Mutant Genetic Background Affects the Functional Rearrangement and Kinetic Properties of JMJD2b Histone Demethylase

Abstract

We have studied JMJD2b histone demethylase, which antagonizes H3K9me3 in the pericentromeric heterochromatin. In cells with a deficiency in the histone methyltransferase SUV39h, the level of full-length JMJD2b (JMJD2b-GFP-1086) at chromocenters was reduced, corresponding to a global decrease in JMJD2b and H3K9me3. In wild-type fibroblasts, the chromatin of ribosomal genes, which is dense with H3K9 methylation, lacked JMJD2b-GFP-1086, while mutant and truncated forms of JMJD2b densely occupied the nucleolar compartment. This implies that the PHD Zn-fingers and Tudor domains, which were removed in truncated JMJD2b, are responsible for the aberrant JMJD2b function. Intriguingly, the JMJD2b-GFP-1086 level was significantly higher in tumor cell nucleoli. The kinetic properties of JMJD2b-GFP-1086 in the nucleoli and nucleoplasm of normal and tumor cells were similar; ∼50% recovery of prebleached intensity was reached after <1 s. However, the mobile fraction of JMJD2b-GFP-1086 was increased in SUV39h-deficient cells. Similarly, the mobile fractions of mutant JMJD2b(1–424)H189A-GFP and truncated JMJD2b(1–424)GFP were greater than that measured for the full-length protein. We suggest that nucleoli are the site of an aberrant function of JMJD2b, the kinetic properties of which can be influenced by a mutant genetic background.