Norman J, Badie-Dezfooly B, Nord E P, Kurtz I, Schlosser J, Chaudhari A, Fine L G
Am J Physiol. 1987 Aug;253(2 Pt 2):F299-309. doi: 10.1152/ajprenal.1987.253.2.F299.
The mitogenic effect of epidermal growth factor (EGF) and the characteristics of EGF binding were studied on primary cultures of rabbit proximal tubular cells. EGF was found to be a potent mitogen and stimulated DNA synthesis 18-fold above the level observed in quiescent cells. Using 125I-EGF as a ligand, two classes of specific EGF receptors were identified on the proximal tubular cell in culture, i.e., a high-affinity receptor with a dissociation constant (Kd) of 0.3 nM and maximal binding (Bmax) of 1.7 X 10(4) receptors/cell and a low-affinity receptor with a Kd of 1.9 nM and Bmax of 5.3 X 10(4) receptors/cell. Because angiotensin II (ANG II) appeared to possess many properties common to growth factors, we also examined the interaction of ANG II and EGF on these cells. ANG II was not mitogenic, but it potentiated the mitogenic effect of EGF with a maximal effect at 10(-9) M. The dose-response curve of EGF-induced mitogenesis was shifted to the left in the presence of 10(-9) M ANG II, decreasing the approximate half-maximal stimulatory concentration from 3 X 10(-8) to 5 X 10(-9) M. ANG II also stimulated prostaglandin E2 (PGE2) release, but inhibition of basal and ANG II-stimulated PGE2 synthesis had no effect on mitogenesis. ANG II had no effect on the binding of EGF to the high-affinity receptor from 1 to 20 h and did not alter receptor downregulation. ANG II (10(-9) M) had no effect on cell protein content, RNA and protein synthesis, Na+-H+ antiport, and intracellular free Ca2+ concentration. Higher concentrations of ANG II (5 X 10(-8) to 5 X 10(-6) M) led to a rapid and transient dose-dependent rise in cytosolic free Ca2+ concentration. These studies demonstrate that ANG II potentiates EGF-induced mitogenesis at one or more postreceptor steps that may include small changes in cytosolic Ca2+ concentration.
研究了表皮生长因子（EGF）对兔近端肾小管细胞原代培养物的促有丝分裂作用及其结合特性。发现EGF是一种有效的促有丝分裂剂，可刺激DNA合成，其水平比静止细胞中观察到的高出18倍。以¹²⁵I-EGF作为配体，在培养的近端肾小管细胞上鉴定出两类特异性EGF受体，即解离常数（Kd）为0.3 nM、最大结合量（Bmax）为1.7×10⁴受体/细胞的高亲和力受体，以及Kd为1.9 nM、Bmax为5.3×10⁴受体/细胞的低亲和力受体。由于血管紧张素II（ANG II）似乎具有许多生长因子共有的特性，我们还研究了ANG II与EGF在这些细胞上的相互作用。ANG II没有促有丝分裂作用，但它增强了EGF的促有丝分裂作用，在10⁻⁹ M时具有最大效应。在存在10⁻⁹ M ANG II的情况下，EGF诱导的有丝分裂的剂量反应曲线向左移动，将近似半最大刺激浓度从3×10⁻⁸ M降至5×10⁻⁹ M。ANG II还刺激前列腺素E2（PGE2）释放，但抑制基础和ANG II刺激的PGE2合成对有丝分裂没有影响。ANG II在1至20小时内对EGF与高亲和力受体的结合没有影响，也不会改变受体下调。ANG II（10⁻⁹ M）对细胞蛋白质含量、RNA和蛋白质合成、Na⁺-H⁺反向转运以及细胞内游离Ca²⁺浓度没有影响。更高浓度的ANG II（5×10⁻⁸至5×10⁻⁶ M）导致细胞质游离Ca²⁺浓度迅速且短暂地呈剂量依赖性升高。这些研究表明，ANG II在一个或多个受体后步骤增强EGF诱导的有丝分裂作用，这可能包括细胞质Ca²⁺浓度的微小变化。
