Abstract
DNA mismatch repair (MMR) maintains genome stability primarily by correcting replication errors. MMR deficiency can lead to cancer development and bolsters cancer cell resistance to chemotherapy. However, recent studies have shown that checkpoint blockade therapy is effective in MMR-deficient cancers, thus the ability to identify cancer etiology would greatly benefit cancer treatment. MutS homolog 2 (MSH2) is an obligate subunit of mismatch recognition proteins MutSα (MSH2-MSH6) and MutSβ (MSH2-MSH3). Precise regulation of MSH2 is critical, as either over- or underexpression of MSH2 results in an increased mutation frequency. The mechanism by which cells maintain MSH2 proteostasis is unknown. Using functional ubiquitination and deubiquitination assays, we show that the ovarian tumor (OTU) family deubiquitinase ubiquitin aldehyde binding 1 (OTUB1) inhibits MSH2 ubiquitination by blocking the E2 ligase ubiquitin transfer activity. Depleting OTUB1 in cells promotes the ubiquitination and subsequent degradation of MSH2, leading to greater mutation frequency and cellular resistance to genotoxic agents, including the common chemotherapy agents N-methyl-N'-nitro-N-nitrosoguanidine and cisplatin. Taken together, our data identify OTUB1 as an important regulator of MSH2 stability and provide evidence that OTUB1 is a potential biomarker for cancer etiology and therapy.
Highlights
In addition to correcting replication errors, the mismatch repair (MMR) system maintains genome stability by processing nonmismatch DNA lesions induced by genotoxic agents [1, 2]
It has been noted that the rate of ubiquitination-proteosome system (UPS)-mediated MutSα degradation varies across different cell lines [20], and multiple motifs that can be ubiquitinated are present in MutS homolog 2 (MSH2), which implies that other ubiquitinases/deubiquitinases might regulate MSH2 proteostasis
We found that Flag-MSH2 and HA-OTUB1 pulled each other down (Fig. 1A), which suggests a specific interaction between MSH2 and OTUB1
Summary
In addition to correcting replication errors, the MMR system maintains genome stability by processing nonmismatch DNA lesions induced by genotoxic agents [1, 2]. We obtained similar results in a co-immunoprecipitation experiment to determine endogenous interactions between these two proteins by using an MSH2-specific or an OTUB1 antibody (Fig. 1B).
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