| dc.description.abstract | The Mediator complex, consisting of the head, middle, tail and CDK8 (Cyclin-Dependent Kinase 8) kinase module, is required by almost all the protein coding gene and a variety of non-coding gene transcription in eukaryotic cells. Dysregulation of subunits of the only enzymatic submodule, CKM (CDK8 kinase module), has been linked to diverse human diseases such as cancer. Thus, it is essential to understand the function of CKM in both normal development and tumorigenesis.
To identify interactors of CDK8, we performed a dominant modifier genetic screen in Drosophila based on the defects in vein patterning caused by specific depletion or overexpression of CDK8 or CycC in developing wing imaginal discs. We identified the genetic interactions between the CDK8-CycC and the components of the Decapentaplegic (Dpp, the Drosophila homolog of TGFβ) signaling pathway, where CDK8-CycC positively regulates transcription activated by Dpp signaling pathway primary transcription factor Mad (Mothers against Dpp).
To understand the roles of the four CKM subunits, we depleted different combinations of the four subunits and identified their antagonistic roles in regulating Drosophila eye development, that Med12-Med13 pair is essential for the eye development and depletion CDK8-CycC can partially rescue the defects caused by removal of Med12-Med13. In addition, the asymmetric interdependency of the four subunits was identified.
Finally, we further explore the negative role of CDK8-CycC in regulating SREBP (sterol regulatory element-binding protein). Mutation of CDK8 phosphorylation site on SREBP resulted in stabilized SREBP protein level, stronger binding to chromosome, hyper activation of target gene transcription, and finally more lipid accumulation in vivo in Drosophila. In addition, we identified six amino acids from the N-terminal of SREBP is essential for the interaction between CDK8 and SREBP, which could be required by the phosphorylation.
Taken together, this work expands our knowledge of CDK8 or the CKM function in vivo, which advances our understanding about their roles in regulating transcriptions in different physiological or pathological contexts. | en |
