Ras oncogene mediated transformation of mouse keratinocytes to a benign squamous papilloma phenotype is associated with activation of PKC-alpha. Tumors produced by ras transformation of keratinocytes derived from skin targeted PKC-alpha transgenic mice produced in our laboratory grow faster and achieve a larger size, but do not convert to malignancy at a higher rate. Activation of a PKC-alpha transgene by TPA in mouse epidermis induced a marked intraepidermal neutrophilic infiltrate that mimics the inflammatory response in several human cutaneous diseases including psoriasis. Multiple chemokines are upregulated detected by RT-PCR and RPA assays, and supernatants from cultured transgenic keratinocytes contain chemotactic factors for murine neutrophils. In vitro chemotaxis assays indicate that relevant chemokines are downstream of TNF-alpha. Activation of PKC-alpha in transgenic skin causes epidermal apoptosis, and this is prevented in cultured transgenic keratinocytes by inhibiting AP-1 activity. Microarray analysis of TPA treated transgenic keratinocytes has revealed a spectrum of PKC-alpha regulated genes, including differentiation markers, chemokines/cytokines and proteases and these can be selectively altered by specific inhibitors of the AP-1 and NFkappaB pathways. This model continues to reveal unique insights into the regulation of cutaneous inflammation, the regulation of pro-inflammatory and pro-apoptotic pathways in skin and the contribution of inflammation to cutaneous carcinogenesis. Activation of PKC inactivates the AKT kinase in mouse keratinocytes through prevention or reversal of AKT phosphorylation on serine 473. Inhibition of PKC activity enhances IGF-1- mediated protection from UV induced apoptosis, presumably by enhancing AKT activity as detected by AKT phosphorylation. The specific PKC isoforms targeting AKT appear to be delta and/or epsilon. The genomic structures of C. elegans, mouse, rat and human PKCdelta were analyzed after sequencing a genomic fragment of mouse PKC. Overall exon-intron genomic structure was highly conserved among mammals while significantly diverged in C. elegans. A 1.7 kb region of the PKC-delta promoter revealed a hitherto unknown NFkappaB site, and TNF-alpha was shown to upregulate the expression of the gene. Disruption of the nuclear tumor suppressor gene PML function in skin by targeting the PML-RAR-alpha fusion oncogene to the skin of transgenic mice causes spontaneous skin tumor induction. This is associated with cutaneous retinoid deficiency. Tumor development is independent of ras gene mutations. When PML is targeted to the epidermis in transgenic mice, transgenic keratinocytes in vitro senesce more rapidly, adhere more tightly to collagen substrates and have altered proteolytic activity. In vivo, PML transgenic mice undergo spontaneous alopecia, and have delayed skin tumor formation, smaller tumors and a longer latency to carcinoma formation when treated topically with carcinogens.
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