Dynamic association of MLL1, H3K4 trimethylation with chromatin and Hox gene expression during the cell cycle

Abstract

Mixed lineage leukemias (MLLs) are histone H3 at lysine 4 (H3K4)‐specific methylases that play a critical role in regulating gene expression in humans. As chromatin condensation, relaxation and differential gene expression are keys to correct cell cycle progression, we analyzed the dynamic association of MLL and H3K4 trimethylation at different stages of the cell cycle. Interestingly, MLL1, which is normally associated with transcriptionally active chromatins (G1 phase), dissociates from condensed mitotic chromatin and returns at the end of telophase when the nucleus starts to relax. In contrast, H3K4 trimethylation mark, which is also normally associated with euchromatins (in G1), remains associated, even with condensed chromatin, throughout the cell cycle. The global levels of MLL1 and H3K4 trimethylation are not affected during the cell cycle, and H3Ser28 phosphorylation is only observed during mitosis. Interestingly, MLL target homeobox‐containing (Hox) genes (HoxA5, HoxA7 and HoxA10) are differentially expressed during the cell cycle, and the recruitment of MLL1 and H3K4 trimethylation levels are modulated in the promoter of these Hox genes as a function of their expression. In addition, down‐regulation of MLL1 results in cell cycle arrest at the G2/M phase. The fluctuation of H3K4 trimethylation marks at specific promoters, but not at the global level, indicates that H3K4 trimethylation marks that are present in the G1 phase may not be the same as the marks in other phases of the cell cycle; rather, old marks are removed and new marks are introduced. In conclusion, our studies demonstrate that MLL1 and H3K4 methylation have distinct dynamics during the cell cycle and play critical roles in the differential expression of Hox genes associated with cell cycle regulation.

A role for mitotic bookmarking of SOX2 in pluripotency and differentiation

“…Our results are in contrast to recent immunofluorescence-based experiments reporting that OCT4 does not bind to mitotic chromosomes (Galonska et al 2014). However, several studies reported unclear (Caravaca et al 2013) or false negative results (Chen et al 2002;Blobel et al 2009;Mishra et al 2009;Wu et al 2015) when using immunofluorescence to assess MCB, which was suggested to be due to limited accessibility of epitopes to antibodies within the dense mitotic environment (Chen et al 2002;Kadauke and Blobel 2013;Wu et al 2015) but also formaldehyde fixation artifacts (Pallier et al 2003;Kumar et al 2008). Similar to previous reports on other transcription factors binding to mitotic chromosomes (Pallier et al 2003;Kumar et al 2008;Lerner et al 2016), we were unable to observe mitotic chromosome localization of SOX2 and OCT4 after formaldehyde fixation (data not shown).…”

The homeobox gene Hhex regulates the earliest stages of definitive hematopoiesis

“…40 Evidence from other systems suggest that Mll plays a role in G 2 /M progression, because HeLa cells transfected with an MLL1-antisense-oligoenucletide exhibit an increased percentage of cells in G 2 /M. 41 Analogously, knockdown of Mll5 in HeLa cells resulted in G 2 /M arrest due to increased p21 expression. 42 CD41 ϩ CD45 Ϫ c-kit ϩ and CD41 ϩ CD45 ϩ c-kit ϩ show a statistically significant accumulation of cells in the G 2 phase of the cell cycle, and these observed results suggest that G 2 accumulation by Hhex Ϫ/Ϫ progenitors may in part be due to reduced Mll expression (Table 1; Figure 6).…”

HOXC10 is overexpressed in breast cancer and transcriptionally regulated by estrogen via involvement of histone methylases MLL3 and MLL4

“…Chromatin immunoprecipitation (ChIP) assay was performed using an EZ Chip Chromatin immunoprecipitation kit (Upstate, Billerica, MA, USA) as described previously (Ansari et al 2008, Mishra et al 2009). In brief, estrogen-treated and control cells (JAR) were fixed in 4% formaldehyde, lysed, and sonicated to shear the chromatin.…”