PTEN/MMAC1 enhances the growth inhibition by anticancer drugs with downregulation of IGF-II expression in gastric cancer cells

PTEN/MMAC1 is a tumor suppressor gene that is mutated in a variety of advanced and metastatic cancers. Its major function is likely to be the phosphatase activity that regulates the phosphotidylinositol (PI)3-kinase/Akt pathway. On the other hand, IGF system plays an important role in cell proliferation and cell survival via PI3-kinase/Akt and mitogen-activated protein kinase pathways in many cancer cells. To evaluate effect of PTEN on cell growth and IGF system in gastric cancer, human gastric adenocarcinoma cells (SNU-5 & -216) were transfected with human PTEN cDNA. Those PTEN-transfected gastric cancer cells had a lower proliferation rate than the pcDNA3-transfected cells. PTEN overexpression induced a profound decrease in the IGF-II and IGF-IR expression levels, and downregulation of IGF-II expression by PTEN was mediated through the regulation of the IGF-II promoter. In addition, a Pi3-kinase inhibitor, LY294002, induced the downregulation of IGF-II expression. The PTEN-overexpressing SUN-5 and -216 cells were more sensitive to death induced by etoposide and adriamycin that induce DNA damage than the pcDNA3-transfected cells. These findings suggest that PTEN suppresses the cell growth through modulation of IGF system and sensitizing cancer cells to cell death by anticancer drugs.