Yang-Kao Wang | National Cheng Kung University (original) (raw)

Papers by Yang-Kao Wang

Focal adhesions (FAs) undergo maturation culminating in size and composition changes that modulat... more Focal adhesions (FAs) undergo maturation culminating in size and composition changes that modulate adhesion, cytoskeleton remodeling and differentiation. While it is well-recognized that stimuli for osteogenesis of mesenchymal stem cells (MSCs) drive FA maturation, actin organization, and stress-fiber polarization, the extent to which FA-mediated signals regulated by the FA protein composition specifies MSC commitment remains largely unknown. Here we demonstrate that, upon dexamethasone (osteogenic induction) treatment, guanine nucleotide exchange factor-H1 (GEF-H1) is significantly enriched in FAs. Perturbation of GEF-H1 inhibits FA formation, anisotropic stress-fiber orientation and MSC osteogenesis in an actomyosin contractility-independent manner. To determine the role of GEF-H1 in MSC osteogenesis, we explore the GEF-H1-modulated FA proteome that reveals non-muscle myosin-II heavy chain-B (NMIIB) as a target of GEF-H1 in FAs. Inhibition of targeting NMIIB into FAs suppresses FA formation, stress-fiber polarization, cell stiffness and osteogenic commitments in MSCs. Our data demonstrate FA signaling in specifying MSC commitment.

Journal of Biological …, Jan 1, 2003

The American Journal …, Jan 1, 2012

Lavender essential oil (LEO) is one the most favorite and widely used essential oils in aromather... more Lavender essential oil (LEO) is one the most favorite and widely used essential oils in aromatherapy. Many studies have demonstrated its functions in calming, assisting sleep, reducing pain and muscular spasms and its antiseptic function. To date, however, the mechanism of LEO on inflammation response is not well understood. In this study, we examined the effect of LEO on 5 μg/ml lipopolysaccharide (LPS) induced inflammation reaction in human monocyte THP-1 cells. We found treatment of 0.1% LEO significantly increased cell viability and inhibited the IL-1β and superoxide anion generation in LPS-stimulated THP-1 cells. Treatment with LEO down-regulated both LPS-induced protein levels of phospho-NF-κB and membrane Toll-like receptor 4. To determine whether the chaperone protein was involved in the reaction, we determined the levels of Heat Shock Protein 70 (HSP70). Our results showed that LEO increased HSP70 expression in LPS-stimulated THP-1 cells, suggesting that the LEO inhibited LPS-induced inflammatory effect might be associated with the expression of HSP70.

Molecular Biology of the …, Jan 1, 2011

Journal of Cellular Biochemistry, Jan 1, 2008

Previous study demonstrated that low substratum rigidity down-regulates focal adhesion proteins. ... more Previous study demonstrated that low substratum rigidity down-regulates focal adhesion proteins. In this study we found that cells cultured on collagen gel exhibited higher migration capacity than those cultured on collagen gel-coated dishes. Low rigidity of collagen gel induced delayed but persistent phosphorylation of ERK1/2. Inhibition of collagen gel-induced ERK1/2 phosphorylation by MEK inhibitors and ERK2 kinase mutant induced a rounding up of the cells and prevented collagen gel-induced cell migration. Interestingly, phosphorylated ERK1/2 induced by low rigidity was present in focal adhesion sites and the lipid raft. MβCD (Methyl-β-cyclodextrin), a lipid raft inhibitor, inhibited collagen gel-induced ERK1/2 phosphorylation, and cell migration. Overexpression of FAK C-terminal fragment (FRNK) in MDCK cells triggered ERK phosphorylation. Meanwhile, low substratum rigidity induced degradation of FAK into a 35 kDa C-terminal fragment. A calpain inhibitor that partially rescued FAK degradation also prevented low rigidity-induced ERK phosphorylation. However, MβCD did not prevent low rigidity-induced FAK degradation. Taken together, we demonstrate that the degradation product of FAK induced by collagen gel triggers activation of ERK1/2, which in turn facilitates cell spreading and migration through the lipid raft. J. Cell. Biochem. 103: 1111–1124, 2008. © 2007 Wiley-Liss, Inc.

Journal of Cellular Physiology, Jan 1, 2007

Under normal culture conditions, cells adhere to culture dish, spread out, proliferate, and final... more Under normal culture conditions, cells adhere to culture dish, spread out, proliferate, and finally cover all areas and reach confluence. During the confluent stage, cell proliferation ceases and differentiation is enhanced. Meanwhile, cell death also appears as the monolayer confluence proceeds. To delineate the mechanism of cell death induced by the confluent process, we employed Madin-Darby canine kidney (MDCK) cells. When approaching confluence, MDCK cells exhibited increase the levels of caspase-2 and enhanced the activity of caspase-8. Using various caspase inhibitors to block apoptosis, we found that only z-VAD-fmk and z-IETD-fmk can inhibit confluent cell death, indicating that confluent cell death is mediated by activation of caspase-8. Overexpression of Bcl-2 inhibited confluent cell death, suggesting the involvement of mitochondria-dependent pathway in confluent cell death. Interestingly, the activity of phospho-Erk (p-Erk) was initially decreased before confluence, but markedly increased after confluence. Immunofluorescence staining studies showed that p-Erk was expressed exclusively on dome-forming cells that underwent apoptosis. Treatment of confluent MDCK cells with PD98059 and UO126, the inhibitors of MEK, enhanced apoptosis as well as activity of caspase-8. These data indicate that elevation of p-Erk activity during confluence may serve to suppress confluent cell death. Taken together, activation of caspase-8 contributes to and results in confluent cell death, whereas elevated p-Erk activity serves to prevent confluent cell death by regulating activation of caspase-8. J. Cell. Physiol. 211: 174–182, 2007. © 2007 Wiley-Liss, Inc.

Journal of Biological …, Jan 1, 2007

In this study, we established that collagen gel, but not collagen gel coating, induced apoptosis ... more In this study, we established that collagen gel, but not collagen gel coating, induced apoptosis exclusively in epithelial cell lines, which indicated that low substratum rigidity might trigger cell apoptosis. To confirm this, we used collagen gels with different rigidities due to cross-linking or physical disruption of collagen fibrils caused by sonication. We found that collagen gel-induced apoptosis was inversely correlated with substratum rigidity.

Stem cells and …, Jan 1, 2011

Osteogenic differentiation of human mesenchymal stem cells (hMSCs) is classically thought to be m... more Osteogenic differentiation of human mesenchymal stem cells (hMSCs) is classically thought to be mediated by different cytokines such as the bone morphogenetic proteins (BMPs). Here, we report that cell adhesion to extracellular matrix (ECM), and its effects on cell shape and cytoskeletal mechanics, regulates BMP-induced signaling and osteogenic differentiation of hMSCs. Using micropatterned substrates to progressively restrict cell spreading and flattening against ECM, we demonstrated that BMP-induced osteogenesis is progressively antagonized with decreased cell spreading. BMP triggered rapid and sustained RhoA/Rho-associated protein kinase (ROCK) activity and contractile tension only in spread cells, and this signaling was required for BMPinduced osteogenesis. Exploring the molecular basis for this effect, we found that restricting cell spreading, reducing ROCK signaling, or inhibiting cytoskeletal tension prevented BMP-induced SMA/mothers against decapentaplegic (SMAD)1 c-terminal phosphorylation, SMAD1 dimerization with SMAD4, and SMAD1 translocation into the nucleus. Together, these findings demonstrate the direct involvement of cell spreading and RhoA/ROCK-mediated cytoskeletal tension generation in BMP-induced signaling and early stages of in vitro osteogenesis, and highlight the essential interplay between biochemical and mechanical cues in stem cell differentiation.

Journal of Biomedical Science, Jan 1, 2002

It has been well established that hepatocyte growth factor (HGF) induces branching tubule formati... more It has been well established that hepatocyte growth factor (HGF) induces branching tubule formation of Madin-Darby canine kidney (MDCK) cells cultured in collagen gel. Tubulogenesis per se requires the involvement of cell proliferation, migration, focalization proteolysis, cell-cell interaction and differentiation. However, signaling pathways and proteins involved in HGF-induced tubulogenesis by MDCK cells have not been thoroughly studied. Because cell-matrix interactions play important roles in tubulogenesis, we analyzed whether HGF altered the expression of extracellular matrix receptor (alpha2, alpha3, beta1 and alphavbeta3 integrin). We found that among those proteins examined, alpha2beta1 integrin levels were enhanced by HGF. HGF-induced upregulation of alpha2beta1 integrin was mediated via upregulation of alpha2 integrin mRNA abundance. Cycloheximide blocked the HGF-induced increase in alpha2 integrin mRNA expression. To understand the signaling pathways leading to an HGF-induced increase in alpha2beta1 integrin levels, PD98059 (MEK1 inhibitor), LY294002 (PI3-kinase inhibitor), and GF109203X (PKC inhibitor) were used. We found that PD98059 blocked the HGF-induced increase in alpha2beta1 integrin expression. Furthermore, 5E8 (specific anti-alpha2beta1 integrin antibody) was employed to elucidate the potential role of HGF-induced upregulation of alpha2beta1 integrin in branching morphogenesis. 5E8 did not alter HGF-induced scattering effects but disrupted HGF-induced branching tubulogenesis in collagen gel via inhibition of cell-cell interactions and growth. Taken together, HGF upregulates alpha2beta1 integrin expression via an indirect pathway, the results of which contribute to the regulation of cell-cell interactions and cell growth during branching morphogenesis in collagen gel.

American Journal of Physiology …, Jan 1, 2001

We previously demonstrated that collagen gel overlay induced cell remodeling to form lumen and ap... more We previously demonstrated that collagen gel overlay induced cell remodeling to form lumen and apoptosis in Madin-Darby canine kidney cells. In the present study, we established that collagen gel overlay-induced apoptosis was initiated at areas exclusive of cell remodeling within 24 h (first phase) and extended into areas of cell remodeling within 48 h (second phase). Collagen gel overlay-induced apoptosis was accompanied by selective proteolysis of focal adhesion kinase (FAK), talin, p130(cas), and c-src. Upon collagen gel overlay, FAK was initially degraded into a 90-kDa product during the first phase and subsequently into a 80-kDa product during the second phase. Collagen gel overlay-induced apoptosis of focal adhesion complex proteins and apoptosis of the first phase could be blocked only by a protease inhibitor cocktail. In addition, we found that both DEVD-fmk and ZVAD-fmk inhibited secondary proteolysis of FAK, but only ZVAD-fmk blocked collagen gel overlay-induced apoptosis of the second phase. Finally, collagen gel overlay-induced apoptosis and proteolysis of focal adhesion complex proteins were completely inhibited by the combination of protease inhibitor cocktail and ZVAD-fmk. Taken together, collagen gel overlay induces two phases of apoptosis; the first phase is dependent on proteolysis of focal adhesion complex proteins, and the second phase on activation of caspases.

American Journal of Pathology, Jan 1, 2010

Transforming growth factor-β1 (TGF-β1)-induced epithelial-to-mesenchymal transition (EMT) contrib... more Transforming growth factor-β1 (TGF-β1)-induced epithelial-to-mesenchymal transition (EMT) contributes to the pathophysiological development of kidney fibrosis. Although it was reported that TGF-β1 enhances β1 integrin levels in NMuMG cells, the detailed molecular mechanisms underlying TGF-β1-induced β1 integrin gene expression and the role of β1 integrin during EMT in the renal system are still unclear. In this study, we examined the role of β1 integrin in TGF-β1-induced EMT both in vitro and in vivo. TGF-β1-induced augmentation of β1 integrin expression was required for EMT in several epithelial cell lines, and knockdown of Smad3 inhibited TGF-β1-induced augmentation of β1 integrin. TGF-β1 triggered β1 integrin gene promoter activity as assessed by luciferase activity assay. Both knockdown of Smad3 and mutation of the Smad-binding element to block binding to the β1 integrin promoter markedly reduced TGF-β1-induced β1 integrin promoter activity. Chromatin immunoprecipitation assay showed that TGF-β1 enhanced Smad3 binding to the β1 integrin promoter. Furthermore, induction of unilateral ureteral obstruction triggered increases of β1 integrin in both renal epithelial and interstitial cells. In human kidney with chronic tubulointerstitial fibrosis, we also found a concomitant increase of β1 integrin and α-smooth muscle actin in tubule epithelia. Blockade of β1 integrin signaling dampened the progression of fibrosis. Taken together, β1 integrin mediates EMT and subsequent tubulointerstitutial fibrosis, suggesting that inhibition of β1 integrin is a possible therapeutic target for prevention of renal fibrosis.

Nature Protocols, Jan 1, 2011

Journal of Biological …, Jan 1, 2003

Previous studies have shown that collagen gel overlay induced selective proteolysis of focal adhe... more Previous studies have shown that collagen gel overlay induced selective proteolysis of focal adhesion complex proteins in Madin-Darby canine kidney (MDCK) cells. In this study, we examined whether morphological and biochemical changes were present in cells cultured on collagen gel. We found that focal adhesion complex proteins, including focal adhesion kinase (FAK), talin, paxillin, and p130cas, but not vinculin, were decreased within 1 h when MDCK cells were cultured on collagen gel. Collagen gel-induced selective decrease of focal adhesion proteins was observed in all lines of cells examined, including epithelial, fibroblastic, and cancer cells. Matrigel also induced selective down-regulation of focal adhesion proteins. However, cells cultured on collagen gel- or matrigel-coated dishes did not show any changes of focal adhesion proteins. These data suggest that the physical nature of the gel, i.e. the rigidity, is involved in the expression of focal adhesion proteins. The collagen gel-induced down-regulation of focal adhesion complex proteins was caused by reduction of protein synthesis and activation of proteases such as calpain. Overexpression of a dominant negative mutant of discoidin domain receptor 1 (DDR1) or FAK-related non-kinase (FRNK) did not prevent collagen gel-induced down-regulation of the focal adhesion complex protein, whereas an anti-alpha2beta1 integrin-neutralizing antibody completely blocked it. Taken together, our results indicate that the rigidity of collagen gel controls the expression of focal adhesion complex proteins, which is mediated by alpha2beta1 integrin but not DDR1.

Developmental Biology, Jan 1, 2002

The c-ret gene encodes a receptor tyrosine kinase (RET) essential for the development of the kidn... more The c-ret gene encodes a receptor tyrosine kinase (RET) essential for the development of the kidney and enteric nervous system. Activation of RET requires the secreted neurotrophin GDNF (glial cell line-derived neurotrophic factor) and its high affinity receptor, a glycosyl phosphatidylinositol-linked cell surface protein GFRα1. In the developing kidney, RET, GDNF, and GFRα1 are all required for directed outgrowth and branching morphogenesis of the ureteric bud epithelium. Using MDCK renal epithelial cells as a model system, activation of RET induces cell migration, scattering, and formation of filopodia and lamellipodia. RET-expressing MDCK cells are able to migrate toward a localized source of GDNF. In this report, the intracellular signaling mechanisms regulating RET-dependent migration and chemotaxis are examined. Activation of RET resulted in increased levels of phosphatidylinositol 3-kinase (PI3K) activity and Akt/PKB phosphorylation. This increase in PI3K activity is essential for regulating the GDNF response, since the specific inhibitor, LY294002, blocks migration and chemotaxis of MDCK cells. Using an in vitro organ culture assay, inhibition of PI3K completely blocks the GDNF-dependent outgrowth of ectopic ureter buds. PI3K is also essential for branching morphogenesis once the ureteric bud has invaded the kidney mesenchyme. The data suggest that activation of RET in the ureteric bud epithelium signals through PI3K to control outgrowth and branching morphogenesis.

Nature Methods, Jan 1, 2011

The user has requested enhancement of the downloaded file. brief communications nature methods | ... more The user has requested enhancement of the downloaded file. brief communications nature methods | VOL.7 NO.9 | SEPTEMBER 2010 | 733

Focal adhesions (FAs) undergo maturation culminating in size and composition changes that modulat... more Focal adhesions (FAs) undergo maturation culminating in size and composition changes that modulate adhesion, cytoskeleton remodeling and differentiation. While it is well-recognized that stimuli for osteogenesis of mesenchymal stem cells (MSCs) drive FA maturation, actin organization, and stress-fiber polarization, the extent to which FA-mediated signals regulated by the FA protein composition specifies MSC commitment remains largely unknown. Here we demonstrate that, upon dexamethasone (osteogenic induction) treatment, guanine nucleotide exchange factor-H1 (GEF-H1) is significantly enriched in FAs. Perturbation of GEF-H1 inhibits FA formation, anisotropic stress-fiber orientation and MSC osteogenesis in an actomyosin contractility-independent manner. To determine the role of GEF-H1 in MSC osteogenesis, we explore the GEF-H1-modulated FA proteome that reveals non-muscle myosin-II heavy chain-B (NMIIB) as a target of GEF-H1 in FAs. Inhibition of targeting NMIIB into FAs suppresses FA formation, stress-fiber polarization, cell stiffness and osteogenic commitments in MSCs. Our data demonstrate FA signaling in specifying MSC commitment.

Journal of Biological …, Jan 1, 2003

The American Journal …, Jan 1, 2012

Lavender essential oil (LEO) is one the most favorite and widely used essential oils in aromather... more Lavender essential oil (LEO) is one the most favorite and widely used essential oils in aromatherapy. Many studies have demonstrated its functions in calming, assisting sleep, reducing pain and muscular spasms and its antiseptic function. To date, however, the mechanism of LEO on inflammation response is not well understood. In this study, we examined the effect of LEO on 5 μg/ml lipopolysaccharide (LPS) induced inflammation reaction in human monocyte THP-1 cells. We found treatment of 0.1% LEO significantly increased cell viability and inhibited the IL-1β and superoxide anion generation in LPS-stimulated THP-1 cells. Treatment with LEO down-regulated both LPS-induced protein levels of phospho-NF-κB and membrane Toll-like receptor 4. To determine whether the chaperone protein was involved in the reaction, we determined the levels of Heat Shock Protein 70 (HSP70). Our results showed that LEO increased HSP70 expression in LPS-stimulated THP-1 cells, suggesting that the LEO inhibited LPS-induced inflammatory effect might be associated with the expression of HSP70.

Molecular Biology of the …, Jan 1, 2011

Journal of Cellular Biochemistry, Jan 1, 2008

Previous study demonstrated that low substratum rigidity down-regulates focal adhesion proteins. ... more Previous study demonstrated that low substratum rigidity down-regulates focal adhesion proteins. In this study we found that cells cultured on collagen gel exhibited higher migration capacity than those cultured on collagen gel-coated dishes. Low rigidity of collagen gel induced delayed but persistent phosphorylation of ERK1/2. Inhibition of collagen gel-induced ERK1/2 phosphorylation by MEK inhibitors and ERK2 kinase mutant induced a rounding up of the cells and prevented collagen gel-induced cell migration. Interestingly, phosphorylated ERK1/2 induced by low rigidity was present in focal adhesion sites and the lipid raft. MβCD (Methyl-β-cyclodextrin), a lipid raft inhibitor, inhibited collagen gel-induced ERK1/2 phosphorylation, and cell migration. Overexpression of FAK C-terminal fragment (FRNK) in MDCK cells triggered ERK phosphorylation. Meanwhile, low substratum rigidity induced degradation of FAK into a 35 kDa C-terminal fragment. A calpain inhibitor that partially rescued FAK degradation also prevented low rigidity-induced ERK phosphorylation. However, MβCD did not prevent low rigidity-induced FAK degradation. Taken together, we demonstrate that the degradation product of FAK induced by collagen gel triggers activation of ERK1/2, which in turn facilitates cell spreading and migration through the lipid raft. J. Cell. Biochem. 103: 1111–1124, 2008. © 2007 Wiley-Liss, Inc.

Journal of Cellular Physiology, Jan 1, 2007

Under normal culture conditions, cells adhere to culture dish, spread out, proliferate, and final... more Under normal culture conditions, cells adhere to culture dish, spread out, proliferate, and finally cover all areas and reach confluence. During the confluent stage, cell proliferation ceases and differentiation is enhanced. Meanwhile, cell death also appears as the monolayer confluence proceeds. To delineate the mechanism of cell death induced by the confluent process, we employed Madin-Darby canine kidney (MDCK) cells. When approaching confluence, MDCK cells exhibited increase the levels of caspase-2 and enhanced the activity of caspase-8. Using various caspase inhibitors to block apoptosis, we found that only z-VAD-fmk and z-IETD-fmk can inhibit confluent cell death, indicating that confluent cell death is mediated by activation of caspase-8. Overexpression of Bcl-2 inhibited confluent cell death, suggesting the involvement of mitochondria-dependent pathway in confluent cell death. Interestingly, the activity of phospho-Erk (p-Erk) was initially decreased before confluence, but markedly increased after confluence. Immunofluorescence staining studies showed that p-Erk was expressed exclusively on dome-forming cells that underwent apoptosis. Treatment of confluent MDCK cells with PD98059 and UO126, the inhibitors of MEK, enhanced apoptosis as well as activity of caspase-8. These data indicate that elevation of p-Erk activity during confluence may serve to suppress confluent cell death. Taken together, activation of caspase-8 contributes to and results in confluent cell death, whereas elevated p-Erk activity serves to prevent confluent cell death by regulating activation of caspase-8. J. Cell. Physiol. 211: 174–182, 2007. © 2007 Wiley-Liss, Inc.

Journal of Biological …, Jan 1, 2007

In this study, we established that collagen gel, but not collagen gel coating, induced apoptosis ... more In this study, we established that collagen gel, but not collagen gel coating, induced apoptosis exclusively in epithelial cell lines, which indicated that low substratum rigidity might trigger cell apoptosis. To confirm this, we used collagen gels with different rigidities due to cross-linking or physical disruption of collagen fibrils caused by sonication. We found that collagen gel-induced apoptosis was inversely correlated with substratum rigidity.

Stem cells and …, Jan 1, 2011

Osteogenic differentiation of human mesenchymal stem cells (hMSCs) is classically thought to be m... more Osteogenic differentiation of human mesenchymal stem cells (hMSCs) is classically thought to be mediated by different cytokines such as the bone morphogenetic proteins (BMPs). Here, we report that cell adhesion to extracellular matrix (ECM), and its effects on cell shape and cytoskeletal mechanics, regulates BMP-induced signaling and osteogenic differentiation of hMSCs. Using micropatterned substrates to progressively restrict cell spreading and flattening against ECM, we demonstrated that BMP-induced osteogenesis is progressively antagonized with decreased cell spreading. BMP triggered rapid and sustained RhoA/Rho-associated protein kinase (ROCK) activity and contractile tension only in spread cells, and this signaling was required for BMPinduced osteogenesis. Exploring the molecular basis for this effect, we found that restricting cell spreading, reducing ROCK signaling, or inhibiting cytoskeletal tension prevented BMP-induced SMA/mothers against decapentaplegic (SMAD)1 c-terminal phosphorylation, SMAD1 dimerization with SMAD4, and SMAD1 translocation into the nucleus. Together, these findings demonstrate the direct involvement of cell spreading and RhoA/ROCK-mediated cytoskeletal tension generation in BMP-induced signaling and early stages of in vitro osteogenesis, and highlight the essential interplay between biochemical and mechanical cues in stem cell differentiation.

Journal of Biomedical Science, Jan 1, 2002

It has been well established that hepatocyte growth factor (HGF) induces branching tubule formati... more It has been well established that hepatocyte growth factor (HGF) induces branching tubule formation of Madin-Darby canine kidney (MDCK) cells cultured in collagen gel. Tubulogenesis per se requires the involvement of cell proliferation, migration, focalization proteolysis, cell-cell interaction and differentiation. However, signaling pathways and proteins involved in HGF-induced tubulogenesis by MDCK cells have not been thoroughly studied. Because cell-matrix interactions play important roles in tubulogenesis, we analyzed whether HGF altered the expression of extracellular matrix receptor (alpha2, alpha3, beta1 and alphavbeta3 integrin). We found that among those proteins examined, alpha2beta1 integrin levels were enhanced by HGF. HGF-induced upregulation of alpha2beta1 integrin was mediated via upregulation of alpha2 integrin mRNA abundance. Cycloheximide blocked the HGF-induced increase in alpha2 integrin mRNA expression. To understand the signaling pathways leading to an HGF-induced increase in alpha2beta1 integrin levels, PD98059 (MEK1 inhibitor), LY294002 (PI3-kinase inhibitor), and GF109203X (PKC inhibitor) were used. We found that PD98059 blocked the HGF-induced increase in alpha2beta1 integrin expression. Furthermore, 5E8 (specific anti-alpha2beta1 integrin antibody) was employed to elucidate the potential role of HGF-induced upregulation of alpha2beta1 integrin in branching morphogenesis. 5E8 did not alter HGF-induced scattering effects but disrupted HGF-induced branching tubulogenesis in collagen gel via inhibition of cell-cell interactions and growth. Taken together, HGF upregulates alpha2beta1 integrin expression via an indirect pathway, the results of which contribute to the regulation of cell-cell interactions and cell growth during branching morphogenesis in collagen gel.

American Journal of Physiology …, Jan 1, 2001

We previously demonstrated that collagen gel overlay induced cell remodeling to form lumen and ap... more We previously demonstrated that collagen gel overlay induced cell remodeling to form lumen and apoptosis in Madin-Darby canine kidney cells. In the present study, we established that collagen gel overlay-induced apoptosis was initiated at areas exclusive of cell remodeling within 24 h (first phase) and extended into areas of cell remodeling within 48 h (second phase). Collagen gel overlay-induced apoptosis was accompanied by selective proteolysis of focal adhesion kinase (FAK), talin, p130(cas), and c-src. Upon collagen gel overlay, FAK was initially degraded into a 90-kDa product during the first phase and subsequently into a 80-kDa product during the second phase. Collagen gel overlay-induced apoptosis of focal adhesion complex proteins and apoptosis of the first phase could be blocked only by a protease inhibitor cocktail. In addition, we found that both DEVD-fmk and ZVAD-fmk inhibited secondary proteolysis of FAK, but only ZVAD-fmk blocked collagen gel overlay-induced apoptosis of the second phase. Finally, collagen gel overlay-induced apoptosis and proteolysis of focal adhesion complex proteins were completely inhibited by the combination of protease inhibitor cocktail and ZVAD-fmk. Taken together, collagen gel overlay induces two phases of apoptosis; the first phase is dependent on proteolysis of focal adhesion complex proteins, and the second phase on activation of caspases.

American Journal of Pathology, Jan 1, 2010

Transforming growth factor-β1 (TGF-β1)-induced epithelial-to-mesenchymal transition (EMT) contrib... more Transforming growth factor-β1 (TGF-β1)-induced epithelial-to-mesenchymal transition (EMT) contributes to the pathophysiological development of kidney fibrosis. Although it was reported that TGF-β1 enhances β1 integrin levels in NMuMG cells, the detailed molecular mechanisms underlying TGF-β1-induced β1 integrin gene expression and the role of β1 integrin during EMT in the renal system are still unclear. In this study, we examined the role of β1 integrin in TGF-β1-induced EMT both in vitro and in vivo. TGF-β1-induced augmentation of β1 integrin expression was required for EMT in several epithelial cell lines, and knockdown of Smad3 inhibited TGF-β1-induced augmentation of β1 integrin. TGF-β1 triggered β1 integrin gene promoter activity as assessed by luciferase activity assay. Both knockdown of Smad3 and mutation of the Smad-binding element to block binding to the β1 integrin promoter markedly reduced TGF-β1-induced β1 integrin promoter activity. Chromatin immunoprecipitation assay showed that TGF-β1 enhanced Smad3 binding to the β1 integrin promoter. Furthermore, induction of unilateral ureteral obstruction triggered increases of β1 integrin in both renal epithelial and interstitial cells. In human kidney with chronic tubulointerstitial fibrosis, we also found a concomitant increase of β1 integrin and α-smooth muscle actin in tubule epithelia. Blockade of β1 integrin signaling dampened the progression of fibrosis. Taken together, β1 integrin mediates EMT and subsequent tubulointerstitutial fibrosis, suggesting that inhibition of β1 integrin is a possible therapeutic target for prevention of renal fibrosis.

Nature Protocols, Jan 1, 2011

Journal of Biological …, Jan 1, 2003

Previous studies have shown that collagen gel overlay induced selective proteolysis of focal adhe... more Previous studies have shown that collagen gel overlay induced selective proteolysis of focal adhesion complex proteins in Madin-Darby canine kidney (MDCK) cells. In this study, we examined whether morphological and biochemical changes were present in cells cultured on collagen gel. We found that focal adhesion complex proteins, including focal adhesion kinase (FAK), talin, paxillin, and p130cas, but not vinculin, were decreased within 1 h when MDCK cells were cultured on collagen gel. Collagen gel-induced selective decrease of focal adhesion proteins was observed in all lines of cells examined, including epithelial, fibroblastic, and cancer cells. Matrigel also induced selective down-regulation of focal adhesion proteins. However, cells cultured on collagen gel- or matrigel-coated dishes did not show any changes of focal adhesion proteins. These data suggest that the physical nature of the gel, i.e. the rigidity, is involved in the expression of focal adhesion proteins. The collagen gel-induced down-regulation of focal adhesion complex proteins was caused by reduction of protein synthesis and activation of proteases such as calpain. Overexpression of a dominant negative mutant of discoidin domain receptor 1 (DDR1) or FAK-related non-kinase (FRNK) did not prevent collagen gel-induced down-regulation of the focal adhesion complex protein, whereas an anti-alpha2beta1 integrin-neutralizing antibody completely blocked it. Taken together, our results indicate that the rigidity of collagen gel controls the expression of focal adhesion complex proteins, which is mediated by alpha2beta1 integrin but not DDR1.

Developmental Biology, Jan 1, 2002

The c-ret gene encodes a receptor tyrosine kinase (RET) essential for the development of the kidn... more The c-ret gene encodes a receptor tyrosine kinase (RET) essential for the development of the kidney and enteric nervous system. Activation of RET requires the secreted neurotrophin GDNF (glial cell line-derived neurotrophic factor) and its high affinity receptor, a glycosyl phosphatidylinositol-linked cell surface protein GFRα1. In the developing kidney, RET, GDNF, and GFRα1 are all required for directed outgrowth and branching morphogenesis of the ureteric bud epithelium. Using MDCK renal epithelial cells as a model system, activation of RET induces cell migration, scattering, and formation of filopodia and lamellipodia. RET-expressing MDCK cells are able to migrate toward a localized source of GDNF. In this report, the intracellular signaling mechanisms regulating RET-dependent migration and chemotaxis are examined. Activation of RET resulted in increased levels of phosphatidylinositol 3-kinase (PI3K) activity and Akt/PKB phosphorylation. This increase in PI3K activity is essential for regulating the GDNF response, since the specific inhibitor, LY294002, blocks migration and chemotaxis of MDCK cells. Using an in vitro organ culture assay, inhibition of PI3K completely blocks the GDNF-dependent outgrowth of ectopic ureter buds. PI3K is also essential for branching morphogenesis once the ureteric bud has invaded the kidney mesenchyme. The data suggest that activation of RET in the ureteric bud epithelium signals through PI3K to control outgrowth and branching morphogenesis.

Nature Methods, Jan 1, 2011

The user has requested enhancement of the downloaded file. brief communications nature methods | ... more The user has requested enhancement of the downloaded file. brief communications nature methods | VOL.7 NO.9 | SEPTEMBER 2010 | 733