Epigenetic regulation of DNA repair gene program by Hippo/YAP1-TET1 axis mediates sorafenib resistance in HCC.

Hepatocellular carcinoma (HCC) is a malignancy that occurs worldwide and is generally associated with poor prognosis. The development of resistance to targeted therapies such as sorafenib is a major challenge in clinical cancer treatment. In the present study, Ten-eleven translocation protein 1 (TET1) was found to be highly expressed in sorafenib-resistant HCC cells and knockdown of TET1 can substantially improve the therapeutic effect of sorafenib on HCC, indicating the potential important roles of TET1 in sorafenib resistance in HCC. Mechanistic studies determined that TET1 and Yes-associated protein 1 (YAP1) synergistically regulate the promoter methylation and gene expression of DNA repair-related genes in sorafenib-resistant HCC cells. RNA sequencing indicated the activation of DNA damage repair signaling was extensively suppressed by the TET1 inhibitor Bobcat339. We also identified TET1 as a direct transcriptional target of YAP1 by promoter analysis and chromatin-immunoprecipitation assays in sorafenib-resistant HCC cells. Furthermore, we showed that Bobcat339 can overcome sorafenib resistance and synergized with sorafenib to induce tumor eradication in HCC cells and mouse models. Finally, immunostaining showed a positive correlation between TET1 and YAP1 in clinical samples. Our findings have identified a previously unrecognized molecular pathway underlying HCC sorafenib resistance, thus revealing a promising strategy for cancer therapy.

Suppression of preadipocyte determination by SOX4 limits white adipocyte hyperplasia in obesity.

Preadipocyte determination expanding the pool of preadipocytes is a vital process in adipocyte hyperplasia, but the molecular mechanisms underlying this process are yet to be elucidated. Herein, SRY-related HMG box transcription factor 4 (SOX4) was identified as a critical target in response to BMP4- and TGFß-regulated preadipocyte determination. SOX4 deficiency is sufficient to promote preadipocyte determination in mesenchymal stem cells (MSCs) and acquisition of preadipocyte properties in nonadipogenic lineages, while its overexpression impairs the adipogenic capacity of preadipocytes and converts them into nonadipogenic lineages. Mechanism studies indicated that SOX4 activates and cooperates with LEF1 to retain the nuclear localization of ß-catenin, thus mediating the crosstalk between TGFß/BMP4 signaling pathway and Wnt signaling pathway to regulate the preadipocyte determination. In vivo studies demonstrated that SOX4 promotes the adipogenic-nonadipogenic conversion and suppresses the adipocyte hyperplasia. Together, our findings highlight the importance of SOX4 in regulating the adipocyte hyperplasia in obesity.

TET2 is recruited by CREB to promote Cebpb, Cebpa, and Pparg transcription by facilitating hydroxymethylation during adipocyte differentiation.

Ten-eleven translocation proteins (TETs) are dioxygenases that convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), an important epigenetic mark that regulates gene expression during development and differentiation. Here, we found that the TET2 expression was positively associated with adipogenesis. Further, in vitro and in vivo experiments showed that TET2 deficiency blocked adipogenesis by inhibiting the expression of the key transcription factors CCAAT/enhancer-binding protein beta (C/EBPß), C/EBPα and peroxisome proliferator-activated receptor gamma (PPARγ). In addition, TET2 promoted 5hmC on the CpG islands (CGIs) of Cebpb, Cebpa and Pparg at the initial time point of their transcription, which requires the cAMP-responsive element-binding protein (CREB). At last, specific knockout of Tet2 in preadipocytes enabled mice to resist obesity and attenuated the obesity-associated insulin resistance. Together, TET2 is recruited by CREB to promote the expression of Cebpb, Cebpa and Pparg via 5hmC during adipogenesis and may be a potential therapeutic target for obesity and insulin resistance.

SOX4 promotes beige adipocyte-mediated adaptive thermogenesis by facilitating PRDM16-PPARγ complex.

Brown and beige fat protect against cold environments and obesity by catabolizing stored energy to generate heat. This process is achieved by controlling thermogenesis-related gene expression and the development of brown/beige fat through the induction of transcription factors, most notably PPARγ. However, the cofactors that induce the expression of thermogenic genes with PPARγ are still not well understood. In this study, we explored the role of SOX4 in adaptive thermogenesis and its relationship with PPARγ. Methods: Whole transcriptome deep sequencing (RNA-seq) analysis of inguinal subcutaneous white adipose tissue (iWAT) after cold stimulation was performed to identify genes with differential expression in mice. Indirect calorimetry detected oxygen consumption rate and heat generation. mRNA levels were analyzed by qPCR assays. Proteins were detected by immunoblotting and immunofluorescence. Interaction of proteins was detected by endogenous and exogenous Co-IP. ChIP-qPCR, FAIRE assay and luciferase reporter assays were used to investigate transcriptional regulation. Results: SOX4 was identified as the main transcriptional effector of thermogenesis. Mice with either adipocyte-specific or UCP1+ cells deletion of SOX4 exhibited significant cold intolerance, decreased energy expenditure, and beige adipocyte formation, which was attributed to decreased thermogenic gene expression. In addition, these mice developed obesity on a high-fat diet, with severe hepatic steatosis, insulin resistance, and inflammation. At the cell level, loss of SOX4 from preadipocytes inhibited the development of beige adipocytes, and loss of SOX4 from mature beige adipocytes reduced the expression of thermogenesis-related genes and energy metabolism. Mechanistically, SOX4 stimulated the transcriptional activity of Ucp1 by binding to PPARγ and activating its transcriptional function. These actions of SOX4 were, at least partly, mediated by recruiting PRDM16 to PPARγ, thus forming a transcriptional complex to elevate the expression of thermogenic genes. Conclusion: SOX4, as a coactivator of PPARγ, drives the thermogenic gene expression program and thermogenesis of beige fat, promoting energy expenditure. It has important physiological significance in resisting cold and obesity.