A specific function for phosphatidylinositol 3-kinase α (p85α-p110α) in cell survival and for phosphatidylinositol 3-kinase β (p85α-p110β) in de novo DNA synthesis of human colon carcinoma cells

We have previously shown an important function of phosphatidylinositol 3-kinase (PI3K)alpha(p85 alpha-p110 alpha) and PI3K beta (p85-alpha-p110 beta) for DNA synthesis induced by various mitogens in non transformed fibroblasts and we now report a specific role of these enzymes in human colon cancer cell growth. Using antibodies specific to p110 alpha and to p110 beta catalytic subunits, increase in PI3K alpha and PI3K beta activities,vas detected in 15/19 human tumour biopsies relative to adjacent normal mucosa of human colon and bladder. Increase in such activities was also observed in adenocarcinoma cell lines CaCo2, CO115, HCT 116, LS 174T and WiDr relative to nontransformed fibroblasts. Maximal PI3K alpha activity was observed for LS 174T and PI3K beta activity for WiDr cells. This was partly correlated with an increase in p110 alpha and p110 beta protein levels both in some primary tumours and established cell lines, suggesting that PI3K overexpression is involved in enzymatic deregulation. Functional consequence of such activation was assessed by a microinjection approach. An injection of neutralizing antibody specific to p110 beta in WiDr, HCT116 and CO 115 cells inhibited de novo DNA synthesis, whereas antibodies specific to p110 gamma had no effect. Neutralizing antibodies specific to p110 alpha induced apoptosis, a response that was reverted by treating cells with the caspase inhibitor z-VAD-fmk. However anti-p110 beta and anti-p110 gamma antibodies did not affect cell survival, We concluded that PI3K alpha and PI3K beta play important roles in human colon cancer cell growth with a specific function for PI3K beta in de novo DNA synthesis and an involvement of PI3K alpha in cell survival.