p57^Kip2 Stabilizes the MyoD Protein by Inhibiting Cyclin E-Cdk2 Kinase Activity in Growing Myoblasts

Abstract

We show that expression of p57(Kip2), a potent tight-binding inhibitor of several G(1) cyclin-cyclin-dependent kinase (Cdk) complexes, increases markedly during C2C12 myoblast differentiation. We examined the effect of p57(Kip2) on the activity of the transcription factor MyoD. In transient transfection assays, transcriptional transactivation of the mouse muscle creatine kinase promoter by MyoD was enhanced by the Cdk inhibitors. In addition, p57(Kip2), p21(Cip1), and p27(Kip1) but not p16(Ink4a) induced an increased level of MyoD protein, and we show that MyoD, an unstable nuclear protein, was stabilized by p57(Kip2). Forced expression of p57(Kip2) correlated with hypophosphorylation of MyoD in C2C12 myoblasts. A dominant-negative Cdk2 mutant arrested cells at the G(1) phase transition and induced hypophosphorylation of MyoD. Furthermore, phosphorylation of MyoD by purified cyclin E-Cdk2 complexes was inhibited by p57(Kip2). In addition, the NH2 domain of p57(Kip2) necessary for inhibition of cyclin E-Cdk2 activity was sufficient to inhibit MyoD phosphorylation and to stabilize it, leading to its accumulation in proliferative myoblasts. Taken together, our data suggest that repression of cyclin E-Cdk2-mediated phosphorylation of MyoD by p57(Kip2) could play an important role in the accumulation of MyoD at the onset of myoblast differentiation.

p57KIP2 Modulates Stress-activated Signaling by Inhibiting c-Jun NH2-terminal Kinase/Stress-activated Protein Kinase

“…p57 KIP2 protein also plays a role in the regulation of myoblast differentiation and apoptotic processes (20,24). It has been suggested that JNK/SAPK signaling pathway may be involved in the regulatory mechanism of apoptosis and differentiation (9,10,25,26).…”

“…KIP2 is enhanced during C2C12 myoblast differentiation (20), which can be induced by withdrawing serum from the culture medium. We therefore tested whether the induction of p57 KIP2 expression by serum withdrawal would result in suppression of JNK activity in C2C12 myoblast cells.…”

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.…”

Analysis of the expression of cell cycle regulators in Ewing cell lines: EWS-FLI-1 modulates p57KIP2 and c-Myc expression

“…EW24 Ewing cells were cotransfected by e ectene method (Qiagen) with pPUR (puromycin resistance plasmid from Clontech) and p57 KIP2 encoding vector (Reynaud et al, 1999) or pcDNA3 empty vector in a 1 to 10 ratio. One day after transfection, cells were selected for 24 to 48 h in the presence of 1 mg/ml of puromycin then labelled with 30 mM of BrdU for 30 min at 378C.…”

“…The Ewing EW24 cell line was transfected with either an expression vector encoding a GFP-p57 KIP2 fusion protein (Reynaud et al, 1999) or with a GFP control vector (pEGFP-C1, Clontech). In the days following transfection,¯uorescent cells were counted.…”