E2F-1 lacking the transcriptional activity domain induces autophagy

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.

Keywords: :

• E2F-1
• E2Ftr
• adenovirus
• apoptosis
• autophagy
• melanoma

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

This work was supported by Lung Cancer Research Foundation (JGGG), award numbers R01CA129975 (HSZ) and R01CA90784 (KMM) from the National Cancer Institute and GMB081410 (KMM and HSZ) from the Kentucky Lung Cancer Research Program. AGG received a scholarship from the National Council of Science and Technology (CONACYT) of Mexico. We are grateful to Dr. Brian Seed (Harvard Medical School, Boston, MA) for kindly providing the pEAK12-Actin-LC3-dNGLUC and pEAK12-Actin-flagDEVDG2-dNGLUC plasmids and Dr. Tamotsu Yoshimori (Osaka University, Japan) for kindly providing the EGFP-LC3 plasmid. We thank Margaret A. Abby and Nancy Alsip for editing.

Notes

† These authors contributed equally to this work.