Transcriptional control via CHR promoter elements: signaling proteins in cell cycle regulation

• Applicant: Professor Dr. Kurt Engeland
• Subject Area: Cell Biology
• Term: from 2019 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 424870812

The control of cell division is important to prevent the development of cancer. A central mechanism represents the regulation of transcription. We and others have described the functions of a transcription factor family based on the MuvB core complex. This family controls more than 270 genes which typically play a role in cell cycle regulation. The DREAM, MMB, FOXM1-MMB and FOXM1-MuvB complexes regulate transcription through binding to the CHR (Cell Cycle Genes Homology Region) promoter element. To carry out different functions, the MuvB core exchanges its association partners. When MuvB binds members of the E2F/RB family, the DREAM complex is formed. DREAM functions as a repressor in G0 and the early cell cycle. MuvB changes its function from a repressor to a transcriptional activator during the later cell cycle once MuvB switches its association partners to the oncogenic transcription factors B-MYB or FOXM1 to form the MMB, FOXM1-MMB or FOXM1-MuvB complexes. The importance of this MuvB/CHR system is well established, but understanding of the mechanisms by which signaling proteins trigger the switch between the four MuvB complexes are still limited. Also, it is largely unknown how proteins are recruited to either cause repression or activation in the MuvB/CHR system. Furthermore, the mechanisms by which MuvB complexes modify chromatin and connect to the basal transcriptional machinery remain insufficiently understood. This proposed project aims at identifying currently unknown proteins binding DNA indirectly through CHR sites and at defining their function in signaling through CHR elements. The overall aim is to delineate the role of the newly identified factors in controlling the cell cycle through the MuvB/CHR system. To this end, we will identify proteins that are associated with the MuvB complex by the RIME/MS and APEX /MS methods. We will test whether these factors require the CHR site for indirect DNA binding. The interaction of the newly identified proteins with MuvB components will be examined. These results will elucidate the mechanistic details of signaling upstream of the MuvB complex. We will investigate in knockdown and knockout experiments how loss of the newly identified factors contributes to transcription of CHR-regulated promoters. Furthermore, the impact of these proteins on overall cell cycle regulation will become evident upon knockdown/knockout. In RNA-seq and ChIP-seq experiments we will define the target genes of these proteins and their overall impact on cell cycle regulation through transcription. Taken together, we will identify unknown factors that act as transcription factors, cofactors or signaling proteins as the next level of regulation in the MuvB/CHR system. We will delineate how these factors form yet unknown links to signaling pathways controlling cell division. Besides providing insight into fundamental biological processes, our results will also have implications for understanding the development of cancer.

• DFG Programme: Research Grants