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Hypoxia mediates mitochondrial biogenesis in hepatocellular carcinoma to promote tumor growth through HMGB1 and TLR9 interaction.

ABSTRACT: The ability of cancer cells to survive and grow under hypoxic conditions has been known for decades, but the mechanisms remain poorly understood. Under certain conditions, cancer cells undergo changes in their bioenergetic profile to favor mitochondrial respiration by activating the peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1?) and up-regulating mitochondrial biogenesis. In this study, we hypothesized that augmented mitochondrial biogenesis plays a critical role for cancer cells to survive hypoxia. Consistent with this hypothesis, both hypoxic human hepatocellular carcinoma (HCC) tumors and HCC cell lines subjected to hypoxia increase mitochondrial biogenesis. Silencing of PGC-1? in hypoxic HCC cell lines halts their proliferation. Mechanistic investigations in vitro indicated that intracellular high mobility group box 1 (HMGB1) protein, a nuclear protein overexpressed in HCC, is essential for the process. Silencing of HMGB1 in hypoxic HCC cell lines resulted in a significant decrease in PGC-1? activation and mitochondrial biogenesis. Without HMGB1, hypoxic HCC cells had significantly reduced adenosine triphosphate production, decreased cellular proliferation, and increased apoptosis. In a diethylnitrosamine-induced murine model of HCC, genetic blocking of HMGB1 in hypoxic tumors resulted in a significant decrease in tumor growth. Tumors lacking HMGB1 had a significant reduction in mitochondrial biogenesis and a significant increase in mitochondrial dysfunction. Further in vitro mechanistic experiments indicated that during hypoxia HMGB1 translocates from the nucleus to the cytoplasm and binds to cytoplasmic Toll-like receptor-9. This binding leads to activation of p38 and subsequent phosphorylation of PGC-1?, with resultant up-regulation of mitochondrial biogenesis.Taken together, our findings suggest that during hypoxia HMGB1 up-regulates mitochondrial biogenesis in HCC cancer cells, promoting tumor survival and proliferation. (Hepatology 2017;66:182-197).

SUBMITTER: Tohme S

PROVIDER: S-EPMC5481489 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature

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Hypoxia mediates mitochondrial biogenesis in hepatocellular carcinoma to promote tumor growth through HMGB1 and TLR9 interaction.

Tohme Samer S Yazdani Hamza O HO Liu Yao Y Loughran Patricia P van der Windt Dirk J DJ Huang Hai H Simmons Richard L RL Shiva Sruti S Tai Sheng S Tsung Allan A

Hepatology (Baltimore, Md.) 20170522 1

The ability of cancer cells to survive and grow under hypoxic conditions has been known for decades, but the mechanisms remain poorly understood. Under certain conditions, cancer cells undergo changes in their bioenergetic profile to favor mitochondrial respiration by activating the peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) and up-regulating mitochondrial biogenesis. In this study, we hypothesized that augmented mitochondrial biogenesis plays a critical role f ...[more]

PMID: 28370295

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Project description:BackgroundTumor microenvironment (TME) plays a very important role in cancer progression. The mesenchymal stem cells (MSC), a major compartment of TME, have been shown to promote hepatocellular carcinoma (HCC) progression and metastasis. As hypoxia is a common feature of TME, it is essential to investigate the effects of hypoxia on MSC during HCC progression.MethodsThe effects of hypoxia on MSC mediated cell proliferation and HCC progression were measured by cell counting kit-8 (CCK-8) assay, Edu incorporation assay and xenograft model. The role of cyclooxygenase 2 (COX2) during this process was evaluated via lentivirus mediated COX2 knockdown in MSC. We also assessed the levels and localization of yes-associated protein (YAP) in HCC cells by immunofluorescence, western blot and real-time PCR, in order to detect the alterations of Hippo pathway. The changes in lipogenesis was examined by triacylglycerol (TG) levels, BODIPY staining of neutral lipid, and lipogenic enzyme levels. The alterations in AKT/mTOR/SREBP1 pathway were measured by western blot. In addition, to evaluate the role of prostaglandin E receptor 4 (EP4) in MSC mediated cell proliferation under hypoxia, we manipulated the levels of EP4 in HCC cells via small interfering RNA (siRNA), EP4 antagonist or agonist.ResultsWe found that MSC under hypoxia condition (hypo-MSC) could promote proliferation of HCC cell lines and tumor growth in xenograft model. Hypoxia increased COX2 expression in MSC and promoted the secretion of prostaglandin E2 (PGE2), which then activated YAP in HCC cells and led to increased cell proliferation. Meanwhile, YAP activation enhanced lipogenesis in HCC cell lines by upregulating AKT/mTOR/SREBP1 pathway. Knockdown or overexpression of YAP significantly decreased or increased lipogenesis. Finally, EP4 was found to mediate the effects of hypo-MSC on YAP activation and lipogenesis of HCC cells.ConclusionsHypo-MSC can promote HCC progression by activating YAP and the YAP mediated lipogenesis through COX2/PGE2/EP4 axis. The communication between MSC and cancer cells may be a potential therapeutic target for inhibiting cancer growth.

Dataset Information

Hypoxia mediates mitochondrial biogenesis in hepatocellular carcinoma to promote tumor growth through HMGB1 and TLR9 interaction.

Publications

Hypoxia mediates mitochondrial biogenesis in hepatocellular carcinoma to promote tumor growth through HMGB1 and TLR9 interaction.

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