Saha Kamalika, Eckert Richard L
From the Departments of Biochemistry and Molecular Biology.
From the Departments of Biochemistry and Molecular Biology, Dermatology, and Obstetrics and Gynecology and the Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, Maryland 21201
J Biol Chem. 2015 May 22;290(21):13521-30. doi: 10.1074/jbc.M115.642868. Epub 2015 Apr 7.
Protein arginine methyltransferase 5 (PRMT5) is a key epigenetic regulator that symmetrically dimethylates arginine residues on histones H3 and H4 to silence gene expression. PRMT5 is frequently observed in a complex with the cofactor methylosome protein 50 (MEP50), which is required for PRMT5 activity. PKCδ/p38δ signaling, a key controller of keratinocyte proliferation and differentiation, increases p21(Cip1) expression to suppress keratinocyte proliferation. We now show that MEP50 enhances keratinocyte proliferation and survival via mechanisms that include silencing of p21(Cip1) expression. This is associated with enhanced PRMT5-MEP50 interaction at the p21(Cip1) promoter and enhanced arginine dimethylation of the promoter-associated histones H3 and H4. It is also associated with a MEP50-dependent reduction in the level of p53, a key controller of p21(Cip1) gene expression. We confirm an important biological role for MEP50 and PRMT5 in regulating keratinocyte proliferation using a stratified epidermal equivalent model that mimics in vivo epidermal keratinocyte differentiation. In this model, PRMT5 or MEP50 knockdown results in reduced keratinocyte proliferation. We further show that PKCδ/p38δ signaling suppresses MEP50 expression, leading to reduced H3/H4 arginine dimethylation at the p21(Cip1) promoter, and that this is associated with enhanced p21(Cip1) expression and reduced cell proliferation. These findings describe an opposing action between PKCδ/p38δ MAPK signaling and PRMT5/MEP50 epigenetic silencing mechanisms in regulating cell proliferation.
蛋白质精氨酸甲基转移酶5（PRMT5）是一种关键的表观遗传调节因子，可使组蛋白H3和H4上的精氨酸残基发生对称二甲基化，从而使基因表达沉默。PRMT5常与辅因子甲基osome蛋白50（MEP50）形成复合物，MEP50是PRMT5活性所必需的。PKCδ/p38δ信号通路是角质形成细胞增殖和分化的关键调控因子，它通过增加p21（Cip1）的表达来抑制角质形成细胞的增殖。我们现在发现，MEP50通过包括沉默p21（Cip1）表达在内的机制增强角质形成细胞的增殖和存活。这与p21（Cip1）启动子处PRMT5-MEP50相互作用增强以及启动子相关组蛋白H3和H4的精氨酸二甲基化增强有关。它还与MEP50依赖的p53水平降低有关，p53是p21（Cip1）基因表达的关键调控因子。我们使用模拟体内表皮角质形成细胞分化的分层表皮等效模型，证实了MEP50和PRMT5在调节角质形成细胞增殖中的重要生物学作用。在该模型中，PRMT5或MEP50基因敲低导致角质形成细胞增殖减少。我们进一步表明，PKCδ/p38δ信号通路抑制MEP50表达，导致p21（Cip1）启动子处H3/H4精氨酸二甲基化减少，这与p21（Cip1）表达增强和细胞增殖减少有关。这些发现描述了PKCδ/p38δ MAPK信号通路与PRMT5/MEP50表观遗传沉默机制在调节细胞增殖中的相反作用。
