Clonal growth and origin of two human keratinocyte cell lines transformed by human papillomavirus type 16 DNA

Two human keratinocyte cell lines transformed by human papillomavirus type 16, designated Vp and Up, were compared for their clonal growth potential and clonal origin. Up showed greater anchorage-independent growth in soft agar and higher efficiency of single-cell colony formation than Vp (24.3% compared to approximately 10%). The clonal growth potential of these two cell lines was not related to the level of HPV16 gene expression. Fourteen single cell clones of the Vp and 24 of the Up were selected, propagated and analyzed by Southern and Northern blot analysis. Clonal variations existed among subclones of each cell line and between the two cell lines. These variations included cell morphology, growth potential, and expression levels of involucrin (a differentiation marker of keratinocytes) and of HPV16 mRNAs. The Vp and Up cell lines also showed different patterns of HPV16-DNA integration and RNA transcription. However, all subclones of Vp and subclones of Up displayed identical HPV16 DNA integration and RNA expression patterns. The results suggest that both cell lines were monoclonal in origin and that the host genetic factors play an essential role in determining cell clonality.