A feedforward circuit shaped by ECT2 and USP7 contributes to breast carcinogenesis

Abstract

Rationale: A number of guanine nucleotide exchange factors (GEFs) including epithelial cell transforming factor ECT2 are believed to drive carcinogenesis through activating distinct oncogenic GTPases. Yet, whether GEF-independent activity of ECT2 also plays a role in tumorigenesis remains unclear. Methods: Immunohistochemical (IHC) staining, colony formation and xenograft assays were used to examine the role of ECT2 in breast carcinogenesis. Co-immunoprecipitation, immunofluorescent stainings, in vivo deubiquitination and in vitro deubiquitination experiments were performed to examine the physical and functional interaction between ECT2 and ubiquitin-specific protease USP7. High-throughput RNA sequencing, quantitative reverse transcription-PCR and Western blotting were employed to investigate the biological significance of the interplay between ECT2 and USP7. Results: We report that ECT2 plays a tumor-promoting role in breast cancer, and GEF activity-deficient ECT2 is able to alleviate ECT2 depletion associated growth defects in breast cancer cells. Mechanistically, we demonstrated that ECT2 physically interacts with ubiquitin-specific protease USP7 and functionally facilitates USP7 intermolecular self-association, -deubiquitination and -stabilization in a GEF activity-independent manner. USP7 in turn, deubiquitinates and stabilizes ECT2, resulting in a feedforward regulatory circuit that ultimately sustains the expression of oncogenic protein MDM2. Conclusion: Our study uncovers a GEF-independent role of ECT2 in promoting survival of breast cancer cells, provides a molecular insight for the reciprocal regulation of ECT2 and USP7, and supports the pursuit of ECT2/USP7 as potential targets for breast cancer intervention.

Epithelial cell transforming factor ECT2 is an important regulator of DNA double-strand break repair and genome stability

“…As reported by ourselves and others, ECT2 is a potential oncogene that promotes breast tumorigenesis ( 35 , 40 , 41 , 42 , 43 ). Therefore, we wondered if the high expression level of ECT2 found in breast cancer confers cellular resistance to genotoxic insults.…”

“…Increasing evidence, including our previous study, indicates that dysregulated ECT2 activity is implicated in many types of cancer and that ECT2 depletion suppresses tumorigenesis ( 35 , 41 , 52 , 53 ). These findings suggest that ECT2 acts as an oncogenic protein.…”

“…Although ECT2 is localized at DNA damage sites ( 34 ), it is not known if ECT2 is involved in DSB repair or how it contributes to DDR. Recently, we discovered that ECT2 promotes dimerization and stabilization of the ubiquitin-specific protease USP7 independently of its nuclear GEF activity ( 35 ). This finding prompted us to investigate the role of ECT2 in DSB repair, and whether the repair mechanisms are mediated by the GEF activity of ECT2.…”

Progress of Breast Cancer basic research in China

“…Recent studies showed the effects of FTO 77 , protein arginine methyltransferase 1 (PRMT1) 78 , coactivator associated arginine methyltransferase 1 (CARM1)/PRMT4 79 , Otubain-2 (OTUB2) 80 , RING finger protein 144A (RNF144A) 81 , plant homeodomain finger protein 20-like protein 1 (PHF20L1) 82 , heat shock transcription factor 1 (HSF1) 83 , epithelial cell transforming sequence 2 (ECT2) 84 , pescadillo homolog 1 (PES1) 85 , PHACTR2-AS1 (PAS1) 86 , breast cancer-related transcript 1 (BCRT1) 87 , and circCDYL 88 on progression of breast cancer and they provided novel therapeutic targets. TNBC is especially hard to treat due to the lack of targets.…”

Roles and Mechanisms of Deubiquitinases (DUBs) in Breast Cancer Progression and Targeted Drug Discovery

“…Importantly, USP7 is able to interact with itself and remove its own polyubiquitin chains to sustain self-stability. In addition, this process is observed to be promoted by ECT2, indicating USP7 and ECT2 also construct a positive feedback loop similar to the USP7–PHF8 loop [ 32 ].…”