Maly K, Hochleitner B, Uberall F, Loferer H, Oberhuber H, Doppler W, Grunicke H
Institute for Medical Chemistry and Biochemistry, University of Innsbruck, Austria.
Adv Enzyme Regul. 1990;30:63-74. doi: 10.1016/0065-2571(90)90009-q.
Expression of the transforming Ha-ras oncogene in MMTV-LTR transfected NIH 3T3 cells leads to a growth factor independent activation of the Na+/H(+)-antiporter. The activation of the antiporter is insensitive to the protein kinase inhibitor staurosporine and equally expressed in protein kinase C-depleted cells. It is concluded that the Ha-ras induced activation of the antiporter occurs by a protein kinase C-independent mechanism. An inhibition of the Na+/H(+)-antiporter by dimethylamiloride or a reduction of the extracellular [Na+] concentration results in a depression of the bombesin induced release of Ca2+ from intracellular stores. These results are explained by a steep pH-dependence of the Ca2(+)-mobilizing system which exhibits a maximum at pH 7.1 in the system studied here. Stimulation by growth factors of quiescent cells with a resting pH below 7 results in a shift of the cytosolic pH towards the optimum for the Ca2+ release. In agreement with the proposed interrelationship, pHi and [Ca2+]i rise and peak simultaneously after addition of bombesin to G0 arrested cells.
在MMTV-LTR转染的NIH 3T3细胞中，转化型Ha-ras癌基因的表达导致Na⁺/H⁺逆向转运体的生长因子非依赖性激活。该逆向转运体的激活对蛋白激酶抑制剂星形孢菌素不敏感，并且在蛋白激酶C缺失的细胞中同样表达。由此得出结论，Ha-ras诱导的逆向转运体激活是通过一种不依赖蛋白激酶C的机制发生的。用二甲基amiloride抑制Na⁺/H⁺逆向转运体或降低细胞外[Na⁺]浓度会导致蛙皮素诱导的细胞内钙库中Ca²⁺释放减少。这些结果可以通过Ca²⁺动员系统对pH的强烈依赖性来解释，在此研究的系统中，该依赖性在pH 7.1时达到最大值。用生长因子刺激静息pH低于7的静止细胞会导致胞质pH向Ca²⁺释放的最佳值移动。与所提出的相互关系一致，在向G0期停滞的细胞中添加蛙皮素后，细胞内pH（pHi）和细胞内Ca²⁺浓度（[Ca²⁺]i）同时升高并达到峰值。
