ITGA7 activates HtrA2 protease activity in vivo and in vitro. A: Expression of ITGA7 reduces XIAP in vivo. pCDNA4-ITGA7/pCDNA6 transformed PC3 (PIF1 and PIF3), and DU145 cells (DIF1 and DIF5) were induced with (I) or without tetracycline (U) and treated with siRNA specific for HtrA2 (sH2) or a scrambled control (siScr). The lysates were immunoblotted with the indicated antibodies. An ITGA7 mutant (pcDNA4-ITGA7m), in which 19 amino acids representing the HtrA2 interaction motif were deleted, was transfected into PC3 and DU145 cells. Stably transformed PC3 (PIM1 and PIM8) and DU145 (DIM2 and DIM6) clones were induced with or without tetracycline. The protein extracts were similarly blotted with the indicated antibodies. B: In vitro HtrA2 protease activity. HtrA2 proteins were immunoprecipitated from protein extracts from PIF1, PIF3, DIF1, DIF5, PIM1, PIM8, DIM2, and DIM6 cell lines induced or not with tetracycline. In vitro protease activity was measured as described in Materials and Methods. HtrA2 protease activity from uninduced cell lines was used as the 100% control. Data represent an average of six individual assays. SDs are indicated.