Inactivation of tumor suppressor Runt-related transcription factor 3 (RUNX3) plays an important role during early tumorigenesis. However, posttranslational modifications (PTM)-based mechanism for the inactivation of RUNX3 under hypoxia is still not fully understood. Here, we demonstrate a mechanism that G9a, lysine-specific methyltransferase (KMT), modulates RUNX3 through PTM under hypoxia. Hypoxia significantly increased G9a protein level and G9a interacted with RUNX3 Runt domain, which led to increased methylation of RUNX3 at K129 and K171. This methylation inactivated transactivation activity of RUNX3 by reducing interactions with CBFβ and p300 cofactors, as well as reducing acetylation of RUNX3 by p300, which is involved in nucleocytoplasmic transport by importin-α1. G9a-mediated methylation of RUNX3 under hypoxia promotes cancer cell proliferation by increasing cell cycle or cell division, while suppresses immune response and apoptosis, thereby promoting tumor growth during early tumorigenesis. Our results demonstrate the molecular mechanism of RUNX3 inactivation by G9a-mediated methylation for cell proliferation and antiapoptosis under hypoxia, which can be a therapeutic or preventive target to control tumor growth during early tumorigenesis.

肿瘤抑制因子 Runt 相关转录因子 3 (RUNX3) 的失活在早期肿瘤发生过程中起重要作用。然而，基于翻译后修饰 (PTM) 的 RUNX3 在缺氧条件下失活的机制仍不完全清楚。在这里，我们展示了 G9a 赖氨酸特异性甲基转移酶 (KMT) 在缺氧条件下通过 PTM 调节 RUNX3 的机制。缺氧显着增加了 G9a 蛋白水平，并且 G9a 与 RUNX3 Runt 结构域相互作用，导致 RUNX3 在 K129 和 K171 的甲基化增加。这种甲基化通过减少与 CBFβ 和 p300 辅因子的相互作用，以及减少 p300 对 RUNX3 的乙酰化（通过 importin-α1 参与核质转运）来灭活 RUNX3 的反式激活活性。缺氧条件下 G9a 介导的 RUNX3 甲基化通过增加细胞周期或细胞分裂来促进癌细胞增殖，同时抑制免疫反应和细胞凋亡，从而在早期肿瘤发生过程中促进肿瘤生长。我们的研究结果证明了 G9a 介导的甲基化使 RUNX3 失活在缺氧条件下细胞增殖和抗凋亡的分子机制，这可以作为早期肿瘤发生过程中控制肿瘤生长的治疗或预防靶点。