Tanaka K, Nagayama Y, Nakano T, Takamura N, Namba H, Fukada S, Kuma K, Yamashita S, Niwa M
Department of Pharmacology, Nagasaki University School of Medicine, Sakamoto, Japan.
Endocrinology. 1998 Mar;139(3):852-8. doi: 10.1210/endo.139.3.5791.
Protein tyrosine kinases (PTKs) play a role in regulating the growth and differentiated functions of thyroid cells and are probably involved in tumorigenesis of papillary-type thyroid carcinoma. To better understand the roles of PTKs in the physiology and pathophysiology of the thyroid, we analyzed the expression profile of receptor-type PTKs in normal human thyroid tissues. Highly conserved regions in the catalytic domains of receptor-type PTKs were amplified by RT-PCR using degenerate oligonucleotide primers. Nucleotide sequencing of about 100 clones identified 21 PTKs, including 16 receptor type and 5 nonreceptor type; no novel PTK was identified. Insulin-like growth factor I receptor, platelet-derived growth factor receptor (PDGFR), TrkE, Axl, epidermal growth factor receptor, etc., appear to be the most abundant receptor-type PTKs in the thyroid; many of which (PDGFR, TrkE, Axl, etc.) have never previously been demonstrated to be expressed in the thyroid. The expression of messenger RNAs (mRNAs) for PDGFR, axl, and trkE in normal thyroid cells was confirmed by Northern blot analysis, and interestingly, the expression levels of PDGFR and trkE mRNAs were decreased in all three thyroid carcinoma cell lines examined (FRO, WRO, and NPA), whereas axl mRNA and protein were overexpressed in 2 of 3 thyroid carcinoma cell lines (FRO and WRO) compared with that in normal tissue. The axl gene was, however, neither amplified nor rearranged. The biological activity of the ligand for Axl, the product of growth arrest-specific gene 6 (Gas6), was then evaluated, demonstrating modest mitogenic activity in thyroid carcinoma cells overexpressing Axl. Furthermore, gas6 mRNA was expressed in FRO cells. Thus, we here identify a variety of PTKs expressed in the thyroid gland, many of which may participate in the regulation of thyroid cell function. Variable expression levels of some PTKs in normal and cancerous cells suggest that there may be an imbalance and disarray of phosphorylation events in thyroid carcinoma cells. Furthermore, Gas6 is identified as a novel growth factor for thyroid carcinoma cells overexpressing Axl receptor tyrosine kinase.
蛋白酪氨酸激酶（PTK）在调节甲状腺细胞的生长和分化功能中发挥作用，并且可能参与乳头状甲状腺癌的肿瘤发生过程。为了更好地理解PTK在甲状腺生理和病理生理中的作用，我们分析了正常人甲状腺组织中受体型PTK的表达谱。使用简并寡核苷酸引物通过RT-PCR扩增受体型PTK催化结构域中的高度保守区域。对约100个克隆进行核苷酸测序，鉴定出21种PTK，包括16种受体型和5种非受体型；未鉴定出新型PTK。胰岛素样生长因子I受体、血小板衍生生长因子受体（PDGFR）、TrkE、Axl、表皮生长因子受体等似乎是甲状腺中最丰富的受体型PTK；其中许多（PDGFR、TrkE、Axl等）以前从未被证明在甲状腺中表达。通过Northern印迹分析证实了正常甲状腺细胞中PDGFR、axl和trkE信使RNA（mRNA）的表达，有趣的是，在所检测的所有三种甲状腺癌细胞系（FRO、WRO和NPA）中，PDGFR和trkE mRNA的表达水平均降低，而与正常组织相比，axl mRNA和蛋白在3种甲状腺癌细胞系中的2种（FRO和WRO）中过表达。然而，axl基因既未扩增也未重排。然后评估了Axl配体（生长停滞特异性基因6（Gas6）的产物）的生物学活性，结果表明在过表达Axl的甲状腺癌细胞中具有适度的促有丝分裂活性。此外，gas6 mRNA在FRO细胞中表达。因此，我们在此鉴定出甲状腺中表达的多种PTK，其中许多可能参与甲状腺细胞功能的调节。正常细胞和癌细胞中某些PTK的表达水平变化表明，甲状腺癌细胞中可能存在磷酸化事件的失衡和紊乱。此外，Gas6被鉴定为过表达Axl受体酪氨酸激酶的甲状腺癌细胞的新型生长因子。
