Isoform-specific Intermolecular Disulfide Bond Formation of Heterochromatin Protein 1 (HP1)

Shuichiro Higo,Yoshihiro Asano,Hisakazu Kato,Satoru Yamazaki,Atsushi Nakano,Osamu Tsukamoto,Osamu Seguchi,Mitsutoshi Asai,Masanori Asakura,Hiroshi Asanuma,Shoji Sanada,Tetsuo Minamino,Issei Komuro,Masafumi Kitakaze,Seiji Takashima

doi:10.1074/jbc.m110.155788

Abstract

Three mammalian isoforms of heterochromatin protein 1 (HP1), α, β, and γ, play diverse roles in gene regulation. Despite their structural similarity, the diverse functions of these isoforms imply that they are additionally regulated by post-translational modifications. Here, we have identified intermolecular disulfide bond formation of HP1 cysteines in an isoform-specific manner. Cysteine 133 in HP1α and cysteine 177 in HP1γ were involved in intermolecular homodimerization. Although both HP1α and HP1γ contain reactive cysteine residues, only HP1γ readily and reversibly formed disulfide homodimers under oxidative conditions. Oxidatively dimerized HP1γ strongly and transiently interacted with TIF1β, a universal transcriptional co-repressor. Under oxidative conditions, HP1γ dimerized and held TIF1β in a chromatin component and inhibited its repression ability. Our results highlight a novel, isoform-specific role for HP1 as a sensor of the cellular redox state.

Highlights

Heterochromatin protein 1 (HP1) was originally characterized as an abundant protein that binds pericentric heterochromatin [1]
HP1␣ Forms Dimers via Disulfide Bonds through Cysteine 133—During purification of HP1␣ in our previous work [24], we found that endogenous HP1␣ separates into two peaks by fractionation using reverse-phase HPLC
We identified isoform-specific disulfide bond formation, which is a novel post-translational modification of HP1, using a unique column chromatography method

Summary

Introduction

Heterochromatin protein 1 (HP1) was originally characterized as an abundant protein that binds pericentric heterochromatin [1]. E, equal quantities of cytosolic and nuclear fractions from HEK293T cells expressing HP1␣-FLAG were resolved by SDS-PAGE and probed with the indicated antibodies. F, nuclear extract from HEK293T cells expressing HP1␣-FLAG was directly applied to a reverse-phase column, and the eluted fractions were resolved by reducing SDS-PAGE and probed with the indicated antibodies.

Results

Conclusion