TGF-β regulation of gene expression at early and late stages of HPV16-mediated transformation of human keratinocytes.

In our in vitro model for HPV16-mediated transformation, HPV16-immortalized human keratinocytes (HKc/HPV16) give rise to differentiation resistant, premalignant cells (HKc/DR). HKc/DR, but not HKc/HPV16, are resistant to growth inhibition by transforming growth factor beta (TGF-β), due to a partial loss of TGF-β receptor type I. We show that TGF-β activates a Smad-responsive reporter construct in HKc/DR to about 50% of the maximum levels of activation observed in HKc/HPV16. To investigate the functional significance of residual TGF-β signaling in HKc/DR, we compared gene expression profiles elicited by TGF-β treatment of HKc/HPV16 and HKc/DR on Agilent 44k human whole genome microarrays. TGF-β altered the expression of cell cycle and MAP kinase pathway genes in HKc/HPV16, but not in HKc/DR. However, epithelial-mesenchymal transition (EMT) responses to TGF-β were comparable in HKc/HPV16 and HKc/DR, indicating that the signaling pathways through which TGF-β elicits growth inhibition diverge from those that induce EMT in HPV16-transformed cells.