Colorectal cancer (CRC) is the world third most commonly diagnosed cancer with an overall 5-year survival rate of 60-70%. Hyperactivation of Wnt/β-catenin signaling is found in most cases and a hallmark of CRC and thus, an interesting therapeutic target. Considering functional Wnt signaling is essential for intestinal homeostasis complicates the development of inhibitors. Cyclin Dependent Kinase 8 (CDK8), a transcriptional regulator as part of the Mediator complex, is amplified and overexpressed in a substantial fraction of CRC cases and regulates β-catenin activity, making it a promising target for CRC treatment. This study aims to utilize intestinal organoids and mouse models to investigate the role of CDK8 and CDK19, a paralog of CDK8 with unknown functions, in regulating intestinal homeostasis and to identify the therapeutic value of inhibiting CDK8/19 for CRC treatment.
We generated a genetic mouse model allowing a tamoxifen-inducible deletion of CDK8 specifically in intestinal epithelial cells (IECs), whereas its paralog CDK19 was constitutively deleted in the whole body using CRISPR Cas9. Intestinal organoids were isolated from these mice and CDK8 deletion induced ex vivo. We found that CDK8 and CDK19 in a redundant fashion are essential for organoid survival. Transcriptomic analysis and immunofluorescent staining revealed that CDK8/19 depletion in organoids led to the disruption of secretory lineage (e.g. Paneth cells) and thus impaired stem cell function. This effect was IEC-intrinsic, as the addition of Wnt3-conditioned media or co-culture with primary intestinal fibroblasts was able to rescue organoid growth. In line with this, deletion of CDK8/19 in mice did not show significant pathological changes, suggesting CDK8/19 are dispensable for murine intestinal homeostasis. Collectively, these data provide a safety profile for CDK8/19 inhibition in CRC treatment without interfering with homeostatic Wnt signaling. Based on the results, we are currently investigating the functions of CDK8/19 in CRC development with an Apc mutated CRC mouse model.