Relation of the induction of epidermal ornithine decarboxylase and hyperplasia to the different skin tumor-promotion susceptibilities of protein kinase C alpha, -delta and -epsilon transgenic mice

To define the in vivo role of individual PKC isoforms in mouse skin carcino genesis, we previously characterized FVB/n transgenic mice that over-expres sed epitope-tagged PKC delta (T7-PKC delta) or PKC epsilon (T7-PKC epsilon) isoforms under the regulation of the human K14 promoter. In continuation o f our prior PKC isoform specificity studies, we now report the generation o f FVB/n transgenic mice with K14-regulated, epitope-tagged PKC alpha (T7-PK C alpha). T7-PKC alpha transgenic mice (line 115) express 8-fold more PKC a lpha protein than wild-type mice. Using high-resolution immunogold cytochem istry, we determined that transgenic over-expression of T7-PKC alpha did no t alter the subcellular localization of PKC alpha but that the density of P KC alpha staining increased. PKC alpha localized primarily to the cytoskele ton (tonofilaments, tight junctions) and cell membranes, with modest but de finite nuclear labeling also identified. Also, PKC alpha over-expression di d not alter the immunoreactive protein levels of other PKC isoforms (delta, epsilon, eta, zeta, mu) in the epidermis. Skin tumor-promotion susceptibil ity was compared among all 3 lines of T7-PKC transgenic mice (alpha, delta and epsilon). While T7-PKC alpha had no effect on skin tumor promotion by T PA, T7-PKC delta reduced papilloma burden by 76% compared to wild-type cont rols. T7-PKC epsilon further reduced papilloma burden to 93% compared to wi ld-type controls but still resulted in the development of squamous-cell car cinoma. To find potential mechanisms of PKC-associated differences in tumor promotion, the induction of known downstream effectors of tumor promotion, ornithine decarboxylase (ODC) activity and epidermal hyperplasia, was dete rmined. Despite long-term papilloma inhibition in both PKC delta and PKC ep silon transgenic mice, the induction of ODC by TPA was not attenuated in PK C delta and epsilon mouse lines. Both PKC transgenic and wild-type mice exh ibited sustained hyperplasia after repeated TPA treatments. However, TPA-in duced epidermal hyperplasia in T7-PKC epsilon mice was significantly increa sed (52%) compared with T7-PKC alpha, T7-PKC delta and wild-type mice. TPA- induced ODC activity and the resultant accumulation of polyamines may play different roles (e.g., induction of apoptosis vs. proliferation) in the pat hways leading to the induction of cancer in PKC alpha, PKC delta and PKC ep silon transgenic mice. (C) 2001 Wiley-Liss, Inc.