The influence of WD40 domain and JMJC domain proteins on histone H3 lysine 4 methylation and gene expression.

Douglas Patrick Mersman, Purdue University

Abstract

The identification of histone methyltransferase complexes and histone demethylases has uncovered a dynamic methylation system that is needed to modulate appropriate levels of gene expression. The observations that histone methyltransferases and demethylases play important roles in the appropriate expression of developmental genes such as the HOX gene clusters and that demethylases have distinct patterns of embryonic and adult expression highlight their importance not only in proper development but also in human disease. Indeed, recent work has implicated these enzymes not in only a variety of cancers, including leukemia and breast cancer, but also in other diseases ranging from X-linked mental retardation to obesity. Despite the importance of histone methyltransferase complexes and histone demethylases, how they are regulated is only beginning to be explored. Furthermore, the functions of the various members of histone methyltransferase complexes and how they interact have not yet been completely described. My studies concerning Jhd2p, a JmjC domain-containing histone demethylase, and Swd1p, a WD40 domain-containing member of the Set1 histone H3 lysine 4 (H3 K4) methyltransferase complex seeks to shed light on these questions. They reveal that Jhd2p protein levels are tightly controlled through ubiquitin-mediated degradation and that Not4p is the E3 ubiquitin ligase responsible for ubiquitination of Jhd2p. Loss of Not4p results in increased levels of Jhd2p and a corresponding decrease in H3 K4 trimethylation, leading to defects in gene expression. Importantly, the human homolog of Not4p is able to ubiquitinate the human homolog of Jhd2p in vitro, suggesting that this may be a conserved mechanism of regulating the activity of histone demethylases. In addition, my studies show that Swd1p is important for mono-, di-, and trimethylation of H3 K4 as well as for Set1p protein stability. Furthermore, I show that Swd1p and Set1p can interact through a series of acidic residues in the C-terminus of Swd1p and a series of basic residues in the nSet domain of Set1p. Loss of either the acidic patches of Swd1p or the basic patch of Set1p disrupts the Swd1p/Set1p interaction in vitro and results in loss of H3 K4 methylation and Set1p protein levels in vivo. These studies, therefore, provide new insight into both a novel regulatory mechanism of histone demethylation by JmjC domain-containing proteins as well as the importance of WD40 domain-containing proteins in H3 K4 methylation.

Degree

Ph.D.

Advisors

Briggs, Purdue University.

Subject Area

Molecular biology|Genetics

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