Genetic suppression reveals DNA repair-independent antagonism between BRCA1 and COBRA1 in mammary gland development

Abstract

The breast cancer susceptibility gene BRCA1 is well known for its function in double-strand break (DSB) DNA repair. While BRCA1 is also implicated in transcriptional regulation, the physiological significance remains unclear. COBRA1 (also known as NELF-B) is a BRCA1-binding protein that regulates RNA polymerase II (RNAPII) pausing and transcription elongation. Here we interrogate functional interaction between BRCA1 and COBRA1 during mouse mammary gland development. Tissue-specific deletion of Cobra1 reduces mammary epithelial compartments and blocks ductal morphogenesis, alveologenesis and lactogenesis, demonstrating a pivotal role of COBRA1 in adult tissue development. Remarkably, these developmental deficiencies due to Cobra1 knockout are largely rescued by additional loss of full-length Brca1. Furthermore, Brca1/Cobra1 double knockout restores developmental transcription at puberty, alters luminal epithelial homoeostasis, yet remains deficient in homologous recombination-based DSB repair. Thus our genetic suppression analysis uncovers a previously unappreciated, DNA repair-independent function of BRCA1 in antagonizing COBRA1-dependent transcription programme during mammary gland development.

Cell-type-specific epigenomic variations associated withBRCA1mutation in pre-cancer human breast tissues

“…2c). A number of BRCA1-associated processes, including progesterone metabolism (Katiyar et al 2006;Ma et al 2006;Calvo and Beato 2011;Davaadelger et al 2019), RNA polymerase II transcription (Scully et al 1997;Krum et al 2003;Nair et al 2016), and unfolded protein response (UPR) (Yeung et al 2008), were enriched in both BCs and SCs. BRCA1 has been shown to inhibit progesterone signaling (Ma et al 2006) and reduction in BRCA1 level has been shown to increase expression of GRP78, a key UPR regulating gene (Yeung et al 2008).…”

Gene-Specific Genetic Complementation between Brca1 and Cobra1 During Mouse Mammary Gland Development

“…Using mammary epithelial-specific knockout (KO) mouse models for Brca1 and Cobra1 , we recently demonstrated genetic complementation between these two genes during normal mammary gland development and tumor suppression 36 , 37 . Tissue-specific deletion of Cobra1 blocked ductal morphogenesis and alveologenesis, demonstrating a crucial role of COBRA1/NELF-B in adult tissue development.…”

“…Tissue-specific deletion of Cobra1 blocked ductal morphogenesis and alveologenesis, demonstrating a crucial role of COBRA1/NELF-B in adult tissue development. Of note, these resulting developmental defects of Cobra1 ablation were largely rescued by the loss of full-length BRCA1 expression through deletion of Brca1 exon 11 37 . Reciprocally, Cobra1 deletion reduced mammary tumorigenesis associated with Brca1 inactivation 37 .…”

“…Of note, these resulting developmental defects of Cobra1 ablation were largely rescued by the loss of full-length BRCA1 expression through deletion of Brca1 exon 11 37 . Reciprocally, Cobra1 deletion reduced mammary tumorigenesis associated with Brca1 inactivation 37 . We further showed that the functional antagonism between Brca1 and Cobra1 in mammary gland development and tumorigenesis is independent of the role of BRCA1 in HR repair 36 , 37 .…”

Transcription pausing regulates mouse embryonic stem cell differentiation

“…In addition, deletion of Nelf-b in mESCs causes proliferation defects together with a blunted response to differentiation signals (Williams et al, 2015). Although these studies suggest crucial roles of NELF-mediated pausing in mouse embryonic development, the interpretation of these results could be complicated by other functions of NELF-B, such as the physical and functional interaction of NELF-B with the DNA repair protein BRCA1 (Aiyar et al, 2007; Nair et al, 2016; Ye et al, 2001). Thus, the direct role of Pol II pausing in mammalian embryonic development remains to be elucidated.…”