Mitsiades N, Poulaki V, Tseleni-Balafouta S, Koutras D A, Stamenkovic I
Massachusetts General Hospital, Harvard Medical School, Charlestown 02129, USA.
Cancer Res. 2000 Aug 1;60(15):4122-9.
Fas (APO-1/CD95) is a transmembrane protein of the tumor necrosis factor (TNF)/nerve growth factor receptor superfamily that induces apoptosis in susceptible normal and neoplastic cells upon cross-linking by its ligand (FasL). TNF-related apoptosis-inducing ligand (TRAIL) is a more recently identified member of the TNF superfamily that has been shown to selectively kill neoplastic cells by engaging two cell-surface receptors, DR4 and DR5. Two additional TRAIL receptors (DcR1 and DcR2) do not transmit an apoptotic signal and have been proposed to confer protection from TRAIL-induced apoptosis. We addressed the expression of Fas, DR4, and DR5 in thyroid carcinoma cell lines and in 31 thyroid carcinoma specimens by Western blot analysis and immunohistochemistry, respectively, and tested the sensitivity of thyroid carcinoma cell lines to Fas- and TRAIL-induced apoptosis. Fas was found to be expressed in most thyroid carcinoma cell lines and tissue specimens. Although cross-linking of Fas did not induce apoptosis in thyroid carcinoma cell lines, Fas-mediated apoptosis did occur in the presence of the protein synthesis inhibitor cycloheximide, suggesting the presence of a short-lived inhibitor of the Fas pathway in these cells. Cross-linking of Fas failed to induce recruitment and activation of caspase 8, whereas transfection of a constitutively active caspase 8 construct effectively killed the SW579 papillary carcinoma cell line, arguing that the action of the putative inhibitor occurs upstream of caspase 8. By contrast, recombinant TRAIL induced apoptosis in 10 of 12 thyroid carcinoma cell lines tested, by activating caspase-10 at the receptor level and triggering a caspase-mediated apoptotic cascade. Resistance to TRAIL did not correlate with DcR1 or DcR2 protein expression and was overcome by protein synthesis inhibition in 50% of the resistant cell lines. One medullary carcinoma cell line was resistant to Fas-and TRAIL-induced apoptosis, even in the presence of cycloheximide, and to transfection of constitutively active caspase-8, suggesting a different regulation of the apoptotic pathway. Our observations indicate that TRAIL effectively kills carcinomas that originate from the follicular epithelium of the thyroid gland, by inducing caspase-mediated apoptosis, and may provide a potentially potent therapeutic reagent against thyroid cancer.
Fas（APO-1/CD95）是肿瘤坏死因子（TNF）/神经生长因子受体超家族的一种跨膜蛋白，在被其配体（FasL）交联后可诱导敏感的正常细胞和肿瘤细胞发生凋亡。肿瘤坏死因子相关凋亡诱导配体（TRAIL）是TNF超家族中最近发现的成员，已证明它通过与两种细胞表面受体DR4和DR5结合来选择性杀伤肿瘤细胞。另外两种TRAIL受体（DcR1和DcR2）不传递凋亡信号，有人提出它们可提供对TRAIL诱导凋亡的保护作用。我们分别通过蛋白质印迹分析和免疫组织化学方法研究了Fas、DR4和DR5在甲状腺癌细胞系及31例甲状腺癌标本中的表达情况，并检测了甲状腺癌细胞系对Fas和TRAIL诱导凋亡的敏感性。发现大多数甲状腺癌细胞系和组织标本中均有Fas表达。虽然Fas交联未诱导甲状腺癌细胞系发生凋亡，但在存在蛋白质合成抑制剂环己酰亚胺的情况下，Fas介导的凋亡确实发生了，这表明这些细胞中存在一种Fas途径的短寿命抑制剂。Fas交联未能诱导半胱天冬酶8的募集和激活，而转染组成型活性半胱天冬酶8构建体可有效杀死SW579乳头状癌细胞系，这表明假定抑制剂的作用发生在半胱天冬酶8的上游。相比之下，重组TRAIL通过在受体水平激活半胱天冬酶-10并触发半胱天冬酶介导的凋亡级联反应，在12种受试甲状腺癌细胞系中的10种中诱导了凋亡。对TRAIL的抗性与DcR1或DcR2蛋白表达无关，并且在50%的抗性细胞系中通过蛋白质合成抑制得以克服。一种髓样癌细胞系对Fas和TRAIL诱导的凋亡具有抗性，即使在存在环己酰亚胺的情况下也是如此，并且对组成型活性半胱天冬酶-8的转染也具有抗性，这表明凋亡途径存在不同的调节机制。我们的观察结果表明，TRAIL通过诱导半胱天冬酶介导的凋亡有效地杀死源自甲状腺滤泡上皮的癌，并可能为甲状腺癌提供一种潜在的有效治疗试剂。
