Moraitis Dimitrios, Karanikou Maria, Liakou Chryssa, Dimas Konstantinos, Tzimas George, Tseleni-Balafouta Sofia, Patsouris Efstratios, Rassidakis George Z, Kouvaraki Maria A
Department of Surgery, Hygeia Hospital, Athens, Greece.
First Department of Pathology, National and Kapodistrian University of Athens School of Medicine, Athens, Greece.
Surgery. 2014 Dec;156(6):1542-8; discussion 1548-9. doi: 10.1016/j.surg.2014.08.095. Epub 2014 Nov 11.
Mammalian target of rapamycin (mTOR) forms 2 active complexes in the cell: the rapamycin-sensitive mTOR-Raptor (mTORC1) and the rapamycin-insensitive mTOR-Rictor (mTORC2). The latter activates AKT kinase, which promotes tumor cell survival and proliferation by multiple downstream targets. Mammalian stress-activated protein kinase interacting protein 1 (SIN1), an essential subunit of the mTORC2 complex, maintains the integrity of the complex and substrate specificity and regulates Akt activation. The role of mTOR-Rictor complex activation in thyroid carcinogenesis remains unknown. Therefore, we investigated expression patterns of Sin1 in the cells lines of thyroid carcinoma and tumors and their association with AKT activation, histologic type, and tumor aggressiveness.
Tissue specimens from 42 patients with thyroid cancer, including follicular (5), papillary (18), medullary (16), and poorly differentiated (3) carcinomas were analyzed via immunohistochemistry for SIN1 expression and AKT phosphorylation at Ser473 residue (Ser473-p-AKT). Eight of 18 papillary carcinomas were aggressive histologic variants. In addition, expression of Sin1 and activation of AKT kinase were analyzed in fresh-frozen tissue samples (normal/tumor), primary cell cultures (papillary thyroid carcinoma [PTC]), and an established thyroid cancer cell line (medullary thyroid carcinoma) by Western blotting.
With immunohistochemistry, we found that Sin1 was overexpressed in medullary thyroid carcinomas and aggressive variants of papillary thyroid carcinoma compared with conventional papillary and follicular carcinomas (P < .001). Sin1 expression correlated with AKT activation in the entire study group (P = .002). Using Western blot analysis, we found that Sin1 and p-AKT were detected at a greater level in cultured primary cells from aggressive PTC compared with conventional PTC as well as in cell lines of medullary and anaplastic thyroid carcinoma. High expression levels of SIN1 were detected in papillary thyroid carcinomas compared with benign nodules in immunoblots in which we used fresh-frozen patient samples. Two of the Sin1 protein isoforms, p76 and p55, were detected predominantly in PTC samples.
Sin1, a critical factor of the mTORC2 complex is overexpressed in clinically aggressive thyroid cancer types and is associated strongly with activation of AKT kinase. Sin1-dependent AKT activation might represent a target for experimental therapy.
雷帕霉素哺乳动物靶点（mTOR）在细胞中形成两种活性复合物：对雷帕霉素敏感的mTOR- Raptor（mTORC1）和对雷帕霉素不敏感的mTOR- Rictor（mTORC2）。后者激活AKT激酶，该激酶通过多个下游靶点促进肿瘤细胞的存活和增殖。哺乳动物应激激活蛋白激酶相互作用蛋白1（SIN1）是mTORC2复合物的一个必需亚基，维持复合物的完整性和底物特异性，并调节Akt激活。mTOR- Rictor复合物激活在甲状腺癌发生中的作用尚不清楚。因此，我们研究了Sin1在甲状腺癌细胞系和肿瘤中的表达模式及其与AKT激活、组织学类型和肿瘤侵袭性的关系。
通过免疫组织化学分析42例甲状腺癌患者的组织标本，包括滤泡状癌（5例）、乳头状癌（18例）、髓样癌（16例）和低分化癌（3例）中SIN1的表达以及Ser473残基处的AKT磷酸化（Ser473-p-AKT）。18例乳头状癌中有8例为侵袭性组织学变异型。此外，通过蛋白质印迹法分析新鲜冷冻组织样本（正常/肿瘤）、原代细胞培养物（甲状腺乳头状癌[PTC]）和已建立的甲状腺癌细胞系（甲状腺髓样癌）中Sin1的表达和AKT激酶的激活情况。
通过免疫组织化学，我们发现与传统乳头状癌和滤泡状癌相比，Sin1在甲状腺髓样癌和乳头状癌的侵袭性变异型中过表达（P <.001）。在整个研究组中，Sin1表达与AKT激活相关（P =.002）。使用蛋白质印迹分析，我们发现与传统PTC相比，侵袭性PTC培养的原代细胞以及甲状腺髓样癌和间变性甲状腺癌细胞系中检测到的Sin1和p-AKT水平更高。在使用新鲜冷冻患者样本的免疫印迹中，与良性结节相比，乳头状甲状腺癌中检测到SIN1的高表达水平。Sin1蛋白的两种同工型p76和p55主要在PTC样本中检测到。
Sin1是mTORC2复合物的关键因子，在临床侵袭性甲状腺癌类型中过表达，并且与AKT激酶的激活密切相关。Sin1依赖性AKT激活可能是实验性治疗的靶点。
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