Reduced abundance of the E3 ubiquitin ligase E6AP contributes to decreased expression of the INK4/ARF locus in non–small cell lung cancer Academic Article uri icon

abstract

  • The tumor suppressor p16INK4a, one protein encoded by the INK4/ARF locus, is frequently absent in multiple cancers, including non-small cell lung cancer (NSCLC). Whereas increased methylation of the encoding gene (CDKN2A) accounts for its loss in a third of patients, no molecular explanation exists for the remainder. We unraveled an alternative mechanism for the silencing of the INK4/ARF locus involving the E3 ubiquitin ligase and transcriptional cofactor E6AP (also known as UBE3A). We found that the expression of three tumor suppressor genes encoded in the INK4/ARF locus (p15INK4b, p16INK4a, and p19ARF) was decreased in E6AP-/- mouse embryo fibroblasts. E6AP induced the expression of the INK4/ARF locus at the transcriptional level by inhibiting CDC6 transcription, a gene encoding a key repressor of the locus. Luciferase assays revealed that E6AP inhibited CDC6 expression by reducing its E2F1-dependent transcription. Chromatin immunoprecipitation analysis indicated that E6AP reduced the amount of E2F1 at the CDC6 promoter. In a subset of NSCLC samples, an E6AP-low/CDC6-high/p16INK4a-low protein abundance profile correlated with low methylation of the gene encoding p16INK4a (CDKN2A) and poor patient prognosis. These findings define a previously unrecognized tumor-suppressive role for E6AP in NSCLC, reveal an alternative silencing mechanism of the INK4/ARF locus, and reveal E6AP as a potential prognostic marker in NSCLC.

authors

  • Gamell, Cristina
  • Gulati, Twishi
  • Levav-Cohen, Yaara
  • Young, Richard J
  • Do, Hongdo
  • Pilling, Pat
  • Takano, Elena
  • Watkins, Neil
  • Fox, Stephen B
  • Russell, Prudence
  • Ginsberg, Doron
  • Monahan, Brendon J
  • Wright, Gavin
  • Dobrovic, Alex
  • Haupt, Sue
  • Solomon, Ben
  • Haupt, Ygal

publication date

  • 2017

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