An important characteristic of multicellular organisms is the control that tissue architecture exerts on the growth and differentiation of individual cells. Epithelial cells sense their location through interactions with the extracellular matrix (ECM) as well as neighboring cells. These interactions generate input signals, including survival, that are critical to maintain tissue and cellular homeostasis. When attachment is compromised, epithelial cells undergo an intrinsically programmed cell death (apoptosis) that is termed anoikis (from the Greek "loss of home"). Importantly, failure to execute the anoikis program could result in adherent epithelial cells surviving in suspension or being able to proliiferate at sites different from their original environment. Thus, anoikis is a line of defense that must be circumvented by cancerous epithelial cells for them to leave their home niche, thrive in inappropriate ECM environments, and establish long distance metastases. Thus, elucidating how epithelial cancer cells escape anoikis is critical to understanding cancer progression.

In order to uncover genes that modulate the anoikis response and are altered in human cancers, we performed a functional genomics study. We couple genome wide RNAi to identify gene functions that, when silenced, induce resistance to anoikis with a novel computational method, ISAR-DEL, specifically aimed at pinpointing candidate tumor suppressor genes based on recurrent loss of copy number. Our studies identified Bridging Integrator 3 (BIN3) as a novel tumor suppressor located on the chromosomal region 8p21.3, one of the most frequently lost regions in epithelial cancers.

Mechanistically, we link BIN3 tumor suppression function to its ability to sense changes in the curvature of the cell membrane and relocate to the cell membrane after cell detachment to induce a proapoptotic cascade. Once BIN3 has translocated to the cell membrane it modulates the relocation and function of CDC42. In these conditions, CDC42 transmits the signal that leads to the activation of the stress protein P38-α and programmed cell death mediated by accumulation of the apoptotic facilitator BimEL. Overall, our results explain how changes in cell geometry are integrated in the cellular signaling network and present, for the first time, BIN3 as a novel breast cancer tumors suppressor.

Citation Format: Silva J, Marshall N, Sanchez-Garcia F, Parsons R, Pe'er D. BIN3 is an 8p21 tumor suppressor regulating the epithelial attachment checkpoint. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-06-02.