MIF is a 3\u2019 flap nuclease that facilitates DNA replication and promotes tumor growth

Janice Ortega,Guo-Min Li,Jennifer E. Wang,Lei Bao,Yijie Wang,Weibo Luo,Kara Y. Chan,Yanan Wang,Deepak Nijhawan,Weizhi Xu,Yan Chen,Chenliang Wang,Yingfei Wang,Mingming Yang,Emanuela Capota,BongWoo Kim

doi:10.1038/s41467-021-23264-z

Abstract

How cancer cells cope with high levels of replication stress during rapid proliferation is currently unclear. Here, we show that macrophage migration inhibitory factor (MIF) is a 3’ flap nuclease that translocates to the nucleus in S phase. Poly(ADP-ribose) polymerase 1 co-localizes with MIF to the DNA replication fork, where MIF nuclease activity is required to resolve replication stress and facilitates tumor growth. MIF loss in cancer cells leads to mutation frequency increases, cell cycle delays and DNA synthesis and cell growth inhibition, which can be rescued by restoring MIF, but not nuclease-deficient MIF mutant. MIF is significantly upregulated in breast tumors and correlates with poor overall survival in patients. We propose that MIF is a unique 3’ nuclease, excises flaps at the immediate 3’ end during DNA synthesis and favors cancer cells evading replication stress-induced threat for their growth.

Highlights

How cancer cells cope with high levels of replication stress during rapid proliferation is currently unclear
To study whether migration inhibitory factor (MIF) excises misincorporated nucleotides at the 3’ end of Y-shaped dsDNA, which mimics the intermediate products during DNA replication, we designed a series of “damaged” dsDNA substrates based on its stem-loop (SL) ssDNA substrate identified recently[19] but removed the loop and altered the length of mismatched nucleotides at the 3’ end with or without biotin labeling for in vitro nuclease assay (Fig. 1a)
We found that MIF cleaved away unpaired nucleotides varying from 1 to 7 nt at the 3’ end of nonbiotin-labeled dsDNA substrates, which had the Y-shaped structure but no loop structure (Fig. 1b, c)

Summary

Introduction

How cancer cells cope with high levels of replication stress during rapid proliferation is currently unclear. Poly(ADP-ribose) polymerase 1 colocalizes with MIF to the DNA replication fork, where MIF nuclease activity is required to resolve replication stress and facilitates tumor growth. We propose that MIF is a unique 3’ nuclease, excises flaps at the immediate 3’ end during DNA synthesis and favors cancer cells evading replication stress-induced threat for their growth. Cancer cells have evolved in certain ways to cope with DNA replication stress for their survival. Understanding and targeting these intrinsic DNA replication stress-resolving mechanisms in cancer cells may lead to developing a promising strategy to eliminate tumors. Pol δ and Pol ε are able to excise the mis-incorporated nucleotides at the 3′ end with their 3’

Methods

Results

Conclusion