Increased stability of nucleophosmin/B23 in anti-apoptotic effect of Ras during serum deprivation

We obtained evidence that increased stability of nucleophosmin/B23 is involved in antiapoptotic effect of ras during serum deprivation. Nucleophosmin/B23 in serum-deprived (0% serum) NIH-3T3 cells was found to be highly unstable with a half-life less than 4 h. In contrast, nucleophosmin/B23 in serum-deprived ras-transformed (RAS-3T3) cells was as stable as that in serum-supplemented NIH-3T3 or RAS-3T3 cells. Treatment of RAS-3T3 cells with nucleophosmin/B23 antisense oligomer significantly potentiated the apoptosis induced by serum deprivation. Much less caspase-3 activity was noted in the lysate derived from serum-deprived RAS-3T3 cells compared with that in the lysate of serum-deprived NIH-3T3 cells. Cell permeable caspase-3 inhibitor added in the medium blocked the decrease of nucleophosmin/B23 and apoptosis induced by serum deprivation in NIH-3T3 cells. The inhibitor, on the other hand, promoted significant decrease of nucleolin/C23 in NIH-3T3 cells during serum deprivation. Unlike nucleolin/C23, down-regulation of nucleophosmin/B23 was thus not proliferation-dependent but caspase-3- and apoptosis-dependent. Our results indicate important relationships among ras, nucleophosmin/B23, activation of caspase-3, and induction of apoptosis.