CAMP response element-binding protein (CREB) is required for epidermal growth factor (EGF)-induced cell proliferation and serum response element activation in neural stem cells isolated from the forebrain subventricular zone of adult mice

Abstract

Neurogenesis, which occurs not only in the developing brain but also in restricted regions in the adult brain including the forebrain subventricular zone (SVZ), is regulated by a variety of environmental factors, extracellular signals, and intracellular signal transduction pathways. We investigated whether the transcription factor cAMP response element (CRE)-binding protein (CREB) is involved in the regulation of cell proliferation of neural stem cells (NSCs) isolated from the SVZ of adult mice. Treatment of NSCs with the protein kinase A (PKA) inhibitors H89 and KT5720 inhibited epidermal growth factor (EGF)-stimulated NSC proliferation. Similar inhibition was observed when a dominant-negative mutant of CREB (MCREB) was expressed. EGF treatment increased CRE-mediated transcriptional activity, but this increase was much less than that caused by treatment with the adenylate cyclase activator forskolin, which changed neither basal nor EGF-stimulated proliferation of NSCs. Neither PKA inhibitors nor MCREB expression blocked EGF-induced phosphorylation of extracellular signal-regulated kinase (ERK), a protein kinase mediating EGF's mitogenic action. However, MCREB suppressed EGF-induced expression of several immediately early genes including c-fos, c-jun, jun-B, and fra-1 and subsequent AP-1 transcriptional activation. MCREB expression also inhibited the ability of EGF to stimulate transcriptional activation mediated by the serum response element (SRE), a promoter sequence regulating c-fos gene expression. These results suggest that basal activity of CREB is required for the mitogenic signaling of EGF in NSCs at a level between ERK activation and SRE-mediated transcriptional activation.