Preoptic regulatory factor 2 inhibits proliferation and enhances drug induced apoptosis in neural stem cells.

摘要

Neural stem cells (NSCs) exist in both the developing and adult brain. In the developing central nervous system (CNS), NSCs shape the structural and functional layout of the brain. After development, NSCs still contribute to low level neurogenesis in several brain areas including the subventricular zone (SVZ) and hippocampal dentate gyrus (DG). NSCs are important in cancer research and treatment. NSCs are a possible origin of brain-cancer stem cells when the strict control of cell growth is disturbed. They are also important resources for therapeutic transplantation in diverse diseases, including neurodegenerative disorders, brain and spinal cord injuries, stroke and epilepsy. Thus elucidating the growth-regulatory mechanism of NSCs will be helpful for understanding brain development, turmorigenesis and providing a platform for NSCs' clinical application. Preoptic regulatory factor-2 (Porf-2) is a Rho GTPase activator protein (GAP) domain-containing protein found in the CNS. It has been proposed to have a role in gender-related brain development and function. However, the direct effects of Porf-2 on NSCs are not known. The current studies were designed to knock down the expression of Porf-2 in C17.2 cells, a mouse cerebellar NSC line, and investigate the effects of Porf-2 on cell proliferation, apoptosis and differentiation. The mechanisms responsible for the effects of Porf-2 on cell proliferation and apoptosis were also studied. Knockdown of Porf-2 was performed by transducing short hairpin RNA (shRNA) lentivirus into C17.2 cells and confirmed by quantitative RT-PCR and Western blot analysis. Porf-2 knockdown cells exhibited increased proliferative activities and decreased drug induced apoptosis compared to control cells (p0.05). There was no difference in differentiation directions between Porf-2 knockdown cells and control cells. Mechanistic studies yielded three findings. First, knockdown of Porf-2 lowered the expression level of cyclin kinase inhibitor p21 and expedited G1 to S cell cycle transition. Second, bleomycin, a genotoxic reagent, caused an elevation in p53 transcriptional activity, p21 expression and Bax expression in C17.2 cells. Knockdown of Porf-2 partially blocked the changes caused by bleomycin. Third, staurosporine (STS), a broad-spectrum kinase inhibitor, enhanced the expression of Bax but did not change the transcriptional activity of p53 or expression of p21 in C17.2 cells. Knockdown of Porf-2 had no influence on the enhancement of Bax expression in response to STS treatment. Three conclusions were drawn from these data. First, Porf-2 inhibits NSC proliferation by enhancing p21 expression followed by G1 cell cycle arrest. Second, Porf-2 plays pro-apoptotic roles in response to drug treatment in NSCs through both p53 transcription dependent and independent pathways. Third, Porf-2 shows no influence on NSC differentiation directions.