Replication fork stability during DNA replication is vital for maintenance of genomic stability and suppression of cancer development in mammals. ATR (ataxia‐telangiectasia mutated [ATM] and RAD3‐related) is a master regulatory kinase that activates the replication stress response to overcome replication barriers. Although many downstream effectors of ATR have been established, the upstream regulators of ATR and the effect of such regulation on liver cancer remain unclear. The ubiquitin conjugase BRUCE (BIR Repeat containing Ubiquitin‐Conjugating Enzyme) is a guardian of chromosome integrity and activator of ATM signaling, which promotes DNA double‐strand break repair through homologous recombination. Here we demonstrate the functions for BRUCE in ATR activation in vitro and liver tumor suppression in vivo. BRUCE is recruited to induced DNA damage sites. Depletion of BRUCE inhibited multiple ATR‐dependent signaling events during replication stress, including activation of ATR itself, phosphorylation of its downstream targets CHK1 and RPA, and the mono‐ubiquitination of FANCD2. Consequently, BRUCE deficiency resulted in stalled DNA replication forks and increased firing of new replication origins. The in vivo impact of BRUCE loss on liver tumorigenesis was determined using the hepatocellular carcinoma model induced by genotoxin diethylnitrosamine. Liver‐specific knockout of murine Bruce impaired ATR activation and exacerbated inflammation, fibrosis and hepatocellular carcinoma, which exhibited a trabecular architecture, closely resembling human hepatocellular carcinoma (HCC). In humans, the clinical relevance of BRUCE down‐regulation in liver disease was found in hepatitis, cirrhosis, and HCC specimens, and deleterious somatic mutations of the Bruce gene was found in human hepatocellular carcinoma in the Cancer Genome Atlas database. Conclusion: These findings establish a BRUCE‐ATR signaling axis in accurate DNA replication and suppression of liver cancer in mice and humans and provides a clinically relevant HCC mouse model.

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#VanguardSTEM is an online community and platform that centers women, girls, and non-binary people of color in science, technology, engineering, and mathematics (STEM) fields. We publish original and curated content, using cultural production to include a multiplicity of identities as worthy of recognition and thus redefine STEM identity and belonging. #VanguardSTEM is rooted firmly in Queer, Black feminisms which delineate the experiences and critiques of Black women matter and that these insights can foster a restorative and regenerative construction of the cultures in which we exist. In describing how #VanguardSTEM descended from counterspaces, we draw on speculative fiction to define a #VanguardSTEM hyperspace as a fluid “place-time” that is born digital and enabled by social media, but materializes in the physical world for specific purposes. As Black women in STEM, we consider how our situated knowledges and scientific expertise inform our process. We propose an intersectional scientific methodology to address the influence of embodied observation, embedded context and collective impact on scientific inquiry. Through #VanguardSTEM, we assert, without apology, the right of Black, Indigenous, women of color to self-advocate by fully representing ourselves, our STEM identities and interests, without assimilation.

BACKGROUND BIR repeat-containing ubiquitin conjugating enzyme (BRUCE) is a liver tumor suppressor, which is downregulated in a large number of patients with liver diseases. BRUCE facilitates DNA damage repair to protect the mouse liver against the hepatocarcinogen diethylnitrosamine (DEN)-dependent acute liver injury and carcinogenesis. While there exists an established pathologic connection between fibrosis and hepatocellular carcinoma (HCC), DEN exposure alone does not induce robust hepatic fibrosis. Further studies are warranted to identify new suppressive mechanisms contributing to DEN-induced fibrosis and HCC. AIM To investigate the suppressive mechanisms of BRUCE in hepatic fibrosis and HCC development. METHODS Male C57/BL6/J control mice [loxp/Loxp; albumin-cre (Alb-cre) - ] and BRUCE Alb-Cre KO mice (loxp/Loxp; Alb-Cre + ) were injected with a single dose of DEN at postnatal day 15 and sacrificed at different time points to examine liver disease progression. RESULTS By using a liver-specific BRUCE knockout (LKO) mouse model, we found that BRUCE deficiency, in conjunction with DEN exposure, induced hepatic fibrosis in both premalignant as well as malignant stages, thus recapitulating the chronic fibrosis background often observed in HCC patients. Activated in fibrosis and HCC, β-catenin activity depends on its stabilization and subsequent translocation to the nucleus. Interestingly, we observed that livers from BRUCE KO mice demonstrated an increased nuclear accumulation and elevated activity of β-catenin in the three stages of carcinogenesis: Pre-malignancy, tumor initiation, and HCC. This suggests that BRUCE negatively regulates β-catenin activity during liver disease progression. β-catenin can be activated by phosphorylation by protein kinases, such as protein kinase A (PKA), which phosphorylates it at Ser-675 (pSer-675-β-catenin). Mechanistically, BRUCE and PKA were colocalized in the cytoplasm of hepatocytes where PKA activity is maintained at the basal level. However, in BRUCE deficient mouse livers or a human liver cancer cell line, both PKA activity and pSer-675-β-catenin levels were observed to be elevated. CONCLUSION Our data support a “BRUCE-PKA-β-catenin” signaling axis in the mouse liver. The BRUCE interaction with PKA in hepatocytes suppresses PKA-dependent phosphorylation and activation of β-catenin. This study implicates BRUCE as a novel negative regulator of both PKA and β-catenin in chronic liver disease progression. Furthermore, BRUCE-liver specific KO mice serve as a promising model for understanding hepatic fibrosis and HCC in patients with aberrant activation of PKA and β-catenin.