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Abstract Background Although hepatitis B virus (HBV) infection is a major risk factor for hepatic cancer, the majority of HBV carriers do not develop this lethal disease. Additional molecular alterations are thus implicated in the process of liver tumorigenesis. Since phosphatase and tensin homolog (PTEN) is decreased in approximately half of liver cancers, we investigated the significance of PTEN deficiency in HBV-related hepatocarcinogenesis. Methods HBV-positive human liver cancer tissues were checked for PTEN expression. Transgenic HBV, Alb-Cre and Pten fl/fl mice were inter-crossed to generate WT, HBV, Pten −/− and HBV; Pten −/− mice. Immunoblotting, histological analysis and qRT-PCR were used to study these livers. Gp73 −/− mice were then mated with HBV; Pten −/− mice to illustrate the role of hepatic tumor biomarker golgi membrane protein 73 (GP73)/ golgi membrane protein 1 (GOLM1) in hepatic oncogenesis. Results Pten deletion and HBV transgene synergistically aggravated liver injury, inflammation, fibrosis and development of mixed hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC). GP73 was augmented in HBV; Pten −/− livers. Knockout of GP73 blunted the synergistic effect of deficient Pten and transgenic HBV on liver injury, inflammation, fibrosis and cancer development. Conclusions This mixed HCC-ICC mouse model mimics liver cancer patients harboring HBV infection and PTEN/AKT signaling pathway alteration. Targeting GP73 is a promising therapeutic strategy for cancer patients with HBV infection and PTEN alteration.

Abstract. Background:. Liver cancer is largely resistant to chemotherapy. This study aimed to identify the effective chemotherapeutics for β-catenin-activated liver cancer which is caused by gain-of-function mutation of catenin beta 1 (CTNNB1), the most frequently altered proto-oncogene in hepatic neoplasms. Methods:. Constitutive β-catenin-activated mouse embryonic fibroblasts (MEFs) were established by deleting exon 3 (β-cateninΔ(ex3)/+), the most common mutation site in CTNNB1 gene. A screening of 12 widely used chemotherapy drugs was conducted for the ones that selectively inhibited β-cateninΔ(ex3)/+ but not for wild-type MEFs. Untargeted metabolomics was carried out to examine the alterations of metabolites in nucleotide synthesis. The efficacy and selectivity of methotrexate (MTX) on β-catenin-activated human liver cancer cells were determined in vitro. Immuno-deficient nude mice subcutaneously inoculated with β-catenin wild-type or mutant liver cancer cells and hepatitis B virus (HBV); β-cateninlox(ex3)/+ mice were used, respectively, to evaluate the efficacy of MTX in the treatment of β-catenin mutant liver cancer. Results:. MTX was identified and validated as a preferential agent against the proliferation and tumor formation of β-catenin-activated cells. Boosted nucleotide synthesis was the major metabolic aberration in β-catenin-active cells, and this alteration was also the target of MTX. Moreover, MTX abrogated hepatocarcinogenesis of HBV; β-cateninlox(ex3)/+ mice, which stimulated concurrent Ctnnb1-activated mutation and HBV infection in liver cancer. Conclusion:. MTX is a promising chemotherapeutic agent for β-catenin hyperactive liver cancer. Since repurposing MTX has the advantages of lower risk, shorter timelines, and less investment in drug discovery and development, a clinical trial is warranted to test its efficacy in the treatment of β-catenin mutant liver cancer.

Abstract The BRCA1/BARD1 complex plays a key role in the repair of DNA double-strand breaks (DSBs) in both somatic cells and germ cells. However, the underlying molecular mechanism by which this complex mediates DSB repair is not fully understood. Here, we examined the XY body of male germ cells, where DSBs are accumulated. We show that the recruitment of the BRCA1/BARD1 complex to the unsynapsed axis of the XY body is mediated by pre-ribosomal RNA (pre-rRNA). Similarly, the BRCA1/BARD1 complex associates with pre-rRNA in somatic cells, which not only forms nuclear foci in response to DSBs, but also targets the BRCA1/BARD1 complex to DSBs. The interactions between the BRCT domains of the BRCA1/BARD1 complex and pre-rRNA induce liquid–liquid phase separations, which may be the molecular basis of DSB-induced nuclear foci formation of the BRCA1/BARD1 complex. Moreover, cancer-associated mutations in the BRCT domains of BRCA1 and BARD1 abolish their interactions with pre-rRNA. Pre-rRNA also mediates BRCA1-dependent homologous recombination, and suppression of pre-rRNA biogenesis sensitizes cells to PARP inhibitor treatment. Collectively, this study reveals that pre-rRNA is a functional partner of the BRCA1/BARD1 complex in the DSB repair.

Abstract Background The expression of pyruvate kinase muscle 2 (PKM2) is augmented in macrophages of patients with atherosclerotic coronary artery disease. The role of PKM2 in atherosclerosis is to be determined. Methods Global and myeloid cell‐specific PKM2 knock‐in mice with ApoE−/− background (ApoE−/−, PKM2KI/KI and Lyz2‐cre, ApoE−/−, and PKM2flox/flox) were produced to evaluate the clinical significance of PKM2 in atherosclerosis development. Wild‐type and PKM2 knock‐in macrophages were isolated to assess the function of PKM2 in macrophage phagocytosis. Atherosclerotic mice were treated with PKM2 inhibitor shikonin (SKN) to evaluate the therapeutic potential of PKM2 suppression in atherosclerosis. Results Oxidized low‐density lipoprotein (oxLDL) upregulated PKM2 in macrophages. PKM2 in return promoted the uptake of oxLDL by macrophages. Overexpressed PKM2 accelerated atherosclerosis in mice. SKN blocked the progress of mouse atherosclerosis. Conclusions PKM2 accelerates macrophage phagocytosis and atherosclerosis. Targeting PKM2 is a potential therapy for atherosclerosis.

Abstract Background Although β-catenin signaling cascade is frequently altered in human cancers, targeting this pathway has not been approved for cancer treatment. Methods High-throughput screening of an FDA-approved drug library was conducted to identify therapeutics that selectively inhibited the cells with activated β-catenin. Efficacy of iron chelator and mitochondrial inhibitor was evaluated for suppression of cell proliferation and tumorigenesis. Cellular chelatable iron levels were measured to gain insight into the potential vulnerability of β-catenin-activated cells to iron deprivation. Extracellular flux analysis of mitochondrial function was conducted to evaluate the downstream events of iron deprivation. Chromatin immunoprecipitation, real-time quantitative PCR and immunoblotting were performed to identify β-catenin targets. Depletion of iron-regulatory protein 2 (IRP2), a key regulator of cellular iron homeostasis, was carried out to elucidate its significance in β-catenin-activated cells. Online databases were analyzed for correlation between β-catenin activity and IRP2-TfR1 axis in human cancers. Results Iron chelators were identified as selective inhibitors against β-catenin-activated cells. Deferoxamine mesylate, an iron chelator, preferentially repressed β-catenin-activated cell proliferation and tumor formation in mice. Mechanically, β-catenin stimulated the transcription of IRP2 to increase labile iron level. Depletion of IRP2-sequered iron impaired β-catenin-invigorated mitochondrial function. Moreover, mitochondrial inhibitor S-Gboxin selectively reduced β-catenin-associated cell viability and tumor formation. Conclusions β-catenin/IRP2/iron stimulation of mitochondrial energetics is targetable vulnerability of β-catenin-potentiated cancer.

Abstract In response to genotoxic stress‐induced DNA damage, TopBP1 mediates ATR activation for signaling transduction and DNA damage repair. However, the detailed molecular mechanism remains elusive. Here, using unbiased protein affinity purification and RNA sequencing, it is found that TopBP1 is associated with pre‐ribosomal RNA (pre‐rRNA). Pre‐rRNA co‐localized with TopBP1 at DNA double‐strand breaks (DSBs). Similar to pre‐rRNA, ribosomal proteins also colocalize with TopBP1 at DSBs. The recruitment of TopBP1 to DSBs is suppressed when cells are transiently treated with RNA polymerase I inhibitor (Pol I‐i) to suppress pre‐rRNA biogenesis but not protein translation. Moreover, the BRCT4‐5 of TopBP1 recognizes pre‐rRNA and forms liquid–liquid phase separation (LLPS) with pre‐rRNA, which may be the molecular basis of DSB‐induced foci of TopBP1. Finally, Pol I‐i treatment impairs TopBP1‐associated cell cycle checkpoint activation and homologous recombination repair. Collectively, this study reveals that pre‐rRNA plays a key role in the TopBP1‐dependent DNA damage response.

RAD51-associated protein 1 (RAD51AP1) is known to promote homologous recombination (HR) repair. However, the precise mechanism of RAD51AP1 in HR repair is unclear. Here, we identify that RAD51AP1 associates with pre-rRNA. Both the N terminus and C terminus of RAD51AP1 recognize pre-rRNA. Pre-rRNA not only colocalizes with RAD51AP1 at double-strand breaks (DSBs) but also facilitates the recruitment of RAD51AP1 to DSBs. Consistently, transient inhibition of pre-rRNA synthesis by RNA polymerase I inhibitor suppresses the recruitment of RAD51AP1 as well as HR repair. Moreover, RAD51AP1 forms liquid-liquid phase separation in the presence of pre-rRNA in vitro, which may be the molecular mechanism of RAD51AP1 foci formation. Taken together, our results demonstrate that pre-rRNA mediates the relocation of RAD51AP1 to DSBs for HR repair. [ABSTRACT FROM AUTHOR]