WW Domain-containing E3 Ubiquitin Protein Ligase 1 (WWP1) Delays Cellular Senescence by Promoting p27Kip1 Degradation in Human Diploid Fibroblasts

Xiaoxiao Cao,Lixiang Xue,Limin Han,Liwei Ma,Tianda Chen,Tanjun Tong

doi:10.1074/jbc.m111.225565

Abstract

WW domain-containing E3 ubiquitin protein ligase 1 (WWP1) plays an important role in the proliferation of tumor cells and the lifespan of Caenorhabditis elegans. However, the role of WWP1 in cellular senescence is still unknown. Here, we show that the expression patterns of p27(Kip1) and WWP1 are inversely correlated during cellular senescence. Moreover, the overexpression of WWP1 delayed senescence, whereas the knockdown of WWP1 led to premature senescence in human fibroblasts. Furthermore, we demonstrate that WWP1 repressed endogenous p27(Kip1) expression through ubiquitin-proteasome-mediated degradation. Additionally, WWP1 had a strong preference for catalyzing the Lys-48-linked polyubiquitination of p27(Kip1) in vitro. Finally, we demonstrate that WWP1 markedly inhibited the replicative senescence induced by p27(Kip1) by promoting p27(Kip1) degradation. Therefore, our study provides a new molecular mechanism for the regulation of cellular senescence.

Highlights

The majority of proteins involved in replicative senescence are modified by polyubiquitin, which directs proteins for degradation by the 26 S proteasome
In Caenorhabditis elegans, WWP1 is a positive regulator of lifespan, acting through diet restriction and the DAF-2 insulin/insulin-like growth factor-1 signaling pathway (19, 20)
Expression of WWP1 Is Decreased during Replicative Senescence in Human Fibroblasts—In view of the positive effect of WWP1 on the proliferation of prostate and breast epithelial cancer cells and the role of WWP1 in increasing the lifespan of C. elegans, we speculated that WWP1 might be involved in cellular senescence

Summary

Introduction

The majority of proteins involved in replicative senescence are modified by polyubiquitin, which directs proteins for degradation by the 26 S proteasome. Western blot analysis revealed that the expression of WWP1 was high in young cells but decreased significantly during cellular senescence, whereas the expression of p16INK4a, p21Cip1, and p27Kip1 increased in senescent cells (Fig. 1A). To determine the effect of WWP1 on cellular senescence, WWP1 was overexpressed and silenced, respectively, with a retrovirus expression system in young 2BS and WI38 cells.

Results

Conclusion