Abstract C71: DEAR1 orchestrates selective control over the epithelial-mesenchymal transition axis of TGFβ's function

Little is known about the cellular mechanisms that govern the context dependent roles of the critical cytokine TGFβ, which functions in breast cancer as either a tumor suppressor to restrict proliferation in early stage disease or a master driver of epithelial-mesenchymal transition during invasion and metastasis. We previously reported the discovery of the TRIM protein DEAR1(annotated as TRIM62) as a gene that is mutated and homozygously deleted in early onset breast cancers and functions as a dominant regulator of acinar morphogenesis in three dimensional (3D) culture, suggesting that DEAR1 is a novel tumor suppressor that regulates both polarity and tissue architecture. Herein we demonstrate that loss of function of DEAR1 in immortal mammary epithelial cells (HMECs) resulted in a failure of acinar morphogenesis in the presence of TGFβ and was required for TGFβ-induced cell migration, invasion and anoikis resistance, all of which key indicators of TGFB-driven EMT. However, DEAR1 loss did not affect TGFβ-induced proliferation suppression, indicative that DEAR1 exerts a selective negative control over TGFβ-mediated EMT oncogenic functions while preserving TGFβ's growth suppressive functions. These results indicate that the mechanisms governing the dual functions of TGFβ are separable and that it is possible to selectively block the deleterious arm of TGFβ's function. In addition, DEAR1 suppressed TGFβ-SMAD3 signaling by binding to and ubiquitinating SMAD3, the major effector of TGFβ-meditated EMT. Furthermore, treatment of DEAR1 knockdown HMECs with a SMAD3 inhibitor or SMAD3 shRNA rescued the DEAR1 loss of function phenotype as evidence by the downregulation of expression of EMT markers and inhibition of migration induced by TGFβ in strong support that DEAR1 specifically blocks TGFβ-induced EMT through the regulation of SMAD3 protein levels and suggestive that results could have clinical significance for stratifying breast cancers for targeted therapies aimed at the oncogenic arm of this pathway. These data demonstrate a significant role for DEAR1 in the control of TGFβ-induced EMT as well as present a novel paradigm for regulation of one of the most important pathways aberrant in human breast cancer. Citation Format: Nanyue Chen, Ret., Seetharaman Balasenthil, Yu Cao, Ann M. Killary. DEAR1 orchestrates selective control over the epithelial-mesenchymal transition axis of TGFβ's function. [abstract]. In: Proceedings of the AACR Special Conference on Tumor