The von Hippel-Lindau tumor suppressor protein promotes c-Cbl-independent poly-ubiquitylation and degradation of the activated EGFR

PLoS One. 2011;6(9):e23936. doi: 10.1371/journal.pone.0023936. Epub 2011 Sep 16.

Abstract

Somatic mutations or reduced expression of the von Hippel-Lindau (VHL) tumor suppressor occurs in the majority of the clear cell renal cell carcinoma (ccRCC) and is a causal factor for the pathogenesis of ccRCC. pVHL was reported to suppress the oncogenic activity of Epidermal Growth Factor Receptor (EGFR) by reducing the expression of the EGFR agonist TGF-α and by reducing the translation efficiency of EGFR itself. Furthermore, it was reported that pVHL down-regulates activated EGFR by promoting efficient lysosomal degradation of the receptor. These modes of negative regulation of EGFR by pVHL were dependent on Hypoxia Inducible Factor (HIF). In this study, we report that HIF was not the only factor stabilizing the activated EGFR in VHL-deficient ccRCC cells. Down-regulation of endogenous HIF in these cells had little effect on the turnover rates of the activated EGFR. Furthermore, neither pretreatment with lysosomal inhibitors pretreatment nor down-regulation of c-Cbl, a major E3 ubiquitin ligase that targets the activated EGFR for lysosomal degradation, significantly increased the stabilities of EGFR in VHL-expressing ccRCC cells. In contrast, pretreatment with proteasomal inhibitors extended EGFR lifetime and led to similar EGFR half-lives in VHL-expressing and VHL-deficient ccRCC cells. Down-regulation of c-Cbl in VHL-deficient ccRCC cells revealed that the c-Cbl and pVHL collaborated to down-regulate the activated EGFR. Finally, we found that pVHL promoted the poly-ubiquitylation of the activated EGFR, and this function was c-Cbl-independent. Thus these results indicate that pVHL limits EGFR signaling by promoting c-Cbl-independent poly-ubiquitylation of the activated receptor, which likely results in its degradation by proteasome.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Basic Helix-Loop-Helix Transcription Factors / genetics
  • Basic Helix-Loop-Helix Transcription Factors / metabolism
  • Blotting, Western
  • Carcinoma, Renal Cell / genetics
  • Carcinoma, Renal Cell / metabolism
  • Carcinoma, Renal Cell / pathology
  • Cell Line, Tumor
  • Chloroquine / pharmacology
  • Cysteine Proteinase Inhibitors / pharmacology
  • Down-Regulation / drug effects
  • Enzyme Activation / drug effects
  • ErbB Receptors / genetics
  • ErbB Receptors / metabolism*
  • Humans
  • Kidney Neoplasms / genetics
  • Kidney Neoplasms / metabolism
  • Kidney Neoplasms / pathology
  • Leupeptins / pharmacology
  • Proto-Oncogene Proteins c-cbl / genetics
  • Proto-Oncogene Proteins c-cbl / metabolism*
  • RNA Interference
  • Ubiquitination*
  • Von Hippel-Lindau Tumor Suppressor Protein / genetics
  • Von Hippel-Lindau Tumor Suppressor Protein / metabolism*

Substances

  • Basic Helix-Loop-Helix Transcription Factors
  • Cysteine Proteinase Inhibitors
  • Leupeptins
  • endothelial PAS domain-containing protein 1
  • Chloroquine
  • Proto-Oncogene Proteins c-cbl
  • Von Hippel-Lindau Tumor Suppressor Protein
  • ErbB Receptors
  • CBL protein, human
  • VHL protein, human
  • benzyloxycarbonylleucyl-leucyl-leucine aldehyde