Abstract C297: PARP1 and BIN1 cooperate to act as a novel co-repressor for E2F1.
Authors: Kumari Alpana , Pyndiah Slovénie , Cassimere Erica K. , Sakamuro Daitoku 
Published: August 2014

Abstract
Background: Bridging integrator 1 (BIN1) is a transcriptional co-repressor and inhibits oncogenic activities of c-MYC and E1A oncoproteins1. BIN1 inhibits c-MYC through direct interaction, whereas the mechanism by which BIN1 attenuates the oncogenic transformation mediated by adenovirus E1A remains elusive. Since BIN1 does not physically interact with E1A, we hypothesized that BIN1 diminishes a cellular effector, which can be activated by E1A and is essential for E1A transformation. One of the well-recognized cellular effectors for E1A transformation is the E2F1 transcription factor. Although retinoblastoma (RB) protein is an authentic E2F1 inhibitor, loss of RB does not immediately result in cancer development, suggesting that an anti-E2F1 function, which is independent of RB, compensates for RB deficiency. BIN1 was recently shown to interact with poly (ADP-ribose) polymerase1 (PARP1), a component of transcriptional complex2. Given that PARP1 also interacts with E2F1, we hypothesized functional cross talk between BIN1 and PARP1 to curb E2F1 activity.
Experimental Procedures: E2F1 activity was determined using an adenovirus-driven E2F1-sensitive luciferase reporter vector, E2A-Luc. Protein-protein interaction was studied by co-immunoprecipitation followed by Western blot analysis. Chromatin immunoprecipitation assay was used to demonstrate protein-DNA interaction. Colony formation and foci formation assays were performed to investigate BIN1-mediated tumor suppression in the presence and absence of PARP1.
Results: We discovered that BIN1 physically interacts with E2F1 and inhibits its transactivation. Interestingly, depletion of PARP1 released endogenous E2F1 activity, regardless of the status of RB expression. Furthermore, BIN1 failed to inhibit E2F1 activity in the absence of PARP1, but RB does not need PARP1 to inhibit E2F1 activity. Chromatin immunoprecipitation assays suggested that BIN1 and PARP1 co-existed on an E2F-responsive promoter. Moreover, in the absence of PARP1, the binding affinities of both BIN1 and E2F1 to the promoter were significantly reduced. In addition, only in the presence of PARP1, ectopically expressed BIN1 inhibited tumor colony formation and HPV16 E7 oncoprotein-dependent cellular transformation. Our results suggest that BIN1 and PARP1 cooperate to inhibit E2F1 activity and suppress oncogenic transformation.
Conclusion: We conclude that BIN1 is a novel E2F1 corepressor in cooperation with PARP1. BIN1-PARP1 interaction may serve as a safety device to control deregulated E2F1 activity due to RB loss.
This study was supported by NIH R01CA140379 (to D.S.).
Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C297.
Citation Format: Alpana Kumari, Slovénie Pyndiah, Erica K. Cassimere, Daitoku Sakamuro. PARP1 and BIN1 cooperate to act as a novel co-repressor for E2F1. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C297.