Ras-PI3K信号负性调节的H3K56乙酰化促进乳腺癌细胞MCF-7的增殖和迁移能力

Ras蛋白常见的第12、13氨基酸残基突变引起的Ras信号通路异常与人类恶性肿瘤发生相关。然而，Ras致瘤信号通路是否涉及表观遗传学因素尚不明了。本研究旨在阐明人乳腺癌MCF-7细胞中组蛋白H3第56位赖氨酸残基乙酰化修饰（H3K56ac）水平是否受Ras信号通路调控，以及H3K56ac水平对MCF-7细胞增殖和迁移能力的影响。点突变结合基因转染揭示，与野生型比较，第12位氨基酸突变的Ras质粒（pEGFP-H-RasG12V）转染导致MCF-7细胞内H3K56ac水平明显降低。采用可特异激活Ras下游3条通路（Ras-Raf、Ras-RalGEF和Ras-PI3K）的3种质粒（pEGFP-H-RasG12V T35S，pEGFP-H-RasG12V E37G和pEGFP-H-RasG12V Y40C）转染证明，只有转染pEGFP-H-RasG12V Y40C的MCF-7细胞内不仅有Ras-PI3K-AKT通路被激活，且与H3K56ac水平下调相伴；而其他两条通路的激活不影响H3K56ac水平。MTT法结合Transwell、软琼脂克隆形成能力实验证明，RasG12V Y40C转染增强细胞增殖、迁移和克隆形成能力。上述结果表明，MCF-7细胞中H3K56ac水平受Ras-PI3K通路的负性调控，但不受Raf和RalGEF通路影响。Ras-PI3K激活导致的H3K56ac水平降低可增强乳腺癌MCF-7细胞的增殖和迁移能力。总之，这些结果提示，组蛋白H3K56ac是Ras-PI3K致瘤信号通路中的重要成员。Ras信号通路与组蛋白修饰相结合研究将会加深对乳腺癌细胞增殖和迁移调控机制的认识。

H3K56ac Negatively Regulated by Ras-PI3K Pathway Promotes Proliferation and Invasion Abilities of MCF-7 Breast Cancer Cells

The deregulation of Ras signaling pathway is associated with tumorigenesis when the most common mutations at the codons for amino acids 12 and 13 of Ras protein occur. However, less is known about the involvement of epigenetic factor(s) in Ras mediated tumorigenesis. This study aims to clarify that if the acetylation of histone H3 at lysine 56 (H3K56ac) in human breast cancer MCF-7 cells is regulated by Ras signaling, and the effect of H3K56 acetylation on proliferation and migration abilities of MCF-7 cells. Point mutation and transfection revealed that the levels of acetyl-H3K56 in mutated Ras (pEGFP-H-RasG12V) transfected MCF-7 cells were significantly reduced. Moreover, the down-regulation of H3K56 acetylation was detected in the pEGFP-H-RasG12V Y40C transfected MCF-7 cells where Ras-PI3K (phosphatidylinositol-3-kinase) signaling was activated, but not in pEGFP-H-RasG12V T35S or pEGFP-H-RasG12V E37G transfected cells where Ras-Raf or Ras-RalGEF (Ral guanine nucleotide exchange factors) signaling was activated. MTT, transwell and soft agar colony formation assays showed that pEGFP-H-RasG12VY40C transfection enhanced the proliferation and migration abilities of MCF-7 cells. Together, these data indicated that H3K56 acetylation was negatively regulated by Ras-PI3K signaling pathway, but not Ras-Raf and Ras-RalGEF pathways. Down-regulation of H3K56ac by Ras-PI3K activation may promote the proliferation and migration abilities of MCF-7 breast cancer cells. These data also suggested that acetylation of H3K56ac was a critical component of Ras-PI3K pathway, which may deepen our understanding of the crosstalk of Ras signaling and histone modifications in the mechanisms of proliferation and migration of breast cancer.