Robb Victoria A, Astrinidis Aristotelis, Henske Elizabeth P
Fox Chase Cancer Center, Philadelphia, PA 19111, USA.
Mod Pathol. 2006 Jun;19(6):839-46. doi: 10.1038/modpathol.3800610.
Lymphangioleiomyomatosis is a progressive lung disease characterized by a diffuse proliferation of pulmonary smooth muscle cells and cystic degeneration. Lymphangioleiomyomatosis can occur either independently of other disease or in association with tuberous sclerosis complex, a tumor-suppressor gene syndrome caused by mutations that inactivate either TSC1 or TSC2. TSC2 mutations and loss of heterozygosity have been identified in sporadic lymphangioleiomyomatosis-associated angiomyolipomas, thus implicating the TSC/Ras homolog-enriched in brain (Rheb)/mammalian target of Rapamycin (mTOR)/p70 S6 kinase signaling pathway in their pathogenesis. This study was undertaken to determine whether the mTOR/p70 S6 kinase signaling pathway is activated in lymphangioleiomyomatosis-associated angiomyolipomas lacking TSC1/TSC2 loss of heterozygosity. Phospho-ribosomal protein S6 (Ser235/236) immunohistochemistry was performed on five lymphangioleiomyomatosis-associated angiomyolipomas, two matched lymphangioleiomyomatosis pulmonary samples, and three sporadic angiomyolipomas. TSC1/TSC2 loss of heterozygosity was previously excluded in these angiomyolipomas. Moderate or strong phospho-ribosomal protein S6 immunoreactivity was found in all lymphangioleiomyomatosis-associated and sporadic angiomyolipomas, suggesting a high incidence of mTOR/p70 S6 kinase signaling pathway activation despite a lack of TSC1/TSC2 loss of heterozygosity. Focally positive phospho-S6 staining was also evident in both lymphangioleiomyomatosis pulmonary samples. We hypothesized that this S6 hyperphosphorylation could reflect mutational activation of Rheb or Rheb-like protein (RhebL1), Ras family members which directly activate mTOR. Mutational analysis performed on DNA from these eight angiomyolipomas plus five additional sporadic angiomyolipomas did not reveal mutations in exons 3 and 4 (homologous sites of Ras activating mutations) of either Rheb or RhebL1. These data suggest that activation of the Rheb/mTOR/p70 S6 kinase pathway is related to the pathogenesis of lymphangioleiomyomatosis-associated and sporadic angiomyolipomas lacking TSC1/TSC2 loss of heterozygosity. This high incidence of mTOR signaling pathway activation suggests that treatment with mTOR inhibitors, such as Rapamycin, may benefit patients with angiomyolipomas independent of the detection of TSC1/TSC2 loss of heterozygosity.
淋巴管平滑肌瘤病是一种进行性肺部疾病，其特征为肺平滑肌细胞的弥漫性增殖和囊性退变。淋巴管平滑肌瘤病可独立于其他疾病发生，也可与结节性硬化症相关，后者是一种由TSC1或TSC2失活突变引起的肿瘤抑制基因综合征。在散发性淋巴管平滑肌瘤病相关的血管平滑肌脂肪瘤中已鉴定出TSC2突变和杂合性缺失，这表明TSC/富含脑的Ras同源物（Rheb）/雷帕霉素哺乳动物靶标（mTOR）/p70 S6激酶信号通路在其发病机制中起作用。本研究旨在确定在缺乏TSC1/TSC2杂合性缺失的淋巴管平滑肌瘤病相关血管平滑肌脂肪瘤中，mTOR/p70 S6激酶信号通路是否被激活。对5例淋巴管平滑肌瘤病相关血管平滑肌脂肪瘤、2例匹配的淋巴管平滑肌瘤病肺组织样本和3例散发性血管平滑肌脂肪瘤进行了磷酸化核糖体蛋白S6（Ser235/236）免疫组化检测。这些血管平滑肌脂肪瘤先前已排除TSC1/TSC2杂合性缺失。在所有淋巴管平滑肌瘤病相关和散发性血管平滑肌脂肪瘤中均发现中度或强磷酸化核糖体蛋白S6免疫反应性，这表明尽管缺乏TSC1/TSC2杂合性缺失，但mTOR/p70 S6激酶信号通路激活的发生率较高。在淋巴管平滑肌瘤病肺组织样本中也可见局灶性阳性磷酸化S期激酶相关蛋白2（p-S6）染色。我们推测这种S6过度磷酸化可能反映了Rheb或Rheb样蛋白（RhebL1）的突变激活，Rheb或RhebL1是直接激活mTOR的Ras家族成员。对这8例血管平滑肌脂肪瘤以及另外5例散发性血管平滑肌脂肪瘤的DNA进行的突变分析未发现Rheb或RhebL1外显子3和4（Ras激活突变的同源位点）存在突变。这些数据表明，Rheb/mTOR/p70 S6激酶通路的激活与缺乏TSC1/TSC2杂合性缺失的淋巴管平滑肌瘤病相关和散发性血管平滑肌脂肪瘤的发病机制有关。mTOR信号通路激活的高发生率表明，使用mTOR抑制剂（如雷帕霉素）进行治疗可能使血管平滑肌脂肪瘤患者受益，而与TSC1/TSC2杂合性缺失的检测无关。
