生长抑素受体在人神经内分泌癌组织中的表达及受体激活对细胞生长的抑制

生长抑素（somatostatin，SST）通过与细胞膜上的G蛋白偶联的生长抑素受体（somatostatin receptors，SSTRs）结合而发挥其抑制细胞增殖的作用，因而生长抑素类似物（somatostatin analogue, SSA）常被用于肿瘤辅助治疗。然而，治疗效果存在相当大的个体差异，推测生长抑素类似物治疗效果不佳，与内源性生长抑素受体表达缺失或者表达量和亚型组合有关。为此，检测各亚型SSTR在几例罕见的神经内分泌肿瘤中的表达，并检测过表达SSTR2和SSTR5以及受体激活对细胞增殖的抑制效果，分析受体激活的可能机制，有助于临床筛选适合SSA肿瘤辅助治疗的病例，预估SSA的治疗效果。免疫组化检测肿瘤组织SSTR1-5的表达。在培养的293T细胞中过表达SSTR2和SSTR5，免疫共沉淀检测受体相互作用，免疫荧光和共聚焦显微镜检测受体细胞内定位。用MTT法检测受体过表达及激活对培养的人肺癌细胞NCI-H460细胞增殖的影响，用流式细胞技术检测细胞周期分布。SSTR1-5在10例神经内分泌肿瘤组织中均有不同程度的表达，表达亚型及表达量与肿瘤类型和年龄无关，SSTR5在所有肿瘤组织中均表达。SSTR2与SSTR5可形成受体相互作用。SSTR2与SSTR5活化后相互作用增加并定位于细胞质。共表达SSTR2和SSTR5显著抑制细胞增殖，并与受体激活剂呈现剂量相关性。SSTR2/SSTR5的共表达及激活显著减少S期的细胞而滞留于G₁期。

Expression of Somatostatin Receptor in Human Neuroendocrine Tumor Tissues and Inhibition of Cell Proliferation Mediated by Receptor Activation

Somatostatin receptors (SSTRs), SSTR1-5, are G-protein coupled plasma membrane receptors that are expressed in various normal and solid tumor tissues including neuroendocine carcinoma. Activation of SSTRs usually results in inhibition of cell proliferation and somatostatin analogues (SSA) have been used in cancer treatment. However, the variable outcomes of SSA treatment were believed to be the consequences of loss-of-expression of SSTRs and/or subtype specific effects. The expression levels of five SSTR subtypes were determined in ten rare neuroendocrine tumors using immunohistochemical staining. Futhermore, HA-SSTR2 and MYC-SSTR5 were transiently overexpressed in cultured 293T cells. Co-immunoprecipitation and immunofluorescence were used to test potential interaction between SSTR2 and SSTR5 and their cellular localization. Cell proliferation was analyzed using MTT assay. Flow cytometry was used to monitor the influence of SSTR2 and SSTR5 expression/activation on cell proliferation. All five SSTR subtypes were expressed at variable levels in tumor tissues and SSTR5 was expressed in all samples. The expression of SSTRs was not correlated with the patient age, histological type or the staging of cancer. The interaction of SSTR2/SSTR5 was elevated and the receptors translocated into cytoplasm in respond to activation using octreotide. The proliferation of cultured NCI-H460 cells was significantly inhibited by overexpression of SSTR2/SSTR5 and was further inhibited when SSTR2/SSTR5 was activated by octreotide. Overexpression and activation of SSTR2 and SSTR5 resulted in S-phase inhibition and G₁-phase arrest in NCI-H460 cells.