Assessment of TGF-beta1-mediated growth inhibition of HPV-16- and HPV-18-transfected foreskin keratinocytes during and following immortalization.

The responsiveness to transforming growth factor-beta1 (TGF-beta1) of two human keratinocyte cell lineages (FK16A and FK18B) generated after transfection with HPV-16 and HPV-18, respectively, was investigated. Both cell lineages revealed loss of heterozygosity (LOH) at 18q and/or 3p associated with the acquisition of the immortal phenotype. These loci harbour genes (TGF-beta receptor II gene at 3p, and Smad2 and Smad4 genes at 18q) encoding products involved in the TGF-beta1 signalling pathway. Mortal and early immortal stages of both cell lineages displayed growth reduction upon exposure to TGF-beta1 concentrations in the range 100 pg/ml to 1 ng/ml. However, the late immortal stages were resistant to TGF-beta1 at concentrations up to 10 ng/ml. TGF-beta1 receptors type I and II were expressed at all stages in both cell lineages. Moreover, mRNA levels of Smad2 and Smad4 genes were nearly constant throughout. TGF-beta1 expression and secretion, which were demonstrated in all analysed stages, may provide selective conditions underlying unresponsiveness to TGF-beta1 upon prolonged monolayer culturing. Thus, LOH at 3p and/or 18q seen during HPV-mediated immortalization of human keratinocytes was not associated with resistance to TGF-beta1-mediated growth inhibition or a marked reduction in TGF- beta1 receptors and mRNA levels of Smad2 or Smad4. Therefore, alternative events are likely to underlie unresponsiveness to TGF- beta1 in late-passage FK16A and FK18B cells.