Division of Medicinal Chemistry, College of Pharmacy, University of Texas, Austin, Texas 78712, USA.
J Biol Chem. 2011 May 13;286(19):17069-78. doi: 10.1074/jbc.M111.230961. Epub 2011 Mar 22.
Gene expression is regulated by a number of interrelated posttranslational modifications of histones, including citrullination. For example, peptidylarginine deminase 4 (PAD4) converts peptidyl arginine to citrulline in histone H3 and can repress gene expression. However, regulation of gene expression through citrullination of non-histone proteins is less well defined. Herein, we identify a tumor suppressor protein, inhibitor of growth 4 (ING4), as a novel non-histone substrate of PAD4. ING4 is known to bind p53 via its nuclear localization signal (NLS) region and to enhance transcriptional activity of p53. We show that PAD4 preferentially citrullinates ING4 in the same NLS region and thereby disrupts the interaction between ING4 and p53. A citrulline-mimicking Arg-NLS-Gln ING4 mutant, which has all Arg residues in the NLS mutated to Gln, loses its affinity for p53, can no longer promote p53 acetylation, and results in repression of downstream p21 expression. In addition, we found that citrullination leads to increased susceptibility of ING4 to degradation, likely impacting p53-independent pathways as well. These findings elucidate an interaction between posttranslational citrullination, acetylation, and methylation and highlight an unusual mechanism whereby citrullination of a non-histone protein impacts gene regulation.
基因表达受组蛋白多种相互关联的翻译后修饰调控，包括瓜氨酸化。例如，肽基精氨酸脱亚氨酶 4（PAD4）将肽基精氨酸转化为组蛋白 H3 中的瓜氨酸，可抑制基因表达。然而，通过非组蛋白蛋白的瓜氨酸化来调节基因表达的机制尚未明确。在此，我们发现肿瘤抑制蛋白 4（ING4）是 PAD4 的一种新型非组蛋白底物。ING4 已知通过其核定位信号（NLS）区域与 p53 结合，并增强 p53 的转录活性。我们表明，PAD4 优先在相同的 NLS 区域瓜氨酸化 ING4，从而破坏 ING4 与 p53 之间的相互作用。一个瓜氨酸模拟的 Arg-NLS-Gln ING4 突变体，其中 NLS 中的所有 Arg 残基突变为 Gln，失去与 p53 的亲和力，不能再促进 p53 的乙酰化，导致下游 p21 表达受到抑制。此外，我们发现瓜氨酸化导致 ING4 更容易降解，可能也会影响非 p53 依赖的途径。这些发现阐明了翻译后瓜氨酸化、乙酰化和甲基化之间的相互作用，并强调了一种非典型机制，即非组蛋白蛋白的瓜氨酸化会影响基因调控。
