Epithelium and fibroblast-like phenotypes derived from HPV16 E6/E7-immortalized human gingival keratinocytes following chronic ethanol treatment

Epithelial-mesenchymal transition (EMT) may be critical for neoplastic progression and its eventual tumorigenicity of epithelia. In this context, we investigated whether EMT and EMT-associated features occurred after chronic ethanol treatment of human gingival keratinocytes immortalized with the E6/E7 oncogenes of human papillomavirus (HPV) type 16. Following a nine-week treatment of cells with 30 mM ethanol in keratinocyte growth medium, they were cultured in normal DMEM with 10% serum. These cell populations were able to proliferate in this medium gradually exhibiting elongated morphology indicating that these cells underwent EMT. Control cells without ethanol treatment did not survive subcultures in DMEM. Upon long-term subcultures of ethanol-treated cells, two phenotypes were obtained exhibiting epithelium-like and spindle-shape fibroblast-like morphology (respectively, termed as EPI and FIB cells), the latter indicating EMT. In comparison to EPI cells, the phenotypic transition to FIB cells was concomitant with a decrease in the expression of keratins, desmoplakins and a complete loss of K14. Moreover, FIB cell transition strongly correlates with an increase in the expression of vimentin and simple epithelial keratin K18. These alterations in FIB cells were associated with the ability of these cells to exhibit anchorage-independent growth, while EPI cells exhibited anchorage-dependent growth. Concerning the transformation stage, FIB cells represent a progressively more advanced transformed phenotype which may reflect an early step during HPV- and ethanol-dependent multi-step carcinogenesis.

Epidermal Ras blockade demonstrates spatially localized Ras promotion of proliferation and inhibition of differentiation

While important in carcinogenesis, the role of Ras in normal self-renewing tissues such as epidermis is unclear. To address this, we altered Ras function in undifferentiated and differentiating epidermal layers. Ras blockade within undifferentiated basal epidermal cells leads to decreased integrin expression, diminished growth capacity and induction of differentiation. Ras blockade in post-mitotic suprabasal epidermis exerts no effect. In contrast, regulated Ras and Raf activation inhibits differentiation. These findings indicate that spatially restricted Ras/Raf signaling divides epidermis into an undifferentiated proliferative compartment and a differentiating post-mitotic compartment and suggest a new role for Ras in tissue homeostasis.