SPOC1 modulates DNA repair by regulating key determinants of chromatin compaction and DNA damage response.

Andreas Mund,Hannah Staege,Anne-Sophie Hoffbeck,Kerstin Reumann,Malte Kriegs,Hans Will,Tobias Schubert,Sarah Kinkley,Lauriane Fritsch,Slimane Ait-Si-Ali,Evi Soutoglou,Valentine Battisti

doi:10.1093/nar/gkaa754

Abstract

Survival time-associated plant homeodomain (PHD) finger protein in Ovarian Cancer 1 (SPOC1, also known as PHF13) is known to modulate chromatin structure and is essential for testicular stem-cell differentiation. Here we show that SPOC1 is recruited to DNA double-strand breaks (DSBs) in an ATM-dependent manner. Moreover, SPOC1 localizes at endogenous repair foci, including OPT domains and accumulates at large DSB repair foci characteristic for delayed repair at heterochromatic sites. SPOC1 depletion enhances the kinetics of ionizing radiation-induced foci (IRIF) formation after γ-irradiation (γ-IR), non-homologous end-joining (NHEJ) repair activity, and cellular radioresistance, but impairs homologous recombination (HR) repair. Conversely, SPOC1 overexpression delays IRIF formation and γH2AX expansion, reduces NHEJ repair activity and enhances cellular radiosensitivity. SPOC1 mediates dose-dependent changes in chromatin association of DNA compaction factors KAP-1, HP1-α and H3K9 methyltransferases (KMT) GLP, G9A and SETDB1. In addition, SPOC1 interacts with KAP-1 and H3K9 KMTs, inhibits KAP-1 phosphorylation and enhances H3K9 trimethylation. These findings provide the first evidence for a function of SPOC1 in DNA damage response (DDR) and repair. SPOC1 acts as a modulator of repair kinetics and choice of pathways. This involves its dose-dependent effects on DNA damage sensors, repair mediators and key regulators of chromatin structure.

Highlights

Elevated SPOC1 RNA levels of the human SPOC1 gene are associated with unresectable carcinomas and shorter survival in ovarian cancer patients, implicating a possible role in oncogenesis [1]
We provide the first evidence that SPOC1-expression levels have an impact on DNA damage response (DDR), DNA repair kinetics and pathway choice, as well as on cellular radiosensitivity
We propose a molecular mechanism that is predominantly deduced from the following observations: (i) ATM kinase-dependent recruitment of SPOC1 to double-strand breaks (DSBs); (ii) SPOC1 accumulation at endogenous and experimentally induced repair foci with slow repair kinetics; (iii) SPOC1-dependent differences in the number of ionizing radiation-induced foci (IRIF) formed early after g-IR; (iv) altered kinetics of g-IR-inducible DSB repair; (v) altered cellular radiosensitivity; (vi) the ability of SPOC1 to modulate dose-dependently both non-homologous end-joining (NHEJ) and homologous recombination (HR) activity and (vii) SPOC1’s interaction with, and modulation of proteins that have intertwined functions in regulating chromatin structure as well as DDR and DNA repair

Summary

Introduction

Elevated SPOC1 RNA levels of the human SPOC1 gene are associated with unresectable carcinomas and shorter survival in ovarian cancer patients, implicating a possible role in oncogenesis [1]. In a mouse SPOC1 knockout model, SPOC1 protein expression was recently shown to be indispensable for testis stem-cell differentiation and sustained spermatogenesis [4]. These findings imply that SPOC1 plays a role in stem-cell maintenance, chromatin structure, and presumably in oncogenesis. Considering these data and published evidence that chromatin structure plays a crucial role in radiosensitivity, DNA repair and mutation rates in cancer cells [5], we wanted to examine whether SPOC1 has an impact on DNA damage response (DDR) and DNA repair

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