIGN AND METHODS Participants were from the Targeting Inflammation Using Salsalate for Type 2 Diabetes (TINSAL-T2D) study, which examined the impact of salsalate treatment on hemoglobin A1c (HbA1c) and a wide variety of other parameters. One hundred eighteen participants received salsalate, 3.5 g/day for 48 weeks, and 109 received placebo. Early glycation product levels (HbA1c and fructoselysine [measured as furosine]) and AGE levels (glyoxal and methylglyoxal hydroimidazolones [G-(1)H, MG-(1)H], carboxymethyllysine [CML], carboxyethyllysine [CEL], pentosidine) were measured in patient serum samples. RESULTS Forty-eight weeks of salsalate treatment lowered levels of HbA1c and serum furosine (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001) and CML compared with placebo. The AGEs CEL and G-(1)H and MG-(1)H levels were unchanged, whereas pentosidine levels increased more than twofold (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001). Among salsalate users, increases in adiponectin levels were associated with lower HbA1c levels during follow-up (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001). Changes in renal and inflammation factor levels were not associated with changes in levels of early or late glycation factors. Pentosidine level changes were unrelated to changes in levels of renal function, inflammation, or cytokines. CONCLUSIONS Salsalate therapy was associated with a reduction in early but not late glycation end products. There was a paradoxical increase in serum pentosidine levels suggestive of an increase in oxidative stress or decreased clearance of pentosidine precursor.

Research paper thumbnail of P408 LIVER-SPECIFIC IKK-β ACTIVATION SEVERELY AGGRAVATES ATHEROSCLEROSIS DEVELOPMENT IN APOE*3-LEIDEN MICE

Atherosclerosis Supplements, 2010

Research paper thumbnail of Evidence for the presence of somatostatin 28 in plasma

Research paper thumbnail of The Insulin Receptor Juxtamembrane Region Contains Two Independent Tyrosine/#Turn Internalization Signals

We have investigated the role of tyrosine residues in the insulin receptor cytoplasmic juxtamem- ... more We have investigated the role of tyrosine residues in the insulin receptor cytoplasmic juxtamem- brahe region (Tyr953 and Tyro) during endocytosis. Analysis of the secondary structure of the juxtarnem- brahe region by the Chou-Fasman algorithms predicts that both the sequences GPLY953 and NPEY~ form tyrosine-containing E-turns. Similarly, analysis of model peptides by 1-D and 2-D NMR show that these sequences

Research paper thumbnail of Substitution of the insulin receptor transmembrane domain with the c-neu/erbB2 transmembrane domain constitutively activates the insulin receptor kinase in vitro

The Journal of biological chemistry, Jan 25, 1992

To examine the role of the transmembrane domain (TM) of the insulin receptor in insulin-induced r... more To examine the role of the transmembrane domain (TM) of the insulin receptor in insulin-induced receptor kinase activation, we prepared four mutated insulin receptors: 1) a Val938----Asp substitution (IR/TMv----D), 2) insertion of a 3-amino acid repeat (Val938-Phe939-Leu940) (IR/TM+3), or the entire TM was replaced by the corresponding domain of either the 3) platelet-derived growth factor (PDGF) receptor (IR/TMPDGFR) or 4) c-neu/erbB2 proto-oncogene product (IR/TMc-neu). Each mutant receptor was stably expressed in Chinese hamster ovary cells, assessed by fluorescence-activated cell sorting, insulin binding, and biosynthetic labeling. All mutant receptors exhibited normal affinity for insulin. Pulse-chase experiments showed that each proreceptor was processed into alpha- and beta-subunits, although the rate of IR/TMV----D conversion was reduced approximately 3-fold. With IR/TMPDGFR, IR/TMV----D, and IR/TM+3 basal and insulin-stimulated levels of autophosphorylation and tyrosine kin...

Research paper thumbnail of Cellular effects of phosphotyrosine-binding domain inhibitors on insulin receptor signaling and trafficking

Molecular and cellular biology, 1997

Shc and insulin receptor substrate 1 (IRS-1) are cytoplasmic substrates of tyrosine kinase recept... more Shc and insulin receptor substrate 1 (IRS-1) are cytoplasmic substrates of tyrosine kinase receptors that engage, localize, and activate downstream SH2 enzymes. Each contains a phosphotyrosine-binding (PTB) domain that is structurally unrelated to SH2 domains. We have designed high-affinity, cellular inhibitors of the Shc PTB domain by incorporating nonnatural, phosphatase-resistant amino acids into short peptides. None of the inhibitors bind the IRS-1 PTB domain, consistent with distinct specificities for domains. The best inhibitor of the Shc domain was introduced by electroporation into Rat1 fibroblasts that express human insulin receptors. Insulin-stimulated phosphorylation of Shc was inhibited, with no effect on IRS-1, and downstream effects on mitogen-activated protein kinase and DNA synthesis were both inhibited. The PTB domain inhibitor had less influence on epidermal growth factor-induced effects and essentially no impact on serum- or phorbol ester-induced effects. The inhi...

Research paper thumbnail of Tyrosine-phosphorylated Cbl binds to Crk after T cell activation

Journal of immunology (Baltimore, Md. : 1950), 1996

Crk is a Src homology 2 (SH2)/Src homology 3 (SH3)-containing adapter protein that has been impli... more Crk is a Src homology 2 (SH2)/Src homology 3 (SH3)-containing adapter protein that has been implicated in intracellular signaling in fibroblasts and PC12 pheochromocytoma cells. Crk has been shown to bind to a tyrosine-phosphorylated protein of 116 kDa after TCR-mediated T cell activation. Here we demonstrate that the Crk-associated p116 phosphoprotein is not the Crk-associated substrate (Cas) but, rather, is a protein product of the c-cbl proto-oncogene. Whereas Cas was not tyrosine-phosphorylated after T cell activation, Cbl became highly phosphorylated. Crk immunoprecipitates from activated T cell lysates contain tyrosine-phosphorylated Cbl. This association is mediated by the SH2 domain of Crk, as evidenced by the interaction between Cbl and the fusion protein product of a glutathione S-transferase (GST) expression construct encoding the Crk-SH2 domain in vitro. Furthermore, phosphopeptide-binding studies revealed that the GST-Crk SH2 domain binds to a tyrosine-phosphorylated pe...

Research paper thumbnail of Structural basis for IL-4 receptor phosphopeptide recognition by the IRS-1 PTB domain

Nature structural biology, 1996

We present the NMR structure of the PTB domain of insulin receptor substrate-1 (IRS-1) complexed ... more We present the NMR structure of the PTB domain of insulin receptor substrate-1 (IRS-1) complexed to a tyrosine-phosphorylated peptide derived from the IL-4 receptor. Despite the lack of sequence homology and different binding specificity, the overall fold of the protein is similar to that of the Shc PTB domain and closely resembles that of PH domains. However, the PTB domain of IRS-1 is smaller than that of Shc (110 versus 170 residues) and binds to phosphopeptides in a distinct manner. We explain the phosphopeptide binding specificity based on the structure of the complex and results of site-directed mutagenesis experiments.

Research paper thumbnail of Crystal structure of the PI 3-kinase p85 amino-terminal SH2 domain and its phosphopeptide complexes

Nature structural biology, 1996

Crystal structures of the amino-terminal SH2 domain of the p85alpha subunit of phosphatidylinosit... more Crystal structures of the amino-terminal SH2 domain of the p85alpha subunit of phosphatidylinositol (PI) 3-kinase, alone and in complex with phosphopeptides bearing pTyr-Met/Val-Xaa-Met motifs, show that phosphopeptides bind in the two-pronged manner seen in high-affinity Lck and Src SH2 complexes, with conserved interactions between the domain and the peptide segment from phosphotyrosine to Met+3. Peptide binding requires the rearrangement of a tyrosyl side chain in the BG loop to create the hydrophobic Met+3 binding pocket. The structures suggest a mechanism for the biological specificity exhibited by PI 3-kinase in its interactions with phosphoprotein partners.

Research paper thumbnail of Insulin receptor autophosphorylation occurs asymmetrically

The Journal of biological chemistry, Jan 25, 1993

The unoccupied insulin receptor is a structurally symmetric, disulfide-linked dimer, comprising t... more The unoccupied insulin receptor is a structurally symmetric, disulfide-linked dimer, comprising two alpha beta halves, each with a potential insulin binding alpha subunit and a kinase active beta subunit. In the accompanying paper (Shoelson, S. E., Lee, J., Lynch, C. S., Backer, J. M., and Pilch, P. F. (1993) J. Biol. Chem. 268, 4085-4091), we described the utility of a novel insulin analogue, L-benzoylphenylalanineB25,B29 epsilon-biotin insulin (BBpa insulin)1 as a probe for receptor behavior, and we determined that binding and cross-linking of one BBpa insulin molecule could fully stimulate insulin receptor autophosphorylation. Here we use this analogue to determine the symmetry of the autophosphorylation reaction. The alpha beta half-receptor that does not covalently couple to BBpa insulin incorporates 50% more orthophosphate than the alpha beta half that becomes coupled to the insulin analogue. Phosphopeptide mapping of each receptor half shows minimal differences in the phospho...

Research paper thumbnail of Phosphoinositide 3-kinase is activated by phosphopeptides that bind to the SH2 domains of the 85-kDa subunit

The Journal of biological chemistry, Jan 5, 1993

Tyrosine-phosphorylated peptides based on the regions of polyoma virus middle t antigen and the p... more Tyrosine-phosphorylated peptides based on the regions of polyoma virus middle t antigen and the platelet-derived growth factor receptor that bind phosphoinositide 3-kinase are shown to activate this enzyme 2-3-fold in vitro. The concentrations of the peptides required to activate the enzyme are at least 10-1000-fold higher than the dissociation constants of these peptides for the individual SH2 domains of the 85-kDa subunit (KD < 100 nM). Doubly phosphorylated peptides are more effective than singly phosphorylated peptides. The results suggest that a fraction of the cellular phosphoinositide 3-kinase has SH2 domains with relatively low affinity for phosphopeptides and that binding of phosphopeptides to these enzymes causes activation. Thus, SH2 domains may be involved not only in recruiting the enzyme but also in regulating activity.

Research paper thumbnail of A photoaffinity scan maps regions of the p85 SH2 domain involved in phosphoprotein binding

The Journal of biological chemistry, Jan 15, 1993

Src homology 2 (SH2) domains are modular phosphotyrosine binding pockets found within a wide vari... more Src homology 2 (SH2) domains are modular phosphotyrosine binding pockets found within a wide variety of cytoplasmic signaling molecules. Here we develop a new approach to analyzing protein-protein interfaces termed photoaffinity scanning, and apply the method to map regions of the phosphatidylinositol 3-kinase p85 SH2 domain that participate in phospho-protein binding. Each residue except phosphotyrosine (pY) within a tightly binding, IRS-1-derived phosphopeptide (GNGDpYMPMSPKS) was substituted with the photoactive amino acid, benzoylphenylalanine (Bpa). Whereas most substitutions had little effect on binding affinity, Bpa substitution of either Met (+1 and +3 with respect to pY) reduced affinity 50-100-fold to confirm their importance in the pYMXM recognition motif. In three cases photolysis of SH2 domain/Bpa phosphopeptide complexes led to cross-linking of > 50% of the SH2 domain; cross-link positions were identified by microsequence, amino acid composition, and electrospray ma...

Research paper thumbnail of Structure of the regulatory domains of the Src-family tyrosine kinase Lck

Nature, Jan 21, 1994

The kinase p56lck (Lck) is a T-lymphocyte-specific member of the Src family of non-receptor tyros... more The kinase p56lck (Lck) is a T-lymphocyte-specific member of the Src family of non-receptor tyrosine kinases. Members of the Src family each contain unique amino-terminal regions, followed by Src-homology domains SH3 and SH2, and a tyrosine kinase domain. SH3 and SH2 domains mediate critical protein interactions in many signal-transducing pathways. They are small, independently folded modules of about 60 and 100 residues, respectively, and they are often but not always found together in the same molecule. Like all nine Src-family kinases (reviewed in ref. 3), Lck is regulated by phosphorylation of a tyrosine in the short C-terminal tail of its catalytic domain. There is evidence that binding of the phosphorylated tail to the SH2 domain inhibits catalytic activity of the kinase domain and that the SH3 and SH2 domains may act together to effect this regulation. Here we report the crystal structures for a fragment of Lck bearing its SH3 and SH2 domains, alone and in complex with a phos...

Research paper thumbnail of Polyoma virus middle T antigen-pp60c-src complex associates with purified phosphatidylinositol 3-kinase in vitro

The Journal of biological chemistry, Jan 15, 1992

Reconstitution of the polyoma virus middle T antigen (mT)-pp60-src complex and phosphatidylinosit... more Reconstitution of the polyoma virus middle T antigen (mT)-pp60-src complex and phosphatidylinositol 3-kinase (PtdIns 3-kinase) has been accomplished in vitro with immunopurified baculovirus-expressed mT-pp60c-src and PtdIns 3-kinase purified from rat liver. Both the 110- and 85-kDa subunits of the PtdIns 3-kinase associated with the mT-pp60c-src complex. The association of PtdIns 3-kinase with the mT-pp60c-src complex was dependent on the protein-tyrosine kinase activity of pp60c-src as a kinase-inactive mutant (pp60(295c-src)) still complexed with mT, but the mT-pp60(295c-src)) complex was unable to bind PtdIns 3-kinase. The mT-pp60c-src complex phosphorylated both subunits of PtdIns 3-kinase on tyrosine residues. The immunopurified mT-pp60c-src complex also associated with PtdIns 3-kinase activity from whole cell lysates, and this association was dependent upon the protein-tyrosine kinase activity of pp60c-src. Comparison of 35S-labeled proteins from whole cell lysates which assoc...

Research paper thumbnail of Regulation of diet-induced adipose tissue and systemic inflammation by salicylates and pioglitazone

PloS one, 2013

It is increasingly accepted that chronic inflammation participates in obesity-induced insulin res... more It is increasingly accepted that chronic inflammation participates in obesity-induced insulin resistance and type 2 diabetes (T2D). Salicylates and thiazolidinediones (TZDs) both have anti-inflammatory and anti-hyperglycemic properties. The present study compared the effects of these drugs on obesity-induced inflammation in adipose tissue (AT) and AT macrophages (ATMs), as well as the metabolic and immunological phenotypes of the animal models. Both drugs improved high fat diet (HFD)-induced insulin resistance. However, salicylates did not affect AT and ATM inflammation, whereas Pioglitazone improved these parameters. Interestingly, HFD and the drug treatments all modulated systemic inflammation as assessed by changes in circulating immune cell numbers and activation states. HFD increased the numbers of circulating white blood cells, neutrophils, and a pro-inflammatory monocyte subpopulation (Ly6C(hi)), whereas salicylates and Pioglitazone normalized these cell numbers. The drug tre...

Research paper thumbnail of Insulin biosynthesis, processing, and chemistry

Research paper thumbnail of Shf, a Shb-like adapter protein, is involved in PDGF-α-receptor regulation of apoptosis

Research paper thumbnail of Circulating forms of somatostatinlike immunoreactivity in human plasma

Circulating forms of somatostatinlike immunoreactivity (SLI) in humans were characterized using s... more Circulating forms of somatostatinlike immunoreactivity (SLI) in humans were characterized using several chromatographic techniques. After gelfiltration chromatography on Bio-Gel P-6 columns greater than 90% of circulating SLI was of high molecular weight (MW) and eluted in the void volume. When plasma samples were passed through protein A-Sepharose columns, more than 85% of the high MW SLI was removed, indicating that this form of plasma SLI is mainly due to cross-reacting immunoglobulins. Extraction of 10-ml plasma samples from normal subjects on octadecyl silyl silica cartridges eliminated the high MW material. In addition, this extraction technique concentrated the two lower MW forms of SLI, which coelute on gel filtration chromatography with somatostatin-28 (S-28) and the tetradecapeptide form of somatostatin (S-14), respectively. Extracted plasma SLI was further analyzed by high-pressure liquid chromatography (HPLC). The results confirmed the identity of S-28 and demonstrated that S-14 is converted, in part, to Des-Alasomatostatin (S-13) following secretion into the circulation. At least four forms of SLI are thus present in human plasma: cross-reacting immunoglobulins, S-28, S-14, and S-13. Concentrations of SLI forms in the plasma of normal controls and patients with renal failure or cirrhosis were measured to assess the role of circulating somatostatin in health and disease. High MW SLI was elevated above normal in the plasma of patients with cirrhosis, but was not significantly elevated in patients with chronic renal failure. On the other hand, concentrations of plasma S-28 and S-13/14 (total concentrations of S-13 plus S-14) were elevated in patients with either chronic renal failure or cirrhosis.

Research paper thumbnail of Solid-phase synthesis of nonhydrolyzable phosphotyrosyl peptide analogues with N α-Fmoc-(O, O-di-t-butyl) phosphono-p-methylphenylalanine

Research paper thumbnail of Nonphosphorylatable substrate analogs selectively block autophosphorylation and activation of the insulin receptor, epidermal growth factor receptor, and pp60v-src kinases

The receptors for insulin and epidermal growth factor undergo tyrosine autophosphorylation in res... more The receptors for insulin and epidermal growth factor undergo tyrosine autophosphorylation in response to ligand stimulation, while pp60v-src is an unregulated tyrosine kinase. In this report we show that each of the kinases phosphorylates an exogenous peptide that corresponds to the insulin proreceptor sequence 1142-1153. When the kinases were pre-phosphorylated, saturable Michaelis-Menten kinetics were observed. However, when the kinases had not been pre-phosphorylated biphasic kinetics were observed; at progressively higher substrate concentrations (greater than Km) less substrate phosphorylation was seen. Furthermore, when the kinases had not been pre-phosphorylated kinase autophosphorylation was inhibited at high substrate concentrations. On this basis we postulated that the substrate inhibition of substrate phosphorylation resulted directly from substrate inhibition of kinase autophosphorylation. To test this we designed additional peptides to function specifically as inhibitors of the kinases. Each of the 3 tyrosine residues within the substrate sequence were replaced either by 4-methoxyphenylalanine or phenylalanine, residues structurally similar to tyrosine but unable to accept phosphoryl transfer. Both analogs inhibited insulin and epidermal growth factor receptor autophosphorylation, whereas only the Phe-substituted analog inhibited pp60v-src phosphorylation. These data suggest that autophosphorylation of tyrosine residues near the kinase active site is a generalized mechanism for tyrosine kinase activation and that activation can be selectively blocked by substrates and nonphosphorylatable analogs.