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Protein Kinase C Overexpressing Transgenic Mice Are Resistant to Chemically but not to UV Radiation–Induced Development of Squamous Cell Carcinomas: A Possible Link to Specific Cytokines and Cyclooxygenase-2

¹ Department of Human Oncology, Medical School, University of Wisconsin, Madison, Wisconsin and ² Fred Hutchinson Cancer Research Center Division of Basic Sciences, Seattle, Washington

Requests for reprints: Ajit K. Verma, Department of Human Oncology, Medical School, University of Wisconsin, Madison, WI 53792. Phone: 608-263-9163; Fax: 608-262-6654; E-mail: akverma{at}facstaff.wisc.edu.

Protein kinase C (PKC), a Ca²⁺-independent, phospholipid-dependent serine/threonine kinase, is among the novel PKCs (, , and ) expressed in mouse epidermis. We reported that FVB/N transgenic mice that overexpress (8-fold) PKC protein in basal epidermal cells and cells of the hair follicle are resistant to the development of both skin papillomas and squamous cell carcinoma (SCC) elicited by 7,12-dimethylbenz(a)anthracene initiation and 12-O-tetradecanoylphorbol-13-acetate (TPA) promotion protocol. We now present that PKC overexpression in transgenic mice failed to suppress the induction of SCC developed by repeated exposures to UV radiation (UVR), the environmental carcinogen linked to the development of human SCC. Both TPA and UVR treatment of wild-type mice (a) increased the expression of proliferating cell nuclear antigen (PCNA) and apoptosis; (b) stimulated the expression of cytokines tumor necrosis factor- (TNF-), granulocyte macrophage colony-stimulating factor (GM-CSF), and granulocyte CSF (G-CSF); and (c) increased cyclooxygenase-2 (COX-2) expression and expression of phosphorylated Akt (p-Akt), p38, extracellular signal-regulated kinase-1 (ERK1), and ERK2. PKC overexpression in transgenic mice enhanced TPA-induced but not UVR-induced apoptosis and suppressed TPA-stimulated but not UVR-stimulated levels of cell PCNA, cytokines (TNF-, G-CSF, and GM-CSF), and the expression of COX-2, p-Akt, and p38. The results indicate that UVR-mediated signal transduction pathway to the induction of SCC does not seem to be sensitive to PKC overexpression. The proapoptotic activity of PKC coupled with its ability to suppress TPA-induced expression of proinflammatory cytokines, COX-2 expression, and the phosphorylation of Akt and p38 may play roles in the suppression of TPA-promoted development of SCC. (Cancer Res 2006; 66(2): 713-22)

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