TGF alpha and v-fos cooperation in transgenic mouse epidermis induces aberrant keratinocyte differentiation and stable, autonomous papillomas.

To assess the synergistic effect of growth and transcription factor deregulation on carcinogenesis in vivo, mating experiments were performed between transgenic mice expressing human TGF alpha or v-fos exclusively in the epidermis by means of a human keratin K1-based targeting vector (HK1.fos, HK1.TGF alpha and HK1.fos/alpha). While HK1.TGF alpha mice exhibited mild epidermal hyperplasia resulting in a wrinkled appearance, this hyperplasia was significantly increased in HK1.fos/alpha mice which also exhibited a novel opalescent and peeling skin phenotype. HK1.fos/alpha keratinocyte differentiation was considerably deregulated with cornified cells appearing in the granular layer, granular cells in the spinous layer and a sixfold increase in BrdU labeling over normal. In addition, hyperplastic HK1.fos/alpha epidermis exhibited aberrant loricrin, filaggrin and novel K13 expression associated with v-fos expression. Unlike adult HK1.TGF alpha controls, hyperplasia persisted in HK1.fos/alpha adults which also rapidly developed autonomous squamous cell papillomas. These results demonstrate that v-fos and TGF alpha over-expression can cooperate to reprogram keratinocyte differentiation and elicit the early stages of neoplasia. Moreover, TGF alpha over-expression appeared to play an early, initiating role in HK1.fos/alpha papilloma etiology, and a promotion role in the accelerated appearance of v-fos wound-associated preneoplastic phenotypes. However, the stable persistence of HK1.fos/alpha papillomas for up to 12 months, suggests that additional events are required for malignant conversion.