# contributed equally to the work Running title: FAM35A is a novel DNA repair factor.

The heterochromatin protein HP1 plays a central role in the maintenance of genome stability but little is known about how HP1 is controlled. Here, we show that the zinc finger protein POGZ promotes the presence of HP1 at DNA double-strand breaks (DSBs) in human cells. POGZ depletion delays the resolution of DSBs and sensitizes cells to different DNA-damaging agents, including cisplatin and talazoparib. Mechanistically, POGZ promotes homology-directed DNA repair by retaining the BRCA1/BARD1 complex at DSBs in an HP1-dependent manner. In vivo CRISPR inactivation of Pogz is embryonically lethal. Pogz haploinsufficiency (Pogz + /delta) results in developmental delay, impaired intellectual abilities, hyperactive behaviour and a compromised humoral immune response in mice, recapitulating the main clinical features of the White Sutton syndrome (WHSUS). Pogz + /delta mice are further radiosensitive and accumulate DSBs in diverse tissues, including the spleen and brain. Altogether, our findings identify POGZ as an important player in homology-directed DNA repair both in vitro and in vivo.

Egr‐1 is a transcription factor implicated in the regulation of several growth‐related cascades. It has been suggested to participate in the development of vascular disease processes such as intimal thickening following vascular injury, atherosclerosis and cardiac hypertrophy. Upregulation of Egr‐1 was recently shown to be a key contributing factor in stimuli‐induced VSMC proliferation and hypertrophy. Ang‐II, a potent vasoactive peptide with pathogenic role in vascular disease, has been demonstrated to contribute to aberrant remodeling of the vessel wall. This is mainly due to the ability of Ang‐II to activate hypertrophic and proliferative pathways such as the mitogen‐activated protein kinase and the phosphatidylinositol‐3‐kinase pathways in VSMC. It has been shown earlier that Ang‐II requires H2O2 generation to activate these signaling pathways and we have shown that Ca2+, calmodulin (CaM) and Ca2+/CaM‐dependent protein kinase II(CaMKII), play a critical role to trigger H2O2‐induced effects in VSMC. We have also shown that endothelin‐1, another mitogenic vasoactive peptide, requires CaMKII to upregulate Egr‐1 expression and to mediate its physiological responses. However, Ang‐II‐induced modulation of Egr‐1 expression in VSMC and the implication of CaMKII in this process remain unexplored. Therefore these studies were undertaken to characterize the effect of Ang‐II on Egr‐1 expression in A10 VSMC and to examine the role of Ca2+, CaM and CaMKII on this response. Ang‐II, at 100nM, induced an increase in Egr‐1 expression in a time‐dependent fashion in the nucleus of A10 VSMC. Pharmacological blockade of CaM and CaMKII by calmidazolium and KN‐93 respectively, significantly attenuated Ang‐II‐induced Egr‐1 expression. These results demonstrate that Egr‐1 expression is upregulated in response to Ang‐II via CaM/CaMKII‐dependent pathways in VSMC. Grant Funding Source: Supported by the Canadian Institutes of Health Research

Homologous recombination (HR) plays an essential role in the maintenance of genome stability by promoting the repair of cytotoxic DNA double strand breaks (DSBs). More recently, the HR pathway has emerged as a core component of the response to replication stress, in part by protecting stalled replication forks from nucleolytic degradation. In that regard, the mammalian RAD51 paralogs (RAD51B, RAD51C, RAD51D, XRCC2, and XRCC3) have been involved in both HR-mediated DNA repair and collapsed replication fork resolution. Still, it remains largely obscure how they participate in both processes, thereby maintaining genome stability and preventing cancer development. To gain better insight into their contribution in cellulo, we mapped the proximal interactome of the classical RAD51 paralogs using the BioID approach. Aside from identifying the well-established BCDX2 and CX3 sub-complexes, the spliceosome machinery emerged as an integral component of our proximal mapping, suggesting a crosstalk between this pathway and the RAD51 paralogs. Furthermore, we noticed that factors involved RNA metabolic pathways are significantly modulated within the BioID of the classical RAD51 paralogs upon exposure to hydroxyurea (HU), pointing towards a direct contribution of RNA processing during replication stress. Importantly, several members of these pathways have prognostic potential in breast cancer (BC), where their RNA expression correlates with poorer patient outcome. Collectively, this study uncovers novel functionally relevant partners of the different RAD51 paralogs in the maintenance of genome stability that could be used as biomarkers for the prognosis of BC.