Fig. 3.

HPV proteins activate low levels of caspases upon differentiation while simultaneously increasing levels of antiapoptotic proteins. (A) Analysis of caspase activation in apoptotic vs. differentiating HFK-31 cells. HFK-31 cells were treated with 0.5 μM staurosporine (ST) for 12 h or were suspended in methylcellulose to induce differentiation. Whole cell lysates were harvested from undifferentiated monolayer cultures (T0) or from cells suspended in methylcellulose for 24 and 48 h. Immunoblots were probed by using primary antibodies that recognize either the active form of caspase-3 and -7 or the procaspase forms. GAPDH was used as a loading control. *, nonspecific band. (B) Analysis of antiapoptotic proteins in HPV-31-positive cells induced to differentiate in methylcellulose. Whole cell lysates were harvested from HPV-31-positive HFKs (HFK-31) and untransfected HFKs at time 0 (undifferentiated) and 12, 24, and 48 h after suspension in methylcellulose to induce differentiation. Blots were probed with antibodies to Bcl-2, Bax, and survivin. GAPDH served as a loading control. The data shown are representative of three independent experiments.