Deletion of Gab2 in mice protects against hepatic steatosis and steatohepatitis: a novel therapeutic target for fatty liver disease

Molecular targets for management of diabetes: Remodelling of white adipose to brown adipose tissue

Diabetes mellitus is a disorder characterised metabolic dysfunction that results in elevated glucose level in the bloodstream. Diabetes is of two types, type1 and type 2 diabetes. Obesity is considered as one of the major reasons intended for incidence of diabetes hence it turns out to be essential to study about the adipose tissue which is responsible for fat storage in body. Adipose tissues play significant role in maintaining the balance between energy stabilization and homeostasis. The three forms of adipose tissue are - White adipose tissue (WAT), Brown adipose tissue (BAT) and Beige adipose tissue (intermediate form). The amount of BAT gets reduced, and WAT starts to increase with the age. WAT when exposed to certain stimuli gets converted to BAT by the help of certain transcriptional regulators. The browning of WAT has been a matter of study to treat the metabolic disorders and to initiate the expenditure of energy. The three main regulators responsible for the browning of WAT are PRDM16, PPARγ and PGC-1α via various cellular and molecular mechanism. Presented review article includes the detailed elaborative aspect of genes and proteins involved in conversion of WAT to BAT.

β-Glucan produced by Lentinus edodes suppresses breast cancer progression via the inhibition of macrophage M2 polarization by integrating autophagy and inflammatory signals

BACKGROUND

β-Glucan from Lentinus edodes (LNT), an edible mushroom, possesses strong anticancer activity. However, the therapeutic effects of LNT during the occurrence and progression of breast cancer and their underlying molecular mechanisms have not been elucidated.

METHODS

Mouse mammary tumor virus-polyoma middle tumor-antigen (MMTV-PyMT) transgenic mice were used as a breast cancer mouse model. Hematoxylin and eosin, immunohistochemical, and immunofluorescence staining were performed for histopathological analysis. Moreover, we developed an inflammatory cell model using tumor necrosis factor-α (TNF-α). Macrophage polarization was assessed using western blot analysis and immunofluorescence.

RESULTS

Orphan nuclear receptor 77 (Nur77) and sequestosome-1 (p62) were highly expressed and positively correlated with each other in breast cancer tissues. LNT significantly inhibited tumor growth, ameliorated inflammatory cell infiltration, and induced tumor cell apoptosis in PyMT transgenic mice. Moreover, LNT attenuated the ability of tumors to metastasize to lung tissue. Mechanistically, LNT treatment restrained macrophage polarization from M1 to M2 phenotype and promoted autophagic cell death by inhibiting Nur77 expression, AKT/mTOR signaling, and inflammatory signals in breast tumor cells. However, LNT did not exhibit a direct pro-autophagic effect on tumor cell death, except for its inhibitory effect on Nur77 expression. LNT-mediated autophagic tumor cell death depends on M1 macrophage polarization. In in vitro experiments, LNT inhibited the upregulation of p62, autophagy activation, and inflammatory signaling pathways in Nur77 cells.

CONCLUSION

LNT inhibited macrophage M2 polarization and subsequently blocked the AKT/mTOR and inflammatory signaling axes in breast cancer cells, thereby promoting autophagic tumor cell death. Thus, LNT may be a promising therapeutic strategy for breast cancer.

Integrative global co-expression analysis identifies Key MicroRNA-target gene networks as key blood biomarkers for obesity

Obesity is associated with the quantitative changes in miRNAs and their target genes. However, the molecular basis of their dysregulation and expression status correlations is incompletely understood. Therefore, this study aims to examine the shared differentially expressed miRNAs and their target genes between blood and adipose tissues of obese individuals to identify potential blood-based biomarkers. In this study, 3 gene expression datasets (two mRNA and one miRNA), generated from blood and adipose tissues of 68 obese and 39 lean individuals, were analyzed by a series of robust computational concepts, like protein interactome mapping, functional enrichment of biological pathways and construction of miRNA-mRNA and transcription factor gene networks. The comparison of blood versus tissue datasets has revealed the shared differential expression of 210 genes (59.5% upregulated) involved in lipid metabolism and inflammatory reactions. The blood miRNA (GSE25470) analysis has identified 79 differentially expressed miRNAs (71% downregulated). The miRNA-target gene scan identified regulation of 30 shared genes by 22miRNAs. The gene network analysis has identified the inverse expression correlation between 8 target genes (TP53, DYSF, GAB2, GFRA2, NACC2, FAM53C, JNK and GAB2) and 3 key miRNAs (hsa-mir-940, hsa-mir-765, hsa-mir-612), which are further regulated by 24 key transcription factors. This study identifies potential obesity related blood biomarkers from largescale gene expression data by computational miRNA-target gene interactome and transcription factor network construction methods.

Effect of exercise and diet intervention in NAFLD and NASH via GAB2 methylation

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is a disorder that extends from simple hepatic steatosis to nonalcoholic steatohepatitis (NASH), which is effectively alleviated by lifestyle intervention. Nevertheless, DNA methylation mechanism underling the effect of environmental factors on NAFLD and NASH is still obscure. The aim of this study was to investigate the effect of exercise and diet intervention in NAFLD and NASH via DNA methylation of GAB2.

METHODS

Methylation of genomic DNA in human NAFLD was quantified using Infinium Methylation EPIC BeadChip assay after exercise (Ex), low carbohydrate diet (LCD) and exercise plus low carbohydrate diet (ELCD) intervention. The output Idat files were processed using ChAMP package. False discovery rate on genome-wide analysis of DNA methylation (q < 0.05), and cytosine-guanine dinucleotides (CpGs) which are located in promoters were used for subsequent analysis (|Δβ|≥ 0.1). K-means clustering was used to cluster differentially methylated genes according to 3D genome information from Human embryonic stem cell. To quantify DNA methylation and mRNA expression of GRB2 associated binding protein 2 (GAB2) in NASH mice after Ex, low fat diet (LFD) and exercise plus low fat diet (ELFD), MassARRAY EpiTYPER and quantitative reverse transcription polymerase chain reaction were used.

RESULTS

Both LCD and ELCD intervention on human NAFLD can induce same DNA methylation alterations at critical genes in blood, e.g., GAB2, which was also validated in liver and adipose of NASH mice after LFD and ELFD intervention. Moreover, methylation of CpG units (i.e., CpG_10.11.12) inversely correlated with mRNA expression GAB2 in adipose tissue of NASH mice after ELFD intervention.

CONCLUSIONS

We highlighted the susceptibility of DNA methylation in GAB2 to ELFD intervention, through which exercise and diet can protect against the progression of NAFLD and NASH on the genome level, and demonstrated that the DNA methylation variation in blood could mirror epigenetic signatures in target tissues of important biological function, i.e., liver and adipose tissue. Trial registration International Standard Randomized Controlled Trial Number Register (ISRCTN 42622771).

Gab2 deficiency suppresses high-fat diet-induced obesity by reducing adipose tissue inflammation and increasing brown adipose function in mice

Obesity is caused by a long-term imbalance between energy intake and consumption and is regulated by multiple signals. This study investigated the effect of signaling scaffolding protein Gab2 on obesity and its relevant regulation mechanism. Gab2 knockout (KO) and wild-type (WT) mice were fed with a standard diet (SD) or high-fat diet (HFD) for 12 weeks. The results showed that the a high-fat diet-induced Gab2 expression in adipose tissues, but deletion of Gab2 attenuated weight gain and improved glucose tolerance in mice fed with a high-fat diet. White adipose tissue and systemic inflammations were reduced in HFD-fed Gab2 deficiency mice. Gab2 deficiency increased the expression of Ucp1 and other thermogenic genes in brown adipose tissue. Furthermore, the regulation of Gab2 on the mature differentiation and function of adipocytes was investigated in vitro using primary or immortalized brown preadipocytes. The expression of brown fat-selective genes was found to be elevated in differentiated adipocytes without Gab2. The mechanism of Gab2 regulating Ucp1 expression in brown adipocytes involved with its downstream PI3K (p85)-Akt-FoxO1 signaling pathway. Our research suggests that deletion of Gab2 suppresses diet-induced obesity by multiple pathways and Gab2 may be a novel therapeutic target for the treatment of obesity and associated complications.

Interaction Mechanisms Between Major Depressive Disorder and Non-alcoholic Fatty Liver Disease

Major depressive disorder (MDD), which is highly associated with non-alcoholic fatty liver disease (NAFLD), has complex pathogenic mechanisms. However, a limited number of studies have evaluated the mutual pathomechanisms involved in MDD and NAFLD development. Chronic stress-mediated elevations in glucocorticoid (GC) levels play an important role in the development of MDD-related NAFLD. Elevated GC levels can induce the release of inflammatory factors and changes in gut permeability. Elevated levels of inflammatory factors activate the hypothalamic-pituitary-adrenal (HPA) axis, which further increases the release of GC. At the same time, changes in gut permeability promote the release of inflammatory factors, which results in a vicious circle among the three, causing disease outbreaks. Even though the specific role of the thyroid hormone (TH) in this pathogenesis has not been fully established, it is highly correlated with MDD and NAFLD. Therefore, changing lifestyles and reducing psychological stress levels are necessary measures for preventing MDD-related NAFLD. Among them, GC inhibitors and receptor antagonists may be key in the alleviation of early and mid-term disease progression. However, combination medications may be important in late-stage diseases, but they are associated with various side effects. Traditional Chinese medicines have been shown to be potential therapeutic alternatives for such complex diseases.

Aberrant methylation of WD-repeat protein 41 contributes to tumour progression in triple-negative breast cancer

WD-repeat proteins are implicated in a variety of biological functions, most recently in oncogenesis. However, the underlying function of WD-repeat protein 41 (WDR41) in tumorigenesis remains elusive. The present study was aimed to explore the role of WDR41 in breast cancer. Combined with Western blotting and immunohistochemistry, the results showed that WDR41 was expressed at low levels in breast cancer, especially in triple-negative breast cancer (TNBC). Using methylation-specific PCR (MSP), we observed that WDR41 presented hypermethylation in MDA-MB-231 cells. Methylation inhibitor 5-aza-2'-deoxycytidine (5-aza-dC) management increased the expression of WDR41 in MDA-MB-231 cells, but not in MCF-10A (normal mammary epithelial cells) or oestrogen receptor-positive MCF-7 breast cancer cells. WDR41-down-regulation promoted, while WDR41-up-regulation inhibited the tumour characteristics of TNBC cells including cell viability, cell cycle and migration. Further, WDR41-up-regulation dramatically suppressed tumour growth in vivo. Mechanistically, WDR41 protein ablation activated, while WDR41-up-regulation repressed the AKT/GSK-3β pathway and the subsequent nuclear activation of β-catenin in MDA-MB-231 cells, and 5-aza-dC treatment enhanced this effect. After treatment with the AKT inhibitor MK-2206, WDR41-down-regulation-mediated activation of the GSK-3β/β-catenin signalling was robustly abolished. Collectively, methylated WDR41 in MDA-MB-231 cells promotes tumorigenesis through positively regulating the AKT/GSK-3β/β-catenin pathway, thus providing an important foundation for treating TNBC.

The Effects of RKI-1447 in a Mouse Model of Nonalcoholic Fatty Liver Disease Induced by a High-Fat Diet and in HepG2 Human Hepatocellular Carcinoma Cells Treated with Oleic Acid

Background

This study aimed to investigate the effects of RKI-1447, a selective inhibitor of Rho-associated ROCK kinases, in a mouse model of nonalcoholic fatty liver disease (NAFLD) induced by a high-fat diet, and in oleic acid-treated HepG2 human hepatocellular carcinoma cells in vitro.

Material/Methods

Four study groups of mice included: the control group; the high-fat diet (HFD) group; the HFD+RKI-1447 (2 mg/kg) group; and the HFD+RKI-1447 (8 mg/kg) group. Mice were fed a high-fat diet for 12 weeks. Mice in the HFD+RKI-1447 groups were fed a high-fat diet for 12 weeks and treated with RKI-1447 twice weekly for three weeks. The HepG2 human hepatocellular carcinoma cells were treated with or without RKI-1447 for 2 h and treated with oleic acid for 24 h.

Results

In the mouse model of NAFLD, RKI-1447 reduced insulin resistance and the levels of alanine aminotransferase (ALT), aspartate transaminase (AST), total cholesterol, triglyceride, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), malondialdehyde (MDA), and superoxide dismutase (SOD). RKI-1447 reduced the histological changes in the mouse model of NAFLD in mice fed a high-fat diet and significantly inhibited the generations of triglyceride, IL-6, and TNF-α. RKI-1447 reduced the levels of oxidative stress in HepG2 cells treated with oleic acid and significantly down-regulated the expression of RhoA, ROCK1, ROCK2, toll-like receptor 4 (TLR4), p-TBK1, and p-IRF3. RKI-1447 treatment also inhibited RhoA expression.

Conclusions

In a mouse model of NAFLD, RKI-1447 inhibited ROCK and modulated insulin resistance, oxidative stress, and inflammation through the ROCK/TLR4/TBK1/IRF3 pathway.

Tetrandrine Ameliorates Airway Remodeling of Chronic Asthma by Interfering TGF-β1/Nrf-2/HO-1 Signaling Pathway-Mediated Oxidative Stress

Background

Imbalanced oxidative stress and antioxidant defense are involved in airway remodeling in asthma. It has been demonstrated that Tetrandrine has a potent role in antioxidant defense in rheumatoid arthritis and hypertension. However, the correlation between Tetrandrine and oxidative stress in asthma is utterly blurry. This study aimed to investigate the role of Tetrandrine on oxidative stress-mediated airway remolding.

Materials and Methods

Chronic asthma was established by ovalbumin (OVA) administration in male Wistar rats. Histopathology was determined by HE staining. Immunofluorescence was employed to detect the expression of α-SMA and Nrf-2. Level of oxidative stress and matrix metalloproteinases were examined by ELISA kits. Cell viability and cell cycle of primary airway smooth muscle cells (ASMCs) were evaluated by CCK8 and flow cytometry, respectively. Signal molecules were detected using western blot.

Results

Tetrandrine effectively impairs OVA-induced airway inflammatory and airway remodeling by inhibiting the expression of CysLT1 and CysLTR1. The increase of oxidative stress and subsequent enhancement of MMP9 and TGF-β1 expression were rescued by the administration of Tetrandrine in the rat model of asthma. In in vitro experiments, Tetrandrine markedly suppressed TGF-β1-evoked cell viability and cell cycle promotion of ASMCs in a dose-dependent manner. Furthermore, Tetrandrine promoted Nrf-2 nuclear transcription and activated its downstream HO-1 in vivo and in vitro.

Conclusion

Tetrandrine attenuates airway inflammatory and airway remodeling in rat model of asthma and TGF-β1-induced cell proliferation of ASMCs by regulating oxidative stress in primary ASMCs, suggesting that Tetrandrine possibly is an effective candidate therapy for asthma.

Inhibition of high mobility group box 1 (HMGB1) attenuates podocyte apoptosis and epithelial-mesenchymal transition by regulating autophagy flux

BACKGROUND

Podocyte injury, characterized by podocyte hypertrophy, apoptosis, and epithelial-mesenchymal transition (EMT), is the major causative factor of diabetic nephropathy (DN). Autophagy dysfunction is regarded as the major risk factor for podocyte injury including EMT and apoptosis. High mobility group box 1 (HMGB1) is involved in the progression of DN through the induction of autophagy. However, the underlying mechanism remains unknown.

METHODS

Plasma HMGB1 concentrations were determined in DN patients using ELISA. Apoptosis of DN serum-treated podocytes was evaluated by flow cytometry. Podocyte autophagy flux was measured using immunofluorescence. Western blotting analysis was used to investigate HMGB1 expression, EMT, and autophagy-related signaling pathways.

RESULTS

Upregulation of HMGB1 was found in DN patients and DN serum-treated podocytes. Removal of HMGB1 inhibited DN serum-mediated podocyte apoptosis by inhibiting autophagy and activating AKT/mammalian target of rapamycin (mTOR) signaling. In addition, HMGB1 depletion repressed the progression of podocyte EMT by inhibiting transforming growth factor (TGF)-β/smad1 signaling in vitro and in vivo. The combination of HMGB1 short interference (si) RNA and the autophagy activator rapamycin protected against podocyte apoptosis and EMT progression by inhibiting the AKT/mTOR and TGF-β/smad signaling pathway, respectively.

CONCLUSIONS

Although HMGB1 siRNA and rapamycin treatment had opposite effects on autophagy and AKT/mTOR signaling, there was no contradiction about the role of HMGB1 siRNA and rapamycin on AKT/mTOR pathway because autophagy and AKT/mTOR signaling play dual roles in intracellular biological processes. Based on the findings of this study, we may assume that HMGB1-initiated autophagy is harmful, whereas rapamycin is beneficial to podocyte survival. Possibly combined treatment with HMGB1 siRNA and rapamycin improved podocyte damage and EMT by regulating autophagy homeostasis.

Oleic acid-induced perilipin 5 expression and lipid droplets formation are regulated by the PI3K/PPARα pathway in HepG2 cells

Perilipin 5 (Plin5), a member of the PAT (Perilipin, ADRP, and Tip47) protein family, has been implicated in the regulation of cellular neutral lipid accumulation in nonalcoholic fatty liver diseases. However, the underlying regulatory mechanisms of Plin5 are not clear. The goal of the present study was to explore the mechanism of oleic acid (OA)-induced Plin5 expression in HepG2 cells. We found that the expression of Plin5 was increased during OA-induced lipid droplets formation in a dose- and time-dependent manner. During this process of OA-stimulated lipid droplets formation, peroxisome proliferator-activated receptor alpha (PPARα) was also upregulated. When PPARα activation was blocked by GW6471, OA-induced Plin5 expression and lipid droplets formation were effectively ablated. We further found that the phosphoinositide 3-kinase (PI3K) inhibitor LY294002 was able to downregulate both PPARα and Plin5 expression and lipid droplets formation. Thus, we concluded that PI3K may, at least in part, act upstream of PPARα to regulate Plin5 expression and lipid droplets formation in HepG2 cells.

Hepatocellular iNOS protects liver from NASH through Nrf2-dependent activation of HO-1

Multiple molecular events are involved in non-alcoholic steatohepatitis (NASH). There is no consensus on the role of inducible nitric oxide synthase (iNOS) in the progression of NASH. The present study therefore investigated the role of iNOS in NASH pathogenesis using bone marrow-transplanted iNOS chimeric mice under high-fat diet (HFD) conditions. The chimeric mice were fed a HFD for 16 wk, and primary hepatocytes were stimulated with oleic acid (OA). The molecular mechanisms underlying the role of iNOS in NASH were investigated. Marked hepatic steatosis and injury observed in the HFD mice and OA-stimulated hepatocytes were reduced by hepatocyte-derived iNOS. Mechanistically, iNOS upregulated heme oxygenase 1 (HO-1) by augmenting nuclear factor erythroid 2-related factor 2 (Nrf-2) binding to the HO-1 gene promoter. In conclusion, hepatocyte-derived iNOS may play a protective role against the progression of NASH by upregulating HO-1 through Nrf-2. Upregulation of hepatocellular iNOS may represent a potentially new therapeutic paradigm to combat NASH.

Exosome secreted from adipose-derived stem cells attenuates diabetic nephropathy by promoting autophagy flux and inhibiting apoptosis in podocyte

Background

It is confirmed that adipose-derived stem cells (ADSCs) transplantation effectively relieves kidney fibrosis and type 2 diabetes disease in mice. Currently, exosome from urine-derived stem cells (USCs) can protect type 1 diabetes-mediated kidney injury and attenuate podocyte damage in diabetic nephropathy (DN). Exosome derived from USCs has evolved into the strategy for DN treatment, but the role of ADSCs-derived exosome (ADSCs-Exo) in DN remains unclear. The present study is aimed to investigate the therapeutic action and molecular mechanism of ADSCs-derived exosome on DN.

Methods

ADSCs and exosome were authenticated by immunofluorescence and flow cytometry. Morphology and the number of exosome were evaluated by electron microscope and Nanosight Tracking Analysis (NTA), respectively. Cell apoptosis was assessed using flow cytometry. Podocyte autophagy and signaling transduction were measured by immunofluorescence and immunoblotting. Dual Luciferase Reporter assay was employed to detect the regulatory relationship between miR-486 and Smad1.

Results

ADSCs-Exo attenuated spontaneous diabetes by reducing levels of urine protein, serum creatinine (Scr), blood urea nitrogen (BUN), and podocyte apoptosis in mice. In in vitro experiment, ADSCs-Exo also reversed high glucose-induced decrease of cell viability and the increase of cell apoptosis in MPC5 cells. In terms of mechanism, ADSCs-Exo could enhance autophagy flux and reduce podocyte injury by inhibiting the activation of mTOR signaling in MPC5 and spontaneous diabetic mice. Eventually, we found that miR-486 was the key factors in ADSCs and in the process of ADSCs-Exo-mediated improvement of DN symptom in vivo and in vitro. miR-486 reduced Smad1 expression by target regulating Smad1 whose reduction could inhibit mTOR activation, leading to the increase of autophagy and the reduction of podocyte apoptosis.

Conclusions

In conclusion, we illustrated that ADSCs-Exo vividly ameliorated DN symptom by enhancing the expression of miR-486 which led to the inhibition of Smad1/mTOR signaling pathway in podocyte. Possibly, ADSCs-Exo was used as a main therapeutic strategy for DN in future.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1177-1) contains supplementary material, which is available to authorized users.

Interaction of WBP2 with ERα increases doxorubicin resistance of breast cancer cells by modulating MDR1 transcription

BACKGROUND

Surgery combined with new adjuvant chemotherapy is the primary treatment for early stage invasive and advanced stage breast cancer. Growing evidence indicates that patients with ERα-positive breast cancer show poor response to chemotherapeutics. However, ERα-mediated drug-resistant mechanisms remain unclear.

METHODS

Levels of WW domain-binding protein 2 (WBP2) and drug-resistant gene were determined by western blotting and RT-PCR, respectively. Cell viability was measured by preforming MTT assay. CD243 expression and apoptosis rate were evaluated by flow cytometry. Interactions of WBP2/ERα and ERα/MDR1 were detected by co-immunoprecipitation and chromatin immunoprecipitation (ChIP) assay, respectively.

RESULTS

There was an intrinsic link between WBP2 and ERα in drug-resistant cancer cells. Upregulation of WBP2 in MCF7 cells increased the chemoresistance to doxorubicin, while RNAi-mediated knockdown of WBP2 in MCF7/ADR cells sensitised the cancer cells to doxorubicin. Further investigation in in vitro and in vivo models demonstrated that WBP2 expression was directly correlated with MDR1, and WBP2 could directly modulate MDR1 transcription through binding to ERα, resulting in increased chemotherapy drug resistance.

CONCLUSIONS

Our finding provides a new mechanism for the chemotherapy response of ERα-positive breast tumours, and WBP2 might be a key molecule for developing new therapeutic strategies to treat chemoresistance in breast cancer patients.

Gab2 mediates hepatocellular carcinogenesis by integrating multiple signaling pathways

Our previous studies have found that Growth factor receptor-bound protein 2-associated binding protein 2 (Gab2)-a docking protein-governs the development of fatty liver disease. Here, we further demonstrate that Gab2 mediates hepatocarcinogenesis. Compared with a faint expression in para-carcinoma tissue, Gab2 was highly expressed in ∼60-70% of human hepatocellular carcinoma (HCC) specimens. Deletion of Gab2 dramatically suppressed diethylnitrosamine-induced HCC in mice. The oncogenic effects of Gab2 in HepG2 cells were promoted by Gab2 overexpression but were rescued by Gab2 knockdown. Furthermore, Gab2 knockout in HepG2 cells restrained cell proliferation, migration and tumor growth in nude mice. Signaling pathway analysis with protein kinase inhibitors demonstrated that oncogenic regulation by Gab2 in hepatic cells involved multiple signaling molecules, including ERK, Akt, and Janus kinases (Jaks), especially those that mediate inflammatory signaling. IL-6 signaling was increased by Gab2 overexpression and impaired by Gab2 deletion via regulation of Jak2 and signal transducer and activator of transcription 3 phosphorylation and the expression of downstream genes, such as Bcl-2 (B-cell lymphoma 2), c-Myc, MMP7 (matrix metalloproteinase-7), and cyclin D1in vitro and in vivo These data indicate that Gab2 mediates the pathologic progression of HCC by integrating multiple signaling pathways and suggest that Gab2 might be a powerful therapeutic target for HCC.-Cheng, J., Zhong, Y., Chen, S., Sun, Y., Huang, L., Kang, Y., Chen, B., Chen, G., Wang, F., Tian, Y., Liu, W., Feng, G.-S., Lu, Z. Gab2 mediates hepatocellular carcinogenesis by integrating multiple signaling pathways.