Schulze-Lohoff E, Köhler M, Fees H, Reindl N, Sterzel R B
Medizinische Klinik IV, Universität Erlangen-Nürnberg, Germany.
J Hypertens. 1993 Feb;11(2):127-34. doi: 10.1097/00004872-199302000-00003.
The vasoactive peptides arginine vasopressin (AVP) and angiotensin II (Ang II) induce similar second messengers in cultured glomerular mesangial cells, as shown by the rise in intracellular calcium and the activation of phospholipases C and A2. In contrast, AVP is a strong mitogen for cultured rat mesangial cells while Ang II is not. To elucidate the level of signal divergence, we examined the effects of AVP and Ang II on the expression of the immediate early genes c-fos, c-jun and Egr-1, which have been associated with cell growth. We also tested the effect of AVP and Ang II on the induction of the ornithine decarboxylase gene and enzyme in order to examine a process that is induced in cell activation, e.g. it has been associated with the G1 phase after mitogen-receptor binding.
Cellular effects of Ang II and AVP were studied in rat mesangial cells in conventional two-dimensional culture. Proliferation of the mesangial cells was measured by cell-counting and by [3H]-thymidine uptake. The presence of receptors for Ang II and AVP was assessed by measurement of prostaglandin E2 by a radioimmunoassay following stimulation with vasoactive peptides and a receptor-binding assay for Ang II. Messenger (m)RNA levels of c-fos, c-jun Egr-1 and ornithine decarboxylase were determined by Northern blot analysis. Ornithine decarboxylase activity was measured by an enzyme substrate assay.
AVP (10(-7) mol/l) stimulated [3H]-thymidine uptake by 3.7-fold after 48 h and increased mesangial cell counts by 42% (P < 0.05), while Ang II was not mitogenic. Stimulation of resting mesangial cells with AVP (10(-9) to 10(-6) mol/l) caused maximal expression of the immediate early genes after 0.5-1 h, which disappeared after 2-4 h. The relative increases were: c-fos, 15-fold; c-jun, 12-fold; Egr-1, sixfold. Ang II (10(-9) to 10(-6) mol/l) did not induce these genes at any time. In contrast, ornithine decarboxylase mRNA and enzyme activity were induced by both AVP and Ang II.
The results demonstrate that AVP, but not Ang II, is a strong inducer of the immediate early genes c-fos, c-jun and Egr-1 in cultured mesangial cells. We conclude that signalling pathways activated by AVP and Ang II in mesangial cells diverge within 30 min after ligand-receptor binding and proximal to the transient expression of immediate early genes. While mitogenesis of cultured mesangial cells, as effected by AVP, involves the expression of immediate early genes, Ang II-induced non-mitogenic changes in the mesangial cell phenotype do not. The increase in ornithine decarboxylase mRNA and enzyme activity following stimulation with both AVP and Ang II indicates that its induction can occur independently of the immediate early gene expression and mitogenesis.
血管活性肽精氨酸加压素（AVP）和血管紧张素II（Ang II）在培养的肾小球系膜细胞中可诱导产生相似的第二信使，这表现为细胞内钙升高以及磷脂酶C和A2的激活。相比之下，AVP是培养的大鼠系膜细胞的强有丝分裂原，而Ang II则不是。为了阐明信号分歧的程度，我们研究了AVP和Ang II对即刻早期基因c-fos、c-jun和Egr-1表达的影响，这些基因与细胞生长有关。我们还测试了AVP和Ang II对鸟氨酸脱羧酶基因和酶诱导的影响，以研究细胞激活过程中诱导的一个过程，例如它与有丝分裂原受体结合后的G1期有关。
在传统二维培养的大鼠系膜细胞中研究Ang II和AVP的细胞效应。通过细胞计数和[3H] - 胸腺嘧啶核苷摄取来测量系膜细胞的增殖。在用血管活性肽刺激后，通过放射免疫测定法测量前列腺素E2以及对Ang II进行受体结合测定来评估Ang II和AVP受体的存在。通过Northern印迹分析确定c-fos、c-jun、Egr-1和鸟氨酸脱羧酶的信使（m）RNA水平。通过酶底物测定法测量鸟氨酸脱羧酶活性。
48小时后，AVP（10(-7) mol/L）刺激[3H] - 胸腺嘧啶核苷摄取增加3.7倍，系膜细胞计数增加42%（P < 0.05），而Ang II没有促有丝分裂作用。用AVP（10(-9)至10(-6) mol/L）刺激静息的系膜细胞，在0.5 - 1小时后导致即刻早期基因的最大表达，2 - 4小时后消失。相对增加倍数为：c-fos，15倍；c-jun，12倍；Egr-1，6倍。Ang II（10(-9)至10(-6) mol/L）在任何时候都不诱导这些基因。相反，AVP和Ang II均可诱导鸟氨酸脱羧酶mRNA和酶活性。
结果表明，AVP而非Ang II是培养的系膜细胞中即刻早期基因c-fos、c-jun和Egr-1的强诱导剂。我们得出结论，在系膜细胞中，AVP和Ang II激活的信号通路在配体 - 受体结合后30分钟内以及靠近即刻早期基因的瞬时表达处发生分歧。虽然AVP诱导的培养系膜细胞的有丝分裂涉及即刻早期基因的表达，但Ang II诱导的系膜细胞表型的非有丝分裂变化则不然。AVP和Ang II刺激后鸟氨酸脱羧酶mRNA和酶活性的增加表明其诱导可独立于即刻早期基因表达和有丝分裂发生。
