THE ROLE OF MASTL IN COLITIS RECOVERY AND COLITIS-ASSOCIATED CANCER DEVELOPMENT

Background: Colitis-associated cancer (CAC) is one of the most devastating complications of longstanding inflammatory bowel disease (IBD). CAC occurs in only 3.7% of ulcerative colitis (UC) patients, but accounts for as much as 15% of IBD patient deaths. Despite the global rise in IBD, IBD and CAC remain critically understudied. In order to generate novel approaches to IBD management and CAC prevention, we must understand the mechanisms underlying mucosal healing and the switch from damage to metaplasia in chronic colitis. Microtubule-associated serine-threonine kinase-like (MASTL), a key player in cell growth and repair, is also upregulated in sporadic colorectal cancer and CAC. Therefore, we sought to determine the contribution of MASTL to colitis recovery and CAC development. Methods: In order to do so, we assessed the responses of our novel intestine-localized inducible MASTL knockdown mice [MK^fl/+ Vil1-Cre/ERT2-inducible, or MK^fl/+ VCI)] to dextran sodium sulfate (DSS) colitis and to exposure to azoxymethane followed by three cycles of DSS (AOM/DSS) to include CAC. To inform and guide our in vivo studies, we performed single cell RNA sequencing (ssRNA-seq) of colon samples from our homozygous Control (MK^fl/fl) and induced MK^fl/fl VCI mice. Results: ssRNA-seq analysis revealed that MASTL localizes to the colonic stem cell and transit-amplifying cell compartments, and that MASTL knockout resulted in profound loss of epithelial cells and changes in numerous signaling pathways across colon cellular compartments. Across three separate DSS recovery experiments, MASTL KD impeded colon epithelial recovery and resulted in greater crypt damage and inflammation compared to controls. Interestingly, in the CAC model, there was a significant difference in inflammatory injury parameters between MK^fl/+ VCI AOM/DSS mice and MK^fl/+ VCI mice that received AOM alone and between Control (MK^fl/+) and MK^fl/+ VCI mice treated with AOM, but not between Control AOM/DSS and MK^fl/+ VCI AOM/DSS mice. Additionally, the frequency of high-grade tumors was greater in Control AOM/DSS mice than in MK^fl/+ VCI AOM/DSS mice. Conclusions: MASTL localizes to colon stem and transit-amplifying cells and is involved in promoting colon epithelial repair following colitis. Similarly, MASTL knockdown in AOM/DSS mice increases inflammatory injury but may reduce the risk of tumor formation. Future Directions: With the aid of our ssRNA-seq findings and in vitro cancer stem cell models, we will continue to investigate how MASTL knockdown modulates CAC tumorigenesis, and whether it involves alteration of DNA damage repair mechanisms and colonocyte differentiation.