Van Sande Jacqueline, Dequanter Didier, Lothaire Philippe, Massart Claude, Dumont Jacques E, Erneux Christophe
Institute of Interdisciplinary Research, Campus Erasme Building C, 808 Route de Lennik, 1070 Brussels, Belgium.
J Clin Endocrinol Metab. 2006 Mar;91(3):1099-107. doi: 10.1210/jc.2005-1324. Epub 2005 Dec 29.
Dual activation by TSH of the phospholipase C and cAMP cascades has been reported in human thyroid cells. In contrast, Singh et al. reported convincing data in FRTL-5 thyrocytes arguing against such an effect in this model. Their data in FRTL-5 cells indicated no increase in inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] in response to TSH. Therefore, the authors questioned results previously obtained on human cells by cruder methodology.
We investigated the formation of inositol phosphates by HPLC techniques in human thyroid slices to separate the inositol phosphate isomers.
Ins(1,4,5)P3, inositol 1,3,4-trisphosphate, and inositol 1,3,4,5-tetrakisphosphate were increased after TSH stimulation. The effect of TSH in human thyroid cells was reproduced by recombinant TSH and prevented by antibodies blocking the TSH receptor. Thyroid-stimulating antibodies at concentrations eliciting a cAMP response equivalent to TSH failed to stimulate inositol phosphate generation.
TSH, but not thyroid-stimulating antibodies, activates both cAMP and the phospholipase C cascade in human thyroid as now demonstrated by an increase in Ins(1,4,5)P3 and its inositol phosphate metabolites. Therefore, this effect cannot be extrapolated to the FRTL-5 cell line. The apparent discrepancy may be due to a difference between species (human vs. rat) or to the loss of the fresh tissue properties in a cell line. The dual effect of TSH in human cells, through cAMP on secretion of thyroid hormones and through the diacylglycerol, Ins(1,4,5)P3 Ca2+ pathway on thyroid hormone synthesis, implies the possible separation of these effects in thyroid disease.
据报道，促甲状腺激素（TSH）可在人甲状腺细胞中双重激活磷脂酶C和环磷酸腺苷（cAMP）信号级联反应。相比之下，辛格等人在FRTL-5甲状腺细胞中报告了令人信服的数据，反对在该模型中存在这种效应。他们在FRTL-5细胞中的数据表明，对TSH刺激，肌醇1,4,5-三磷酸[Ins(1,4,5)P3]没有增加。因此，作者对之前用更粗糙方法在人细胞上获得的结果提出质疑。
我们采用高效液相色谱（HPLC）技术研究人甲状腺切片中肌醇磷酸的形成，以分离肌醇磷酸异构体。
TSH刺激后，Ins(1,4,5)P3、肌醇1,3,4-三磷酸和肌醇1,3,4,5-四磷酸增加。重组TSH重现了TSH对人甲状腺细胞的作用，而阻断TSH受体的抗体可阻止该作用。浓度相当于TSH且能引发cAMP反应的促甲状腺素抗体未能刺激肌醇磷酸生成。
如现在因Ins(1,4,5)P3及其肌醇磷酸代谢产物增加所证明的，TSH而非促甲状腺素抗体可激活人甲状腺中的cAMP和磷脂酶C信号级联反应。因此，这种效应不能外推至FRTL-5细胞系。明显的差异可能是由于物种差异（人vs大鼠）或细胞系中新鲜组织特性的丧失。TSH在人细胞中的双重作用，通过cAMP影响甲状腺激素分泌，通过二酰甘油、Ins(1,4,5)P3-Ca2+途径影响甲状腺激素合成，这意味着在甲状腺疾病中可能分离这些效应。
