| dc.description.abstract | Transcription facilitates cell cycle division and progression as it orchestrates the timely expression of genes crucial for each cell cycle phase. Two waves of gene expression prime the cell for replication: the first wave (DNA replication genes) produces the needed cell machinery for DNA replication, and the second wave of gene expression (mitotic genes) encodes the mitotic regulators required for cell division. The B-MYB/MuvB(MMB)-FOXM1 complex coordinates the expression of mitotic genes. This dissertation investigates the inter-dependence between B-MYB and FOXM1 and their requirement for mitosis.
We show that knockout of MMB-FOXM1 complex components B-MYB, LIN54, or FOXM1 confers resistance to CHK1 and ATR inhibition. In addition, we demonstrate that the loss of B-MYB impedes arrest following contact inhibition. Cell cycle kinetic studies reveal that the knockout of B-MYB or FOXM1 has profound effects on the progression of every cell cycle phase. These findings indicate the MMB-FOXM1 complexes function as global coordinators of cell cycle progression and establish the MMB-FOXM1 as a crucial signaling node in response to cellular stress.
During early S phase, B-MYB binds to MuvB to form the MMB complex. The MMB complex recruits FOXM1, and both B-MYB and FOXM1 contribute to activating mitotic genes. In this dissertation, we extend these findings by showing that MMB enhanced FOXM1 binding to DNA, and B-MYB-mediated recruitment of FOXM1 was critical for the onset of mitotic gene expression. We found that FOXM1 was required to properly dissociate B-MYB from DNA in G2 and degradation of B-MYB and other DNA machinery in mitosis. These findings prove that B-MYB and FOXM1 functionally cooperate and rely on mutually interdependent interactions to activate mitotic genes.
The CHR motif, recognized by the MuvB complex, is primarily enriched at mitotic gene promoters, while canonical MYB and forkhead DNA motifs are less abundant. Current models propose that B-MYB and FOXM1 stabilize MuvB complexes at CHR elements by binding largely non-sequence-specific DNA. Using high-resolution chromatin profiling, we show that B-MYB and FOXM1 binding is correlated but also distinct. We observed that B-MYB binding was enriched at mitotic gene promoters and contained canonical MYB and CHR DNA recognition motifs. In addition, we found that MuvB component LIN9 binding follows the pattern of BMYB rather than FOXM1. We demonstrate that FOXM1 binds to mitotic and DNA damage gene promoters. FOXM1 gene targets were enriched for canonical forkhead DNA recognition motifs. Combining nascent transcript analysis (PRO-seq), RNA-seq, and Cut\&Run sequencing, we define FOXM1 as a critical transcriptional driver of cell cycle gene expression. Collectively, these findings indicate that B-MYB and FOXM1 cooperatively regulate the expression of cell cycle genes, where the MMB complex defines mitotic genes through association with MYB and CHR recognition motifs and enhances recruitment of FOXM1 to mitotic gene promoters, where FOXM1 drives transcription of mitotic genes and DNA repair genes. | |
