Authors: Aracely Garcia-Garcia, Humberto Rodriguez-Rocha, Michael T. Tseng, Roberto Montes de Oca-Luna, H. Sam Zhou, Kelly M. McMasters and Jorge G. Gomez-Gutierrez

Aracely Garcia-Garcia

Department of Surgery; James Graham Brown Cancer Center; Louisville, KY USA; Departamento de Histología; Facultad de Medicina; Universidad Autónoma de Nuevo León; Monterrey, Mexico
These authors contributed equally to this work.

Humberto Rodriguez-Rocha

Department of Surgery; James Graham Brown Cancer Center; Louisville, KY USA

Michael T. Tseng

Department of Anatomical Sciences and Neurobiology; University of Louisville of School of Medicine; Louisville, KY USA

Roberto Montes de Oca-Luna

Departamento de Histología; Facultad de Medicina; Universidad Autónoma de Nuevo León; Monterrey, Mexico

H. Sam Zhou

Department of Surgery; James Graham Brown Cancer Center; Louisville, KY USA; James Graham Brown Cancer Center; Louisville, KY USA

Kelly M. McMasters

Corresponding author: mcmasters@louisville.edu
Department of Surgery; James Graham Brown Cancer Center; Louisville, KY USA; James Graham Brown Cancer Center; Louisville, KY USA

Jorge G. Gomez-Gutierrez

Corresponding author: jgguti01@louisville.edu
Department of Surgery; James Graham Brown Cancer Center; Louisville, KY USA
These authors contributed equally to this work.

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.

Received: April 3, 2012; Accepted: June 17, 2012; Published Online: July 24, 2012

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