118 CDK12 regulates gene expression of DNMT1 and ERBB3 by altering transcription of MIR-152

Objectives The DNA-damage-response (DDR) pathway is a cellular mechanism which has evolved to protect cellular integrity by detection and repair of DNA lesions. Cyclin-dependent kinase 12 (CDK12) maintains genome stability via regulation of transcription of DDR genes, specifically, BRCA1, RAD51. Importantly, down-regulation of the CDK12 caused induction of the 53BP1 and γH2AX foci and accumulation of cells in the G2-M phase of the cell cycle. Since various microRNA (miRNA) are situated within coding genes, such as DDR, we hypothesize that expression of some of them might be also affected by CDK12 depletion. Methods A pilot study focused on identification of candidate miRNAs in ovarian cancer cells that might be significantly altered in CDK12 deficient cells. Indeed, downregulation of CDK12 protein level led to aberrant expression of several miRNAs. Among studied miRNAs, the level of miR-152 was significantly elevated. By using predictive algorithm, several proteins that might be targeted by miR-152 were examined. Results Upregulated expression of miR-152 leads to decreased expression of DNMT1 (DNA methyl transferase 1), RICTOR and MET proteins, which are often found deregulated in rather wide spectrum of oncogenic diseases. In addition to DNMT1, the protein level of ERBB3 was also affected by downregulation of CDK12 in various ovarian cancer cells, such as PEO1, COV362 and OVCAR5. Conclusions We speculate CDK12 participates in DDR machinery by two distinct mechanisms, either by orchestrating transcription of DDR genes or by stabilization of DNMT1 protein by blocking expression of miR-152 targeting DNMT1. The project is supported by the grant of the Ministry of Health AZV16–34152A.