Deletion of chromosome 1p35 is a common event in epithelial malignancies. We report that DEAR1 (annotated as TRIM62) is a chromosome 1p35 tumor suppressor that undergoes mutation, copy number variation, and loss of expression in human tumors. Targeted disruption in the mouse recapitulates this human tumor spectrum, with both Dear1(-/-) and Dear1(+/-) mice developing primarily epithelial adenocarcinomas and lymphoma with evidence of metastasis in a subset of mice. DEAR1 loss of function in the presence of TGF-β results in failure of acinar morphogenesis, upregulation of epithelial-mesenchymal transition (EMT) markers, anoikis resistance, migration, and invasion. Furthermore, DEAR1 blocks TGF-β-SMAD3 signaling, resulting in decreased nuclear phosphorylated SMAD3 by binding to and promoting the ubiquitination of SMAD3, the major effector of TGF-β-induced EMT. Moreover, DEAR1 loss increases levels of SMAD3 downstream effectors SNAIL1 and SNAIL2, with genetic alteration of DEAR1/SNAIL2 serving as prognostic markers of overall poor survival in a cohort of 889 cases of invasive breast cancer.
Significance: Cumulative results provide compelling evidence that DEAR1 is a critical tumor suppressor involved in multiple human cancers and provide a novel paradigm for regulation of TGF-β-induced EMT through DEAR1's regulation of SMAD3 protein levels. DEAR1 loss of function has important therapeutic implications for targeted therapies aimed at the TGF-β-SMAD3 pathway.