The ability of cells to preserve genome integrity is fundamental to cellular homeostasis. Failure to properly repair DNA damage can lead to chromosomal instability, mutations, cell death, or inappropriate growth [1], [2], [3], [4]. Among the most deleterious forms of DNA lesions are DNA double-strand breaks (DSBs) which arise from both exogenous sources, such as ionizing radiation, and endogenous processes like transcription, replication stress, and oxidative metabolism [5], [6]. Because unrepaired or misrepaired DSBs can cause disease or death, cells have evolved robust DSB repair mechanisms, which cluster into non-homologous end joining (NHEJ) and homologous recombination (HR) repair pathways. DSB repair pathway choice is tightly regulated: in response to a DSB, repair is channeled toward either NHEJ or HR [1], [7]. NHEJ repairs DSBs by ligating the two broken ends of the DNA molecule together, which can lead to insertion or deletion of sequence, or chromosomal translocations [8]. This repair process is predominant during the G1 phase of the cell cycle. In contrast, HR uses a sister chromatid –or an exogenous homologous DNA molecule– as a template to faithfully restore the broken DNA sequence, which limits HR to late S or G2 [1], [7], [9].

Key decision points between these two pathways are likely influenced by 5′ DSB end resection, which permits the loading of RAD51 onto single-stranded DNA (ssDNA) exposed by resection. These processes convert double stranded DNA (dsDNA) at a DSB into a ssDNA nucleoprotein filament that facilitates homology search and strand invasion during HR [4], [6], [10], [11]. Resection and RAD51 loading also prevent NHEJ because the ligase, LIG4, requires dsDNA as a template. Core events in NHEJ and HR have largely been characterized in vitro. However, screens for factors required for DSB repair can identify players that do not have a known catalytic role in these processes. Some of these uncharacterized factors likely have bona fide roles in DSB repair. For example, the RAD51 paralogs, RAD51B, RAD51C, RAD51D, XRCC2, and XRCC3 act to promote the assembly and stabilization of the RAD51 filament [12]. Mutations in the genes encoding RAD51B, RAD51C, and RAD51D have been found to be associated with ovarian, prostate and breast cancers [13], [14], [15].

In this study, we identify the multifunctional RNA-binding protein Splicing Factor Proline and Glutamine rich (SFPQ), as a regulator of DSB repair via HR. SFPQ, also known as PSF, is implicated in diverse aspects of RNA metabolism including splicing, transcriptional regulation, R-loop resolution, and RNA transport [16], [17], [18], [19]. SFPQ is a key component of paraspeckles, which are subnuclear condensates that regulate stress responses in viral infection, cancer, development, and neurodegeneration [20]. Importantly, SFPQ dysfunction has been linked to multiple cancers including ovarian, breast, and prostate malignancies; as well as neurodegenerative diseases, such as ALS and frontotemporal dementia [16], [21], [22], [23], [24], [25]. SFPQ has been previously linked to DSB repair through reported interactions with RAD51 protein in vitro [26] and colocalization with DNA damage-induced regions by laser microirradiation [27], [28]. SFPQ has also been implicated in strand invasion during HR, through biochemical studies demonstrating direct SFPQ-RAD51 binding and modulation of RAD51 strand-exchange activity in vitro [29]. Here, we report that SFPQ depletion significantly impairs recombination, mimicking the effect of RAD51 depletion. This recombination phenotype for SFPQ has already been reported by others [30]; however, contrary to previous reports, we observe that SFPQ does not localize to DSBs. Instead, our data indicate that SFPQ depletion reduces the expression of RAD51 and its paralogs. Moreover, this effect occurs independently of p53 activation and does not require DNA damage induction. Overall, we propose that SFPQ promotes HR indirectly by binding to and stabilizing RAD51-family mRNAs. Our findings underscore the importance of post-transcriptional regulation in DSB repair and highlight a previously uncharacterized role for SFPQ in maintaining genome integrity via stabilization of mRNAs encoding HR factors.