p57Kip2 is a repressor of Mash1 activity and neuronal differentiation in neural stem cells

Abstract

Mammalian central nervous system (CNS) development is a highly organized process involving the precise and coordinated timing of cell-cycle exit, differentiation, survival, and migration. These events require proper expression of pro-neuronal genes but also repression of alternative cell fates and restriction of cell-type-specific gene expression. Here, we show that the cyclindependent kinase (CDK) inhibitor p57Kip2 interacted with pro-neuronal basic helix-loop-helix (bHLH) factors such as Mash1, NeuroD, and Nex/Math2. Increased levels of p57Kip2 inhibited Mash1 transcriptional activity independently of CDK interactions and acted as a direct repressor in transcriptional assays. Proliferating telencephalic neural progenitors co-expressed basal levels of Mash1 and p57Kip2, and endogenous p57Kip2 accumulated transiently in the nuclei of neural stem cells (NSCs) during early stages of astrocyte differentiation mediated by ciliary neurotrophic factor (CNTF), independent of cell-cycle exit and at times when Mash1 expression was still prominent. In accordance with these observations, gain-and loss-of-function studies showed that p57Kip2 repressed neuronal differentiation after mitogen withdrawal, but exerted little or no effect on CNTFmediated astroglial differentiation of NSCs. Our data suggest a novel role for p57Kip2 as a context-dependent repressor of neurogenic transcription factors and telencephalic neuronal differentiation. The development of the mammalian central nervous system (CNS) critically relies on a tight coordination among cell proliferation, survival, migration, and differentiation. 1,2 Proper neuronal differentiation does not only require pro-neuronal genes but also regulated repression of other cell fates, such as glial differentiation. 2 Thus, early neural progenitors preferentially differentiate into neurons and do not respond properly to astrocyte-inducing cytokines, at least in part due to DNA methylation of astrocyte-characteristic genes such as glial fibrillary acidic protein (GFAP). 3,4 In line with these observations, it has been shown that loss of the DNA methyl transferase DNMT1 results in hypomethylation and precocious onset of astrocytic genes at the expense of neurogenesis in early neural precursors. 5 In later progenitors, astrocytic genes become demethylated. 3,4 Transcriptional repression of astrocytic genes and thus the correct numbers of progenitors and neurons at these late events, instead depends on other factors such as the Notch-regulated transcription factor CSL/RBP-Jk and the co-repressors N-CoR and SMRT. 6,7 In addition, neurogenic members of the basic helix-loop-helix (bHLH) family of transcription factors, such as Mash1 and Neurogenin (Ngn) 2, interferes with astrocyte differentiation in multipotent neural progenitors at least in part by sequestering the coactivators CBP/p300 required for astrocyte differentiation. 8 Less is understood regarding a corresponding repression of neuronal differentiation during glial differentiation. Hes transcription factors repress neurogenic ...

The Cdk inhibitor p57Kip2 controls LIM-kinase 1 activity and regulates actin cytoskeleton dynamics

“…Kip2 is a multifunctional protein (Joseph et al, 2003(Joseph et al, , 2009Vlachos et al, 2007). Altogether, these results demonstrated that the presence of p57…”

“…, most probably because of its Cdk inhibitory function, is frequently considered as a nuclear protein; however, cytoplasmic expression of this protein has been demonstrated in various tissue, tumors and derived cell lines (www.proteinatlas.org; Barbe et al, 2008;Nan et al, 2005;Matsumoto et al, 2000;Pateras et al, 2006;Bozdogan et al, 2008;Joseph et al, 2009). In fact, as for the other members of the family, p21…”

“…Kip2 has been shown to have cell-cycle independent functions, it influences cell differentiation (Dyer and Cepko, 2000;Joseph et al, 2003Joseph et al, , 2009Jia et al, 2007), apoptosis (Samuelsson et al, 2002;Vlachos et al, 2007) and cell migration (Sakai et al, 2004;Fan et al, 2006;Itoh et al, 2007;Jin et al, 2008) implying that p57…”

p57kip2 regulates glial fate decision in adult neural stem cells

“…The observation that glial cell derivatives were not preferentially surviving or proliferating at higher rates in response to p57kip2 knockdown indicates that p57kip2 is an intrinsic adult neural stem cell regulator and that it plays a role in glial fate decision. During development, p57kip2 was shown to inhibit Mash1 (Ascl1) expression and to prevent neuronal differentiation of embryonal neural stem and progenitor cells (Joseph et al, 2009). No overlap of p57kip2 and neuronal markers such as NeuN was detected in our SGZ sections.…”

p57Kip2 and Cancer: Time for a Critical Appraisal

“…The N-terminal domain of p57 Kip2 is also the site of interaction with MyoD and other basic helix-loop-helix (b-HLH) transcription factors, such as Mash1, NeuroD, and Nex/Math2 (35)(36)(37)(38)(39). p57 Kip2 has also been reported to interact with Nuclear Receptor Related 1 (NURR1) protein.…”