Induction of apoptosis upon expression of HNF4α8. (A) Western blotting of whole cell extracts of the INS-1 α8/CMV-138 cell lines (#1 and #2) and the α8/CMV-Wt cell line with the HNF4α-antibody C-19 (Santa Cruz). Cells were cultured with the indicated concentrations of tetracycline for 3 days. 20 μg of total protein were loaded per lane and the signal for the exogenous (exo) as well as endogenous (endo) HNF4α is marked. (B) Caspase 3/7 activity assay. The indicated INS-1 cell lines were treated with the indicated tetracycline concentrations for 3 days, lysed and caspase 3/7 activity was assessed. The relative caspase activity was calculated using the appropriate uninduced cells as a reference. Data are mean ± SD of six determinations and significant differences (p-value < 0.01) are indicated with an asterisk.