Nuclear localization of Beclin 1 promotes radiation-induced DNA damage repair independent of autophagy

Fei Xu,Chaorong Ge,Ni An,Suping Zhang,Xiaoying Zhang,Jialing Xie,Yan Cao,Lan Xu,Yixuan Fang,Lili Yan,Daohong Zhou,Gaoyue Jiang,Jianrong Wang,Li Xu,Na Yuan

doi:10.1038/srep45385

Abstract

Beclin 1 is a well-established core mammalian autophagy protein that is embryonically indispensable and has been presumed to suppress oncogenesis via an autophagy-mediated mechanism. Here, we show that Beclin 1 is a prenatal primary cytoplasmic protein but rapidly relocated into the nucleus during postnatal development in mice. Surprisingly, deletion of beclin1 in in vitro human cells did not block an autophagy response, but attenuated the expression of several DNA double-strand break (DSB) repair proteins and formation of repair complexes, and reduced an ability to repair DNA in the cells exposed to ionizing radiation (IR). Overexpressing Beclin 1 improved the repair of IR-induced DSB, but did not restore an autophagy response in cells lacking autophagy gene Atg7, suggesting that Beclin 1 may regulate DSB repair independent of autophagy in the cells exposed to IR. Indeed, we found that Beclin 1 could directly interact with DNA topoisomerase IIβ and was recruited to the DSB sites by the interaction. These findings reveal a novel function of Beclin 1 in regulation of DNA damage repair independent of its role in autophagy particularly when the cells are under radiation insult.

Highlights

Beclin 1 was initially identified as a Bcl-2-interacting coiled-coil protein that was expected to play a role in antiviral host defenses[1]
This finding was confirmed by immunoblot, which demonstrates that while total cellular levels of Beclin 1 were relatively stable during the course of mouse development (Fig. S1A), Beclin 1 relocated from cytoplasma to nucleus within a few weeks after birth (Fig. S1B)
To determine whether Beclin 1 regulates DNA double-strand break (DSB) repair in an autophagy-dependent manner, we examined whether beclin[1] deletion affects the autophagy response using image flow cytometry to visually and statistically analyze LC3b spot counts, a marker used for measuring the formation of autophagasomes

Summary

Introduction

Beclin 1 was initially identified as a Bcl-2-interacting coiled-coil protein that was expected to play a role in antiviral host defenses[1]. Studies have shown that Beclin 1 interacts with an increasing number of cofactors, including Atg14L, UVRAG, Bif-1, Rubicon, Ambra[1], HMGB1, nPIST, VMP1, SLAM, IP(3) R, PINK and survivin, to regulate the lipid kinase Vps[34] and to promote the formation of Beclin 1-Vps34-Vps[15] core complexes, which induces autophagy[5,6,7,8,9,10,11]. These findings establish that Beclin 1 plays a central role in mammalian autophagy. Nuclear Beclin 1 protects genomic integrity by collaborating with DNA topoisomerase IIβduring DNA damage repair

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Results

Conclusion