Morphological and biochemical mechanisms linked to the development of papilloma-independent metastatic squamous cell carcinoma in PKC epsilon overexpression transgenic mice

We have previously shown that targeted overexpression of protein kinase C epsilon (PKCepsilon) to mouse skin resulted in the development of papilloma-independent squamous cell carcinomas (SCC) elicited by 7,12-dimethylbenz(a)anthracene (DMBA) initiation and 12-O-tetradecanoylphorbol-13-acetate (TPA) promotion. Skin histology showed 1x TPA application to DMBA-initiated skin resulted in extensive infiltration of polymorphonuclear neutrophils (PMNs) into the epidermis at 24 h after TPA treatment in PKCepsilon Tg mice while wild type (WT) mouse skin showed focal infiltration by PMNs. Epidermal destruction and regeneration beginning from hair follicles were observed at 48 and 72 h, respectively, in PKCepsilon Tg mice only. To evaluate the role of cell death in tumorigenesis, double-initiation experiments were performed. Reductions in papilloma formation were observed in double-initiated WT and single-/double-initiated PKCepsilon Tg mice, and were inversely correlated with indices of cell death of interfollicular keratinocytes. These data suggested that the origin of papillomas is in interfollicular epidermis. In PKCepsilon Tg mice, 1xDMBA-1xTPA treatment led to epidermal destruction eliminating the initiated interfollicular cells originally destined to become papillomas; after multiple TPA treatments, epidermal destruction did not occur, presumably reflecting adaptation of epidermis to chronic TPA treatment. Histology studies showed an increase in mitosis in hair follicles of PKCepsilon Tg mice chronically treated with TPA; SCC arose from sites immediately adjacent to hyperplastic hair follicles.; Since PKCs are major causes of posttranslational modifications via phosphorylations, we analyzed the subcellular distribution of PKCepsilon using immunogold electron microscopy (EM). Numerous differences in PKCepsilon distributions in analysis of interfollicular or follicular epidermis treated with single or multiple TPA treatments in WT versus PKCepsilon Tg mice were observed. In all cases, changes involved mitochondria or plasma membrane, organelles previously proven to regulate cell proliferation. Comparing PKCepsilon Tg mice after 18x or 40x TPA treatments immunogold EM showed significantly increased PKCepsilon localization associated with decreased oxidative damage in plasma membranes. Since mice treated with 40x but not 18x TPA had multiple SCC, we postulate that redistribution of PKCepsilon to the plasma membrane and reduced plasma membrane oxidative damage in follicular epidermal cells may be important features of preneoplastic skin that may contribute to SCC formation in PKCepsilon Tg mice.