STAT3在SAMe抑制HepG2细胞VEGF表达中的作用

Role of STAT3 in Inhibition of VEGF by S-Adenosylmethionine in HepG2

目的研究肝癌细胞(HepG2)和正常胎肝细胞(CL-48)血管内皮生长因子(VEGF)和信号转导与转录激活因子3(STAT3)的表达状态,以及S-腺苷甲硫氨酸(SAM e)对其的干预作用,为HepG2和CL-48的不同调控途径提供功能性依据。方法在对数生长期的CL-48和HepG2细胞中加入不同浓度的SAM e(0、0.5、1.0 mmol/L)作用72 h,分别采用Northern印迹法、实时荧光定量PCR、W estern印迹法以及[3H]胸腺嘧啶脱氧核苷掺入法(3H-Tdr)和细胞克隆形成法,观察VEGF和STAT3表达的变化趋势,分析DNA合成及细胞生长能力的变化。结果SAM e作用前(SAM e 0 mmol/L),HepG2和CL-48均呈现VEGF和STAT3高表达状态。SAM e作用后:HepG2的VEGF和STAT3表达明显降低,并呈现剂量-效应关系,DNA合成和细胞生长能力明显受限;CL-48的STAT3表达虽然受到抑制,但VEGF的高表达状态无明显降低趋势,且DNA合成和细胞生长能力无显著变化。结论虽然HepG2和CL-48均呈现VEGF和STAT3的高表达,但二者具有不同的调控途径;SAM e通过抑制STAT3的组成性活化而降低VEGF的高表达状态,可能是SAM e的肝脏保护机制之一。

Objective To compare the expression of vascular endothelial growth factor（VEGF） and signal transducers and activators of transcription-3 （ STAT3 ） in HepG2 and CL-48, to evaluate the effect of S-adenosylmethionine （SAMe） on them, and to find out the different regulation mechanism of HepG2 and CL-48. Methods VEGF expression in HepG2 and CL-48 were detected using Northern blot and real time PCR. 3H-TdR uptake and colony formation were employed to analyze DNA synthesis and cell growth ability after SAMe administration. The tendency of STAT3 was estimated using Western blot before and after SAMe administration. Results High level of VEGF and STAT3 were identified in HepG2 and CL-48. Remarkable decrease of VEGF and STAT3 were observed in HepG2 after SAMe administration in a dose dependent manner with inhibition of DNA synthesis and cell growth ability. Although STAT3 expression was decreased, VEGF remained relatively high level after SAMe without DNA synthesis and change of cell growth ability. Conclusion In spite of high expression level in HepG2 and CL-48, they may have different regulation mechanism. SAMe could inhibit phosphorylation of STAT3, consequently influence VEGF expression.The transcription regulation by STAT3 may be considered as a novel mechanism in SAMe-mediated hepato-protection.Down-regulation of VEGF after SAMe treatment makes it possible for SAMe to be used as chemoprevention agent in hepatocellular carcinoma.