IKK Regulates Histone Methyltransferase G9a to Promote Cancer Progression
Date Issued
2014
Date
2014
Author(s)
Lei, Kai-Hang
Abstract
G9a, also known as EHMT2, is a histone H3 lysine 9 methyltransferase, has been observed overexpression in various human cancers and contributes to the epigenetic silencing of tumor suppressor genes to promote cancer progression. Post-translational modification (PTM) is very important to regulate protein function. It has been shown that several epigenetic regulators were regulated by different PTMs. The post translational modification that regulates function of G9a had not been reported yet, therefore it is necessary to investigate the PTM of G9a. Interestingly, from the bioinformatics prediction, we found that G9a contains IKKa/b consensus phosphorylation site, suggesting a possible interaction between IKKa/b and G9a.
In this study, we used the co-immunoprecipitation in 293T cells, MCF-7 and BT549 breast cancer cells and GST pull down assay to prove that G9a interacted with IKKa and b in vivo and in vitro. By using in vitro kinase assay, we proved that G9a can be phosphorylated by both IKKa and b. To investigate the regulation of G9a by IKKa/b, we overexpressed IKKa/b in 293T cells and found the protein expression level of G9a was increased but not the RNA level. It suggested that IKKa/b may regulate the translation activity or protein stability of G9a. For this reason, we added cycloheximide in 293T cells to examine the half-life of G9a. The cells with overexpression of IKKa/b can prolong the half-life of G9a, on the contrary, knockdown of IKKa/b decreased G9a protein level in MCF-7 cells. Furthermore, the cytokine IL-1b can also enhance the protein level of G9a in MCF-7 cells, suggesting that the kinase activity of IKKa/b regulated protein stability of G9a. Knockdown of IKKa/b in MCF-7 cells inhibited cell growth, decreased migration and invasion ability, and increased the RNA level of the genes that suppressed by G9a.
G9a had played an important role in cancer progression, this study reveals that IKKa/b can phosphorylate G9a to promote cancer progression. Targeting IKK and G9a in the cancer patients with G9a overexpression may potentially enhance the therapeutic efficacy in the future.
Subjects
IKK
組蛋白甲基轉移酶 G9a
SDGs
Type
thesis
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