Abstract 1992: A novel RB1 E3 ligase TRIM37 contributes to palbociclib resistance in breast cancer

Abstract

<p>The tripartite motif-containing 37 (TRIM37) is a RING finger E3 ubiquitin ligase and is a poor prognostic factor in breast cancer patients. The gene is located in chromosome 17q23, a region amplified in up to 40% of breast cancers. We observed that activation of androgen receptor (AR) could induce resistance to the CDK4/6 inhibitor Palbociclib, the mechanism yet to be clarified. ChIP-sequencing data suggested that AR binds to the TRIM37 promoter, with AR activation resulting in TRIM37 expression. We hypothesized that TRIM37 might be involved in Palbociclib resistance. Using an ER+ve cell line MCF7 and a TNBC cell line MDA-MB 453, we found that overexpression of TRIM37 could induce Palbociclib resistance. TRIM37 overexpression resulted in RB1 protein downregulation, which is the primary downstream target of CDK4/6, while TRIM37 knockdown enhanced RB1 protein expression. Ubiquitination assay demonstrated TRIM37 overexpression increased the level of RB1 protein ubiquitination. The co-immunoprecipitation (Co-IP) assay confirmed that TRIM37 protein could interact with the RB1 protein. These results suggest that TRIM37 could be the E3 ligase that regulates RB1 degradation. Various deletion mutants of TRIM37 were cloned for Co-IP experiments between these mutants and RB1. Results show that the MATH and c-terminal domains of TRIM37 was the essential region for the interaction. Overexpression of the mutant with the TRIM37 MATH and c-terminal domains (TRIM37-MATH/C) could enhance RB1 protein level. This might be due to competition of TRIM37-MATH/C with wild-type TRIM37 for RB1 binding. Our findings suggest TRIM37 is a novel RB1 E3 ligase, and it binds to the RB1 protein via the MATH and C-terminal domains to regulate protein degradation. Our study also suggests that high expression of TRIM37 mediated by AR activation could deplete RB1, which is the target of Palbociclib, eventually leading to resistance. These findings are supportive of the contribution of AR activation to Palbociclib resistance.<br></p>