The N-terminal region of p27 inhibits HIF-1α protein translation in ribosomal protein S6-dependent manner by regulating PHLPP-Ras-ERK-p90RSK axis.

D Zhang,J Liu,J Li,X Mi,Y Liang,C Huang

doi:10.1038/cddis.2014.496

Abstract

P27 was identified as a tumor suppressor nearly two decades, being implicated in cell-cycle control, differentiation, senescence, apoptosis and motility. Our present study, for the first time to the best of our knowledge, revealed a potential role of p27 in inhibiting S6-mediated hypoxia-inducible factor-1α (HIF-1α) protein translation, which contributed to the protection from environmental carcinogen (sodium arsenite)-induced cell transformation. Our findings showed that depletion of p27 expression by knockout and knockdown approaches efficiently enhanced S6 phosphorylation in arsenite response via overactivating Ras/Raf/MEK/ERK pathway, which consequently resulted in the stimulation of p90RSK (90 kDa ribosomal S6 kinase), a direct kinase for S6 phosphorylation. Although PI3K/AKT pathway was also involved in S6 activation, blocking AKT and p70S6K activation did not attenuate arsenite-induced S6 activation in p27−/− cells, suggesting p27 specifically targeted Ras/ERK pathway rather than PI3K/AKT pathway for inhibition of S6 activation in response to arsenite exposure. Further functional studies found that p27 had a negative role in cell transformation induced by chronic low-dose arsentie exposure. Mechanistic investigations showed that HIF-1α translation was upregulated in p27-deficient cells in an S6 phosphorylation-dependent manner and functioned as a driving force in arsenite-induced cell transformation. Knockdown of HIF-1α efficiently reversed arsenite-induced cell transformation in p27-depleted cells. Taken together, our findings provided strong evidence showing that by targeting Ras/ERK pathway, p27 provided a negative control over HIF-1α protein synthesis in an S6-dependent manner, and abrogated arsenite-induced cell transformation via downregulation of HIF-1α translation.

Highlights

Binding protein 1, increased expression of eukaryotic elongation factor 2 kinase and decreased expression of programmed cell death protein 4 have been categorized as four major aberrations of the translation process implicated in breast cancer when predicting overall survival or recurrence-free survival of patients.[11,14,15] targeting S6 phosphorylation and its related signaling pathway is a conventional strategy implicated in therapeutic intervention of human cancers.[16]
To show explicitly the role of S6 phosphorylation in hypoxia-inducible factor1α (HIF-1α) protein translation under the control of the p27 signaling in arsenite response, we introduced S6 S235/236A double mutant, which abolished phosphorylation of Ser235/236 in endogenous S6.18 As shown in Figure 7j, ectopic expression of HA-S6 S235/236A in p27 − / − (Δ51) cells efficiently attenuated arseniteinduced HIF-1α upregulation
A variety of research studies has shown that p27 performs cyclin-CDK-independent functions such as mediation of apoptosis, cytoskeleton rearrangements and transcriptional regulation,[23,24,37,38,39,40,41,42,43,44,45,46,47] the effect of p27 on modulation of protein translation remains largely untouched up to now

Summary

Introduction

Binding protein 1, increased expression of eukaryotic elongation factor 2 kinase and decreased expression of programmed cell death protein 4 have been categorized as four major aberrations of the translation process implicated in breast cancer when predicting overall survival or recurrence-free survival of patients.[11,14,15] targeting S6 phosphorylation and its related signaling pathway is a conventional strategy implicated in therapeutic intervention of human cancers.[16]. P27 regulating cell transformation via S6-mediated HIF-1α protein translation D Zhang et al MEK/ERK pathway that was responsible for the stimulation of p90RSK (90 kDa ribosomal S6 kinase), the direct kinase for S6 phosphorylation. Further functional studies demonstrated that through inhibiting S6-mediated hypoxia-inducible factor1α (HIF-1α) translation, p27 contributed to the protection from environmental carcinogen (sodium arsenite)-induced cell transformation. From a novel point of view, our findings provide one more piece of strong evidence for the suppressive role of p27 in the process of tumor promotion and progression in arsenic response, which is achieved by inhibition of HIF-1α protein translation

Methods

Results

Conclusion