The DNA replication factor MCM5 is essential for Stat1-mediated transcriptional activation

Abstract

The eukaryotic minichromosome maintenance (MCM) family of proteins (MCM2-MCM7) is evolutionarily conserved from yeast to human. These proteins are essential for DNA replication. The signal transducer and activator of transcription proteins are critical for the signal transduction of a multitude of cytokines and growth factors leading to the regulation of gene expression. We previously identified a strong interaction between Stat1 and MCM5. However, the physiological significance of this interaction was not clear. We show here by chromatin immunoprecipitation (ChIP) analyses that the MCM5 protein, as well as other members of the MCM family, is inducibly recruited to Stat1 target gene promoters in response to cytokine stimulation. Furthermore, the MCM proteins are shown to move along with the RNA polymerase II during transcription elongation. We have also identified an independent domain in MCM5 that mediates the interaction between Stat1 and MCM5; overexpression of this domain can disrupt the interaction between Stat1 and MCM5 and inhibit Stat1 transcriptional activity. Finally, we used the RNA interference technique to show that MCM5 is essential for transcription activation of Stat1 target genes. Together, these results demonstrate that, in addition to their roles in DNA replication, the MCM proteins are also necessary for transcription activation.RNA polymerase II ͉ DNA helicase ͉ IFN-␥ T he evolutionarily conserved eukaryotic minichromosome maintenance (MCM) family of proteins consists of six members: MCM2-MCM7 (reviewed in refs. 1 and 2). The molecular structure and in vitro analyses of these proteins suggest that they function as a DNA helicase (3); they form a heterohexamer complex that binds to DNA replication origins and moves along with the DNA polymerase during DNA replication elongation (4, 5). In addition to the hexamer complex, the MCM proteins also form subcomplexes containing some members of the family, such as MCM4͞6͞7 or MCM3͞5 (3,[6][7][8]. It has been suggested that these subcomplexes represent segments during the assembly of the hexameric MCM complex (9). The MCM proteins are also highly abundant, and their number far exceeds that of the replication origins in yeast (8,(10)(11)(12). These observations have led to the suggestion that the MCM proteins may play additional roles in other biological processes, such as DNA repair, chromatin remodeling, and transcription (2, 13).The signal transducer and activator of transcription (STAT) family of transcription factors mediates a multitude of cytokineregulated gene transcription (reviewed in refs. 14 and 15). In response to ligand binding to cell surface receptors, the STATs are activated through tyrosine phosphorylation, form dimers, enter the nucleus, and bind to specific DNA sequences for transcription activation. The transcriptional activity of STATs are mediated by the transcription activation domain (TAD) located in the C terminus of the molecule (16). The STAT TADs can function independently of the rest of the STAT molecule, and their activit...

Excess MCM proteins protect human cells from replicative stress by licensing backup origins of replication

“…The poor definition of mammalian origins of replication has made difficult to quantify with precision the amount of chromatin-bound MCM complexes relative to the number of origins. In any case, there must be a large excess of MCM relative to the number of replication forks, because the majority of chromatin-associated MCM complexes do not localize with sites of DNA synthesis (21 (22), and Mcm7 interacts with Rad17 and ATRIP and is likely required for activation of the DDR (23,24).…”

Cyclin E-dependent localization of MCM5 regulates centrosome duplication

“…Additionally, this large pool of MCM proteins is required, because even a partial reduction in MCM level that does not greatly affect DNA replication leads to increased recombination events, chromosome loss and checkpoint sensitivity (Bell and Dutta, 2002;Liang et al, 1999). The excess level of MCM proteins along with broad binding on chromatin has been termed the 'MCM paradox' (Forsburg, 2004;Hyrien et al, 2003;Laskey and Madine, 2003) and further studies have shown that MCM proteins have multiple functions outside of DNA replication, including transcriptional activation and repression, chromatin remodeling, meiotic recombination, chromatin cohesion, and checkpoint responses (Agarwal et al, 2007;Forsburg, 2004;Gauthier et al, 2002;Snyder et al, 2005;Sterner et al, 1998). It is significant that, in addition to the localization of MCM5 on centrosomes that is reported here, localization of both Orc2 and geminin has also been reported on centrosomes (Prasanth et al, 2004b;Stuermer et al, 2007;Tachibana et al, 2005).…”

Crif1 is a novel transcriptional coactivator of STAT3

“…However, these coactivators are not specific to STAT3, but are also implicated in the functions of other STAT family members as well as in oncoproteins (such as Myb, Jun, and Fos), transforming viral proteins (such as E1A, E6, and large T antigen) and tumor-suppressor proteins (such as p53, E2F, Rb, Smads, RUNX, and BRCA1) (Shuai, 2000;Litterst and Pfitzner, 2002;Iyer et al, 2004). Recently, MCM5 and CoaSt6 have been suggested as specific coactivators of STAT1 and STAT6, respectively, although their in vivo relevance needs to be determined (Snyder et al, 2005;Goenka and Boothby, 2006). These findings raise the possibility of the existence of an additional coactivator that binds specifically to STAT3 and modulates its transcriptional activity.…”