HnRNPA1 couples nuclear export and translation of specific mRNAs downstream of FGF-2/S6K2 signalling.

Rajat Roy,Martin Holcik,Lin Guo,Bing-Qian Liu,Hui Li,Michael J Seckl,Olivier E Pardo,Danielle Durie,Francesco Mauri,Mattia Barbareschi,Lucia Veronica Cuorvo,John Mark Skehel

doi:10.1093/nar/gku953

Abstract

The increased cap-independent translation of anti-apoptotic proteins is involved in the development of drug resistance in lung cancer but signalling events regulating this are poorly understood. Fibroblast growth factor 2 (FGF-2) signalling-induced S6 kinase 2 (S6K2) activation is necessary, but the downstream mediator(s) coupling this kinase to the translational response is unknown. Here, we show that S6K2 binds and phosphorylates hnRNPA1 on novel Ser4/6 sites, increasing its association with BCL-XL and XIAP mRNAs to promote their nuclear export. In the cytoplasm, phosphoS4/6-hnRNPA1 dissociates from these mRNAs de-repressing their IRES-mediated translation. This correlates with the phosphorylation-dependent association of hnRNPA1 with 14-3-3 leading to hnRNPA1 sumoylation on K183 and its re-import into the nucleus. A non-phosphorylatible, S4/6A mutant prevented these processes, hindering the pro-survival activity of FGF-2/S6K2 signalling. Interestingly, immunohistochemical staining of lung and breast cancer tissue samples demonstrated that increased S6K2 expression correlates with decreased cytoplasmic hnRNPA1 and increased BCL-XL expression. In short, phosphorylation on novel N-term sites of hnRNPA1 promotes translation of anti-apoptotic proteins and is indispensable for the pro-survival effects of FGF-2.

Highlights

Deregulation of apoptotic cell death is a hallmark of cancer and is involved in the development of resistance to therapy
We have shown that Fibroblast growth factor 2 (FGF-2) signalling leads to the assembly of a multi-protein complex comprising BRaf, protein kinase C⑀ and ribosomal S6 kinase 2 (S6K2) but not S6K1
To help focus on changes linked to the pro-survival activity of FGF-2, we repeated the quantitative phosphoproteomic experiments in the presence of an alternate stimulus, stem cell factor (SCF) (Supplementary Table S3), which is involved in the proliferation [29,30,31], but not survival, of lung cancer cells

Summary

Introduction

Deregulation of apoptotic cell death is a hallmark of cancer and is involved in the development of resistance to therapy This is a leading cause of fatalities from common cancers including lung cancer. Several proteins can mediate cell death resistance [1,2,3] including fibroblast growth factor 2 (FGF2) [4,5,6]. Activated S6K2 enhances the translation of anti-apoptotic proteins such as BCL-XL and X chromosome-linked inhibitor of apoptosis (XIAP) [4] Translation of these mRNAs under conditions of cellular stress including anti-cancer therapies is mediated by an internal ribosomal entry site (IRES) located in the 5 untranslated region (UTR) [8,9,10]. In addition to its diffuse nuclear localization, a proportion of S6K2, but not S6K1, has been shown to co-localize with CTR453 and ␥ tubulin at the level of the centrosome [7]

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Results

Conclusion