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      Exogenous Nitric Oxide Upregulates p21 waf1/cip1 in Pulmonary Microvascular Smooth Muscle Cells

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          The histopathology of chronic pulmonary hypertension includes microvascular proliferation and neointimal formation. Nitric oxide (NO) has been implicated in the regulation of these mechanisms, but how NO controls microvascular proliferation and its effect on pulmonary microvascular cells is still unclear. In this study, we characterized the in vitro effects of NO on rat pulmonary microvascular smooth muscle cell (PMVSMC) proliferation and investigated the contribution of the p42/44 mitogen-activated protein kinase (MAPK) pathway and p21<sup>waf1/cip1</sup> induction to this response. NO donors inhibited PMVSMC proliferation in a dose-dependent manner. In the presence of hypoxia, the degree of inhibition was significantly enhanced. This inhibition was reversible and independent of apoptosis. The soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) had no impact on proliferation rates, suggesting a cyclic guanosine monophosphate-independent process. Administration of MEK1/2 inhibitors failed to abrogate the antimitotic effect of NO. There was a two- fold induction of the cyclin-dependent kinase inhibitor p21 in PMVSMC treated with NO donors. Under hypoxic conditions, NO caused a three-fold increase in p21 levels. These results demonstrate that NO inhibits PMVSMC proliferation and that this inhibition is not the result of p42/44 MAPK activation. The ability of NO to induce p21 upregulation may be a mechanism by which it exerts antiproliferative effects in PMVSMC.

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          Most cited references 15

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          Activation of MAP kinase kinase is necessary and sufficient for PC12 differentiation and for transformation of NIH 3T3 cells.

          The MAP kinase pathway is activated by a wide variety of external signals leading to cell proliferation or differentiation. However, it is not clear whether activation of this pathway is required for cellular responses or whether it is only one branch point in signal transduction. To investigate these questions, we generated constitutively activated and interfering mutants of MAP kinase kinase 1. The activated mutants stimulated PC12 cell neuronal differentiation and transformed NIH 3T3 cells. The interfering mutants inhibited growth factor-induced PC12 differentiation, growth factor stimulation of proliferation, and reverted v-src- and ras-transformed cells. These results therefore show that, depending on cellular context, activation of MAP kinase kinase is necessary and sufficient for cell differentiation or proliferation.
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            Signals from Ras and Rho GTPases interact to regulate expression of p21Waf1/Cip1.

            Small GTPases act as molecular switches in intracellular signal-transduction pathways. In the case of the Ras family of GTPases, one of their most important roles is as regulators of cell proliferation, and the mitogenic response to a variety of growth factors and oncogenes can be blocked by inhibiting Ras function. But in certain situations, activation of Ras signalling pathways arrests the cell cycle rather than causing cell proliferation. Extracellular signals may trigger different cellular responses by activating Ras-dependent signalling pathways to varying degrees. Other signalling pathways could also influence the consequences of Ras signalling. Here we show that when signalling through the Ras-related GTPase Rho is inhibited, constitutively active Ras induces the cyclin-dependent-kinase inhibitor p21Waf1/Cip1 and entry into the DNA-synthesis phase of the cell cycle is blocked. When Rho is active, induction of p21Waf1/Cip1 by Ras is suppressed and Ras induces DNA synthesis. Cells that lack p21Waf1/Cip1 do not require Rho signalling for the induction of DNA synthesis by activated Ras, indicating that, once Ras has become activated, the primary requirement for Rho signalling is the suppression of p21Waf1/Cip1 induction.
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              Differential activation of mitogen-activated protein kinases by nitric oxide-related species.

              Many studies have identified nitric oxide (NO) and related chemical species (NOx) as having critical roles in neurotransmission, vasoregulation, and cellular signaling. Previous work in this laboratory has focused on elucidating the mechanism of NOx signaling in cells. We have demonstrated that NOx-induced activation of the guanine nucleotide-binding protein p21(ras) leads to nuclear translocation of the transcription factor NFkappaB. Here, we investigated whether intermediary signaling elements, namely the mitogen-activated protein (MAP) kinases, are involved in mediating NOx signaling. We found that NOx activates the extracellular signal-regulated kinase (ERK), p38, and c-Jun NH2-terminal kinase (JNK) subgroups of MAP kinases in human Jurkat T cells. JNK was found to be 100-fold more sensitive to NOx stimulation than p38 and ERK. In addition, the activation of JNK and p38 by NOx was more rapid than ERK activation. Depletion of intracellular glutathione augmented the NOx-induced increase in kinase activity. Furthermore, endogenous NO, generated from NO synthase, activated ERK, and NOx-induced MAP kinase activation was effectively blocked by the farnesyl transferase inhibitor alpha-hydroxyfarnesylphosphonic acid. These data support the hypothesis that critical signaling kinases, such as ERK, p38, and JNK, are activated by NO-related species and thus participate in NO signal transduction. These findings establish a role for multiple MAP kinase signaling pathways in the cellular response to NOx.

                Author and article information

                J Vasc Res
                Journal of Vascular Research
                S. Karger AG
                June 2004
                30 June 2004
                : 41
                : 3
                : 211-219
                Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Md., USA
                77577 J Vasc Res 2004;41:211–219
                © 2004 S. Karger AG, Basel

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                Page count
                Figures: 7, References: 36, Pages: 9
                Research Paper


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