Histone demethylase Kdm4b functions as a co-factor of C/EBPβ to promote mitotic clonal expansion during differentiation of 3T3-L1 preadipocytes

CCAAT/enhancer-binding protein (C/EBP) beta is required for both mitotic clonal expansion (MCE) and terminal adipocyte differentiation of 3T3-L1 preadipocytes. Although the role of C/EBP beta in terminal adipocyte differentiation is well defined, its mechanism of action during MCE is not. In this report, histone demethylase Kdm4b, as well as cell cycle genes Cdc45I (cell division cycle 45 homolog), Mcm3 (mini-chromosome maintenance complex component 3), Gins1 (GINS complex subunit 1) and Cdc25c (cell division cycle 25 homolog c), were identified as potential C/EBP beta target genes during MCE by utilizing promoter-wide chromatin immunoprecipitation (ChIP)-on-chip analysis combined with gene expression microarrays. The expression of Kdm4b is induced during MCE and its induction is dependent on C/EBP beta. ChIP, Electrophoretic Mobility Shift Assay (EMSA) and luciferase assay confirmed that the promoter of Kdm4b is bound and activated by C/EBP beta. Knockdown of Kdm4b impaired MCE. Furthermore, Kdm4b interacted with C/EBP beta and was recruited to the promoters of C/EBP beta-regulated cell cycle genes, including Cdc45I, Mcm3, Gins1, and Cdc25c, demethylated H3K9me3 and activated their transcription. These findings suggest a novel feed forward mechanism involving a DNA binding transcription factor (C/EBP beta) and a chromatin regulator (Kdm4b) in the regulation of MCE by controlling cell cycle gene expression. Cell Death and Differentiation (2012) 19, 1917-1927; doi:10.1038/cdd.2012.75; published online 22 June 2012