Publications (32)188.78 Total impact
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Article: A splice variant of alpha 6 integrin is associated with malignant conversion in mouse skin tumorigenesis.
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ABSTRACT: The epithelial-specific integrin alpha 6 beta 4 is suprabasally expressed in benign skin tumors (papillomas) and is diffusely expressed in carcinomas associated with an increase in the proliferating compartment. Analysis of RNA samples by reverse transcriptase-PCR and DNA sequencing revealed that chemically or oncogenically induced papillomas (n = 8) expressed a single transcript of the alpha 6 subunit, identified as the alpha 6 A splice variant. In contrast, carcinomas (n = 13) expressed both alpha 6A and an alternatively spliced form, alpha 6B. Primary keratinocytes and a number of keratinocyte cell lines that vary in biological potential from normal skin, to benign papillomas, to well-differentiated slowly growing carcinomas exclusively expressed alpha 6A. However, I7, an oncogene-induced cell line that produces highly invasive carcinomas, expressed both alpha 6A and alpha 6B transcript and protein. The expression of alpha 6B in I7 cells was associated with increased attachment to a laminin matrix compared to cell lines exclusively expressing alpha 6A. Furthermore, introduction of an alpha 6B expression vector into a papilloma cell line expressing alpha 6A increased laminin attachment. When a papilloma cell line was converted to an invasive carcinoma by introduction of the v-fos oncogene, the malignant cells expressed both alpha 6A and alpha 6B, while the parent cell line and cells transduced with v-jun or c-myc, which retained the papilloma phenotype, expressed only alpha 6A. Comparative analysis of alpha 6B expression in cell lines and their derived tumors indicate that alpha 6B transcripts are more abundant in tumors than cell lines, and alpha 6B is expressed to a greater extent in poorly differentiated tumors. These results establish a link between malignant conversion and invasion of squamous tumor cells and the regulation of transcript processing of the alpha 6 beta 4 integrin.Proceedings of the National Academy of Sciences 08/1995; 92(15):7041-5. · 9.68 Impact Factor -
Article: Mouse skin tumor progression results in differential expression of retinoic acid and retinoid X receptors.
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ABSTRACT: Retinoids are powerful regulators of epidermal cell growth and differentiation and are widely used in the prevention and treatment of skin disorders and cancers in humans. Since many of the effects of retinoids on cell growth and differentiation are mediated by nuclear retinoid receptors (RARs and RXRs), we were interested in determining RAR and RXR gene expression during mouse skin tumor progression. The two-stage system of mouse skin carcinogenesis was used to generate papillomas and carcinomas, and the different stages of malignant progression (papillomas, differentiated squamous cell carcinomas, undifferentiated squamous cell carcinomas, and spindle cell carcinomas) were characterized in each tumor by specific keratin expression prior to receptor characterization. Using in situ hybridization analysis, we show that the two major RAR isoforms (alpha 1 and gamma 1), which account for most of RARs in the skin, were expressed in both the basal and suprabasal layers in mouse epidermis. In contrast, RXR alpha transcripts were compartmentalized to the basal cell layers and concentrated in hair follicles. During skin tumor progression, RAR (alpha 1 and gamma 1) transcripts were down-modulated in malignant tumor cells, whereas RXR (alpha and beta) transcript expression was expanded in papillomas and carcinomas as the number of undifferentiated cells also increased. RXR gamma was not detected in the skin or at any stage during skin tumor progression. Spindle cell tumors lacked markers of the keratinocyte phenotype and lost RAR expression, yet retained expression of RXR alpha and beta. The increased abundance of transcripts for RXRs and decreased presence of RARs in skin tumor progression may favor other nuclear signal transduction pathways requiring RXR for heterodimer formation and contribute to phenotypic progression of cancer cells.Cancer Research 08/1995; 55(13):2774-82. · 7.86 Impact Factor -
Article: Targeted disruption of mouse EGF receptor: effect of genetic background on mutant phenotype.
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ABSTRACT: Gene targeting was used to create a null allele at the epidermal growth factor receptor locus (Egfr). The phenotype was dependent on genetic background. EGFR deficiency on a CF-1 background resulted in peri-implantation death due to degeneration of the inner cell mass. On a 129/Sv background, homozygous mutants died at mid-gestation due to placental defects; on a CD-1 background, the mutants lived for up to 3 weeks and showed abnormalities in skin, kidney, brain, liver, and gastrointestinal tract. The multiple abnormalities associated with EGFR deficiency indicate that the receptor is involved in a wide range of cellular activities.Science 08/1995; 269(5221):230-4. · 31.20 Impact Factor -
Article: The role of growth factors in mouse skin tumor promotion and premalignant progression.
Progress in clinical and biological research 02/1995; 391:39-48. -
Article: Isolation and utilization of epidermal keratinocytes for oncogene research.
Methods in Enzymology 02/1995; 254:3-20. · 2.04 Impact Factor -
Article: Role of oncogenes and tumor suppressor genes in multistage carcinogenesis.
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ABSTRACT: The introduction of the techniques of molecular biology as tools to study skin carcinogenesis has provided more precise localization of biochemical pathways that regulate the tumor phenotype. This approach has identified genetic changes that are characteristic of each of the specific stages of squamous cancer pathogenesis: initiation, exogenous promotion, premalignant progression, and malignant conversion. Initiation can result from mutations in a single gene, and the Harvey allele of the ras gene family has been identified as a frequent site for initiating mutations. Heterozygous activating mutations in c-rasHa are dominant, and affected keratinocytes hyperproliferate and are resistant to signals for terminal differentiation. An important pathway impacted by c-rasHa activation is the protein kinase C (PKC) pathway, a major regulator of keratinocyte differentiation. Increased activity of PKC alpha and suppression of PKC delta by tyrosine phosphorylation contribute to the phenotypic consequences of rasHa gene activation in keratinocytes. Tumor promoters disturb epidermal homeostasis and cause selective clonal expansion of initiated cells to produce multiple benign squamous papillomas. Resistance to differentiation and enhanced growth rate of initiated cells impart a growth advantage when the epidermis is exposed to promoters. The frequency of premalignant progression varies among papillomas, and subpopulations at high risk for progression have been identified. These high-risk papillomas overexpress the alpha 6 beta 4 integrin and are deficient in transforming growth factor beta 1 and beta 2 peptides, two changes associated with a very high proliferation rate in this subset of tumors. The introduction of an oncogenic rasHa gene into epidermal cells derived from transgenic mice with a null mutation in the TGF beta 1 gene have an accelerated rate of malignant progression when examined in vivo. Thus members of the TGF beta gene family contribute a tumor-suppressor function in carcinogenesis. Accelerated malignant progression is also found with v-rasHa transduced keratinocytes from skin of mice with a null mutation in the p53 gene. The similarities in risk for malignant conversion by initiated keratinocytes from TG beta 1 and p53 null geneotypes suggest that a common, growth-related pathway may underly the tumor-suppressive functions of these proteins in the skin carcinogenesis model.Journal of Investigative Dermatology 12/1994; 103(5 Suppl):90S-95S. · 6.31 Impact Factor -
Article: The suprabasal expression of alpha 6 beta 4 integrin is associated with a high risk for malignant progression in mouse skin carcinogenesis.
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ABSTRACT: Enhanced expression of the alpha 6 beta 4 integrin complex has been linked to malignant progression in mouse skin carcinogenesis. To determine if alpha 6 beta 4 expression can predict risk for malignant conversion among populations of benign skin tumors, we analyzed the distribution of alpha 6 beta 4 and other markers of progression in papillomas at high and low risk for malignant progression. After initiation with 7,12-dimethylbenz[a]anthracene, mice were promoted with 12-O-tetradecanoylphorbol-13-acetate to induce predominantly low risk tumors or promoted with mezerein to produce predominantly high risk tumors. When tumors first appeared at 8 weeks after promotion, high risk papillomas demonstrated basal and suprabasal alpha 6 beta 4 expression, loss of keratin 1, and aberrant expression of keratin 13. In these tumors alpha 6 beta 4 expression coincided with an expansion of the proliferating compartment as indicated by suprabasal bromodeoxyuridine labeling. In contrast, alpha 6 beta 4 immunostaining was confined to basal cells in low risk tumors, keratin 1 was abundant, and keratin 13 was absent in the majority of this group, while proliferating cells were largely in the basal compartment. By 33 weeks, alpha 6 beta 4 suprabasal expression continued to distinguish groups at higher risk for malignant conversion, but keratin 13 was expressed in all groups. At this time, high risk tumors displayed focal expression of keratin 8 and gamma-glutamyltranspeptidase, markers also found in chemically induced carcinomas. Keratin 8 and gamma-glutamyltranspeptidase were expressed only in alpha 6 beta 4 positive cells. These results indicate that expression of alpha 6 beta 4 integrin in suprabasal strata serves as an early predictive marker to identify benign squamous tumors at high risk for malignant progression.Cancer Research 11/1993; 53(20):4803-10. · 7.86 Impact Factor -
Article: Loss of expression of transforming growth factor beta in skin and skin tumors is associated with hyperproliferation and a high risk for malignant conversion.
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ABSTRACT: Mouse skin carcinomas arise from a small subpopulation of benign papillomas with an increased risk of malignant conversion. These papillomas arise with limited stimulation by tumor promoters, appear rapidly, and do not regress, suggesting that they differ in growth properties from the majority of benign tumors. The transforming growth factor beta (TGF-beta) proteins are expressed in the epidermis and are growth inhibitors for mouse keratinocytes in vitro; altered TGF-beta expression could influence the growth properties of high-risk papillomas. Normal epidermis, tumor promoter-treated epidermis, and skin papillomas at low risk for malignant conversion express TGF-beta 1 in the basal cell compartment and TGF-beta 2 in the suprabasal strata. In low-risk tumors, 90% of the proliferating cells are confined to the basal compartment. In contrast, the majority of high-risk papillomas are devoid of both TGF-beta 1 and TGF-beta 2 as soon as they arise; these tumors have up to 40% of the proliferating cells in the suprabasal layers. Squamous cell carcinomas are also devoid of TGF-beta, suggesting that they arise from the TGF-beta-deficient high-risk papillomas. In some high-risk papillomas, TGF-beta 1 loss can occur first and correlates with basal cell hyperproliferation, while TGF-beta 2 loss correlates with suprabasal hyperproliferation. Similarly, TGF-beta 1-null transgenic mice, which express wild-type levels of TGF-beta 2 in epidermis but no TGF-beta 1 in the basal layer, have a hyperproliferative basal cell layer without suprabasal proliferation. In tumors, loss of TGF-beta is controlled at the posttranscriptional level and is associated with expression of keratin 13, a documented marker of malignant progression. These results show that TGF-beta expression and function are compartmentalized in epidermis and epidermal tumors and that loss of TGF-beta is an early, biologically relevant risk factor for malignant progression.Proceedings of the National Academy of Sciences 08/1993; 90(13):6076-80. · 9.68 Impact Factor -
Article: Epidermal growth factor receptor ligands regulate keratin 8 expression in keratinocytes, and transforming growth factor alpha mediates the induction of keratin 8 by the v-rasHa oncogene.
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ABSTRACT: Cytokeratins 8 and 18 (Endo A and B) are among the earliest expressed embryonic genes and the major components of the cytoskeleton in simple epithelia of the adult. Recent data indicate that these cytokeratins are aberrantly expressed in several epithelial tumor types and that expression in cultured mouse keratinocytes is linked to activation of the rasHa oncogene. Furthermore, up-regulation of K8/K18 in keratinocytes is associated with reciprocal suppression of K1. We now show that the aberrant expression of K8 and K18 and suppression of K1 in cultured keratinocytes transduced with the v-rasHa gene are mediated by a factor secreted into the culture medium. Furthermore, transforming growth factor alpha (TGF-alpha) and epidermal growth factor elicit an identical pattern of K8/K18 expression and K1 suppression in normal keratinocytes. The factor in medium from v-rasHa keratinocytes is TGF-alpha, as a specific blocking antibody for rat and mouse TGF-alpha prevents the expression of K8 and restores expression of K1. The tyrosine kinase inhibitor genistein also prevents K8 induction in v-rasHa keratinocytes and in normal keratinocytes treated with TGF-alpha- or v-rasHa-conditioned medium. However, simply stimulating proliferation of keratinocytes by cholera toxin does not result in expression of K8 or suppression of K1. Finally, tumor grafts from neoplastic epidermal cells overexpressing TGF-alpha via retroviral transduction of human TGF-alpha complementary DNA in vitro show coordinate expression of K8 and human TGF-alpha. These studies indicate that K8 expression in keratinocytes, and derivative neoplastic cells, in vivo and in vitro is regulated by epidermal growth factor receptor ligands. Since the expression of cytokines and K8/K18 in early embryogenesis is often coincident, cytokines may be the physiological mediators of K8/K18 expression in embryonic cells.Cell growth & differentiation: the molecular biology journal of the American Association for Cancer Research 05/1993; 4(4):317-27. -
Article: Critical aspects of initiation, promotion, and progression in multistage epidermal carcinogenesis.
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ABSTRACT: Carcinogenesis in mouse skin can be divided into three distinct stages: initiation, promotion, and progression (malignant conversion). Initiation, induced by a single exposure to a genotoxic carcinogen, can result from a mutation in a single critical gene (e.g., rasHa), apparently in only a few epidermal cells. The change is irreversible. Promotion, resulting in the development of numerous benign tumors (papillomas), is accomplished by the repeated application of a nonmutagenic tumor promoter. The effects of single applications of tumor promoters are reversible since papillomas do not develop after insufficient exposure of initiated skin to promoters or when the interval between individual promoter applications is increased sufficiently. The reversibility of promotion suggests an epigenetic mechanism. Promoter treatment provides an environment that allows the selective clonal expansion of foci of initiated cells. The conversion of squamous papillomas to carcinomas (termed progression or malignant conversion) occurs spontaneously at a low frequency. The rate of progression to malignancy can be significantly increased by treatment of papilloma-bearing mice with certain genotoxic agents. These progressor agents or converting agents are likely to act via a second genetic change in papillomas already bearing the initiating mutation. Progression in the skin is characterized by genetic changes that result in several distinct changes in the levels or activity of structural proteins, growth factors, and proteases. The mechanisms involved in progression are being studied in epidermal cell culture. In order to determine the in vivo phenotype of cultured cells, a grafting system was developed in which the cells were transferred from culture to a prepared skin bed in athymic mice. Introduction of an activated v-fos oncogene into initiated cells bearing an activated rasHa gene produced cells with a carcinoma phenotype, i.e., carcinomas formed when the cells were grafted as part of reconstituted skin. Grafted keratinocytes containing the rasHa gene alone produced papillomas; with v-fos alone, normal skin formed when grafted. The rasHa/fos carcinomas showed changes in differentiation markers characteristic of chemically induced carcinomas. A cell culture assay utilizing cells initiated by the introduction of an activated rasHa oncogene was developed to study progression. After exposure of initiated cells to progressor agents under conditions in which the proliferation of the rasHa-initiated cells was suppressed, proliferating foci developed, with a good correlation of activity in the assay with activity in the progression stage in vivo. The cell culture assay provides a quantitative model to study chemically induced neoplastic progression and may be useful to identify potential progressor agents.Proceedings of The Society for Experimental Biology and Medicine 02/1993; 202(1):1-8. -
Article: Extracellular matrix receptors and mouse skin carcinogenesis: altered expression linked to appearance of early markers of tumor progression.
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ABSTRACT: Interaction of cells with the basement membrane is important for cell proliferation and differentiation. Disruption of the basement membrane is an early event during progression of benign tumors to cancer. Using the techniques of immunohistochemistry and immunofluorescence, we show that cell-matrix interactions via the cell surface integrin receptors alpha 3 beta 1, alpha 5 beta 1, alpha 6 beta 4, the Mr 67,000 laminin receptor (67LR) laminin-binding protein, and the secreted matrix protein laminin are strictly regulated during differentiation of mouse epidermis. While alpha 6 beta 4 and alpha 5 beta 1 are polarized to the basal surface of basal cells in contact with the basement membrane, alpha 3 beta 1 and the non-integrin 67LR are primarily detected in the cell periphery of suprabasal cells, where cell to cell contacts are found. Sequential changes in expression of matrix receptors occur following multistage carcinogenesis of mouse skin. In an analysis of benign and malignant skin tumors induced by chemical carcinogens or oncogene transduction, we found that alpha 3 beta 1 and alpha 5 beta 1 as well as the non-integrin 67LR are sequentially down-regulated in the progression from benign to malignant, while alpha 6 beta 4 is the predominant receptor expressed in the carcinomas. Tumor expression of alpha 6 beta 4 is not polarized and is dissociated from its colocalized normal partner bullous pemphigoid antigen, which remains restricted to the basement membrane. The changes in matrix receptors are linked to appearance of keratin 13 in suprabasal regions, but always in alpha 6 beta 4 negative cells. The predominance of alpha 6 beta 4 in the proliferating cells during progression is associated with decreased expression of keratin 13 in carcinomas. These results suggest that matrix interactions with its receptors are important determinants of ordered differentiation in normal skin and show characteristic alterations during carcinogenesis that parallel changes in differentiation of the tumors.Cancer Research 06/1992; 52(10):2966-76. · 7.86 Impact Factor -
Article: Insulin receptor regulation of cell surface integrins: a possible mechanism contributing to the development of diabetic complications.
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ABSTRACT: Insulin plays a central role in regulating cellular growth in addition to its classic effects to regulate fuel metabolism. In a previous study, we have identified a patient who was homozygous for a deletion of the insulin receptor gene. In our current investigation, we used cultured skin fibroblasts from this patient as a model system in which to investigate the mechanisms whereby insulin regulates cellular growth in vitro. After cell division, skin fibroblasts from normal individuals migrate on the tissue culture plate and appear to be distributed randomly over the surface of the plate. In contrast, the patient's cells grew in clumps. Furthermore, the patient's fibroblasts exhibited a marked increase in the expression of several integrin subunits, especially the alpha5- and beta1-subunits that comprise the fibronectin receptor. Because the cellular growth pattern was restored to normal when cells were cultivated in the presence of blocking antibodies directed against either alpha5- or beta1-integrin subunits, we infer that increased expression of alpha5beta1-integrin may be the cause of the observed abnormality in the growth of the patient's cells in vitro. Furthermore, insulin stimulation led to downregulation of the levels of the alpha5- and beta1-integrin subunits in normal human fibroblasts but not in the patient's cells that lacked insulin receptors. Taken together, these data suggest that insulin's ability to regulate the expression of cell surface integrins may contribute to the mechanisms whereby insulin regulates cell growth. In light of the important role of integrins in mediating interactions between cells and the basement membrane, we suggest that dysregulation of integrin expression might contribute to the abnormalities in the structure of the basement membranes associated with the chronic microvascular complications of diabetes.Proceedings of the Association of American Physicians 110(4):333-9.
Top co-authors
Top Journals
Institutions
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2007
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Deutsches Krebsforschungszentrum
Heidelberg, Baden-Wuerttemberg, Germany
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2000–2001
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Tel Aviv University
- Department of Pathology
Tel Aviv, Tel Aviv, Israel
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1998–2001
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Bar Ilan University
- Faculty of Life Sciences
Ramat Gan, Tel Aviv, Israel
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1993–1996
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National Cancer Institute (USA)
- Cancer Etiology Branch (CEB)
Bethesda, MD, USA
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1992–1996
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National Institutes of Health
- Laboratory of Human Carcinogenesis
Bethesda, MD, USA
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