Necrosis Factor Death Factor-induced Apoptosis by Potentiating Tumor Insulin-like Growth Factor-I Protects Colon Cancer Cells from Updated Version

Resistance of cancer cells against apoptosis induced by death factors contributes to the limited efficiency of immuneand drug-induced destruction of tumors. We report here that insulin and insulin-like growth factor-I (IGF-I) fully protect HT29-D4 colon carcinoma cells from IFNg/tumor necrosis factor-a (TNF) induced apoptosis. Survival signaling initiated by IGF-I was not dependent on the canonical survival pathway involving phosphatidylinositol 3*-kinase. In addition, neither pp70 nor protein kinase C conveyed IGF-I antiapoptotic function. Inhibition of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) with the MAPK/ERK kinase inhibitor PD098059 and MAPK/p38 with the specific inhibitor SB203580 partially reversed, in a nonadditive manner, the IGF-I survival effect. Inhibition of nuclear factor kB (NF-kB) activity by preventing degradation of the inhibitor of NF-kB (IkB-a) with BAY 11-7082 also blocked in part the IGF-I antiapoptotic effect. However, the complete reversal of the IGF-I effect was obtained only when NF-kB and either MAPK/ERK or MAPK/p38 were inhibited together. Because these pathways are also those used by TNF to signal inflammation and survival, these data point to a cross talk between IGF-Iand TNF-induced signaling. We further report that TNF-induced IL-8 production was indeed strongly enhanced upon IGF-I addition, and this effect was totally abrogated by both MAPK and NF-kB inhibitors. The IGF-I antiapoptotic function was stimulus-dependent because Fasand IFN/Fas-induced apoptosis was not efficiently inhibited by IGF-I. This was correlated with the weak ability of Fas ligation to enhance IL-8 production in the presence or absence of IGF-I. These findings indicate that the antiapoptotic function of IGF-I in HT29-D4 cells is based on the enhancement of the survival pathways initiated by TNF, but not Fas, and mediated by MAPK/p38, MAPK/ERK, and NF-kB, which act in concert to suppress the proapoptotic signals. In agreement with this model, we show that it was possible to render HT29-D4 cells resistant to Fas-induced apoptosis provided that IGF-I and TNF receptors were activated simultaneously.