Mechanismen der zellzyklusabhängigen Transkriptionsregulation durch MuvB-Komplexe
Biochemie
Zusammenfassung der Projektergebnisse
The cell division cycle is substantially regulated through transcription, with differential gene expression driving its progression. Deregulation of these processes contributes to oncogenic transformation. Key regulators of the S, G2, and M phase transitions are repressed in quiescent cells and early G1 but are activated to enable cell cycle progression. Our work, along with that of others, has shown that this regulation depends to a large extend on DREAM/MuvB complexes, which repress target genes in quiescent cells by binding to CHR and E2F promoter sites. During late G1, DREAM components dissociate from the MuvB core complex and are replaced by oncogenic transcription factors B-MYB and FOXM1, which activate previously repressed genes via MuvB complexes bound to CHR sites. Our previous work revealed that FOXM1 does not directly bind DNA but instead indirectly acts through MuvB, which directly contacts CHR sites. This switch in complex composition drives gene expression in the late cell cycle phases and can be reversed by p53 activation via the p53-p21-DREAM pathway, halting the cell cycle in response to DNA damage. In this project, we aimed to further investigate the mechanisms of DREAM/MuvB-dependent transcription and their role in regulating the cell cycle, particularly in inducing cell cycle arrest. With deletion of LIN37, a DREAM/MuvB component, we made substantial progress in understanding the mechanism of transcriptional repression by DREAM and added an important tool for our studies to elucidate cell cycle regulation by DREAM/MuvB complexes. We discovered that DREAM’s repressor function is disrupted in LIN37-/- cells. However, we found that loss of LIN37 does not affect assembly of the remaining DREAM complex and LIN37 does not contribute to activation by MuvB complexes. We also investigated the transcriptional regulation of important cell cycle regulators by DREAM and MuvB. One prominent example is the MKI67 gene, which encodes the Ki-67 cancer marker. Our findings elucidate the regulation of MKI67 transcription and Ki-67 protein synthesis during the cell cycle, including during the p53-mediated DNA damage response, thereby establishing the basis for Ki-67's diagnostic significance. Additionally, we found that the central DNA repair proteins BRCA1 and BRCA2 are expressed during the cell cycle under the control of DREAM/MuvB and RB. Upon DNA damage induction, BRCA1 and BRCA2 expression is repressed by the p53-p21-DREAM/RB pathways. The downregulation of BRCA1/2 following p53 activation triggers a shift in DNA repair pathways. Our results integrate signaling pathways governing cell cycle regulation and DNA repair induction. Using LIN37/DREAM and RB knockout cell lines, we investigated the role of DREAM/MuvB complexes in regulating the cell cycle, particularly in response to DNA damage. Our results show that LIN37/RB double knockout cells lose the ability to exit the cell cycle. This demonstrates that both DREAM and RB:E2F complexes are crucial for enabling cells to enter G0 arrest and stop proliferation.
Projektbezogene Publikationen (Auswahl)
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Cell cycle transcription control: DREAM/MuvB and RB-E2F complexes. Critical Reviews in Biochemistry and Molecular Biology, 52(6), 638-662.
Fischer, Martin & Müller, Gerd A.
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The DREAM complex through its subunit Lin37 cooperates with Rb to initiate quiescence. eLife, 6.
Mages, Christina FS; Wintsche, Axel; Bernhart, Stephan H. & Müller, Gerd A.
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DREAM and RB cooperate to induce gene repression and cell-cycle arrest in response to p53 activation. Nucleic Acids Research, 47(17), 9087-9103.
Uxa, Sigrid; Bernhart, Stephan H.; Mages, Christina F. S.; Fischer, Martin; Kohler, Robin; Hoffmann, Steve; Stadler, Peter F.; Engeland, Kurt & Müller, Gerd A.
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Ki-67 gene expression. Cell Death & Differentiation, 28(12), 3357-3370.
Uxa, Sigrid; Castillo-Binder, Paola; Kohler, Robin; Stangner, Konstanze; Müller, Gerd A. & Engeland, Kurt
