Lian Eric Y, Maritan Sarah M, Cockburn Jessica G, Kasaian Katayoon, Crupi Mathieu J F, Hurlbut David, Jones Steven J M, Wiseman Sam M, Mulligan Lois M
Division of Cancer Biology and GeneticsCancer Research Institute, Queen's University, Kingston, Ontario, Canada.
Department of Pathology & Molecular MedicineQueen's University, Kingston, Ontario, Canada.
Endocr Relat Cancer. 2017 Jan;24(1):53-69. doi: 10.1530/ERC-16-0393. Epub 2016 Nov 21.
The RET receptor tyrosine kinase mediates cell proliferation, survival and migration in embryogenesis and is implicated in the transformation and tumour progression in multiple cancers. RET is frequently mutated and constitutively activated in familial and sporadic thyroid carcinomas. As a result of alternative splicing, RET is expressed as two protein isoforms, RET9 and RET51, which differ in their unique C-terminal amino acids. These isoforms have distinct intracellular trafficking and associated signalling complexes, but functional differences are not well defined. We used shRNA-mediated knockdown (KD) of individual RET isoforms or of total RET to evaluate their functional contributions in thyroid carcinoma cells. We showed that RET is required for cell survival in medullary (MTC) but not papillary thyroid carcinoma (PTC) cells. In PTC cells, RET depletion reduced cell migration and induced a flattened epithelial-like morphology. RET KD decreased the expression of mesenchymal markers and matrix metalloproteinases and reduced anoikis resistance and invasive potential. Further, we showed that RET51 depletion had significantly greater effects on each of these processes than RET9 depletion in both MTC and PTC cells. Finally, we showed that expression of RET, particularly RET51, was correlated with malignancy in a panel of human thyroid tumour tissues. Together, our data show that RET expression promotes a more mesenchymal phenotype with reduced cell-cell adhesion and increased invasiveness in PTC cell models, but is more important for tumour cell survival, proliferation and anoikis resistance in MTC models. Our data suggest that the RET51 isoform plays a more prominent role in mediating these processes compared to RET9.
RET受体酪氨酸激酶在胚胎发育过程中介导细胞增殖、存活和迁移，并与多种癌症的转化和肿瘤进展有关。RET在家族性和散发性甲状腺癌中经常发生突变并持续激活。由于选择性剪接，RET以两种蛋白异构体RET9和RET51的形式表达，它们在独特的C末端氨基酸上有所不同。这些异构体具有不同的细胞内运输和相关的信号复合物，但功能差异尚不明确。我们使用shRNA介导的单个RET异构体或总RET的敲低（KD）来评估它们在甲状腺癌细胞中的功能贡献。我们发现RET是髓样甲状腺癌（MTC）细胞存活所必需的，但在乳头状甲状腺癌（PTC）细胞中并非如此。在PTC细胞中，RET的缺失减少了细胞迁移并诱导了扁平的上皮样形态。RET KD降低了间充质标志物和基质金属蛋白酶的表达，并降低了失巢凋亡抗性和侵袭潜力。此外，我们发现，在MTC和PTC细胞中，RET51的缺失对这些过程中的每一个的影响都比RET9的缺失显著更大。最后，我们发现RET，特别是RET51的表达与一组人类甲状腺肿瘤组织中的恶性程度相关。总之，我们的数据表明，在PTC细胞模型中，RET的表达促进了一种更具间充质特征的表型，细胞间粘附减少，侵袭性增加，但在MTC模型中，RET对肿瘤细胞存活、增殖和失巢凋亡抗性更为重要。我们的数据表明，与RET9相比，RET51异构体在介导这些过程中发挥着更突出的作用。
