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Hepatitis C virus inhibits AKT-tuberous sclerosis complex (TSC), the mechanistic target of rapamycin (MTOR) pathway, through endoplasmic reticulum stress to induce autophagy.

ABSTRACT: Hepatitis C virus (HCV) is able to induce autophagy via endoplasmic reticulum (ER) stress, but the exact molecular signaling pathway is not well understood. We found that the activity of the mechanistic target of rapamycin complex 1 (MTORC1) was inhibited in Huh7 cells either harboring HCV-N (genotype 1b) full-genomic replicon or infected with JFH1 (genotype 2a) virus, which led to the activation of UNC-51-like kinase 1 (ULK1) and thus to autophagy. We then analyzed activity upstream of MTORC1, and found that both protein kinase, AMP-activated, ? (PRKAA, including PRKAA1 and PRKAA2, also known as AMP-activated protein kinase, AMPK?) and AKT (refers to pan AKT, including three isoforms of AKT1-3, also known as protein kinase B, PKB) were inhibited by HCV infection. The inhibition of the AKT-TSC-MTORC1 pathway contributed to upregulating autophagy, but inhibition of PRKAA downregulated autophagy. The net effect on autophagy was from AKT, which overrode the inhibition effect from PRKAA. It was further found that HCV-induced ER stress was responsible for the inhibition of the AKT pathway. Metformin, a PRKAA agonist, inhibited HCV replication not only by activating PRKAA as previously reported, but also by activating AKT independently of the autophagy pathway. Taken together, our data suggested HCV inhibited the AKT-TSC-MTORC1 pathway via ER stress, resulting in autophagy, which may contribute to the establishment of the HCV-induced autophagy.

SUBMITTER: Huang H

PROVIDER: S-EPMC3552882 | biostudies-other | 2013 Feb

REPOSITORIES: biostudies-other

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Hepatitis C virus inhibits AKT-tuberous sclerosis complex (TSC), the mechanistic target of rapamycin (MTOR) pathway, through endoplasmic reticulum stress to induce autophagy.

Huang He H Kang Rongyan R Wang Ji J Luo Guangxiang G Yang Wei W Zhao Zhendong Z

Autophagy 20121120 2

Hepatitis C virus (HCV) is able to induce autophagy via endoplasmic reticulum (ER) stress, but the exact molecular signaling pathway is not well understood. We found that the activity of the mechanistic target of rapamycin complex 1 (MTORC1) was inhibited in Huh7 cells either harboring HCV-N (genotype 1b) full-genomic replicon or infected with JFH1 (genotype 2a) virus, which led to the activation of UNC-51-like kinase 1 (ULK1) and thus to autophagy. We then analyzed activity upstream of MTORC1, ...[more]

PMID: 23169238

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Project description:Tuberous sclerosis complex (TSC) is a model disorder for understanding brain development because the genes that cause TSC are known, many downstream molecular pathways have been identified, and the resulting perturbations of cellular events are established. TSC, therefore, provides an intellectual framework to understand the molecular and biochemical pathways that orchestrate normal brain development. The TSC1 and TSC2 genes encode Hamartin and Tuberin which form a GTPase activating protein (GAP) complex. Inactivating mutations in TSC genes (TSC1/TSC2) cause sustained Ras homologue enriched in brain (RHEB) activation of the mammalian isoform of the target of rapamycin complex 1 (mTORC1). TOR is a protein kinase that regulates cell size in many organisms throughout nature. mTORC1 inhibits catabolic processes including autophagy and activates anabolic processes including mRNA translation. mTORC1 regulation is achieved through two main upstream mechanisms. The first mechanism is regulation by growth factor signaling. The second mechanism is regulation by amino acids. Gene mutations that cause too much or too little mTORC1 activity lead to a spectrum of neuroanatomical changes ranging from altered brain size (micro and macrocephaly) to cortical malformations to Type I neoplasias. Because somatic mutations often underlie these changes, the timing, and location of mutation results in focal brain malformations. These mutations, therefore, provide gain-of-function and loss-of-function changes that are a powerful tool to assess the events that have gone awry during development and to determine their functional physiological consequences. Knowledge about the TSC-mTORC1 pathway has allowed scientists to predict which upstream and downstream mutations should cause commensurate neuroanatomical changes. Indeed, many of these predictions have now been clinically validated. A description of clinical imaging and histochemical findings is provided in relation to laboratory models of TSC that will allow the reader to appreciate how human pathology can provide an understanding of the fundamental mechanisms of development.

Project description:BACKGROUND:The treatment of tuberous sclerosis complex (TSC) using mammalian target of rapamycin (mTOR) inhibitors is clinically promising. The aim of the present study was to evaluate the efficacy and safety of mTOR inhibitors for improving the clinical symptoms of TSC. METHODS:We performed a systematic search of major electronic databases (PubMed, EMBASE, Cochrane Library and WanFang, CNKI, and VIP databases) to identify randomized controlled trials (RCTs) and quasi-randomized studies from the date of database inception to November 2017; the Chinese Food and Drug Administration and clinicaltrials.gov were also searched for unpublished studies. The endpoints of the study were the tumor response rate and seizure frequency response rate (the proportion of patients achieving a???50% reduction relative to the baseline). Two researchers screened articles, assessed the risk of bias and extracted data independently. The included RCTs were analyzed using RevMan 5.3, which was provided by the Cochrane Collaboration. RESULTS:Compared with the placebo, mTOR inhibitors significantly reduced tumor volume in both angiomyolipoma (AML) (RR?=?24.69, 95% CI?=?3.51,173.41, P?=?0.001) and subependymal giant cell astrocytoma (SEGA) (RR?=?27.85, 95% CI?=?1.74,444.82, P?=?0.02). Compared with the placebo, mTOR inhibitors significantly reduced seizure frequency (RR?=?2.12, 95% CI?=?1.41,3.19, P?=?0.0003). Regarding safety, compared with patients who did not receive mTOR inhibitors, those who did had a higher risk of suffering stomatitis (RR?=?3.20, 95% CI?=?1.49,6.86, P?=?0.003). In contrast, patients who did and did not receive mTOR inhibitors experienced similar adverse events, such as upper respiratory tract infections (RR?=?1.08, 95% CI?=?0.81,1.45, P?=?0.59) and nasopharyngitis (RR?=?0.86, 95% CI?=?0.60,1.21, P?=?0.38). CONCLUSION:In view of the efficacy and safety associated with tumor and seizure frequency in the TSC patients, mTOR inhibitors is a good therapeutic choice. Unlike the risks of upper respiratory tract infections and nasopharyngitis, mTOR inhibitors seem to increase the risk of stomatitis, mostly grade 1 and 2.

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Dataset Information

Hepatitis C virus inhibits AKT-tuberous sclerosis complex (TSC), the mechanistic target of rapamycin (MTOR) pathway, through endoplasmic reticulum stress to induce autophagy.

Publications

Hepatitis C virus inhibits AKT-tuberous sclerosis complex (TSC), the mechanistic target of rapamycin (MTOR) pathway, through endoplasmic reticulum stress to induce autophagy.

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