Mediator Kinase as a Transducer and Therapeutic Target in Oncogenic WNT/β‐ CATENIN Signaling

Abstract

Colorectal cancer (CRC) is the second and third most commonly diagnosed cancer in women and men, respectively. Few treatment options exist for advanced stage disease, thus, the development of targeted therapies is crucial for treatment. The canonical wingless related integration site (WNT)/β‐CATENIN pathway is a driver in >90% of CRCs. The mediator kinase module (mediator complex subunit 12 (MED12), mediator complex subunit 13 (MED13), CYCLIN C, and cyclin dependent kinase 8 (CDK8)) is a key node of oncogenic activation within the WNT/β‐CATENIN pathway, since β‐CATENIN activates transcription through its direct physical interaction with MED12. Additionally, CDK8 is an oncoprotein required for β‐CATENIN‐dependent gene activation and CRC growth.The objective of this study was to investigate the effects of genetic (disruption of MED12:CYCLIN C interface) and chemical inhibition of Mediator Kinase activity on CRC cell oncogenic properties and gene regulation. Oncogenic properties were assessed by colony formation and cell proliferation assays. Chromatin immunoprecipitation sequencing and RNA sequencing were used to evaluate gene regulation. Interestingly, genetic but not chemical inhibition led to a significant reduction in oncogenic properties. Superenhancer alterations and differential expression of superenhancer‐associated genes were observed with both genetic and chemical inhibition. However, little overlap was found for down‐regulated superenhancer‐associated genes.Based on the significant reduction in oncogenic properties, genetic disruption of the MED12:CYCLIN C interface appears to be an attractive target for the development of targeted molecular therapies for CRC. The difference in effect on oncogenic properties with chemical versus genetic inhibition is likely explained by the differences in down‐regulated superenhancer‐associated genes. Concordantly, genes involved in the WNT/β‐CATENIN pathway were down‐regulated with genetic but not chemical inhibition.Support or Funding InformationLindsey Barron was supported by a CPRIT postdoctoral training fellowship, the CPRIT Research Training Award (RP170345) and is currently supported by an IRACDA Grant (K12GM111726).