E2F-1 lacking the transcriptional activity domain induces autophagy

Cancer Biol Ther. 2012 Sep;13(11):1091-101. doi: 10.4161/cbt.21143. Epub 2012 Jul 24.

Abstract

The transcription factor E2F-1 plays a crucial role in the control of cell proliferation. E2F-1 has tumor suppressive properties by inducing apoptosis and autophagy. In this study, E2F-1 and its truncated form (E2Ftr), lacking the transactivation domain (TAD), were compared for their ability to induce autophagy. In Gaussia luciferase-based assays, both E2F-1 and E2Ftr induced the proteolytic cleavage of the autophagic marker LC3. In addition, LC3 and autophagy protein 5 (Atg5) were upregulated by E2F-1 and E2Ftr. Likewise, both E2F proteins induced a punctate pattern of GFP-tagged LC3, indicating autophagosome formation. The presence of double-membrane autophagic vesicles induced by E2F-1 and E2Ftr was confirmed by transmission electron microscopy (TEM). The application of z-VAD-fmk, a caspase inhibitor, partially blocked both E2F-1 and E2Ftr-mediated cytotoxicity. Moreover, Atg5 (-/-) cells were more resistant to the E2F-1 or E2Ftr-induced cell killing effect than Atg5 wt cells. The TAD of E2F-1 is not essential for induction of autophagy; apoptosis and autophagy cooperate for an efficient cancer cell killing effect induced by E2F-1 or E2Ftr. E2Ftr-induced autophagy is a promising approach to destroy tumors that are resistant to conventional treatments.

Publication types

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

MeSH terms

  • Apoptosis / genetics
  • Autophagy / genetics*
  • Cell Line, Tumor
  • E2F1 Transcription Factor / genetics*
  • E2F1 Transcription Factor / metabolism
  • HEK293 Cells
  • Humans
  • Melanoma / genetics
  • Melanoma / pathology
  • Protein Structure, Tertiary
  • Transfection
  • Up-Regulation

Substances

  • E2F1 Transcription Factor
  • E2F1 protein, human