PL48: mechanism of a new cell growth regulatory gene that inhibits proliferation and promotes differentiation in human cytotrophoblast

Introduction: PL48 is a novel human placental differentiation-associated gene that is widely expressed in normal tissues. Methods: To determine the effect and mechanism of PL48 on cell proliferation, apoptosis, and cytotrophoblast differentiation, several cell models were used. Results: Antisense PL48 transfection into term human trophoblast reduced spontaneous cytotrophoblast differentiation into syncytium by 19.9 + 1.1 %. Transiently transfected MCF-7 cells demonstrated a 19.5-25.7% decrease in ³ H-thymidine uptake concomitantly with a 20% decrease in cell number and 3-fold increase in apoptotic cells shown by TUNEL labeling. Stable retroviral transfection of PL48 into MCF-7 cells resulted in a 50% decrease in ³ H-thymidine uptake after gene promoter induction. Estrogen-induced proliferation of MCF-7 cells was not affected by PL48 induction with or without tamoxifen, indicating PL48 does not act through the estrogen receptor. Transfected MDA-MB231 cells showed a 20% decrease in ³ H-thymidine uptake but no induction of apoptosis indicating that a functional p53 is required for PL48-induced apoptosis. Stably transfected MCF-7 cells showed an upregulation of p53 and p21 mRNA. Peroxynitrite, but none of xanthine/xanthine oxidase, hypoxia, or cytokines (EGF, IFNγ, TNFα, TGFβ) induced PL48 in trophoblast cells.10cGy gamma irradiation did not induce PL48 in MCF-7 cells. Discussion: We conclude that PL48 has multiple actions including inhibition of proliferation independently of p53, induction of apoptosis through the p53 pathway, and enhancing differentiation in cytotrophoblast.