Abstract 282: PAI-2 promotes astrocyte differentiation from glial precursor cells via enhancing STAT3 signaling

Abstract

Abstract Regulation of the generation of astrocytes and oligodendrocytes is a key process in the development of normal central nervous system (CNS) and glial tumors including oligodendrocytoma, astrocytoma and glioblastoma. Glial cell differentiation occurs in two sequentially generated glial progenitor cells, the glial-restricted precursor (GRP) cells and the oligodendrocyte-type-2 astrocyte (O-2A) progenitor cells. The molecular mechanisms of cell generation in these precursor cells are only incompletely understood. In this study, PAI-2 (Plasminogen Activator inhibitor-2) was identified to be upregulated during glial cell differentiation. Ectopic expression of PAI-2 induced GRP cells to differentiate into astrocytes and inhibited their proliferation. In contrast, suppression of endogenous PAI-2 by small interfering RNA in GRP cells promoted cell proliferation and inhibited their ability to differentiate into astrocytes. More interestingly, we observed a higher Rb protein level and a correlated lower E2F1 transcriptional activity during glial differentiation due to increased PAI-2 protein level. In consistent with these findings, ectopic expression of PAI-2 indeed stabilized Rb protein. We also found that PAI-2 upregulated GFAP expression in glial progenitor cells, an antigenic marker for astrocytes. Astrocytogenesis is controlled by two different signaling, the IL-6, LIF or CNTF-induced STAT3 pathway and the BMP-4-induced SMAD1 pathway. Interestingly, PAI-2 significantly enhanced CNTF, LIF or IL-6-induced GFAP expression as illustrated by both reporter assay and immunostaining, but not BMP4-induced GFAP expression. Furthermore, We demonstrated that PAI-2 could enhance CNTF-induced STAT3 phosphorylation and the complex formation between STAT3 and p300. It has also been reported that Rb could enhance the transcriptional activity of several transcription factors via enhancing p300/CBP activity by releasing them from some inhibitory transcriptional repressors such as EID1 (E1A-like inhibitor of differentiation). Indeed, suppression of Rb by small interfering RNA or overexpression of EID1 abrogated PAI-2's effect on STAT3 activity. Also, suppression of endogenous EID1 by small interfering RNA could further enhance PAI-2's effect. Finally, we illustrated Glial precursor cells from PAI-2 knockout mice are less responsive to CNTF and IL-6 than wild-type cells. Based on these data, we concluded that PAI-2 promotes glial progenitor cells to differentiate into astrocytes via stabilizing Rb, which can abrogate EID's inhibitory effect, and then enhancing STAT3 transcriptional activity induced by CNTF or IL-6. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 282. doi:10.1158/1538-7445.AM2011-282