Michael Lee - Academia.edu (original) (raw)

Papers by Michael Lee

Research paper thumbnail of Subunit composition of neurofilaments specifies axonal diameter

The Journal of cell biology, 1996

Neurofilaments (NFs), which are composed of NF-L, NF-M, and NF-H, are required for the developmen... more Neurofilaments (NFs), which are composed of NF-L, NF-M, and NF-H, are required for the development of normal axonal caliber, a property that in turn is a critical determinant of axonal conduction velocity. To investigate how each subunit contributes to the radial growth of axons, we used transgenic mice to alter the subunit composition of NFs. Increasing each NF subunit individually inhibits radial axonal growth, while increasing both NF-M and NF-H reduces growth even more severely. An increase in NF-L results in an increased filament number but reduced interfilament distance. Conversely, increasing NF-M, NF-H, or both reduces filament number, but does not alter nearest neighbor interfilament distance. Only a combined increase of NF-L with either NF-M or NF-H promotes radial axonal growth. These results demonstrate that both NF-M and NF-H play complementary roles with NF-L in determining normal axonal calibers.

Research paper thumbnail of Endoproteolysis of Presenilin 1 and Accumulation of Processed Derivatives In Vivo

Neuron, 1996

The majority of early-onset cases of familial Alzheimer's disease (FAD) are linked to mutations i... more The majority of early-onset cases of familial Alzheimer's disease (FAD) are linked to mutations in two related genesPS1 and PS2, located on chromosome 14 and 1, respectively. Using two highly specific antibodies against nonoverlapping epitopes of the PS1- encoded polypeptide, termed presenilin 1 (PS1), we document that the preponderant PS1-related species that accumulate in cultured mammalian cells, and in the brains of rodents, primates, and humans are ∼27–28 kDa N-terminal and ∼16–17 kDa C-terminal derivatives. Notably, a FAD-linked PS1 variant that lacks exon 9 is not subject to endoproteolytic cleavage. In brains of transgenic mice expressing human PS1, ∼17 kDa and ∼27 kDa PS1 derivatives accumulate to saturable levels, and at ∼1:1 stoichiometry, independent of transgene-derived mRNA. We conclude that PS1 is subject to endoproteolytic processing in vivo.

Research paper thumbnail of 2Acetylaminofluorene suppresses immune response through the inhibition of nuclear factor-κB activation during the early stage of B cell development

Toxicology Letters - TOXICOL LETT, 2000

2-Acetylaminofluorene (AAF), an arylamide carcinogen, has been known to inhibit humoral and cell-... more 2-Acetylaminofluorene (AAF), an arylamide carcinogen, has been known to inhibit humoral and cell-mediated immune response by lipopolysaccharide (LPS). In the current study we demonstrate that AAF induced the down-regulation of protein kinase C (PKC) that is a key enzyme in the pathways leading to LPS-induced B-cell proliferation, while having no inhibitory effect on intracellular cAMP in spleen cells. Additionally, to identify the mechanism of action of AAF during B-cell development, we determined the effects of AAF on LPS-induced nuclear factor-kB (NF-kB) activation in 70Z/3 murine pre-B cells, CH12 murine mature B cells and S194 murine plasmacytoma cells. LPS-induced NF-kB activation, which is dependent on PKC, was inhibited by pretreatment with AAF for 2 h in the nuclei of 70Z/3 murine pre-B cells by detection of NF-kB specific DNA-protein binding. Conversely, AAF barely inhibited the constitutive NF-kB binding activity in mature B-cells, S194 and CH12. To confirm the effect of AAF on NF-kB activation, a chloramphenicol acetyl transferase (CAT) expression vector containing multiple copies of the NF-kB element (pCAT(kB) 3 ) was transiently transfected into 70Z/3 or S194 cells, and assessed for inducible CAT activity. AAF treatment of 70Z/3 cells resulted in a significant inhibition of CAT activity induced by LPS. However, AAF exhibited no inhibitory effect on constitutive CAT activity in mature B cells, S194, indicating that AAF no longer has suppressive effects on the immune response in differentiated B cells. Taken together, these results suggest that AAF may act to suppress immune response by blocking the activation of PKC and nuclear expression of NF-kB at the early stage of B cell development.

Research paper thumbnail of Altered Reactivity of Superoxide Dismutase in Familial Amyotrophic Lateral Sclerosis

Science, 1996

]. The arterial partial pressure of CO2 and 02 was measured repetitively, and the EEG and electro... more ]. The arterial partial pressure of CO2 and 02 was measured repetitively, and the EEG and electrooculogram (EOG) were recorded continuously. None of the participants broke their fixated gazes, and the EOG showed only eye blinks with an average frequency of 0.2 + 0.

Research paper thumbnail of An adverse property of a familial ALS-linked SOD1 mutation causes motor neuron disease characterized by vacuolar degeneration of mitochondria

Neuron, 1995

Mutations in Cu/Zn superoxide dismutase (SOD1) cause a subset of cases of familial amyotrophic la... more Mutations in Cu/Zn superoxide dismutase (SOD1) cause a subset of cases of familial amyotrophic lateral sclerosis. Four linesof mice accumulating oneof these mutant proteins (G37R) develop severe, progressive motor neuron disease. At lower levels of mutant accumulation, pathology is restricted to lower motor neurons, whereas higher levels cause more severe abnormalities and affect a variety of other neuronal populations. The most obvious cellular abnormality is the presence in axons and dendrites of membrane-bounded vacuoles, which appear to be derived from degenerating mitochondria. Since multiple lines of mice expressing wild-type human SOD1 at similar and higher levels do not show disease, the disease in mice expressing the G37R mutant SOD1 must arise from the acquisition of an adverse property by the mutant enzyme, rather than elevation or loss of SOD1 activity.

Research paper thumbnail of Accelerated Amyloid Deposition in the Brains of Transgenic Mice Coexpressing Mutant Presenilin 1 and Amyloid Precursor Proteins

Neuron, 1997

Missense mutations in two related genes, termed presenilin 1 (PS1) and presenilin 2 (PS2), cause ... more Missense mutations in two related genes, termed presenilin 1 (PS1) and presenilin 2 (PS2), cause dementia in a subset of early-onset familial Alzheimer's disease (FAD) pedigrees. In a variety of experimental in vitro and in vivo settings, FAD-linked presenilin variants influence the processing of the amyloid precursor protein (APP), leading to elevated levels of the highly fibrillogenic Aβ1–42 peptides that are preferentially deposited in the brains of Alzheimer Disease (AD) patients. In this report, we demonstrate that transgenic animals that coexpress an FAD-linked human PS1 variant (A246E) and a chimeric mouse/human APP harboring mutations linked to Swedish FAD kindreds (APP swe) develop numerous amyloid deposits much earlier than age-matched mice expressing APP swe and wild-type Hu PS1 or APP swe alone. These results provide evidence for the view that one pathogenic mechanism by which FAD-linked mutant PS1 causes AD is to accelerate the rate of β-amyloid deposition in brain.

Research paper thumbnail of The expression and posttranslational modification of a neuron-specific ?-tubulin isotype during chick embryogenesis

Cell Motility and The Cytoskeleton, 1990

Five β-tubulin isotypes are expressed differentially during chicken brain development. One of the... more Five β-tubulin isotypes are expressed differentially during chicken brain development. One of these isotypes is encoded by the gene cβ4 and has been assigned to an isotypic family designated as Class III (βIII). In the nervous system of higher vertebrates, βIII is synthesized exclusively by neurons. A βIII-specific monoclonal antibody was used to determine when during chick embryogenesis cβ4 is expressed, the cellular localization of βIII, and the number of charge variants (isoforms) into which βIII can be resolved by isoelectric focusing. On Western blots, βIII is first detectable at stages 12–13. Thereafter, the relative abundance of βIII in brain increases steadily, apparently in conjunction with the rate of neural differentiation. The isotype was not detectable in non-neural tissue extracts from older embryos (days 10–14) and hatchlings. Western blots of protein separated by two-dimensional gel electrophoresis (2D–PAGE) reveal that the number of βIII isoforms increases from one to three during neural development. This evidence indicates that βIII is a substrate for developmentally regulated, multiple-site posttranslational modification. Immunocytochemical studies reveal that while cβ4 expression is restricted predominantly to the nervous system, it is transiently expressed in some embryonic structures. More importantly, in the nervous system, immunoreactive cells were located primarily in the non-proliferative marginal zone of the neural epithelia. Regions containing primarily mitotic neuroblasts were virtually unstained. This localization pattern indicates that cβ4 expression occurs either during or immediately following terminal mitosis, and suggests that βIII may have a unique role during early neuronal differentiation and neurite outgrowth.

Research paper thumbnail of Familial Alzheimer's Disease–Linked Presenilin 1 Variants Elevate Aβ1–42/1–40 Ratio In Vitro and In Vivo

Neuron, 1996

Mutations in the presenilin 1 (PS1) and presenilin 2 genes cosegregate with the majority of early... more Mutations in the presenilin 1 (PS1) and presenilin 2 genes cosegregate with the majority of early-onset familial Alzheimer's disease (FAD) pedigrees. We now document that the Aβ1–42(43)/Aβ1–40 ratio in the conditioned media of independent N2a cell lines expressing three FAD-linked PS1 variants is uniformly elevated relative to cells expressing similar levels of wild-type PS1. Similarly, the Aβ1–42(43)/Aβ1–40 ratio is elevated in the brains of young transgenic animals coexpressing a chimeric amyloid precursor protein (APP) and an FAD-linked PS1 variant compared with brains of transgenic mice expressing APP alone or transgenic mice coexpressing wild-type human PS1 and APP. These studies provide compelling support for the view that one mechanism by which these mutant PS1 cause AD is by increasing the extracellular concentration of Aβ peptides terminating at 42(43), species that foster Aβ deposition.

Research paper thumbnail of Subunit composition of neurofilaments specifies axonal diameter

The Journal of cell biology, 1996

Neurofilaments (NFs), which are composed of NF-L, NF-M, and NF-H, are required for the developmen... more Neurofilaments (NFs), which are composed of NF-L, NF-M, and NF-H, are required for the development of normal axonal caliber, a property that in turn is a critical determinant of axonal conduction velocity. To investigate how each subunit contributes to the radial growth of axons, we used transgenic mice to alter the subunit composition of NFs. Increasing each NF subunit individually inhibits radial axonal growth, while increasing both NF-M and NF-H reduces growth even more severely. An increase in NF-L results in an increased filament number but reduced interfilament distance. Conversely, increasing NF-M, NF-H, or both reduces filament number, but does not alter nearest neighbor interfilament distance. Only a combined increase of NF-L with either NF-M or NF-H promotes radial axonal growth. These results demonstrate that both NF-M and NF-H play complementary roles with NF-L in determining normal axonal calibers.

Research paper thumbnail of Endoproteolysis of Presenilin 1 and Accumulation of Processed Derivatives In Vivo

Neuron, 1996

The majority of early-onset cases of familial Alzheimer's disease (FAD) are linked to mutations i... more The majority of early-onset cases of familial Alzheimer's disease (FAD) are linked to mutations in two related genesPS1 and PS2, located on chromosome 14 and 1, respectively. Using two highly specific antibodies against nonoverlapping epitopes of the PS1- encoded polypeptide, termed presenilin 1 (PS1), we document that the preponderant PS1-related species that accumulate in cultured mammalian cells, and in the brains of rodents, primates, and humans are ∼27–28 kDa N-terminal and ∼16–17 kDa C-terminal derivatives. Notably, a FAD-linked PS1 variant that lacks exon 9 is not subject to endoproteolytic cleavage. In brains of transgenic mice expressing human PS1, ∼17 kDa and ∼27 kDa PS1 derivatives accumulate to saturable levels, and at ∼1:1 stoichiometry, independent of transgene-derived mRNA. We conclude that PS1 is subject to endoproteolytic processing in vivo.

Research paper thumbnail of 2Acetylaminofluorene suppresses immune response through the inhibition of nuclear factor-κB activation during the early stage of B cell development

Toxicology Letters - TOXICOL LETT, 2000

2-Acetylaminofluorene (AAF), an arylamide carcinogen, has been known to inhibit humoral and cell-... more 2-Acetylaminofluorene (AAF), an arylamide carcinogen, has been known to inhibit humoral and cell-mediated immune response by lipopolysaccharide (LPS). In the current study we demonstrate that AAF induced the down-regulation of protein kinase C (PKC) that is a key enzyme in the pathways leading to LPS-induced B-cell proliferation, while having no inhibitory effect on intracellular cAMP in spleen cells. Additionally, to identify the mechanism of action of AAF during B-cell development, we determined the effects of AAF on LPS-induced nuclear factor-kB (NF-kB) activation in 70Z/3 murine pre-B cells, CH12 murine mature B cells and S194 murine plasmacytoma cells. LPS-induced NF-kB activation, which is dependent on PKC, was inhibited by pretreatment with AAF for 2 h in the nuclei of 70Z/3 murine pre-B cells by detection of NF-kB specific DNA-protein binding. Conversely, AAF barely inhibited the constitutive NF-kB binding activity in mature B-cells, S194 and CH12. To confirm the effect of AAF on NF-kB activation, a chloramphenicol acetyl transferase (CAT) expression vector containing multiple copies of the NF-kB element (pCAT(kB) 3 ) was transiently transfected into 70Z/3 or S194 cells, and assessed for inducible CAT activity. AAF treatment of 70Z/3 cells resulted in a significant inhibition of CAT activity induced by LPS. However, AAF exhibited no inhibitory effect on constitutive CAT activity in mature B cells, S194, indicating that AAF no longer has suppressive effects on the immune response in differentiated B cells. Taken together, these results suggest that AAF may act to suppress immune response by blocking the activation of PKC and nuclear expression of NF-kB at the early stage of B cell development.

Research paper thumbnail of Altered Reactivity of Superoxide Dismutase in Familial Amyotrophic Lateral Sclerosis

Science, 1996

]. The arterial partial pressure of CO2 and 02 was measured repetitively, and the EEG and electro... more ]. The arterial partial pressure of CO2 and 02 was measured repetitively, and the EEG and electrooculogram (EOG) were recorded continuously. None of the participants broke their fixated gazes, and the EOG showed only eye blinks with an average frequency of 0.2 + 0.

Research paper thumbnail of An adverse property of a familial ALS-linked SOD1 mutation causes motor neuron disease characterized by vacuolar degeneration of mitochondria

Neuron, 1995

Mutations in Cu/Zn superoxide dismutase (SOD1) cause a subset of cases of familial amyotrophic la... more Mutations in Cu/Zn superoxide dismutase (SOD1) cause a subset of cases of familial amyotrophic lateral sclerosis. Four linesof mice accumulating oneof these mutant proteins (G37R) develop severe, progressive motor neuron disease. At lower levels of mutant accumulation, pathology is restricted to lower motor neurons, whereas higher levels cause more severe abnormalities and affect a variety of other neuronal populations. The most obvious cellular abnormality is the presence in axons and dendrites of membrane-bounded vacuoles, which appear to be derived from degenerating mitochondria. Since multiple lines of mice expressing wild-type human SOD1 at similar and higher levels do not show disease, the disease in mice expressing the G37R mutant SOD1 must arise from the acquisition of an adverse property by the mutant enzyme, rather than elevation or loss of SOD1 activity.

Research paper thumbnail of Accelerated Amyloid Deposition in the Brains of Transgenic Mice Coexpressing Mutant Presenilin 1 and Amyloid Precursor Proteins

Neuron, 1997

Missense mutations in two related genes, termed presenilin 1 (PS1) and presenilin 2 (PS2), cause ... more Missense mutations in two related genes, termed presenilin 1 (PS1) and presenilin 2 (PS2), cause dementia in a subset of early-onset familial Alzheimer's disease (FAD) pedigrees. In a variety of experimental in vitro and in vivo settings, FAD-linked presenilin variants influence the processing of the amyloid precursor protein (APP), leading to elevated levels of the highly fibrillogenic Aβ1–42 peptides that are preferentially deposited in the brains of Alzheimer Disease (AD) patients. In this report, we demonstrate that transgenic animals that coexpress an FAD-linked human PS1 variant (A246E) and a chimeric mouse/human APP harboring mutations linked to Swedish FAD kindreds (APP swe) develop numerous amyloid deposits much earlier than age-matched mice expressing APP swe and wild-type Hu PS1 or APP swe alone. These results provide evidence for the view that one pathogenic mechanism by which FAD-linked mutant PS1 causes AD is to accelerate the rate of β-amyloid deposition in brain.

Research paper thumbnail of The expression and posttranslational modification of a neuron-specific ?-tubulin isotype during chick embryogenesis

Cell Motility and The Cytoskeleton, 1990

Five β-tubulin isotypes are expressed differentially during chicken brain development. One of the... more Five β-tubulin isotypes are expressed differentially during chicken brain development. One of these isotypes is encoded by the gene cβ4 and has been assigned to an isotypic family designated as Class III (βIII). In the nervous system of higher vertebrates, βIII is synthesized exclusively by neurons. A βIII-specific monoclonal antibody was used to determine when during chick embryogenesis cβ4 is expressed, the cellular localization of βIII, and the number of charge variants (isoforms) into which βIII can be resolved by isoelectric focusing. On Western blots, βIII is first detectable at stages 12–13. Thereafter, the relative abundance of βIII in brain increases steadily, apparently in conjunction with the rate of neural differentiation. The isotype was not detectable in non-neural tissue extracts from older embryos (days 10–14) and hatchlings. Western blots of protein separated by two-dimensional gel electrophoresis (2D–PAGE) reveal that the number of βIII isoforms increases from one to three during neural development. This evidence indicates that βIII is a substrate for developmentally regulated, multiple-site posttranslational modification. Immunocytochemical studies reveal that while cβ4 expression is restricted predominantly to the nervous system, it is transiently expressed in some embryonic structures. More importantly, in the nervous system, immunoreactive cells were located primarily in the non-proliferative marginal zone of the neural epithelia. Regions containing primarily mitotic neuroblasts were virtually unstained. This localization pattern indicates that cβ4 expression occurs either during or immediately following terminal mitosis, and suggests that βIII may have a unique role during early neuronal differentiation and neurite outgrowth.

Research paper thumbnail of Familial Alzheimer's Disease–Linked Presenilin 1 Variants Elevate Aβ1–42/1–40 Ratio In Vitro and In Vivo

Neuron, 1996

Mutations in the presenilin 1 (PS1) and presenilin 2 genes cosegregate with the majority of early... more Mutations in the presenilin 1 (PS1) and presenilin 2 genes cosegregate with the majority of early-onset familial Alzheimer's disease (FAD) pedigrees. We now document that the Aβ1–42(43)/Aβ1–40 ratio in the conditioned media of independent N2a cell lines expressing three FAD-linked PS1 variants is uniformly elevated relative to cells expressing similar levels of wild-type PS1. Similarly, the Aβ1–42(43)/Aβ1–40 ratio is elevated in the brains of young transgenic animals coexpressing a chimeric amyloid precursor protein (APP) and an FAD-linked PS1 variant compared with brains of transgenic mice expressing APP alone or transgenic mice coexpressing wild-type human PS1 and APP. These studies provide compelling support for the view that one mechanism by which these mutant PS1 cause AD is by increasing the extracellular concentration of Aβ peptides terminating at 42(43), species that foster Aβ deposition.