EGF-induced increase in diacylglycerol, choline release, and DNA synthesis is extracellular calcium dependent.

Dean NM; Boynton AL

摘要

Previous studies have demonstrated a strict extracellular Ca2+ dependence for the G0 to G1 and G1 to S transition in growth factor-treated T51B rat liver cells that is associated with increased levels of protein kinase C activity. Consequently, we have examined these cells for changes in phospholipid-derived second messengers in response to epidermal growth factor (EGF) and thrombin in order to determine which signals are generated during the initiation of the G0 to G1 transition. Thrombin is coupled to a phosphoinositide hydrolyzing phospholipase C, as we have found a rapid Ca(2+)-independent increase in the levels of inositol 1,4,5-trisphosphate (Ins[1,4,5]P3), inositol 1,4-bisphosphate (Ins[1,4]P2), and inositol 4-monophosphate (Ins[4]P), as well as a concomitant, transient elevation in diacylglycerol. No changes in either intracellular or extracellular choline metabolites, or an increase in DNA synthesis, were found in response to thrombin. By contrast, treatment of T51B cells with EGF results in aslower, more prolonged extracellular Ca(2+)-dependent increase in both [3H]-glycerol radiolabeled diacyl-glycerol, and diacylglycerol mass, an increase in choline release into the extracellular medium, and eventually a substantial DNA synthesis. We were, however, unable to detect any changes in phosphatidylinositol (PtdIns) turnover, either by accumulation of inositol phosphates or by changes in phospholipids in response to EGF. These results indicate that DNA synthesis can readily occur in the absence of stimulated PtdIns turnover, and that PtdIns turnover is not sufficient in itself or necessary to induce DNA synthesis and is not necessary for a Ca(2+)-dependent increase in diacylglycerol. Moreover, we have demonstrated that the extracellular Ca(2+)-dependent increase in diacylglycerol levels in response to EGF is associated with an increase in extracellular choline release, which is indicative of an activation of a phosphatidylcholine-linked phospholipase D. These results suggest that diacylglycerol sources other than PtdIns's may be important in the extracellular Ca(2+)-dependent regulation of EGF-mediated cell replication.

机译：先前的研究已经证明了一个严格的细胞外钙离子依赖性的G0 G1并在增长factor-treated G1年代过渡T51B鼠肝细胞与相关联水平的提高蛋白激酶C活性。因此,我们已经检查了这些细胞phospholipid-derived第二信使的变化针对表皮生长因子(EGF)和凝血酶,以确定哪些信号期间生成的起始G0 G1过渡。磷酸肌醇水解磷脂酶C,我们已经找到了一种快速Ca(2 +)独立增加在肌醇1的水平,4,5-trisphosphate(Ins(1、4、5)P3),肌醇1,4-bisphosphate(Ins [1,4] P2)和肌醇4-monophosphate(Ins [4] P),以及伴随的,瞬态海拔在甘油二酯。细胞内或细胞外胆碱代谢物或DNA合成的增加,在凝血酶被发现。T51B细胞EGF治疗结果aslower、更长期的细胞外Ca(2 +)端依赖增加[3 h]甘油放射性标记的diacyl-glycerol和甘油二酯质量,增加胆碱释放到细胞外介质,最终大量的DNA合成。无法发现任何变化磷脂酰肌醇(PtdIns)营业额,通过积累的肌醇磷酸盐或变化在应对EGF磷脂。结果表明,DNA合成可以很容易在缺乏刺激PtdIns发生营业额,PtdIns营业额不是足够的本身或诱导DNA所必需的合成并不是必需的Ca(2 +)端依赖增加甘油二酯。此外,我们已经证明了细胞外钙(2 +)端依赖增加甘油二酯含量对EGF与细胞外的增加胆碱释放,这是指示性的激活的phosphatidylcholine-linked这些结果表明,磷脂酶d二酰基甘油PtdIns以外的可能来源重要的细胞外钙(2 +)端依赖监管EGF-mediated细胞复制。

EGF-induced increase in diacylglycerol, choline release, and DNA synthesis is extracellular calcium dependent.

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