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Vassar R. Editorial: Implications for BACE1 Inhibitor Clinical Trials: Adult Conditional BACE1 Knockout Mice Exhibit Axonal Organization Defects in the Hippocampus. J Prev Alzheimers Dis 2020; 6:78-84. [PMID: 30756113 DOI: 10.14283/jpad.2019.3] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
BACE1 is the rate-limiting enzyme for the production of the Aβ peptide that forms amyloid plaques in Alzheimer's disease (AD). Small molecule inhibitors of BACE1 are being tested in clinical trials for AD, but the safety and efficacy of BACE1 inhibition has yet to be fully explored. Knockout of the Bace1 gene in the germline of mice causes multiple neurological phenotypes, suggesting that BACE1 inhibition could be toxic. However, these phenotypes could be the result of BACE1 deficiency during development rather than due to the lack of BACE1 function in the adult. To address this problem, we generated tamoxifen-inducible conditional BACE1 knockout mice in which the Bace1 gene may be deleted in the whole body of the adult at will. Importantly, the adult conditional BACE1 knockout mice largely lack phenotypes, indicating that many BACE1 functions are not required in the adult organism. However, a germline phenotype was observed after BACE1 knockout in the adult: reduced length and disorganization of the hippocampal mossy fiber infrapyramidal bundle comprised of axons of dentate gyrus granule cells. The infrapyramidal bundle abnormality correlated with reduced proteolytic processing of the neural cell adhesion protein CHL1 that is involved in axonal guidance. We conclude that BACE1 inhibition in the adult mouse brain does not lead to the phenotypes associated with BACE1 deficiency during embryonic and postnatal development. However, adult conditional BACE1 knockout mice also suggest that BACE1 inhibitor drugs may disrupt the organization of an axonal pathway in the hippocampus, an important structure for learning and memory. Here, I review the adult conditional BACE1 knockout results and consider their implications for BACE1 inhibitor clinical trials.
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Affiliation(s)
- R Vassar
- R. Vassar, Ken and Ruth Davee Department of Neurology, Feinberg School of Medicine, Northwestern University, IL 60611, USA,
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Cole SL, Vassar R. The Basic Biology of BACE1: A Key Therapeutic Target for Alzheimer's Disease. Curr Genomics 2011; 8:509-30. [PMID: 19415126 PMCID: PMC2647160 DOI: 10.2174/138920207783769512] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2007] [Revised: 12/27/2007] [Accepted: 12/27/2007] [Indexed: 11/22/2022] Open
Abstract
Alzheimer’s disease (AD) is an intractable, neurodegenerative disease that appears to be brought about by both genetic and non-genetic factors. The neuropathology associated with AD is complex, although amyloid plaques composed of the β-amyloid peptide (Aβ) are hallmark neuropathological lesions of AD brain. Indeed, Aβ plays an early and central role in this disease. β-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is the initiating enzyme in Aβ genesis and BACE1 levels are elevated under a variety of conditions. Given the strong correlation between Aβ and AD, and the elevation of BACE1 in this disease, this enzyme is a prime drug target for inhibiting Aβ production in AD. However, nine years on from the initial identification of BACE1, and despite intense research, a number of key questions regarding BACE1 remain unanswered. Indeed, drug discovery and development for AD continues to be challenging. While current AD therapies temporarily slow cognitive decline, treatments that address the underlying pathologic mechanisms of AD are completely lacking. Here we review the basic biology of BACE1. We pay special attention to recent research that has provided some answers to questions such as those involving the identification of novel BACE1 substrates, the potential causes of BACE1 elevation and the putative function of BACE1 in health and disease. Our increasing understanding of BACE1 biology should aid the development of compounds that interfere with BACE1 expression and activity and may lead to the generation of novel therapeutics for AD.
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Affiliation(s)
- S L Cole
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, 303 E. Chicago Avenue, Chicago, IL 60611, USA
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Cole SL, Vassar R. Isoprenoids and Alzheimer's disease: a complex relationship. Neurobiol Dis 2006; 22:209-22. [PMID: 16406223 DOI: 10.1016/j.nbd.2005.11.007] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2005] [Revised: 11/04/2005] [Accepted: 11/13/2005] [Indexed: 11/22/2022] Open
Abstract
Cholesterol metabolism has been linked to Alzheimer's disease (AD) neuropathology, which is characterized by amyloid plaques, neurofibrillary tangles and neuroinflammation. Indeed, the use of statins, which inhibit cholesterol and isoprenoid biosynthesis, as potential AD therapeutics is under investigation. Whether statins offer benefit for AD will be determined by the outcome of large, placebo-controlled, randomized clinical trials. However, their use as pharmacological tools has delineated novel roles for isoprenoids in AD. Protein isoprenylation regulates multiple cellular and molecular events and here we review the complex roles of isoprenoids in AD-relevant processes and carefully evaluate isoprenoid pathways as potential AD therapeutic targets.
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Affiliation(s)
- S L Cole
- Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, IL 60611, USA.
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Abstract
Evidence suggests that the beta-amyloid peptide (Abeta) is central to the pathophysiology of Alzheimer's disease (AD). Amyloid plaques, primarily composed of Abeta, progressively develop in the brains of AD patients, and mutations in three genes (APP, PS1, and PS2) cause early onset familial AD (FAD) by directly increasing synthesis of the toxic, plaque-promoting Abeta42 peptide. Given the strong association between Abeta and AD, therapeutic strategies to lower the concentration of Abeta in the brain should prove beneficial for the treatment of AD. One such strategy would involve inhibiting the enzymes that generate Abeta. Abeta is a product of catabolism of the large Typel membrane protein, amyloid precursor protein (APP). Two proteases, called beta- and gamma-secretase, mediate the endoproteolysis of APP to liberate the Abeta peptide. For over a decade, the molecular identities of these proteases were unknown. Recently, the gamma-secretase has been tentatively identified as the presenilin proteins, PS1 and PS2, and the identity of the beta-secretase has been shown to be the novel transmembrane aspartic protease, beta-site APP cleaving enzyme 1 (BACE1; also called Asp2 and memapsin2). BACE2, a novel protease homologous to BACE1, was also identified, and together the two enzymes define a new family of transmembrane aspartic proteases. BACE1 exhibits all the properties of the beta-secretase, and as the key rate-limiting enzyme that initiates the formation of Abeta, BACE1 is an attractive drug target for AD. Here, I review the identification and initial characterization of BACE1 and BACE2, and summarize our current understanding of BACE1 post-translational processing and intracellular trafficking. In addition, I discuss recent studies of BACE1 knockout mice and the BACE1 X-ray structure, and relate implications for BACE1 drug development.
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Affiliation(s)
- R Vassar
- Northwestern University Medical School, Department of Cell and Molecular Biology, Chicago, IL 60611, USA.
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Luo Y, Bolon B, Kahn S, Bennett BD, Babu-Khan S, Denis P, Fan W, Kha H, Zhang J, Gong Y, Martin L, Louis JC, Yan Q, Richards WG, Citron M, Vassar R. Mice deficient in BACE1, the Alzheimer's beta-secretase, have normal phenotype and abolished beta-amyloid generation. Nat Neurosci 2001; 4:231-2. [PMID: 11224535 DOI: 10.1038/85059] [Citation(s) in RCA: 746] [Impact Index Per Article: 32.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Y Luo
- Amgen, One Amgen Center Drive, MS 29-2-B, Thousand Oaks, California 91320, USA
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Bennett BD, Denis P, Haniu M, Teplow DB, Kahn S, Louis JC, Citron M, Vassar R. A furin-like convertase mediates propeptide cleavage of BACE, the Alzheimer's beta -secretase. J Biol Chem 2000; 275:37712-7. [PMID: 10956649 DOI: 10.1074/jbc.m005339200] [Citation(s) in RCA: 198] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The novel transmembrane aspartic protease BACE (for Beta-site APP Cleaving Enzyme) is the beta-secretase that cleaves amyloid precursor protein to initiate beta-amyloid formation. As such, BACE is a prime therapeutic target for the treatment of Alzheimer's disease. BACE, like other aspartic proteases, has a propeptide domain that is removed to form the mature enzyme. BACE propeptide cleavage occurs at the sequence RLPR downward arrowE, a potential furin recognition motif. Here, we explore the role of furin in BACE propeptide domain processing. BACE propeptide cleavage in cells does not appear to be autocatalytic, since an inactive D93A mutant of BACE is still cleaved appropriately. BACE and furin co-localize within the Golgi apparatus, and propeptide cleavage is inhibited by brefeldin A and monensin, drugs that disrupt trafficking through the Golgi. Treatment of cells with the calcium ionophore, leading to inhibition of calcium-dependent proteases including furin, or transfection with the alpha(1)-antitrypsin variant alpha(1)-PDX, a potent furin inhibitor, dramatically reduces cleavage of the BACE propeptide. Moreover, the BACE propeptide is not processed in the furin-deficient LoVo cell line; however, processing is restored upon furin transfection. Finally, in vitro digestion of recombinant soluble BACE with recombinant furin results in complete cleavage only at the established E46 site. Taken together, our results strongly suggest that furin, or a furin-like proprotein convertase, is responsible for cleaving the BACE propeptide domain to form the mature enzyme.
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Affiliation(s)
- B D Bennett
- Department of Neurology, Harvard Medical School, and Center for Neurologic Diseases, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA
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Affiliation(s)
- R Vassar
- Amgen Inc, Thousand Oaks, California 91320, USA.
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Haniu M, Denis P, Young Y, Mendiaz EA, Fuller J, Hui JO, Bennett BD, Kahn S, Ross S, Burgess T, Katta V, Rogers G, Vassar R, Citron M. Characterization of Alzheimer's beta -secretase protein BACE. A pepsin family member with unusual properties. J Biol Chem 2000; 275:21099-106. [PMID: 10887202 DOI: 10.1074/jbc.m002095200] [Citation(s) in RCA: 177] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cerebral deposition of amyloid beta-peptide is an early and critical feature of Alzheimer's disease. Amyloid beta-peptide is released from the amyloid precursor protein by the sequential action of two proteases, beta-secretase and gamma-secretase, and these proteases are prime targets for therapeutic intervention. We have recently cloned a novel aspartic protease, BACE, with all the known properties of beta-secretase. Here we demonstrate that BACE is an N-glycosylated integral membrane protein that undergoes constitutive N-terminal processing in the Golgi apparatus. We have used a secreted Fc fusion-form of BACE (BACE-IgG) that contains the entire ectodomain for a detailed analysis of posttranslational modifications. This molecule starts at Glu(46) and contains four N-glycosylation sites (Asn(153), Asn(172), Asn(223), and Asn(354)). The six Cys residues in the ectodomain form three intramolecular disulfide linkages (Cys(216)-Cys(420), Cys(278)-Cys(443), and Cys(330)-Cys(380)). Despite the conservation of the active site residues and the 30-37% amino acid homology with known aspartic proteases, the disulfide motif is fundamentally different from that of other aspartic proteases. This difference may affect the substrate specificity of the enzyme. Taken together, both the presence of a transmembrane domain and the unusual disulfide bond structure lead us to conclude that BACE is an atypical pepsin family member.
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Affiliation(s)
- M Haniu
- Amgen Inc., Thousand Oaks, California 91320-1799, USA.
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Abstract
Beta-site amyloid precursor protein cleaving enzyme (BACE) is a novel transmembrane aspartic protease that possesses all the known characteristics of the beta-secretase involved in Alzheimer's disease (Vassar, R., Bennett, B. D., Babu-Khan, S., Kahn, S., Mendiaz, E. A., Denis, P., Teplow, D. B., Ross, S., Amarante, P., Loeloff, R., Luo, Y., Fisher, S., Fuller, J., Edenson, S., Lile, J., Jarosinski, M. A., Biere, A. L., Curran, E., Burgess, T., Louis, J. -C., Collins, F., Treanor, J., Rogers, G., and Citron, M. (1999) Science 286, 735-741). We have analyzed the sequence and expression pattern of a BACE homolog termed BACE2. BACE and BACE2 are unique among aspartic proteases in that they possess a carboxyl-terminal extension with a predicted transmembrane region and together they define a new family. Northern analysis reveals that BACE2 mRNA is expressed at low levels in most human peripheral tissues and at higher levels in colon, kidney, pancreas, placenta, prostate, stomach, and trachea. Human adult and fetal whole brain and most adult brain subregions express very low or undetectable levels of BACE2 mRNA. In addition, in situ hybridization of adult rat brain shows that BACE2 mRNA is expressed at very low levels in most brain regions. The very low or undetectable levels of BACE2 mRNA in the brain are not consistent with the expression pattern predicted for beta-secretase.
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Affiliation(s)
- B D Bennett
- Amgen, Inc., Thousand Oaks, California 91320-1799, USA
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Vassar R, Bennett BD, Babu-Khan S, Kahn S, Mendiaz EA, Denis P, Teplow DB, Ross S, Amarante P, Loeloff R, Luo Y, Fisher S, Fuller J, Edenson S, Lile J, Jarosinski MA, Biere AL, Curran E, Burgess T, Louis JC, Collins F, Treanor J, Rogers G, Citron M. Beta-secretase cleavage of Alzheimer's amyloid precursor protein by the transmembrane aspartic protease BACE. Science 1999; 286:735-41. [PMID: 10531052 DOI: 10.1126/science.286.5440.735] [Citation(s) in RCA: 2812] [Impact Index Per Article: 112.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Cerebral deposition of amyloid beta peptide (Abeta) is an early and critical feature of Alzheimer's disease. Abeta generation depends on proteolytic cleavage of the amyloid precursor protein (APP) by two unknown proteases: beta-secretase and gamma-secretase. These proteases are prime therapeutic targets. A transmembrane aspartic protease with all the known characteristics of beta-secretase was cloned and characterized. Overexpression of this protease, termed BACE (for beta-site APP-cleaving enzyme) increased the amount of beta-secretase cleavage products, and these were cleaved exactly and only at known beta-secretase positions. Antisense inhibition of endogenous BACE messenger RNA decreased the amount of beta-secretase cleavage products, and purified BACE protein cleaved APP-derived substrates with the same sequence specificity as beta-secretase. Finally, the expression pattern and subcellular localization of BACE were consistent with that expected for beta-secretase. Future development of BACE inhibitors may prove beneficial for the treatment of Alzheimer's disease.
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Affiliation(s)
- R Vassar
- Amgen, Inc., One Amgen Center Drive, M/S 29-2-B, Thousand Oaks, CA 91320-1799, USA
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11
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Ross SL, Martin F, Simonet L, Jacobsen F, Deshpande R, Vassar R, Bennett B, Luo Y, Wooden S, Hu S, Citron M, Burgess TL. Amyloid precursor protein processing in sterol regulatory element-binding protein site 2 protease-deficient Chinese hamster ovary cells. J Biol Chem 1998; 273:15309-12. [PMID: 9624107 DOI: 10.1074/jbc.273.25.15309] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Amyloid peptides of 39-43 amino acids (Abeta) are the major constituents of amyloid plaques present in the brains of Alzheimer's (AD) patients. Proteolytic processing of the amyloid precursor protein (APP) by the yet unidentified beta- and gamma-secretases leads to the generation of the amyloidogenic Abeta peptides. Recent data suggest that all of the known mutations leading to early onset familial AD alter the processing of APP such that increased amounts of the 42-amino acid form of Abeta are generated by a gamma-secretase activity. Identification of the beta- and/or gamma-secretases is a major goal of current AD research, as they are prime targets for therapeutic intervention in AD. It has been suggested that the sterol regulatory element-binding protein site 2 protease (S2P) may be identical to the long sought gamma-secretase. We have directly tested this hypothesis using over-expression of the S2P cDNA in cells expressing APP and by characterizing APP processing in mutant Chinese hamster ovary cells that are deficient in S2P activity and expression. The data demonstrate that S2P does not play an essential role in the generation or secretion of Abeta peptides from cells, thus it is unlikely to be a gamma-secretase.
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Affiliation(s)
- S L Ross
- Department of Mammalian Cell Molecular Biology, Amgen Inc., Thousand Oaks, California 91320-1789, USA
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Mombaerts P, Wang F, Dulac C, Vassar R, Chao SK, Nemes A, Mendelsohn M, Edmondson J, Axel R. The molecular biology of olfactory perception. Cold Spring Harb Symp Quant Biol 1996; 61:135-45. [PMID: 9246442] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- P Mombaerts
- Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, College of Physicians & Surgeons, Columbia University, New York, New York 10032, USA
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Fülle HJ, Vassar R, Foster DC, Yang RB, Axel R, Garbers DL. A receptor guanylyl cyclase expressed specifically in olfactory sensory neurons. Proc Natl Acad Sci U S A 1995; 92:3571-5. [PMID: 7724600 PMCID: PMC42209 DOI: 10.1073/pnas.92.8.3571] [Citation(s) in RCA: 189] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
We have cloned an additional member (GC-D) of the membrane receptor guanylyl cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2] family that is specifically expressed in a subpopulation of olfactory sensory neurons. The extracellular, putative ligand-binding domain of the olfactory cyclase is similar in primary structure to two guanylyl cyclases expressed in the retina but diverges considerably from other known guanylyl cyclases. The expression of GC-D RNA is restricted to a small, randomly dispersed population of neurons that is within a single topographic zone in the olfactory neuroepithelium and resembles the pattern of the more diverse seven-transmembrane-domain odorant receptors. These observations suggest that GC-D may function directly in odor recognition or in modulating the sensitivity of a subpopulation of sensory neurons to specific odors.
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Affiliation(s)
- H J Fülle
- Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas 75235-9050, USA
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14
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Abstract
The detection of odorant receptor mRNAs within the axon terminals of sensory neurons has permitted us to ask whether neurons expressing a given receptor project their axons to common glomeruli within the olfactory bulb. In situ hybridization with five different receptor probes demonstrates that axons from neurons expressing a given receptor converge on one, or at most, a few glomeruli within the olfactory bulb. Moreover, the position of specific glomeruli is bilaterally symmetric and is constant in different individuals within a species. These data support a model in which exposure to a given odorant may result in the stimulation of a spatially restricted set of glomeruli, such that the individual odorants would be associated with specific topographic patterns of activity within the olfactory bulb.
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Affiliation(s)
- R Vassar
- Department of Biochemistry and Molecular Biophysics, Columbia University College of Physicians and Surgeons, New York, New York 10032
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Fuchs E, Coulombe P, Cheng J, Chan YM, Hutton E, Syder A, Degenstein L, Yu QC, Letai A, Vassar R. Genetic bases of epidermolysis bullosa simplex and epidermolytic hyperkeratosis. J Invest Dermatol 1994; 103:25S-30S. [PMID: 7525738 DOI: 10.1111/1523-1747.ep12398924] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Keratins are the major structural proteins of the epidermis. Analyzing keratin gene sequences, appreciating the switch in keratin gene expression that takes place as epidermal cells commit to terminally differentiate, and elucidating how keratins assemble into 10-nm filaments have provided the foundation that has led to the discoveries of the genetic bases of two major classes of human skin diseases. In this report, we review the cell biology and human genetics of these diseases, epidermolysis bullosa simplex and epidermolytic hyperkeratosis. Both of these diseases are epidermal disorders of keratin, typified by cell fragility as a consequence of defects in the mechanical strength of basal epidermolysis bullosa simplex or suprabasal epidermolytic hyperkeratosis cells.
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Affiliation(s)
- E Fuchs
- Department of Molecular Genetics and Cell Biology, Howard Hughes Medical Institute, University of Chicago, Illinois 60637
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Abstract
The signal elicited by the interaction of odorous ligands with receptors on olfactory sensory neurons must be decoded by the brain to determine which of the numerous receptors have been activated. We have examined the patterns of odorant receptor expression in the rat olfactory epithelium to determine whether the mammalian olfactory system employs spatial segregation of sensory input to encode the identity of an odorant stimulus. In situ hybridization experiments with probes for 11 different odorant receptors demonstrate that sensory neurons expressing distinct receptors are topologically segregated into a small number of broad, yet circumscribed, zones within the olfactory epithelium. Within a given zone, however, olfactory neurons expressing a specific receptor appear to be randomly distributed, rather than spatially localized. The complex mammalian olfactory system may therefore compartmentalize the epithelium into anatomically and functionally discrete units, such that each zone expresses only a subset of the entire receptor repertoire.
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Affiliation(s)
- R Vassar
- Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, College of Physicians and Surgeons, Columbia University, New York, New York 10032
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Vassar R, Hutton ME, Fuchs E. Transgenic overexpression of transforming growth factor alpha bypasses the need for c-Ha-ras mutations in mouse skin tumorigenesis. Mol Cell Biol 1992; 12:4643-53. [PMID: 1406654 PMCID: PMC360391 DOI: 10.1128/mcb.12.10.4643-4653.1992] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The induction of skin papillomas in mice can be divided into two different stages. Chemical initiation frequently elicits mutations in the Ha-ras gene, leading to the constitutive activation of ras. The second step, promotion, involves repetitive topical application of phorbol esters or wounding, leading to epidermal hyperproliferation and papilloma formation. We have found that overexpression of transforming growth factor alpha (TGF-alpha) in the basal epidermal layer of transgenic mice yielded papillomas directly upon wounding or 12-O-tetradecanoylphorbol-13-acetate treatment without the need for an initiator. Moreover, papillomas from TGF-alpha mice did not exhibit mutations in the Ha-ras gene. Interestingly, TGF-alpha acted synergistically with 12-O-tetradecanoylphorbol-13-acetate to enhance epidermal hyperproliferation. Our results demonstrate a central role for TGF-alpha overexpression in tumorigenesis and provide an important animal model for the study of skin tumorigenesis.
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Affiliation(s)
- R Vassar
- Department of Molecular Genetics and Cell Biology, Howard Hughes Medical Institute, University of Chicago, Illinois 60637
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Coulombe PA, Hutton ME, Vassar R, Fuchs E. A function for keratins and a common thread among different types of epidermolysis bullosa simplex diseases. J Biophys Biochem Cytol 1991; 115:1661-74. [PMID: 1721910 PMCID: PMC2289221 DOI: 10.1083/jcb.115.6.1661] [Citation(s) in RCA: 174] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Previously we demonstrated that transgenic mice expressing a mutant keratin in the basal layer of their stratified squamous epithelia exhibited a phenotype bearing resemblance to a subclass (Dowling Meara) of a heterogeneous group of human skin disorders known as epidermolysis bullosa simplex (EBS) (Vassar, R., P. A. Coulombe, L. Degenstein, K. Albers, E. Fuchs. 1991. Cell. 64:365-380.). The extent to which subtypes of EBS diseases might be genetically related is unknown, although they all exhibit skin blistering as a consequence of basal cell cytolysis. We have now examined transgenic mice expressing a range of keratin mutants which perturb keratin filament assembly to varying degrees. We have generated phenotypes which include most subtypes of EBS, demonstrating for the first time that at least in mice, these diseases can be generated by different mutations within a single gene. A strong correlation existed between the severity of the disease and the extent to which the keratin filament network was disrupted, implicating perturbations in keratin networks as an essential component of these diseases. Some keratin mutants elicited subtle perturbations, with no signs of the tonofilament clumping typical of Dowling-Meara EBS and our previous transgenic mice. Importantly, basal cell cytolysis still occurred, thereby uncoupling cytolysis from the generation of large, insoluble cytoplasmic protein aggregates. Moreover, cell rupture occurred in a narrowly defined subnuclear zone, and seemed to involve three factors: (a) filament perturbation, (b) the columnar shape of the basal cell, and (c) physical trauma. This work provides the best evidence to date for a structural function of a cytoplasmic intermediate filament network, namely to impart mechanical integrity to the cell in the context of its tissue.
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Affiliation(s)
- P A Coulombe
- Howard Hughes Medical Institute, Department of Molecular Genetics and Cell Biology, University of Chicago, Illinois 60637
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19
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Abstract
Transforming growth factor-alpha (TGF-alpha) is thought to be the major autocrine factor controlling growth in epidermal cells. To explore further the role of TGF-alpha in epidermal growth and differentiation, we used a human keratin K14 promoter to target expression of rat TGF-alpha cDNA to the stratified squamous epithelia of transgenic mice. Unexpectedly, the only regions of epidermis especially responsive to TGF-alpha overexpression were those that were normally thick and where hair follicle density was typically low. This included most, if not all, body skin from 2-day- to 2-week-old mice, and ear, footpad, tail, and scrotum skin in adult mice. In these regions, excess TGF-alpha resulted in thicker epidermis and more stunted hair growth. Epidermal thickening was attributed both to cell hypertrophy and to a proportional increase in the number of basal, spinous, granular, and stratum corneum cells. During both postnatal development and epidermal differentiation, responsiveness to elevated TGF-alpha seemed to correlate with existing epidermal growth factor (EGF) receptor levels, and we saw no evidence for TGF-alpha-mediated control of EGF receptor (EGFR) expression. In adults, no squamous cell carcinomas were detected, but benign papillomas were common, developing primarily in regions of mechanical irritation or wounding. In addition, adult transgenic skin that was still both sensitive to TGF-alpha and subject to mild irritation displayed localized regions of leukocytic infiltration and granular layer loss, characteristics frequently seen in psoriasis in humans. These unusual regional and developmental effects of TGF-alpha suggest a natural role for the growth factor in (1) controlling epidermal thickness during development and differentiation, (2) involvement in papilloma formation, presumably in conjunction with TGF-beta, and (3) involvement in psoriasis, in conjunction with some as yet unidentified secondary stimulus stemming from mild mechanical irritation/bacterial infection.
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Affiliation(s)
- R Vassar
- Howard Hughes Medical Institute, Department of Molecular Genetics and Cell Biology, University of Chicago, Illinois 60637
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Vassar R, Coulombe PA, Degenstein L, Albers K, Fuchs E. Mutant keratin expression in transgenic mice causes marked abnormalities resembling a human genetic skin disease. Cell 1991; 64:365-80. [PMID: 1703046 DOI: 10.1016/0092-8674(91)90645-f] [Citation(s) in RCA: 344] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
To explore the relationship between keratin gene mutations and genetic disease, we made transgenic mice expressing a mutant keratin in the basal layer of their stratified squamous epithelia. These mice exhibited abnormalities in epidermal architecture and often died prematurely. Blistering occurred easily, and basal cell cytolysis was evidence at the light and electron microscopy levels. Keratin filament formation was markedly altered, with keratin aggregates in basal cells. In contrast, terminally differentiating cells made keratin filaments and formed a stratum corneum. Recovery of outer layer cells was attributed to down-regulation of mutant keratin expression and concomitant induction of differentiation-specific keratins as cells terminally differentiate, and the fact that these cells arose from basal cells developing at a time when keratin expression was relatively low. Collectively, the pathobiology and biochemistry of the transgenic mice and their cultured keratinocytes bore a resemblance to a group of genetic disorders known as epidermolysis bullosa simplex.
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Affiliation(s)
- R Vassar
- Howard Hughes Medical Institute, University of Chicago, Illinois 60637
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Leask A, Rosenberg M, Vassar R, Fuchs E. Regulation of a human epidermal keratin gene: sequences and nuclear factors involved in keratinocyte-specific transcription. Genes Dev 1990; 4:1985-98. [PMID: 1703506 DOI: 10.1101/gad.4.11.1985] [Citation(s) in RCA: 128] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The keratinocyte is a major cell type of the body, and in epidermis, keratinocytes have potential for future gene targeting and drug therapy. Despite the importance of keratinocytes in cell biology and medicine, little is known about the molecular mechanisms underlying keratinocyte-specific gene expression. Here, we report the first detailed characterization of the sequences and factors controlling expression of a human gene expressed specifically in keratinocytes. Using 5' upstream sequence of the human K14 keratin gene coupled to one of two reporter genes, we examined sequences necessary and sufficient for expression of K14 in both cultured human keratinocytes and in mitotically active basal keratinocytes of transgenic mouse epidermis. We demonstrated the existence of distal and proximal elements located 5' from the transcription initiation site of the hK14 gene, which when combined with a TATA box element, appear to act in concert to drive keratinocyte-specific expression. We examined the proximal region in detail. After using CAT assays to narrow a transcriptional activation element to within 110 bp, we demonstrated the existence of a keratinocyte nuclear factor which binds to a 10-bp palindrome, 5'-GCCTGCAGGC-3', within this domain. Using methylation interference analysis, we identified the G residues important for factor binding, and showed that point mutations in these G residues not only blocked factor binding but also resulted in decreased transcriptional activity of an hK14-CAT gene. The factor was most abundant in keratinocytes, was expressed at lower levels in some simple epithelial cell lines, and was not detected in fibroblasts or lymphoma cells. Moreover, the 10-bp sequence was similar to sequences found in the 5' upstream sequences of several other genes expressed in keratinocytes, and at least one of these genes, the human K1 gene, contained a sequence that competed with the hK14 proximal element for binding factor. Collectively, our data suggest that both the sequence and the nuclear factor that we have identified may be involved in controlling keratinocyte-specific expression in vitro and in vivo.
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Affiliation(s)
- A Leask
- Howard Hughes Medical Institute, Department of Molecular Genetics and Cell Biology, University of Chicago, Illinois 60637
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Vassar R, Rosenberg M, Ross S, Tyner A, Fuchs E. Tissue-specific and differentiation-specific expression of a human K14 keratin gene in transgenic mice. Proc Natl Acad Sci U S A 1989; 86:1563-7. [PMID: 2466292 PMCID: PMC286738 DOI: 10.1073/pnas.86.5.1563] [Citation(s) in RCA: 289] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
A construct containing approximately 2500 base pairs (bp) of 5' upstream and approximately 700 bp of 3' downstream sequence was used to drive the expression of an intronless human K14 gene in vitro and in vivo. To track the expression of the gene, a small sequence encoding the antigenic portion of neuropeptide substance P was inserted in frame 5' to the TGA translation stop codon of the gene. Surprisingly, this gene was expressed promiscuously in a wide variety of cultured cells transiently transfected with the construct. In contrast, when introduced into the germ line of transgenic mice, the construct was expressed in a fashion analogous to the endogenous K14 gene--namely, in the basal layer of stratified squamous epithelia. Our results suggest that some regulatory mechanism is overridden as a consequence of transient transfection but that sequences that can control proper K14 expression are present in the construct. The appropriate tissue-specific and differentiation-specific expression of K14.P in transgenic mice is an important first step in characterizing a promoter that could be employed to drive the foreign expression of drug-related genes in the epidermis of skin grafts.
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Affiliation(s)
- R Vassar
- Department of Molecular Genetics and Cell Biology, University of Chicago, IL 60637
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