Tumor necrosis factor-alpha-induced apoptosis in prostate cancer cells through inhibition of nuclear factor-kappa B by an I kappa B alpha "super-repressor"

Prostate cancer patients experiencing a relapse in disease often express hi gh serum tumor necrosis factor-alpha (TNF-alpha) levels. Many androgen-inse nsitive prostate cancer cells are TNF-alpha insensitive because of the expr ession of antiapoptotic genes as part of the nuclear factor-kappa B (NF-kap pa B) family of transcription factors. NF-kappa B stimulates gene transcrip tion when expressed in the nucleus; however, in resting cells, this nuclear import is prevented by association with the cytoplasmic inhibitor I kappa B alpha, This cytoplasmic retention of NF-kappa B is uncoupled by many extr acellular signals including low levels of TNF-alpha. During normal cell act ivation, nuclear translocation of NF-kappa B is preceded by phosphorylation and degradation of I kappa B alpha, When phosphorylation is blocked, I kap pa B alpha remains intact, thereby blocking NF-kappa B translocation to the nucleus and subsequent activation of antiapoptotic genes that cause TNF-al pha insensitivity. We tested whether a "super-repressor" of NF-kappa B acti vity could be transfected into prostate cancer cells and make them TNF-alph a sensitive. PC-3 and LNCaP cells were stimulated with TNF-alpha (10 ng/ml) for 24 h in the presence or absence of the I kappa B alpha "super-represso r" (p6R-I kappa B-S32A + (S36A)) NF-kappa B activity was measured by electr ophoretic mobility shift assay and the steady state levels of the cytoplasm ic I kappa B alpha protein were measured by Western blot. Secretory IL-6 an d IL-6 mRNA were measured by ELISA, p6R-I kappa BS32A + S36A blocked the st imulation of NF-kappa B activity by TNF-alpha in prostate cancer cells. It also subsequently decreased IL-6 production by TNF-alpha. We conclude that these data demonstrate that inhibition of NF-kappa B selectively sensitizes previously insensitive prostate cancer cells to TNF-alpha.