Forkhead Box M1B Transcriptional Activity Requires Binding of Cdk-Cyclin Complexes for Phosphorylation-Dependent Recruitment of p300/CBP Coactivators

Abstract

Previous liver regeneration studies demonstrated that the mouse forkhead box M1B (FoxM1B) transcription factor regulates hepatocyte proliferation through expression of cell cycle genes that stimulate cyclin-dependent kinase 2 (Cdk2) and Cdk1 activity. In this study, we demonstrated that disruption of the FoxM1B Cdk1/2 phosphorylation site at Thr residue 596 significantly reduced both FoxM1B transcriptional activity and Cdk phosphorylation of the FoxM1B T596A mutant protein in vivo. Retention of this FoxM1B 596 Cdk phosphorylation site was found to be essential for recruiting the histone acetyltransferase CREB binding protein (CBP) to the FoxM1B transcriptional activation domain. Consistent with these findings, dominant negative Cdk1 protein significantly reduced FoxM1B transcriptional activity and inhibited FoxM1B recruitment of the CBP coactivator protein. Likewise, Cdc25B-mediated stimulation of Cdk activity together with elevated levels of the CBP coactivator protein provided a 6.2-fold synergistic increase in FoxM1B transcriptional activity. Furthermore, mutation of the FoxM1B Leu 641 residue within an LXL motif (residues 639 to 641) inhibited recruitment of Cdk-cyclin complexes and caused significant reduction in both FoxM1B transcriptional activity and in vivo Cdk phosphorylation of the FoxM1B Thr 596 residue. We demonstrated that FoxM1B transcriptional activity requires binding of either S-phase or M-phase Cdk-cyclin complexes to mediate efficient Cdk phosphorylation of the FoxM1B Thr 596 residue, which is essential for recruitment of p300/CBP coactivator proteins.Cellular proliferation involves stimulation of the mitogenactivated protein kinase (MAPK) pathway, consisting of the Ras/Raf1/MEK/MAPK cascade (19,47), and activation of the phosphoinositol 3-kinase (PI3K) pathway, consisting of the PI3K/phosphoinositide-dependent kinase 1 (PDK1)/Akt cascade (5). However, cell division is tightly regulated at the G 1 /S (DNA replication) and G 2 /M (mitosis) transitions of the cell cycle by temporal activation of multiple cyclin-dependent kinases (Cdks) complexed with their corresponding cyclin regulatory subunits. Cdk2-cyclin E or A and Cdk1-cyclin B kinase activity is essential for progression through the G 1 /S and G 2 /M transitions of the cell cycle, respectively. Furthermore, Cdk activity is negatively regulated by phosphorylation of Thr 14 and Tyr 15 by the dual specific Myt1 kinase (6, 30, 31, 37). Both MAPK and PDK1 phosphorylate and activate the downstream p90 ribosomal S6 kinase (Rsk) (4, 21, 51), which provides inhibitory phosphorylation to the dual Myt1 kinase (44, 45). Simulation of Cdk1 or Cdk2 activity involves removal of inhibitory phosphates at Thr 14 and Tyr 15 by either Cdc25A phosphatase (G 1 /S phase), Cdc25B (late S phase), or Cdc25C phosphatase (G 2 /M phase) (7,41,62). In addition, Cdk activity requires phosphorylation of Thr 160 by the Cdk-activating kinase (CAK) protein, which is also a direct target for MAPK phosphorylation (14,28,55).Cdk1 and Cdk2 proteins are proline-directed kinase...

Cell cycle regulation and hepatocarcinogenesis

“…[87][88][89] The transcriptional activity of Foxm1b appears to require docking with cdk2-cyclin E/A (S Phase) or Cdk1-Cyclin B (G 2 Phase) complexes and recruitment of the p300 coactivator. 90 In a recent study, Kalinchenko et al have validated the importance of Foxm1b for the development of hepatocellular carcinoma in an experimental carcinogenesis model. 91 Foxm1b -/-hepatocytes were found to be resistant to the development of HCC following the diethylnitrosamine/phenobarbital tumor induction protocol.…”

Targeting FoxM1 transcription factor in T-cell acute lymphoblastic leukemia cell line

“…In our study, cell cycle analysis revealed that inhibition of FoxM1 by dexamethasone and siomycin A decreased the proliferation of T-ALL cells significantly through induction of G1 phase arrest. Recent studies have shown that FoxM1 phosphorylation starts at early G1 with cyclin-CDK complexes and continues throughout the G2 phase and mitosis [32,33].…”

“…FoxM1 has been shown to activate the oncogenic pathways that are important in carcinogenesis such as mitogen activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), phosphatdyl inositol 3-kinase (PI3k)/Akt), nuclear factor kappa-B and sonic hedgehog (SHH) [33][34][35][36][37]. Moreover, FoxM1 has been shown to decrease the gene expression levels of the tumor suppressor genes and also the genes involved in cellular senescence like p53 and p21 cip1 [20,38].…”

Roles of CREB-binding protein (CBP)/p300 in respiratory epithelium tumorigenesis

“…The ability of E2F-1 to stimulate transcription appears to be subjected to multiple regulations including co-activation by CBP/p300 and reversal of Rb-mediated repression through Rb phosphorylation [55]. At a molecular level, the Cdk-stimulated interaction of CBP/p300 with E2F-1 may be involved in irreversibly committing cells to cell-cycle progression [56]. Interestingly, although E2F-1 has been shown to be acetylated in vitro by both p/CAF and CBP/p300 at the same lysine residues, a specific role for p/CAF in acetylation-induced stabilisation of E2F-1 in response to DNA damage was recently reported [57].…”