Activator protein 1 transcription factors are fundamental to v-ras(Ha)-induced changes in gene expression in neoplastic keratinocytes

The induction of mouse skin papillomas by initiation-promotion protocols is associated with aberrant expression of epithelial markers in the tumor mas s. Similarly, initiation of mouse keratinocytes with a retrovirus encoding the v-ras(Ha) gene (v-ras(Ha) keratinocytes) causes characteristic alterati ons of epidermal gene expression (A, A. Dlugosz et al., Cancer Res., 54: 64 13-6420, 1994), Because activator protein 1 (AP-1) proteins are likely targ ets of Ras activation, we have examined the role of AP-1 factors in v-ras(H a) keratinocytes. Introduction of v-ras(Ha) into keratinocytes upregulates c-Fos, Delta Fos B, and Fra-1 transcripts and protein levels in nuclear ext racts. The expression of Jun proteins is not significantly altered in v-ras (Ha) keratinocytes, Transduction of cells with v-ras(Ha) results in increas ed AP-1-dependent transcriptional activity, which is also simulated by tran sfection of keratinocytes with either c-Fos or Delta Fos B but not Fra-1, s uggesting that the up-regulation of c-Fos and Delta Fos B contributes to th is effect. To explore the role of AP-I proteins in regulating keratinocyte markers in v-rasHa keratinocytes, we blocked the binding of AP-I proteins t o DNA by infecting keratinocytes with an adenovirus encoding a dominant-neg ative Fos mutant (A-FOS), A-FOS replaces endogenous Fos proteins in the for mation of heterodimers with Jun family members and thus prevents the AP-1 t ranscription factor from binding to DNA, In v-ras(Ha) keratinocytes, the A- FOS virus reversed the suppression of keratins 1 and 10 transcripts and pro tein, which is characteristically seen in tumors and v-ras(Ha) keratinocyte s, A-FOS also increased protein levels but reduced transcripts for the late marker, loricrin, a component of the cornified envelope. These findings in dicate that AP-1 proteins are involved in the changes in gene expression th at define the v-ras(Ha) phenotype in mouse keratinocytes.