Tumour cell-expressed PD-L1 reprograms lipid metabolism via EGFR/ITGB4/SREBP1c signalling in liver cancer.

Background & Aims: The programmed death-ligand 1 (PD-L1) is a major co-inhibitory checkpoint factor that controls T-cell activities in tumours. PD-L1 is expressed on immune cells and tumour cells. Whether tumour cell-expressed PD-L1 affects tumour cells in an immune cell-independent fashion remains largely elusive. In this study, we investigated the significance of tumour cell-expressed PD-L1 with a focus on downstream signals and changes in lipid metabolism. Methods: Immune-independent functions of PD-L1 in tumour growth were investigated in vitro and in immuno-deficient mice in vivo. The global influence of PD-L1 in targeted/untargeted lipidomic metabolites was studied by comprehensive mass spectrometry-based metabolomic analysis in liver cancer. Effects on lipid metabolism were confirmed by triglyceride and cholesterol assays as well as by Oil Red O staining in liver, pancreatic, breast, and oesophageal squamous cancer. Underlying mechanisms were investigated by real-time quantitative PCR, Western blot analysis, co-immunoprecipitation, pull-down assays, immunofluorescence staining, and RNA sequencing. Results: PD-L1 enhanced the accumulation of triglycerides, cholesterol, and lipid droplets in tumours. PD-L1 influenced targeted/untargeted lipidomic metabolites in hepatoma, including lipid metabolism, glucose metabolism, amino acid metabolism, nucleotide metabolism, and energy metabolism, suggesting that PD-L1 globally modulates the metabolic reprogramming of tumours. Mechanistically, PD-L1 activated epidermal growth factor receptor (EGFR) and/or integrin ß4 (ITGB4) by forming a complex of PD-L1/EGFR/ITGB4 in the cell membrane, prior to activating PI3K/mTOR/SREBP1c signalling, leading to reprogramming of lipid metabolism in tumours. Functionally, PD-L1-mediated lipid metabolism reprogramming supported the tumour growth in vitro and in vivo through EGFR and/or ITGB4 in an immune cell-independent manner. Conclusions: Our findings on lipogenesis and EGFR activation by tumour cell-expressed PD-L1 suggest that, in addition to its immunostimulatory effects, anti-PD-L1 may restrict lipid metabolism and EGFR/ITGB4 signalling in liver cancer therapy. Impact and implications: In this study, we present evidence that PD-L1 drives the reprogramming of lipid metabolism in tumours. PD-L1 forms a complex with epidermal growth factor receptor (EGFR) and ITGB4, activating the PI3K/Akt/mTOR/SREBP1c signalling pathway and thereby contributing to lipid metabolism in cancer progression. Our findings offer novel insights into the mechanisms by which PD-L1 initiates the reprogramming of lipid metabolism in tumours. From a clinical perspective, the anti-PD-L1 antibody may alleviate resistance to the anti-EGFR antibody cetuximab and inhibit the reprogramming of lipid metabolism in tumours.

HBx-Induced HSPA8 Stimulates HBV Replication and Suppresses Ferroptosis to Support Liver Cancer Progression.

Hepatitis B virus (HBV) infection is a major driver of hepatocarcinogenesis. Ferroptosis is a type of iron-mediated cell death that can suppress liver transformation. Previous studies have linked HBV to ferroptosis in liver fibrosis and acute liver failure. However, whether ferroptosis is involved in HBV-mediated liver cancer is poorly understood. Here, we identified heat shock protein family A member 8 (HSPA8) as a crucial host factor that modulates HBV replication and ferroptosis in liver cancer. Hepatitis B X protein (HBx) upregulated HSPA8 by coactivating the transcription factor heat shock factor 1 (HSF1) in cells. HSPA8 enhanced HBV replication by recruiting hepatitis B core protein (HBc) to the HBV covalently closed circular DNA (cccDNA) minichromosome, forming a positive feedback loop. Moreover, HSPA8 suppressed ferroptosis in liver cancer cells by upregulating the expression of SLC7A11/GPX4 and decreasing erastin-mediated reactive oxygen species and Fe2+ accumulation in cells in vitro and in vivo. Inhibition of HSPA8 reduced the growth of HBV-positive liver tumors and increased sensitivity to erastin. In conclusion, HBx-elevated HSPA8 regulates both HBV replication and ferroptosis in liver cancer. Targeting HSPA8 could be a promising strategy for controlling HBV and hepatocarcinogenesis. SIGNIFICANCE: HBV-induced upregulation of HSPA8 promotes hepatocarcinogenesis by suppressing ferroptosis and stimulating HBV replication, identifying HSPA8 as a potential therapeutic target in liver cancer.

PRMT5 confers lipid metabolism reprogramming, tumour growth and metastasis depending on the SIRT7-mediated desuccinylation of PRMT5 K387 in tumours.

The protein arginine methyltransferase 5 (PRMT5), which is highly expressed in tumour tissues, plays a crucial role in cancer development. However, the mechanism by which PRMT5 promotes cancer growth is poorly understood. Here, we report that PRMT5 contributes to lipid metabolism reprogramming, tumour growth and metastasis depending on the SIRT7-mediated desuccinylation of PRMT5 K387 in tumours. Mass spectrometric analysis identified PRMT5 lysine 387 as its succinylation site. Moreover, the desuccinylation of PRMT5 K387 enhances the methyltransferase activity of PRMT5. SIRT7 catalyses the desuccinylation of PRMT5 in cells. The SIRT7-mediated dessuccinylation of PRMT5 lysine 387 fails to bind to STUB1, decreasing PRMT5 ubiquitination and increasing the interaction between PRMT5 and Mep50, which promotes the formation of the PRMT5-Mep50 octamer. The PRMT5-Mep50 octamer increases PRMT5 methyltransferase activity, leading to arginine methylation of SREBP1a. The symmetric dimethylation of SREBP1a increases the levels of cholesterol, fatty acid, and triglyceride biogenesis in the cells, escaping degradation through the ubiquitin-proteasome pathway. Functionally, the desuccinylation of PRMT5 K387 promotes lipid metabolism reprogramming, tumour growth and metastasis in vitro and in vivo in tumours.

IFN-α inhibits HBV transcription and replication by promoting HDAC3-mediated de-2-hydroxyisobutyrylation of histone H4K8 on HBV cccDNA minichromosome in liver.

The epigenetic modification of hepatitis B virus (HBV) covalently closed circular DNA (cccDNA) plays a crucial role in cccDNA transcription and viral persistence. Interferon-α (IFN-α) is a pivotal agent against HBV cccDNA. However, the mechanism by which IFN-α modulates the epigenetic regulation of cccDNA remains poorly understood. In this study, we report that IFN-α2b enhances the histone deacetylase 3 (HDAC3)-mediated de-2-hydroxyisobutyrylation of histone H4 lysine 8 (H4K8) on HBV cccDNA minichromosome to restrict the cccDNA transcription in liver. By screening acetyltransferases and deacetylases, we identified that HDAC3 was an effective restrictor of HBV transcription and replication. Moreover, we found that HDAC3 was able to mediate the de-2-hydroxyisobutyrylation of H4K8 in HBV-expressing hepatoma cells. Then, the 2-hydroxyisobutyrylation of histone H4K8 (H4K8hib) was identified on the HBV cccDNA minichromosome, promoting the HBV transcription and replication. The H4K8hib was regulated by HDAC3 depending on its deacetylase domain in the system. The low level of HDAC3 and high level of H4K8hib were observed in the liver tissues from HBV-infected human liver-chimeric mice. The levels of H4K8hib on HBV cccDNA minichromosome were significantly elevated in the liver biopsy specimens from clinical hepatitis B patients, which was consistent with the high transcriptional activity of cccDNA. Strikingly, IFN-α2b effectively facilitated the histone H4K8 de-2-hydroxyisobutyrylation mediated by HDAC3 on the HBV cccDNA minichromosome in primary human hepatocytes and hepatoma cells, leading to the inhibition of HBV transcription and replication. Our finding provides new insights into the mechanism by which IFN-α modulates the epigenetic regulation of HBV cccDNA minichromosome.

HBx represses WDR77 to enhance HBV replication by DDB1-mediated WDR77 degradation in the liver.

Rationale: Hepatitis B x protein (HBx) is required to initiate and maintain the replication of hepatitis B virus (HBV). Protein arginine methyltransferases 5 (PRMT5) negatively regulates HBV transcription. WD repeat domain 77 protein (WDR77) greatly enhances the methyltransferase activity of PRMT5. However, the role of WDR77 in the modulation of cccDNA transcription and HBV replication is poorly understood. In this study, we investigated the mechanism by which HBx modulated HBV replication involving WDR77 in the liver. Methods: A human liver-chimeric mouse model was established. Immunohistochemistry (IHC) staining, Western blot analysis, Southern blot analysis, Northern blot analysis, immunofluorescence assays, ELISA, RT-qPCR, CoIP assays, and ChIP assays were performed in human liver-chimeric mouse model, primary human hepatocytes (PHHs), HepG2-NTCP, dHepaRG and HepG2 cell lines. Results: HBV infection and HBx expression remarkably reduced the protein levels of WDR77 in human liver-chimeric mice and HepG2-NTCP cells. WDR77 restricted cccDNA transcription and HBV replication in PHHs and HepG2-NTCP cells. Mechanically, WDR77 enhanced PRMT5-triggered symmetric dimethylation of arginine 3 on H4 (H4R3me2s) on the cccDNA minichromosome to control cccDNA transcription. HBx drove the cellular DDB1-containing E3 ubiquitin ligase to degrade WDR77 through recruiting WDR77, leading to the disability of methyltransferase activity of PRMT5. Thus, HBx promoted HBV replication by driving a positive feedback loop of HBx-DDB1/WDR77/PRMT5/H4R3me2s/cccDNA/HBV/HBx in the liver. Conclusions: HBx attenuates the WDR77-mediated HBV repression by driving DDB1-induced WDR77 degradation in the liver. Our finding provides new insights into the mechanism by which HBx enhances HBV replication in the liver.

Aspirin modulates 2-hydroxyisobutyrylation of ENO1K281 to attenuate the glycolysis and proliferation of hepatoma cells.

Aspirin can efficiently inhibit the glycolysis and proliferation of cancer cells, however, the underlying mechanism is poorly understood. Here, we report that aspirin attenuates the glycolysis and proliferation of hepatoma cells through modulating the levels of lysine 2-hydroxyisobutyrylation (Khib) of enolase 1 (ENO1). We found that aspirin decreased the levels of glucose consumption and lactate production in hepatoma cells. Moreover, 4 mM aspirin reduced the activities of ENO1, a key enzyme of glycolysis, and decreased the levels of ENO1 Khib in the cells. Interestingly, we identified that 4 mM aspirin could decrease the levels of Khib on many proteins by using pan Khib antibody in the cells. Interestingly, the activities of ENO1 could be rescued by the transient overexpression of ENO1, but not by ENO1 mutant (K281R). Moreover, we identified that the C646, an inhibitor of p300 which is a writer of Khib, could reduce the levels of ENO1 Khib, resulting in the decrease of ENO1 activities. The treatment with PDTC, an inhibitor of NF-κB which is a target of aspirin, could work well as C646 in the cells. Both of aspirin and C646 (or PDTC) displayed a stronger effect than the single treatment in the system. Functionally, ENO1, but not ENO1 mutant (K281R), could rescue the aspirin-induced inhibition of proliferation of liver cancer cells in vitro, suggesting that ENO1K281 is involved in the aspirin-mediated inhibition of liver cancer. Our finding provides new insights into the mechanism by which aspirin attenuates the glycolysis and proliferation of hepatoma cells.

Histone acetyltransferase 1 is a succinyltransferase for histones and non-histones and promotes tumorigenesis.

Lysine succinylation (Ksucc) is an evolutionarily conserved and widespread post-translational modification. Histone acetyltransferase 1 (HAT1) is a type B histone acetyltransferase, regulating the acetylation of both histone and non-histone proteins. However, the role of HAT1 in succinylation modulation remains unclear. Here, we employ a quantitative proteomics approach to study succinylation in HepG2 cancer cells and find that HAT1 modulates lysine succinylation on various proteins including histones and non-histones. HAT1 succinylates histone H3 on K122, contributing to epigenetic regulation and gene expression in cancer cells. Moreover, HAT1 catalyzes the succinylation of PGAM1 on K99, resulting in its increased enzymatic activity and the stimulation of glycolytic flux in cancer cells. Clinically, HAT1 is significantly elevated in liver cancer, pancreatic cancer, and cholangiocarcinoma tissues. Functionally, HAT1 succinyltransferase activity and the succinylation of PGAM1 by HAT1 play critical roles in promoting tumor progression in vitro and in vivo. Thus, we conclude that HAT1 is a succinyltransferase for histones and non-histones in tumorigenesis.

Chronic ethanol consumption and HBV induce abnormal lipid metabolism through HBx/SWELL1/arachidonic acid signaling and activate Tregs in HBV-Tg mice.

Rationale: Chronic ethanol consumption as a public health problem worldwide boosts the development of chronic liver diseases in hepatitis B virus (HBV)-infected patients. Arachidonic acid metabolite prostaglandin E2 (PGE2) activates regulatory T cells (Tregs) function. Here, we aim to investigate the underlying mechanism by which chronic ethanol consumption enriches the HBV-induced abnormal lipid metabolism and Tregs. Methods: The si-RNAs were used to weaken the expression of SWELL1 in HepG2, HepG2.2.15 and K180 cancer cell lines, followed by RNA sequencing from HepG2 cells. Arachidonic acid metabolite PGE2 and LTD4 were measured by ELISA assay in vivo and in vitro. Western blot analysis and RT-qPCR were used to examine HBx and SWELL1 and transcriptional factor Sp1 in clinical HCC samples and cell lines. The effect of chronic ethanol consumption on Tregs was tested by flow cytometry in HBV-Tg mice. The splenic Tregs were collected and analyzed by RNA sequencing. Results: The cooperative effect of ethanol and HBV in abnormal lipid metabolism was observed in vivo and in vitro. The depression of SWELL1 (or HBx) resulted in the reduction of lipid content and arachidonic acid metabolite, correlating with suppression of relative gene atlas. Ethanol and SWELL1 elevated the levels of PGE2 or LTD4 in the liver of mice and cell lines. Interestingly, the ethanol modulated abnormal lipid metabolism through activating HBx/Sp1/SWELL1/arachidonic acid signaling. Chronic ethanol consumption remarkably increased the population of PBL Tregs and splenic Tregs in HBV-Tg mice, consistently with the enhanced expression of PD-L1 in vivo and in vitro. Mechanically, RNA-seq data showed that multiple genes were altered in the transcriptomic atlas of Tregs sorting from ethanol-fed mice or HBV-Tg mice. Conclusion: The chronic ethanol intake enriches the HBV-enhanced abnormal lipid metabolism through HBx/SWELL1/arachidonic acid signaling and activates Tregs in mice.

SPIN1 triggers abnormal lipid metabolism and enhances tumor growth in liver cancer.

Abnormal lipid metabolism plays crucial roles in the development of cancer. Spindlin 1 (SPIN1) involving the process of spindle organization and chromosomal stability serves as an important player in the carcinogenesis. In this study, we try to identify the new function of SPIN1 in lipid metabolism of liver cancer. Tissue microarray showed that 75% (60/80) of hepatocellular carcinoma (HCC) tissues were positive for SPIN1, which was highly expressed in clinical HCC samples and positively associated with malignancy of HCC. Strikingly, SPIN1 could modulate abnormal lipid metabolism by increasing intracellular triglycerides, cholesterols, and lipid droplets in hepatoma cells, which could remarkably enhance the proliferation of hepatoma cells. Mechanistically, SPIN1 up-regulated FASN in hepatoma cells. SPIN1 co-activated transcriptional factor SREBP1c in the promoter of FASN through interaction with SREBP1c. Moreover, SPIN1 promoted the growth of liver cancer in vitro and in vivo and the levels of intracellular triglycerides, cholesterols and lipid droplets were increased in the tumor tissues from mice. In conclusion, SPIN1 modulates abnormal lipid metabolism and enhances growth of liver cancer through SREBP1c-triggered FASN signaling. Therapeutically, SPIN1 may serve as a novel target for HCC.

LncRNA PCNAP1 modulates hepatitis B virus replication and enhances tumor growth of liver cancer.

Rationale: Hepatitis B virus (HBV) is a major risk factor for liver cancer, in which HBV covalently closed circular DNA (cccDNA) plays crucial roles. However, the effect of pseudogene-derived long noncoding RNAs (lncRNAs) acting as functional regulators of their ancestral gene expression on HBV replication and hepatocellular carcinoma (HCC) remains unclear. In this study, we speculated that the pseudogene-derived lncRNA PCNAP1 and its ancestor PCNA might modulate HBV replication and promote hepatocarcinogenesis. Methods: We investigated the roles of lncRNA PCNAP1 in contribution of HBV replication through modulating miR-154/PCNA/HBV cccDNA signaling in hepatocarcinogenesis by using CRISPR/Cas9, Southern blot analysis, confocal assays, et al. in primary human hepatocytes (PHH), HepaRG cells, HepG2-NTCP cells, hepatoma carcinoma cells, human liver-chimeric mice model, transgenetic mice model, in vitro tumorigenicity and clinical patients. Results: Interestingly, the expression levels of PCNAP1 and PCNA were significantly elevated in the liver of HBV-infectious human liver-chimeric mice. Clinically, the mRNA levels of PCNAP1 and PCNA were increased in the liver of HBV-positive/HBV cccDNA-positive HCC patients. Mechanistically, PCNA interacted with HBV cccDNA in a HBc-dependent manner. PCNAP1 enhanced PCNA through sponging miR-154 targeting PCNA mRNA 3'UTR. Functionally, PCNAP1 or PCNA remarkably enhanced HBV replication and accelerated the growth of HCC in vitro and in vivo. Conclusion: We conclude that lncRNA PCNAP1 enhances the HBV replication through modulating miR-154/PCNA/HBV cccDNA signaling and the PCNAP1/PCNA signaling drives the hepatocarcinogenesis. Our finding provides new insights into the mechanism by which lncRNA PCNAP1 enhances HBV replication and hepatocarcinogenesis.