Inhibition of p27^Kip1gene transcription by mitogens

Abstract

How mitogens reduce the abundance of the cell cycle inhibitor p27 Kip1 is an important question, and regulation of p27 Kip1 translation and turnover has been described. Here we show that platelet-derived growth factor (PDGF) reduces the activity of the p27 Kip1 promoter and the abundance of the p27 Kip1 transcript in density-arrested mouse fibroblasts. Inhibition of p27 Kip1 gene expression by PDGF required protein synthesis and histone deacetylase activity but not Akt or ERK activity. PDGF increased the expression of c-Myc in the absence but not presence of a histone deacetylase inhibitor, and c-Myc inhibited p27 Kip1 promoter activity when ectopically expressed in fibroblasts. c-Myc targeted the same region of the p27 Kip1 promoter as did PDGF (deletion analysis) and interacted with this region in vivo (chromatin immunoprecipitation assay). Collectively, these findings suggest that c-Myc mediates the inhibitory effects of PDGF on the p27 Kip1 promoter. We also demonstrate reductions in p27 Kip1 mRNA abundance in primary splenocytes exposed to concanavalin A and in T cells exposed to interleukin-2 (IL-2). In contrast to PDGF in fibroblasts, IL-2 required Akt activity for maximal reductions in p27 Kip1 promoter activity and mRNA abundance in T cells. Thus, mitogens repress p27 Kip1 gene transcription in multiple systems and by multiple mechanisms.

Autophagy regulates T lymphocyte proliferation through selective degradation of the cell-cycle inhibitor CDKN1B/p27Kip1

“…It has been reported that concanavalin A and IL-2 stimulation transcriptionally decrease the abundance of CDKN1B. 40 However, there was no difference in the expression of Cdkn1b at the mRNA level between floxed control and autophagy-deficient T cells (data not shown). IL-7 promotes T cell proliferation through the regulation of stability of CDKN1B at the protein level, which is dependent on PRKCQ/ PKC-u (protein kinase C, theta).…”

Proliferative status regulates HDAC11 mRNA abundance in nontransformed fibroblasts

“…20 It will be important to determine the effects of PDGF and proliferative status on amounts of HDAC11 protein. However, despite use of multiple cell extraction protocols (0.1% Tween-20, 1% NP-40, 6 M Urea, or 0.5% SDS containing lysis buffers) and systematic subcellular fractionation (NE-PER ™ nuclear and cytoplasmic extraction reagent, Pierce) along with use of highly concentrated cell extracts, we could not detect endogenous HDAC11 in Balb/c-3T3 or clone 2 cells.…”

The function of p27KIP1during tumor development

“…The p27 KIP1 protein inhibits cyclin/CDK activity by binding cyclin/CDK complexes through its N-terminal, blocking ATP binding, and physically occluding the catalytic cleft of the CDK (Russo et al, 1996;Hong et al, 2009;Zhang et al, 2009). A major regulatory mechanism of controlling the p27 KIP1 inhibitory function is to regulate p27 KIP1 protein levels through transcriptional, translational, and post-translational mechanisms (Hengst and Reed, 1996;Carrano et al, 1999;Boehm et al, 2002;Bagui et al, 2009;Shin et al, 2009;Trabosh et al, 2009). Recent study revealed that a novel regulatory mechanism during postphosphorylation and polyubiquitination of proteins could be another regulatory mechanism for p27 KIP1 .…”