Translocation of forkhead box O1 to the nuclear periphery induces histone modifications that regulate transcriptional repression of PCK1 in HepG2 cells

Forkhead box O1 in metabolic dysfunction-associated fatty liver disease: molecular mechanisms and drug research

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a chronic liver disease that progresses from hepatic steatosis to non-alcoholic steatohepatitis, cirrhosis, and liver cancer, posing a huge burden on human health. Existing research has confirmed that forkhead box O1 (FOXO1), as a member of the FOXO transcription factor family, is upregulated in MAFLD. Its activity is closely related to nuclear-cytoplasmic shuttling and various post-translational modifications including phosphorylation, acetylation, and methylation. FOXO1 mediates the progression of MAFLD by regulating glucose metabolism, lipid metabolism, insulin resistance, oxidative stress, hepatic fibrosis, hepatocyte autophagy, apoptosis, and immune inflammation. This article elaborates on the regulatory role of FOXO1 in MAFLD, providing a summary and new insights for the current status of drug research and targeted therapies for MAFLD.

Chronic Exposure to Chlorpyrifos Damages Thyroid Activity and Imbalances Hepatic Thyroid Hormones Signaling and Glucose Metabolism: Dependency of T3-FOXO1 Axis by Hyperglycemia

Early life exposure to Endocrine Disruptor Chemicals (EDCs), such as the organophosphate pesticide Chlorpyrifos (CPF), affects the thyroid activity and dependent process, including the glucose metabolism. The damage of thyroid hormones (THs) as a mechanism of action of CPF is underestimated because the studies rarely consider that TH levels and signaling are customized peripherally. Here, we investigated the impairment of metabolism/signaling of THs and lipid/glucose metabolism in the livers of 6-month-old mice, developmentally and lifelong exposed to 0.1, 1, and 10 mg/kg/die CPF (F1) and their offspring similarly exposed (F2), analyzing the levels of transcripts of the enzymes involved in the metabolism of T3 (Dio1), lipids (Fasn, Acc1), and glucose (G6pase, Pck1). Both processes were altered only in F2 males, affected by hypothyroidism and by a systemic hyperglycemia linked to the activation of gluconeogenesis in mice exposed to 1 and 10 mg/kg/die CPF. Interestingly, we observed an increase in active FOXO1 protein due to a decrease in AKT phosphorylation, despite insulin signaling activation. Experiments in vitro revealed that chronic exposure to CPF affected glucose metabolism via the direct modulation of FOXO1 activity and T3 levels in hepatic cells. In conclusion, we described different sex and intergenerational effects of CPF exposure on the hepatic homeostasis of THs, their signaling, and, finally, glucose metabolism. The data points to FOXO1-T3-glucose signaling as a target of CPF in liver.

Role of phosphoenolpyruvate carboxykinase 1 (pck1) in mediating nutrient metabolism in zebrafish

Carbohydrates are the most economical source of energy in fish feeds, but most fish have limited ability to utilize carbohydrates. It has been reported that phosphoenolpyruvate carboxykinase 1 (pck1) is involved in carbohydrate metabolism, lipid metabolism, and other metabolic processes. However, direct evidence is lacking to fully understand the relationship between pck1 and glucose and lipid metabolism. Here, we generated a pck1 knockout zebrafish by CRISPR/cas9 system, and a high-carbohydrate diet was provided to 60 days post-fertilization (dpf) for 8 weeks. We found that pck1-deficient zebrafish displayed decreased plasma glucose, elevated mRNA levels of glycolysis-related genes (gck, pfk, pk), and reduced the transcriptional levels of gluconeogenic genes (pck1, fbp1a) in liver. We also found decreased triglyceride, total cholesterol, and lipid accumulation and in pck1^-/- zebrafish, along with downregulation of genes for lipolysis (acaca) and lipogenesis (cpt1). In addition, the observation of HE staining revealed that the total muscle area of pck1^-/- was substantially less than that of WT zebrafish and real-time PCR suggested that GH/IGF-1 signaling (ulk2, stat1b) may be suppressed in pck1-deficient fish. Taken together, these findings suggested that pck1 may play an important role in the high-carbohydrate diet utilization of fish and significantly affected lipid metabolism and protein synthesis in zebrafish. pck1 knockout mutant line could facilitate a further mechanism study of pck1-associated metabolic regulation and provide new information for improving carbohydrate utilization traits.

Cinobufagin induces FOXO1-regulated apoptosis, proliferation, migration, and invasion by inhibiting G9a in non-small-cell lung cancer A549 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Bufonis (VB), an animal drug called Chansu in China, is the product of the secretion of Bufo gargarizans Cantor or B. melanostictus Schneider. As a traditional Chinese medicine (TCM) for a long time, it has been widely used in the treatment of heart failure, ulcer, pain, and various cancers. Cinobufaginn (CNB), the cardiotonic steroid or bufalene lactone extracted from VB, has the effects of detoxification, detumescence, and analgesia.

AIM OF THE STUDY

The present study aimed to define the effects of CNB on non-small-cell lung cancer (NSCLC) and identify the potential molecular mechanisms.

MATERIALS AND METHODS

A549 cells were treated with cinobufagin and cell viability, apoptosis, migration, and invasion were then evaluated using Cell Counting Kit-8 (CCK8) assays, flow cytometry, and Transwell assays, respectively. Moreover, the levels of proliferating cell nuclear antigen (PCNA), cytokeratin8 (CK8), poly ADP-ribose polymerase (PARP), Caspase3, Caspase8, B-cell lymphoma/lewkmia-2(Bcl-2), Bcl2-Associated X(Bax), forkhead box O1 (FOXO1), and euchromatic histone-lysine N-methyltransferase2 (G9a, EHMT2) in A549 cells were evaluated using qRT-PCR and/or Western blot analysis (WB), Co-IP, immunofluorescence, and immunohistochemistry. An in vivo imaging system, TUNEL, Immunofluorescence, and immunohistochemistry were also used to detect proliferating cell nuclear antigen(PCNA), Ki67, E-Cadherin(E-Cad), FOXO1, and G9a in mouse xenograft model experiments.

RESULTS

CNB suppressed cell proliferation, migration, and invasion but promoted apoptosis in A549 cells in a dose- and time-dependent manner, while cinobufagin had no cytotoxic effect on BEAS-2B cells. In vivo, cinobufagin inhibited the proliferation, migration, and invasion of A549 cells and promoted their apoptosis. The occurrence of the above phenomena was accompanied by an increase in FOXO1 expression and a decrease in G9a expression. In A549 cells, CNB did not reverse the changes in the proliferation, migration, invasion, and apoptosis of A549 cells after FOXO1 was successfully silenced.

CONCLUSION

Our study provides the first evidence that cinobufagin suppresses the malignant biological behaviours of NSCLC cells in vivo and in vitro and suggests that mechanistically, this effect may be achieved by inhibiting the expression of the histone methyltransferase G9a and activating the tumour suppressor gene FOXO1. Taken together, our findings provide important insights into the molecular mechanism underlying cinobufagin's anticancer activity, and suggest that cinobufagin could be a candidate for targeted cancer therapy.

Signaling Induced by Chronic Viral Hepatitis: Dependence and Consequences

Chronic viral hepatitis is a main cause of liver disease and hepatocellular carcinoma. There are striking similarities in the pathological impact of hepatitis B, C, and D, although these diseases are caused by very different viruses. Paired with the conventional study of protein-host interactions, the rapid technological development of -omics and bioinformatics has allowed highlighting the important role of signaling networks in viral pathogenesis. In this review, we provide an integrated look on the three major viruses associated with chronic viral hepatitis in patients, summarizing similarities and differences in virus-induced cellular signaling relevant to the viral life cycles and liver disease progression.

Type 1 Diabetes and the HLA Region: Genetic Association Besides Classical HLA Class II Genes

Type 1 diabetes is an autoimmune disease with rising incidence in high-income countries. Genetic and environmental predisposing factors contribute to the etiology of the disease, although their interaction is not sufficiently understood to allow for preventive action. Strongest known associations with genetic variation map to classical HLA class II genes. Because of its genetic complexity, the HLA region has been under-represented in genome-wide association studies, having potentially hindered the identification of relevant associations underlying the etiology of the disease. Here, we performed a comprehensive HLA-wide genetic association analysis of type 1 diabetes including multi-allelic and rare variants. We used high-density whole-exome sequencing data of the HLA region in the large UK Biobank dataset to apply gene-based association tests with a carefully defined type 1 diabetes phenotype (97 cases and 48,700 controls). Exon-based and single-variant association tests were used to complement the analysis. We replicated the known association of type 1 diabetes with the classical HLA-DQ gene. Tailoring the analysis toward rare variants, we additionally identified the lysine methyl transferase EHMT2 as associated. Deeper insight into genetic variation associated with disease as presented and discussed in detail here can help unraveling mechanistic details of the etiology of type 1 diabetes. More specifically, we hypothesize that genetic variation in EHMT2 could impact autoimmunity in type 1 diabetes development.

Unique adaptations in neonatal hepatic transcriptome, nutrient signaling, and one-carbon metabolism in response to feeding ethyl cellulose rumen-protected methionine during late-gestation in Holstein cows

BACKGROUND

Methionine (Met) supply during late-pregnancy enhances fetal development in utero and leads to greater rates of growth during the neonatal period. Due to its central role in coordinating nutrient and one-carbon metabolism along with immune responses of the newborn, the liver could be a key target of the programming effects induced by dietary methyl donors such as Met. To address this hypothesis, liver biopsies from 4-day old calves (n = 6/group) born to Holstein cows fed a control or the control plus ethyl-cellulose rumen-protected Met for the last 28 days prepartum were used for DNA methylation, transcriptome, metabolome, proteome, and one-carbon metabolism enzyme activities.

RESULTS

Although greater withers and hip height at birth in Met calves indicated better development in utero, there were no differences in plasma systemic physiological indicators. RNA-seq along with bioinformatics and transcription factor regulator analyses revealed broad alterations in 'Glucose metabolism', 'Lipid metabolism, 'Glutathione', and 'Immune System' metabolism due to enhanced maternal Met supply. Greater insulin sensitivity assessed via proteomics, and efficiency of transsulfuration pathway activity suggested beneficial effects on nutrient metabolism and metabolic-related stress. Maternal Met supply contributed to greater phosphatidylcholine synthesis in calf liver, with a role in very low density lipoprotein secretion as a mechanism to balance metabolic fates of fatty acids arising from the diet or adipose-depot lipolysis. Despite a lack of effect on hepatic amino acid (AA) transport, a reduction in metabolism of essential AA within the liver indicated an AA 'sparing effect' induced by maternal Met.

CONCLUSIONS

Despite greater global DNA methylation, maternal Met supply resulted in distinct alterations of hepatic transcriptome, proteome, and metabolome profiles after birth. Data underscored an effect on maintenance of calf hepatic Met homeostasis, glutathione, phosphatidylcholine and taurine synthesis along with greater efficiency of nutrient metabolism and immune responses. Transcription regulators such as FOXO1, PPARG, E2F1, and CREB1 appeared central in the coordination of effects induced by maternal Met. Overall, maternal Met supply induced better immunometabolic status of the newborn liver, conferring the calf a physiologic advantage during a period of metabolic stress and suboptimal immunocompetence.

METTL3 expression is associated with glycolysis metabolism and sensitivity to glycolytic stress in hepatocellular carcinoma

METTL3 is an RNA methyltransferase implicated in the control of cell differentiation and proliferation in embryonic development and cancer. The current study was aimed to explore the function and underlying mechanism of METTL3 in hepatocellular carcinoma (HCC). We evaluated the expression and prognostic significance of METTL3 in 100 HCC cases and TCGA dataset. In HCC cases, both the RNA and protein expression of METTL3 were significantly upregulated and associated with poor prognosis. Gene set enrichment analysis of transcriptional profiles in HCC specimens revealed that METTL3 expression was associated with impaired glucose metabolism and mTOR signal pathway. In Huh‐7 and SMMC‐7721 HCC cells, downregulation of METTL3 by siRNA interference inhibited glycolytic capacity, which was proved by the decreased intracellular glucose uptake and lactate production. In terms of mechanism, we found mTORC1 activity was impaired by downregulation of METTL3, additional silencing of METTL3 cannot further decrease the phosphorylation level of mTORC1 and glycolysis activity in Rapamycin‐treated HCC cells. At last, we observed that downregulation of METTL3 synergizes with the glycolysis inhibitor 2‐deoxyglucose (2‐DG) to inhibit tumor growth in vitro. Our study provided evidence that METTL3 is involved in the regulation of glycolysis activity in HCC, suggesting that suppression of glycolysis via METTL3 inhibition was a potential treating strategy against HCC.

PCK1 Deficiency Shortens the Replicative Lifespan of Saccharomyces cerevisiae through Upregulation of PFK1

The cytosolic isozyme of phosphoenolpyruvate carboxykinase (PCK1) was the first rate-limiting enzyme in the gluconeogenesis pathway, which exerted a critical role in maintaining the blood glucose levels. PCK1 has been established to be involved in various physiological and pathological processes, including glucose metabolism, lipid metabolism, diabetes, and tumorigenesis. Nonetheless, the association of PCK1 with aging process and the detailed underlying mechanisms of PCK1 on aging are still far to be elucidated. Hence, we herein constructed the PCK1-deficient (pck1Δ) and PCK1 overexpression (PCK1 OE) Saccharomyces cerevisiae. The results unveiled that PCK1 deficiency significantly shortened the replicative lifespan (RLS) in the S. cerevisiae, while overexpression of PCK1 prolonged the RLS. Additionally, we noted that the ROS level was significantly enhanced in PCK1-deficient strain and decreased in PCK1 OE strain. Then, a high throughput analysis by deep sequencing was performed in the pck1Δ and wild-type strains, in an attempt to shed light on the effect of PCK1 on the lifespan of aging process. The data showed that the most downregulated mRNAs were enriched in the regulatory pathways of glucose metabolism. Fascinatingly, among the differentially expressed mRNAs, PFK1 was one of the most upregulated genes, which was involved in the glycolysis process and ROS generation. Thus, we further constructed the pfk1Δpck1Δ strain by deletion of PFK1 in the PCK1-deficient strain. The results unraveled that pfk1Δpck1Δ strain significantly suppressed the ROS level and restored the RLS of pck1Δ strain. Taken together, our data suggested that PCK1 deficiency enhanced the ROS level and shortened the RLS of S. cerevisiae via PFK1.

FOXO1 degradation via G9a-mediated methylation promotes cell proliferation in colon cancer

Posttranslational modifications of the Forkhead family transcription factor, FOXO1, have been known to have important regulatory implications in its diverse activities. Several types of modifications of FOXO1, including acetylation, phosphorylation, and ubiquitination, have been reported. However, lysine methylation of FOXO1 has not yet been identified. Here, we reported that FOXO1 is methylated by G9a at K273 residue in vitro and in vivo. Methylation of FOXO1 by G9a increased interaction between FOXO1 and a specific E3 ligase, SKP2, and decreased FOXO1 protein stability. In addition, G9a expression was increased by insulin and resulted in insulin-mediated FOXO1 degradation by K273 methylation. Tissue array analysis indicated that G9a was overexpressed and FOXO1 levels decreased in human colon cancer. Cell proliferation assays revealed that G9a-mediated FOXO1 methylation increased colon cancer cell proliferation. Fluorescence-activated cell sorting (FACS) analysis indicated that apoptosis rates were higher in the presence of FOXO1 than in FOXO1 knock-out cells. Furthermore, we found that G9a protein levels were elevated and FOXO1 protein levels were decreased in human colon cancer patients tissue samples. Here, we report that G9a specific inhibitor, BIX-01294, can regulate cell proliferation and apoptosis by inhibiting G9a-mediated FOXO1 methylation.

Knockdown of the Sonic Hedgehog (SHH) Gene Inhibits Proliferation of Hep3B and SMMC-7721 Hepatocellular Carcinoma Cells via the PI3K/Akt/PCK1 Signaling Pathway

Background

The PCK1 gene encodes phosphoenolpyruvate carboxykinase (PEPCK), which has been shown have a role in metabolic events in hepatocellular carcinoma (HCC). This study aimed to investigate the role of the SHH gene and its encoded protein, sonic hedgehog (SHH), in two human hepatocellular carcinoma (HCC) cell lines.

Material/Methods

The human HCC cell lines Hep3B and SMMC-7721 were cultured. Cells were transfected with plasmids carrying specific SHH gene short-hairpin RNA (shRNA) and negative control (NC) shRNA. The effects of knockdown of expression levels of the SHH gene were studied on cell survival, cell apoptosis, the cell cycle, gluconeogenesis, and the expression of PCK1. Anchorage-independent growth, a characteristic of transformed cells, was detected by the colony formation assay. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) and Western blot were performed 24 h after transfection.

Results

Knockdown of expression levels of the SHH gene reduced cell proliferation and growth of HCC cells and induced cell apoptosis and G1 cell cycle arrest in both HCC cell lines. Knockdown of the SHH gene decreased the levels of glycolysis products and increased the production of glucose and reduced the phosphorylation of PI3K and Akt but induced the expression of PCK1.

Conclusions

Knockdown of the SHH gene reduced cell survival of HCC cells by increasing apoptosis, reducing cell proliferation, inducing G1 cell cycle arrest, and restoring gluconeogenesis, and was associated with the inhibition of the PI3K/Akt axis and induced the expression of PCK1.

FOXO1 and ETV6 genes may represent novel regulators of splicing factor expression in cellular senescence

Cellular plasticity is a key facet of cellular homeostasis requiring correct temporal and spatial patterns of alternative splicing. Splicing factors, which orchestrate this process, demonstrate age-related dysregulation of expression; they are emerging as potential influences on aging and longevity. The upstream drivers of these alterations are still unclear but may involve aberrant cellular signaling. We compared the phosphorylation status of proteins in multiple signaling pathways in early and late passage human primary fibroblasts. We then assessed the impact of chemical inhibition or targeted knockdown of direct downstream targets of the ERK and AKT pathways on splicing factor expression, cellular senescence, and proliferation kinetics in senescent primary human fibroblasts. Components of the ERK and AKT signaling pathways demonstrated altered activation during cellular aging. Inhibition of AKT and ERK pathways led to up-regulation of splicing factor expression, reduction in senescent cell load, and partial reversal of multiple cellular senescence phenotypes in a dose-dependent manner. Furthermore, targeted knockdown of the genes encoding the downstream targets FOXO1 or ETV6 was sufficient to mimic these observations. Our results suggest that age-associated dysregulation of splicing factor expression and cellular senescence may derive in part from altered activity of ERK and AKT signaling and may act in part through the ETV6 and FOXO1 transcription factors. Targeting the activity of downstream effectors of ERK and AKT may therefore represent promising targets for future therapeutic intervention.-Latorre, E., Ostler, E. L., Faragher, R. G. A., Harries, L. W. FOXO1 and ETV6 genes may represent novel regulators of splicing factor expression in cellular senescence.

The Dominant Role of Forkhead Box Proteins in Cancer

Forkhead box (FOX) proteins are multifaceted transcription factors that are significantly implicated in cancer, with various critical roles in biological processes. Herein, we provide an overview of several key members of the FOXA, FOXC, FOXM1, FOXO and FOXP subfamilies. Important pathophysiological processes of FOX transcription factors at multiple levels in a context-dependent manner are discussed. We also specifically summarize some major aspects of FOX transcription factors in association with cancer research such as drug resistance, tumor growth, genomic alterations or drivers of initiation. Finally, we suggest that targeting FOX proteins may be a potential therapeutic strategy to combat cancer.

Liraglutide improves hepatic insulin resistance via the canonical Wnt signaling pathway

Liraglutide, a modified form of glucagon‑like peptide‑1 (GLP‑1), is used in the treatment of diabetes mellitus. However, the underlying mechanism by which liraglutide improves liver insulin resistance remains to be elucidated. The proto‑oncogene Wnt (Wnt) signaling pathway has been reported to be associated with glucose and lipid metabolism. Using in vivo and in vitro models of diabetes and insulin resistance, it was investigated whether the beneficial effects of liraglutide on liver glucose metabolism are mediated by the Wnt signaling pathway. The results of the present study demonstrate that body weight, fasting blood glucose, insulin levels and the homeostasis model assessment for insulin resistance were markedly decreased in db/db mice treated with liraglutide compared with control mice. Liraglutide also improved liver morphology and reduced the accumulation of lipid droplets. Furthermore, the expression of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase was downregulated, whereas the expression of phosphorylated forkhead box O1, Wnt signaling pathway‑associated molecules, β‑catenin, transcription factor 7‑like 2 and phosphorylated glycogen synthase kinase-3β was upregulated in the liver of mice treated with liraglutide. In the in vitro study, increased gluconeogenesis and decreased glucose uptake rates were observed in insulin resistant hepatocytes; treatment with liraglutide significantly reversed this effect. Furthermore, transfection of insulin resistant hepatocytes with β‑catenin small interfering RNA attenuated the effects of liraglutide, suggesting that liraglutide improves insulin resistance via activating the β‑catenin/Wnt signaling pathway. The results of the present study suggest a novel mechanism underlying liraglutide‑mediated improvements in insulin resistance in the liver. The Wnt signaling pathway may be a potential therapeutic target for the treatment of altered hepatic physiology in insulin resistance.

Re-analysis of public genetic data reveals a rare X-chromosomal variant associated with type 2 diabetes

The reanalysis of existing GWAS data represents a powerful and cost-effective opportunity to gain insights into the genetics of complex diseases. By reanalyzing publicly available type 2 diabetes (T2D) genome-wide association studies (GWAS) data for 70,127 subjects, we identify seven novel associated regions, five driven by common variants (LYPLAL1, NEUROG3, CAMKK2, ABO, and GIP genes), one by a low-frequency (EHMT2), and one driven by a rare variant in chromosome Xq23, rs146662075, associated with a twofold increased risk for T2D in males. rs146662075 is located within an active enhancer associated with the expression of Angiotensin II Receptor type 2 gene (AGTR2), a modulator of insulin sensitivity, and exhibits allelic specific activity in muscle cells. Beyond providing insights into the genetics and pathophysiology of T2D, these results also underscore the value of reanalyzing publicly available data using novel genetic resources and analytical approaches.

Genome-wide association studies have uncovered several loci associated with diabetes risk. Here, the authors reanalyse public type 2 diabetes GWAS data to fine map 50 known loci and identify seven new ones, including one near ATGR2 on the X-chromosome that doubles the risk of diabetes in men.

Establishment and phenotyping of disease model cells created by cell-resealing technique

Cell-based assays are growing in importance for screening drugs and investigating their mechanisms of action. Most of the assays use so-called “normal” cell strain because it is difficult to produce cell lines in which the disease conditions are reproduced. In this study, we used a cell-resealing technique, which reversibly permeabilizes the plasma membrane, to develop diabetic (Db) model hepatocytes into which cytosol from diabetic mouse liver had been introduced. Db model hepatocytes showed several disease-specific phenotypes, namely disturbance of insulin-induced repression of gluconeogenic gene expression and glucose secretion. Quantitative image analysis and principal component analysis revealed that the ratio of phosphorylated Akt (pAkt) to Akt was the best index to describe the difference between wild-type and Db model hepatocytes. By performing image-based drug screening, we found pioglitazone, a PPARγ agonist, increased the pAkt/Akt ratio, which in turn ameliorated the insulin-induced transcriptional repression of the gluconeogenic gene phosphoenolpyruvate carboxykinase 1. The disease-specific model cells coupled with image-based quantitative analysis should be useful for drug development, enabling the reconstitution of disease conditions at the cellular level and the discovery of disease-specific markers.

Nucleoplasmic Nup98 controls gene expression by regulating a DExH/D-box protein

The nucleoporin Nup98 has been linked to the regulation of transcription and RNA metabolism, ^1-3 but the mechanisms by which Nup98 contributes to these processes remains largely undefined. Recently, we uncovered interactions between Nup98 and several DExH/D-box proteins (DBPs), a protein family well-known for modulating gene expression and RNA metabolism. ^4-6 Analysis of Nup98 and one of these DBPs, DHX9, showed that they directly interact, their association is facilitated by RNA, and Nup98 binding stimulates DHX9 ATPase activity. ⁷ Furthermore, these proteins were dependent on one another for their proper association with a subset of gene loci to control transcription and modulate mRNA splicing. ⁷ On the basis of these observations, we proposed that Nup98 functions to regulate DHX9 activity within the nucleoplasm. ⁷ Since Nup98 is associated with several DBPs, regulation of DHX9 by Nup98 may represent a paradigm for understanding how Nup98, and possibly other FG-Nup proteins, could direct the diverse cellular activities of multiple DBPs.

The oncoprotein HBXIP suppresses gluconeogenesis through modulating PCK1 to enhance the growth of hepatoma cells

Hepatitis B X-interacting protein (HBXIP) as an oncoprotein plays crucial roles in the development of cancer, involving glucose metabolism reprogramming. In this study, we are interested in whether the oncoprotein HBXIP is involved in the modulation of gluconeogenesis in liver cancer. Here, we showed that the expression level of phosphoenolpyruvate carboxykinase (PCK1), a key enzyme of gluconeogenesis, was lower in clinical hepatocellular carcinoma (HCC) tissues than that in normal tissues. Mechanistically, HBXIP inhibited the expression of PCK1 through down-regulating transcription factor FOXO1 in hepatoma cells, and up-regulated miR-135a targeting the 3'UTR of FOXO1 mRNA in the cells. In addition, HBXIP increased the phosphorylation levels of FOXO1 protein by activating PI3K/Akt pathway, leading to the export of FOXO1 from nucleus to cytoplasm. Strikingly, over-expression of PCK1 could abolish the HBXIP-promoted growth of hepatoma cells in vitro and in vivo. Thus, we conclude that the oncoprotein HBXIP is able to depress the gluconeogenesis through suppressing PCK1 to promote hepatocarcinogenesis, involving miR-135a/FOXO1 axis and PI3K/Akt/p-FOXO1 pathway. Our finding provides new insights into the mechanism by which oncoprotein HBXIP modulates glucose metabolism reprogramming in HCC.