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Proteins from mouse epidermis cytosol extracts react on immunoblots with a polyclonal rabbit antiserum raised against rat skin calcium-binding protein (SCaBP), a parvalbumin of the panniculus carnosus. Three mouse epidermal proteins with molecular weights between 10-12K, which are distinct from SCaBP, are recognized by the antiserum. The synthesis of these proteins in keratinocyte culture is modulated by Ca++, as is the differentiation of the keratinocytes. Proliferating mouse keratinocytes in medium containing 0.07 mM Ca++ (low CaCa++) undergo terminal differentiation when the Ca++ concentration is elevated to 1.8 mM (high Ca++). Synthesis of the 3 antigens can be demonstrated when soluble extracts of keratinocytes labeled with [35S]methionine in low Ca++ medium are immunoprecipitated with anti-SCaBP serum. These antigens are not synthesized in cultures of dermal fibroblasts. When keratinocytes are switched to high Ca++ medium, synthesis of these antigens is greatly diminished over the course of 48-72 h. However, the antigens persist in differentiating cells. When proliferating keratinocytes in low Ca++ medium are exposed to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), differentiation is induced in a subpopulation of cells, and specific antigen synthesis is transiently inhibited. The inhibition correlates with the time when many cells are differentiating in response to TPA. When proliferating keratinocytes are pulse-labeled with 32PO4, the 11 K antigen is phosphorylated and the phosphorylation is not enhanced by TPA exposure. All 3 antigens are synthesized in a reticulocyte lysate preparation with added newborn mouse epidermis messenger RNA or mRNA from keratinocytes cultured in low Ca++ medium. Thus, these antigens are likely to represent unique proteins rather than processed or degraded ones. The coordinately regulated expression of these antigens associated with the differentiation state of the keratinocyte proliferation and differentiation. [ABSTRACT FROM AUTHOR]

Complementary DNA (cDNA) clones constructed to the 55, 59 and 67 kilodalton (K) keratins, the major keratins synthesized in newborn mouse epidermis, were used as molecular hybridization probes to examine the expression of these genes in newborn epidermis and normal and malignantly transformed epidermal cells in culture. Transcripts of these three keratin genes are abundant in newborn epidermis. However, primary cultures of epidermal cells contain very low levels of these RNAs, The decreased expression of these keratin genes in primary cells appears to be due to factors within the culture system. Unlike primary-cell cultures, the malignantly transformed cell line Pam 212 synthesizes keratin proteins and mRNAs similar to newborn epidermis, including the 67 K keratin, However, synthesis of the 67 K keratin in Pam 212 cells is modulated by culture factors. Keratin gene expression in another Pam line, 321, differs from that of Pam 212 cells in that decreased expression of these three keratin genes occurs. These results indicate that keratin genes that are normally expressed in vivo in epidermis may be expressed in malignant epidermal cells under conditions that do not permit expression of these genes in nonmalignant primary epidermal cells. [ABSTRACT FROM AUTHOR]

The polyacrylamide SDS electrophoretic pattern of protein extracted from the stratum corneum obtained by scraping the surface of involved skin of patients with psoriasis was different from that of uninvolved skin and normal controls. The pattern from superficial scales was similar to that of whole stratum corneum in the case of involved psoriatic epidermis but different in uninvolved and normal epidermis. These data indicate that the changes which are observed in the structural proteins during normal keratinization are not seen in involved psoriatic epidermis. In addition, the relative proportion of keratin polypeptides was different in involved psoriatic epidermis compared to normal skin. That these changes are not specific for psoriasis was shown by finding similar electrophoretic patterns with stratum corneum proteins from patients with other keratinizing disorders. [ABSTRACT FROM AUTHOR]

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 PKCα and suppression of PKCδ 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 α6β4 integrin and are deficient in transforming growth factor β1 and β2 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 TGFβ1 gene have an accelerated rate of malignant progression when examined in vivo. Thus members of the TGFβ 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 TGFβ 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. [ABSTRACT FROM AUTHOR]