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

Autophagy. 2013 Feb 1;9(2):175-95. doi: 10.4161/auto.22791. Epub 2012 Nov 20.

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, α (PRKAA, including PRKAA1 and PRKAA2, also known as AMP-activated protein kinase, AMPKα) 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.

Keywords: AKT; ER stress; HCV; MTOR; PRKAA; autophagy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • AMP-Activated Protein Kinases / antagonists & inhibitors
  • AMP-Activated Protein Kinases / metabolism
  • Aminoimidazole Carboxamide / analogs & derivatives
  • Aminoimidazole Carboxamide / pharmacology
  • Autophagy / drug effects*
  • Autophagy-Related Protein-1 Homolog
  • Cell Line, Tumor
  • Endoplasmic Reticulum Stress / drug effects*
  • Enzyme Activation / drug effects
  • Gene Knockdown Techniques
  • Hepacivirus / drug effects
  • Hepacivirus / physiology*
  • Hepatitis C / enzymology
  • Hepatitis C / pathology
  • Hepatitis C / virology
  • Humans
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Mechanistic Target of Rapamycin Complex 1
  • Metformin / pharmacology
  • Models, Biological
  • Multiprotein Complexes / antagonists & inhibitors
  • Multiprotein Complexes / metabolism
  • Phenylbutyrates / pharmacology
  • Protein-Serine-Threonine Kinases / metabolism
  • Proto-Oncogene Proteins c-akt / antagonists & inhibitors*
  • Proto-Oncogene Proteins c-akt / metabolism
  • Ribonucleotides / pharmacology
  • Signal Transduction / drug effects
  • Sirolimus / pharmacology*
  • TOR Serine-Threonine Kinases / antagonists & inhibitors*
  • TOR Serine-Threonine Kinases / metabolism
  • Tuberous Sclerosis Complex 1 Protein
  • Tumor Suppressor Proteins / antagonists & inhibitors*
  • Tumor Suppressor Proteins / metabolism
  • Virus Replication / drug effects

Substances

  • Intracellular Signaling Peptides and Proteins
  • Multiprotein Complexes
  • Phenylbutyrates
  • Ribonucleotides
  • Tuberous Sclerosis Complex 1 Protein
  • Tumor Suppressor Proteins
  • Aminoimidazole Carboxamide
  • 4-phenylbutyric acid
  • Metformin
  • TOR Serine-Threonine Kinases
  • Autophagy-Related Protein-1 Homolog
  • Mechanistic Target of Rapamycin Complex 1
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • ULK1 protein, human
  • AMP-Activated Protein Kinases
  • AICA ribonucleotide
  • Sirolimus