Iacovelli L, Falasca M, Valitutti S, D'Arcangelo D, Corda D
Istituto di Ricerche Farmacologiche Mario Negri, Consorzio Mario Negri Sud, Laboratory of Cellular and Molecular Endocrinology, Chieti, Italy.
J Biol Chem. 1993 Sep 25;268(27):20402-7.
In a continuous line of rat thyroid cells transformed by the k-ras oncogene (KiKi), the expression of ras-p21 correlates with an increased activity of a phosphoinositide-specific phospholipase A2, which leads to elevated levels of glycerophosphoinositols. In this study we have characterized the biological activities of these compounds. Growth and differentiation in thyroid cells are mainly regulated by the activation of adenylylcyclase. Therefore, we have studied the effects of glycerophosphoinositols on the activity of this enzyme using a normal thyroid cell line (FRTL5). Micromolar concentrations of glycerophosphoinositol 4-phosphate (GroPIns-4-P) caused a approximately 50% inhibition of the adenylylcyclase activity in FRTL5 membranes stimulated by the GTP-binding protein activator fluoroaluminate. Similar concentrations of GroPIns-4-P were detected in KiKi cells but not in the normal FRTL5 line. Micromolar GroPIns-4-P was found to be taken up by intact FRTL5 cells and to induce nearly 50% inhibition of the thyrotropin- and cholera toxin-induced increase in cAMP levels. Similar results were also observed in other cell lines (smooth muscle, pituitary cells, and pneumocytes). GroPIns-4-P inhibited cAMP-dependent cellular functions such as iodide uptake and thymidine incorporation in FRTL5 cells when stimulated by thyrotropin and cholera toxin but not when induced by forskolin. These results are consistent with GroPIns-4-P exerting an inhibitory effect on the GTP-binding protein that stimulates adenylycyclase. We propose that GroPIns-4-P might mediate a mechanism of cross-talk between adenylylcyclase and phospholipase A2 in thyroid as well as in other cell systems.
在由k-ras癌基因转化的大鼠甲状腺细胞连续系（KiKi）中，ras-p21的表达与磷酸肌醇特异性磷脂酶A2活性的增加相关，这导致甘油磷酸肌醇水平升高。在本研究中，我们对这些化合物的生物学活性进行了表征。甲状腺细胞的生长和分化主要受腺苷酸环化酶激活的调节。因此，我们使用正常甲状腺细胞系（FRTL5）研究了甘油磷酸肌醇对该酶活性的影响。微摩尔浓度的甘油磷酸肌醇4-磷酸（GroPIns-4-P）对由GTP结合蛋白激活剂氟铝酸盐刺激的FRTL5膜中的腺苷酸环化酶活性产生了约50%的抑制作用。在KiKi细胞中检测到了类似浓度的GroPIns-4-P，但在正常FRTL5系中未检测到。发现微摩尔浓度的GroPIns-4-P可被完整的FRTL5细胞摄取，并诱导对促甲状腺素和霍乱毒素诱导的cAMP水平升高产生近50%的抑制作用。在其他细胞系（平滑肌、垂体细胞和肺细胞）中也观察到了类似结果。当由促甲状腺素和霍乱毒素刺激时，GroPIns-4-P抑制FRTL5细胞中cAMP依赖性细胞功能，如碘摄取和胸苷掺入，但当由福斯可林诱导时则无此作用。这些结果与GroPIns-4-P对刺激腺苷酸环化酶的GTP结合蛋白发挥抑制作用一致。我们提出，GroPIns-4-P可能介导甲状腺以及其他细胞系统中腺苷酸环化酶和磷脂酶A2之间的一种相互作用机制。
