Recruitment of Ataxia-Telangiectasia Mutated to the p21waf1 Promoter by ZBP-89 Plays a Role in Mucosal Protection

Background & Aims: Histone deacetylase inhibitors (HDACi) induce growth arrest, apoptosis, and differentiation, particularly in colon cancer cells where they are potential chemopreventive agents. HDACi induction of the cyclin-dependent kinase inhibitor p21waf1 has been shown to require ataxia-telangiectasia mutated (ATM). Nevertheless, how ATM participates in p21waf1 gene expression has not been defined. Methods: In vivo protein complexes forming in response to butyrate were studied using co-immunoprecipitation and mass spectroscopy. DNA elements in the p21waf1 promoter were analyzed in vivo by chromatin immunoprecipitation and in vitro DNA affinity precipitation assays. The expression of p21waf1 was analyzed by immunoblots and reporter assays. Results: Reduction of ZBP-89 or ATM with small interfering RNAs blocked HDACi-induced p21waf1 expression. Chromatin immunoprecipitation and DNA affinity precipitation assays showed that both ZBP-89 and ATM are recruited to the GC-rich DNA elements of the p21waf1 promoter with HDACi treatment. Co-immunoprecipitation revealed that ATM associates with ZBP-89 in an HDACi-dependent manner. Serial deletions revealed that ATM interacts with both the N-terminal and DNA binding domains of ZBP-89. Moreover, we found that immunodepletion of ZBP-89 prevented recruitment of ATM to the p21waf1 promoter in vitro. Silencing of ZBP-89 expression blocked HDACi-induced phosphorylation of ATMSer1981 and p53Ser15. ATMSer1981 phosphorylation in the colons of mutant mice expressing an N-terminally truncated form of ZBP-89 was not observed after ingestion of dextran sodium sulfate and correlated with exacerbation of the mucosal injury. Conclusions:ZBP-89 interacts with ATM in a butyrate-dependent manner and is essential for colonic homeostasis in the setting of acute mucosal injury.