转化生长因子-β／Smads信号通路在奥曲肽抑制大鼠肝癌形成中的作用

The role of TGF-β1/Smads signaling pathway during OCT-inhibiting hepatocarcinogenesis

目的观察转化生长因子-β（TGF—β）／Smads信号通路在生长抑素类似物奥曲肽（OCT）抑制大鼠肝癌形成中的作用。方法用二乙基亚硝胺溶液（DENA）诱导大鼠肝癌模型，动物分为OCT治疗组和对照组两组，观察两组大鼠存活情况和肝癌发生率，并用免疫组织化学的方法检测肝癌诱导不同时期磷酸化Smad2、Smad4蛋白的表达，半定量逆转录一聚合酶链反应（RT—PCR）检测Smad4mRNA的表达。结果OCT组大鼠的存活率70．0％（7／10）明显高于对照组30．0％（6／20，P〈0．05）；DENA喂养16周时，OCT组大鼠的肝癌发生为0只（0／10），对照组为6只（6／20），但两组比较差异无统计学意义（P〉0．05）；DENA喂养22周时，OCT组肝癌的发生（2／9）显著低于对照组（10／12，P〈0．01）。正常细胞时Smad4很少表达，随着肝硬化的发展，表达明显增强，但DENA喂养22周时肝组织Smad4表达明显下降，肝癌的表达显著低于周边组织（P〈0．05）；磷酸化Smad2的表达可见于正常肝细胞，但诱癌8周时表达明显减少，16、22周时又恢复至正常水平，但肿瘤内表达明显减少；OCT的治疗组诱癌22周的Smad4蛋白和mRNA的表达均显著高于对照组，而磷酸化Smad2的表达两组差异无统计学意义（P〉0．05）。结论Smad4和磷酸化Smad2表达的减少与肝癌的发生关系密切。OCT能有效抑制大鼠肝癌形成，Smad4表达的调节可能是OCT发挥抑癌作用的机制之一。

Objective To investigate the role of TGFβ1/Smads signaling pathway during OCT-in- hibiting hepatocarcinogenesis. Methods Fresh diethylnitrosamine （DENA） solution was given to induce the model of rat hepatocellular carcinoma. The rats were divided into two groups ： OCT treatment group and control group. The survival rate and hepatocarcinogenesis rate were observed. The expression of Smad4 and Phospho-Smad2 proteins were measured by immunohistochemistry. The expression of Smad4 mRNA was de- tected by semi-quantitative RT-PCR. Results The survival rate of OCT treatment group （70.0%, 7/10） was significantly higher than that of control group （30.0%, 6/20, P 〈 0.05 ）. Sixteen weeks after DENA treatment,the difference in hepatocarcinogenesis rate between two groups was not remarkable though liver tumor didn＇ t occur in OCT treatment group （0/10）, and liver tumors were found in 6 rats of control groups （6/20,P 〉 0.05 ）. However, 22 weeks after DENA treatment, hepatocarcinogenesis rate in control group （10/12） was markedly higher than that in OCT treatment group （2/9,P 〈0.01 ）. With development of liver cirrhosis, the expression levels of Smad4 mRNA and protein were increased, and reached the peak at the 16th week after DENA treatment,then began to decrease significantly. The expression of Smad4 mRNA and protein in hepatocellular carcinoma was significantly lower than that in the liver 22 weeks after DENA treatment （ P 〈 0.05 ）. The cells positive for phospho-Smad2 in normal liver were abundant, however,its expression was reduced markedly 8 weeks after DENA treatment. Sixteen and 22 weeks after DENA treatment,its expression was increased and approached the normal level. Nevertheless, the expression of Smad4 in tumors was lower significantly than that at 8th week after DENA treatment. The Smad4 expression in OCT group 22 weeks after DENA treatment was higher significantly than that in control group （P 〈 0.05 ）. Though phospho-Smad2 ex- pression in OCT treatment group was higher than in control group, the difference was not significant. Conclu- sion The decrease of Smad4 and phospho-SInad2 expression is related to hepatocarcinogenesis. The mechanism of OCT-inhibiting hepatocarcinogenesis may be due to the upregulation of Smad4.