The mouse skin multistage carcinogenesis model provides a useful system for the identification and characterization of the sequential events which occur during carcinogenesis. We have found that the epidermis from mice """"""""sensitive"""""""" or """"""""resistant"""""""" to phorbol ester tumor promotion (SSIN and C57BL/61, respectively) each displayed a large induction of ornithine decarboxylase (ODC) when treated with a single dose of 12-O- tetradecanoylphorbol-13-acetate (TPA), while a second TPA treatment 24 hr later did not result in ODC induction (refractory period; 8). Protein kinase C (PKC) was down-regulated at these times. However, by 48 hr (C57B1/6J) or 72 hr (SSIN), a responsive state had returned in which ODC was over-expressed, even though PKC activity levels continued to decrease. The goal of the proposed research is to elucidate the mechanisms by which the induction of ODC and of nuclear proto-oncogenes (c-jun and c-fos) is dissociated from the activation of PKC during multi-stage carcinogenesis in the mouse epidermis. Towards this aim, we will analyze the signal transduction pathways leading to over-expression of ODC in C57BL/6J and SSIN mice during periods of PKC depletion following a single application of TPA to the epidermis, and will also compare the process of ODC induction by PKC activators (TPA) and promoting agents which induce ODC by non-PKC mediated mechanisms (ethyl phenylpropiolate, EPP). These objectives will be pursued through the following specific aims: (1) Determine the status of protein kinase C activity and isozymes, as well as phorbol ester receptors in the epidermis of tumor promotion sensitive and resistant mice at times following TPA treatment when ODC is over-expressed by a subsequent TPA or EPP treatment. (2) Investigate the roles of nuclear oncogenes c- fos and c-jun in the over induction of ODC by TPA and EPP during periods of PKC depletion. (3) Determine whether the over-expression of ODC observed following a second treatment of skin with TPA is due to augmented transcription, translation, or post-translational effects, using Northern and Western blot techniques and ODC enzyme kinetic determinations. (4) Examine the potential role of casein kinase II and S6 kinase as intermediates in the over-expression of ODC during PKC depletion in the skin. (5) Determine the possible involvement of growth factors or cytokines in the over-induction of ODC while PKC is depleted, using an in vitro cell culture model.
