Protein kinase Cepsilon is linked to 12-O-tetradecanoylphorbol-13-acetate-induced tumor necrosis factor-alpha ectodomain shedding and the development of metastatic squamous cell carcinoma in protein kinase Cepsilon transgenic mice.

Protein kinase Cepsilon (PKCepsilon), a Ca(2+)-independent, phospholipid-dependent serine/threonine kinase, is among the PKC isoforms expressed in mouse epidermis. We reported that FVB/N transgenic mice that overexpress ( approximately 18-fold) PKCepsilon protein in basal epidermal cells and cells of the hair follicle develop papilloma-independent metastatic squamous cell carcinoma (mSCC) elicited by 7,12-dimethylbenz(a)anthracene-initiation and 12-O-tetradecanoylphorbol-13-acetate (TPA)-promotion protocol. We now present that PKCepsilon transgenic mice elicit elevated serum tumor necrosis factor (TNF)alpha levels during skin tumor promotion by TPA, and this increase may be linked to the development of mSCC. A single topical application of TPA (5 nmol) to the skin, as early as 2.5 h after treatment, resulted in a significant (P < 0.01) increase (2-fold) in epidermal TNFalpha and more than a 6-fold increase in ectodomain shedding of TNFalpha into the serum of PKCepsilon transgenic mice relative to their wild-type littermates. Furthermore, this TPA-stimulated TNFalpha shedding was proportional to the level of expression of PKCepsilon in the epidermis. Using the TNF-alpha converting enzyme (TACE) inhibitor, TAPI-1, TPA-stimulated TNFalpha shedding could be completely prevented in PKCepsilon transgenic mice and isolated keratinocytes. These results indicate that PKCepsilon signal transduction pathways to TPA-stimulated TNFalpha ectodomain shedding are mediated by TACE, a transmembrane metalloprotease. Using the superoxide dismutase mimetic CuDIPs and the glutathione reductase mimetic ebselen, TPA-stimulated TNFalpha shedding from PKCepsilon transgenic mice could be completely attenuated, implying the role of reactive oxygen species. Finally, i.p. injection of a TNFalpha synthesis inhibitor, pentoxifylline, during skin tumor promotion completely prevented the development of mSCC in PKCepsilon transgenic mice. Taken together, these results indicate that: (a) PKCepsilon activation is an initial signal in TPA-induced shedding of TNFalpha from epidermal keratinocytes; (b) PKCepsilon-mediated signals to TACE are possibly mediated through reactive oxygen species; and (c) TPA-induced TNFalpha shedding may play a role in the development of mSCC in PKCepsilon transgenic mice.