Conditional expression of the DD-HNF4α fusion protein. (A) Western blotting of whole cell extracts of the INS-1 P2/DD-HNF4α8 wild type #1 and C106R-mutant cell line with the HNF4α-antibody C-19 (Santa Cruz). Cells were cultured without (-) or with (+) 50 ng/ml tetracycline and/or 1 μM Shield-1 for 5 days. 15 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 cells were treated with 50 ng/ml tetracycline and/or 1 μM Shield-1 for 5 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.