Special AT-rich Sequence-binding Protein 1 (SATB1) Functions as an Accessory Factor in Base Excision Repair

Simran Kaur,Yan Coulombe,Zubaidah M Ramdzan,Lam Leduy,Jean-Yves Masson,Alain Nepveu

doi:10.1074/jbc.m116.735696

Abstract

Base excision repair is initiated by DNA glycosylases that recognize specific altered bases. DNA glycosylases for oxidized bases carry both a glycosylase activity that removes the faulty base and an apyrimidinic/apurinic lyase activity that introduces a single-strand DNA incision. In particular, the CUT domains within the CUX1 and CUX2 proteins were recently shown to interact with the 8-oxoguanine (8-oxoG) DNA glycosylase and stimulate its enzymatic activities. SATB1, which contains two CUT domains, was originally characterized as a T cell-specific genome organizer whose aberrant overexpression in breast cancer can promote tumor progression. Here we investigated the involvement of SATB1 in DNA repair. SATB1 knockdown caused a delay in DNA repair following exposure to H2O2, an increase in OGG1-sensitive oxidized bases within genomic DNA, and a decrease in 8-oxoG cleavage activity in cell extracts. In parallel, we observed an increase in phospho-CHK1 and γ-H2AX levels and a decrease in DNA synthesis. Conversely, ectopic expression of SATB1 accelerated DNA repair and reduced the levels of oxidized bases in genomic DNA. Moreover, an enhanced GFP-SATB1 fusion protein was rapidly recruited to laser microirradiation-induced DNA damage. Using purified proteins, we showed that SATB1 interacts directly with OGG1, increases its binding to 8-oxoG-containing DNA, promotes Schiff base formation, and stimulates its glycosylase and apyrimidinic/apurinic lyase enzymatic activities. Structure/function analysis demonstrated that CUT domains, but not the homeodomain, are responsible for the stimulation of OGG1. Together, these results identify another CUT domain protein that functions both as a transcription factor and an accessory factor in base excision repair.

Highlights

Several proteins can participate in Base excision repair (BER) complex formation and modulate the enzymatic activities of distinct BER enzymes
We present results indicating that the SATB1 protein plays a direct role in DNA repair as an accessory factor that stimulates the enzymatic activities of the oxoguanine DNA glycosylase 1 (OGG1) DNA glycosylase
As established previously for other CUT domain proteins, CUX1 and CUX2, SATB1 CUT domains play an important role in the stimulation of OGG1 (Fig. 7) (56 –58)

Summary

Introduction

Several proteins can participate in BER complex formation and modulate the enzymatic activities of distinct BER enzymes. Using purified proteins, we showed that SATB1 and smaller recombinant proteins containing SATB1 CUT domains stimulate OGG1 binding to 8-oxoG bases as well as its glycosylase and AP/lyase enzymatic activities. SATB1 Affects the Levels of OGG1-sensitive Sites in Cells— CUX1 and CUX2, two proteins that, like SATB1, contain CUT domains, were shown previously to function as accessory factors for the OGG1 DNA glycosylase [56, 57].

Results

Conclusion