Novel AKT1-GLI3-VMP1 pathway mediates KRAS oncogene-induced autophagy in cancer cells

J Biol Chem. 2012 Jul 20;287(30):25325-34. doi: 10.1074/jbc.M112.370809. Epub 2012 Apr 25.

Abstract

Autophagy is an evolutionarily conserved degradation process of cytoplasmic cellular constituents. It has been suggested that autophagy plays a role in tumor promotion and progression downstream oncogenic pathways; however, the molecular mechanisms underlying this phenomenon have not been elucidated. Here, we provide both in vitro and in vivo evidence of a novel signaling pathway whereby the oncogene KRAS induces the expression of VMP1, a molecule needed for the formation of the authophagosome and capable of inducing autophagy, even under nutrient-replete conditions. RNAi experiments demonstrated that KRAS requires VMP1 to induce autophagy. Analysis of the mechanisms identified GLI3, a transcription factor regulated by the Hedgehog pathway, as an effector of KRAS signaling. GLI3 regulates autophagy as well as the expression and promoter activity of VMP1 in a Hedgehog-independent manner. Chromatin immunoprecipitation assays demonstrated that GLI3 binds to the VMP1 promoter and complexes with the histone acetyltransferase p300 to regulate promoter activity. Knockdown of p300 impaired KRAS- and GLI3-induced activation of this promoter. Finally, we identified the PI3K-AKT1 pathway as the signaling pathway mediating the expression and promoter activity of VMP1 upstream of the GLI3-p300 complex. Together, these data provide evidence of a new regulatory mechanism involved in autophagy that integrates this cellular process into the molecular network of events regulating oncogene-induced autophagy.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Autophagy*
  • CHO Cells
  • Cricetinae
  • Cricetulus
  • Gene Expression Regulation, Neoplastic / genetics
  • HeLa Cells
  • Hedgehog Proteins / genetics
  • Hedgehog Proteins / metabolism
  • Humans
  • Kruppel-Like Transcription Factors / genetics
  • Kruppel-Like Transcription Factors / metabolism*
  • Membrane Proteins / biosynthesis*
  • Membrane Proteins / genetics
  • Mice
  • Neoplasms / genetics
  • Neoplasms / mortality*
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism*
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-akt / genetics
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Proto-Oncogene Proteins p21(ras) / genetics
  • Proto-Oncogene Proteins p21(ras) / metabolism*
  • Response Elements / genetics
  • Signal Transduction*
  • Zinc Finger Protein Gli3
  • p300-CBP Transcription Factors / genetics
  • p300-CBP Transcription Factors / metabolism
  • ras Proteins / genetics
  • ras Proteins / metabolism*

Substances

  • GLI3 protein, human
  • Gli3 protein, mouse
  • Hedgehog Proteins
  • KRAS protein, human
  • Kruppel-Like Transcription Factors
  • Membrane Proteins
  • Nerve Tissue Proteins
  • Proto-Oncogene Proteins
  • VMP1 protein, human
  • Zinc Finger Protein Gli3
  • p300-CBP Transcription Factors
  • p300-CBP-associated factor
  • AKT1 protein, human
  • Akt1 protein, mouse
  • Proto-Oncogene Proteins c-akt
  • Hras protein, mouse
  • Proto-Oncogene Proteins p21(ras)
  • ras Proteins