Angiotensin AT2 receptor stimulates ERK1 and ERK2 in quiescent but inhibits ERK in NGF-stimulated PC12W cells
ABSTRACT To investigate the influence of AT2 receptor stimulation on the ERK pathway and elucidate potential mechanisms of angiotensin II (ANG II)-mediated neuronal differentiation, we analysed tyrosine phosphorylation and activity of ERK after ANG II treatment of both quiescent and NGF-treated PC12W cells. Tyrosine phosphorylation of ERK1 and ERK2 corresponded with the activity of ERK. While ANG II induced an initial activation of ERK in quiescent cells, the NGF-mediated plateau of ERK-stimulation was lowered by costimulation with ANG II. All effects of ANG II were sensitive to AT2 – but not AT1 receptor blockade. Ang II-mediated neurite outgrowth in PC12W cells was inhibited by co-treatment with the MEK inhibitor PD 098059. These findings demonstrate that the AT2 receptor modulates ERK activity depending on the overall cellular input. The distinct regulation of ERK by ANG II and NGF further indicates basic differences in AT2 receptor- and NGF-induced neuronal differentiation.
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ABSTRACT: Angiotensin II (Ang II) is a main effector peptide in the renin-angiotensin system and participates in the regulation of vascular tone. It also has a role in the expression of growth factors that induce neovascularisation which is closely associated to the growth of malignant gliomas. We have shown that the selective blockage of the AT1 receptor of angiotensin inhibits tumour growth, cell proliferation and angiogenesis of C6 rat glioma. The aim of this study was to study the effects of the blockage of AT1 receptor on the synthesis of growth factors, and in the genesis of apoptosis in cultured C6 glioma cells and in rats with C6 glioma. Administration of losartan at doses of 40 or 80 mg kg(-1) to rats with C6 glioma significantly decreased tumoral volume and production of platelet-derived growth factor, vascular endothelial growth factor and basic fibroblast growth factor. It also induced apoptosis in a dose-dependent manner. Administration of Ang II increased cell proliferation of cultured C6 cells which decreased by the administration of losartan. Our results suggest that the selective blockage of AT1 diminishes tumoral growth through inhibition of growth factors and promotion of apoptosis.British Journal of Cancer 05/2005; 92(7):1247-52. DOI:10.1038/sj.bjc.6602483 · 4.82 Impact Factor
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ABSTRACT: The aim of the present study was to investigate whether protein kinase C (PKC) isoforms may be among the putative candidates implicated in the primary effects of the Ang II type 2 (AT2) receptor. Western blot analyses revealed the presence of PKC alpha,epsilon, iota, and zeta in NG108-15 cells. After a 3-d treatment with 3 nm Gö6976, a specific inhibitor of classical PKC isoforms, cells were characterized by the presence of one elongated process similar to that observed after treatment with Ang II or with CGP42112, a selective AT2 receptor agonist. Similar findings were observed in cells expressing a dominant-negative mutant of PKC alpha (K368A). Inhibition of PKC alpha in NG108-15 cells also decreased cell number and proliferation. In conditions of acute stimulation, Ang II induced a time-dependent and transient inhibition of PKC alpha activity, as well as a decrease in PKC alpha levels associated with the membrane. Treatment of cells with Gö6976 was also found to inhibit p21(ras) (between 1-10 min) but stimulated Rap1 activity (1-5 min) in a time-course similar to that of Ang II. Incubation of NG108-15 cells with Gö6976 (3 nm) inhibited basal p42/p44(mapk) phosphorylation, but failed to interfere with its activation by the AT(2) receptor, indicating that inhibition of PKC alpha is not directly involved in the Rap1-MEK-p42/p44(mapk) cascade. Taken together, these results indicate that PKC alpha is a primary target of the AT2 receptor. Inhibition of PKC alpha leads to a decrease in both p21(ras) activity and cell proliferation, which may facilitate AT2 receptor signaling through p42/p44(mapk), thereby leading to neurite outgrowth.Endocrinology 10/2006; 147(9):4263-72. DOI:10.1210/en.2006-0411 · 4.64 Impact Factor
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ABSTRACT: NG108-15 cells, which have a rounding-up morphology when cultured in serum-supplemented medium, extend neurites when stimulated for 3 d with angiotensin II (Ang II). The aim of the present study was to investigate whether growth factor receptors are necessary for mediating the effects of Ang II. A 3-d treatment with AG879, an inhibitor of nerve growth factor receptor TrkA, strongly affected neurite outgrowth and phosphorylation of p42/p44(mapk) induced by Ang II. PD168393, an inhibitor of epidermal growth factor (EGF) receptor slightly decreased Ang II-induced neurite outgrowth, whereas AG213, an inhibitor of both platelet-derived growth factor receptor and EGF receptor, stimulated neurite outgrowth and p42/p44(mapk) phosphorylation on its own, without affecting further stimulation with Ang II. Moreover, Ang II induced the phosphorylation of TrkA (maximum at 5 min of incubation in the presence of serum or at 20 min in cells depleted in serum for 2 h) and a rapid increase in Rap1 activity, both effects abolished in cells preincubated with 10 microm AG879. In summary, the present results demonstrate that AT(2) receptor-induced sustained activation of p42/p44(mapk) and corresponding neurite outgrowth are mediated by phosphorylation of the nerve growth factor TrkA receptor. However, the results also point out that the presence of other growth factors, such as EGF or PDFG, may interfere with the effect of Ang II. Altogether, the current findings clearly indicate that the effects of the AT(2) receptor on neurite outgrowth dynamics are modulated by the presence of growth factors in the culture medium.Endocrinology 11/2006; 147(10):4646-54. DOI:10.1210/en.2005-1315 · 4.64 Impact Factor