Increased K+ efflux and apoptosis induced by the potassium channel modulatory protein KChAP/PIAS3β in prostate cancer cells

K+ channel-associated protein/protein inhibitor of activated STAT (KChAP/PIAS3beta) is a potassium (K+) channel modulatory protein that boosts protein expression of a subset of K+ channels and increases currents without affecting gating. Since increased K+ efflux is an early event in apoptosis, we speculated that KChAP might induce apoptosis through its up-regulation of K+ channel expression. KChAP belongs to the protein inhibitor of activated STAT family, members of which also interact with a variety of transcription factors including the proapoptotic protein, p53. Here we report that KChAP induces apoptosis in the prostate cancer cell line, LNCaP, which expresses both K+ currents and wild-type p53. Infection with a recombinant adenovirus encoding KChAP (Ad/KChAP) increases K+ efflux and reduces cell size as expected for an apoptotic volume decrease. The apoptosis inducer, staurosporine, increases endogenous KChAP levels, and LNCaP cells, 2 days after Ad/KChAP infection, show increased sensitivity to staurosporine. KChAP increases p53 levels and stimulates phosphorylation of p53 residue serine 15. Consistent with activation of p53 as a transcription factor, p21 levels are increased in infected cells. Wild-type p53 is not essential for induction of apoptosis by KChAP, however, since KChAP also induces apoptosis in DU145 cells, a prostate cancer cell line with mutant p53. Consistent with its proapoptotic properties, KChAP prevents growth of DU145 and LNCaP tumor xenografts in nude mice, indicating that infection with Ad/KChAP might represent a novel method of cancer treatment.