The membrane immunoglobulin receptor utilizes a Shc/Grb2/hSOS complex for activation of the mitogen-activated protein kinase cascade in a B-cell line.
Ontology highlight
ABSTRACT:
SUBMITTER: Kumar G
PROVIDER: S-EPMC1136765 | biostudies-other | 1995 Apr
REPOSITORIES: biostudies-other
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Project description:The proliferative effects of gastrin on normal and neoplastic gastro-intestinal tissues have been shown to be mediated by the gastrin/CCKB (G/CCKB) G-protein-coupled receptors. We have recently reported that gastrin stimulates the tyrosine phosphorylation of Shc proteins and their subsequent association with the Grb2/Sos complex, leading to mitogen-activated protein kinase (MAPK) activation, a pathway known to play an important role in cell proliferation. We undertook the present study to characterize the signalling pathways used by this receptor to mediate the activation of the Shc/Grb2 complex. Since G/CCKB receptor occupancy leads to the activation of the phospholipase C (PLC)/protein kinase C (PKC) pathway, we examined whether PKC stimulation and Ca2+ mobilization contribute to the phosphorylation of Shc proteins and their association with Grb2 in response to gastrin. Our results indicate that Shc proteins are tyrosine phosphorylated and associate with Grb2 in response to phorbol esters, suggesting that activation of PKC is a potential signalling pathway leading to activation of the Shc/Grb2 complex. Inhibition of PKC by GF109203X completely blocked the effect of PMA on Shc tyrosine phosphorylation and its subsequent association with Grb2, but had a partial inhibitory effect on the response to gastrin. Depletion of the intracellular Ca2+ pools by treatment with thapsigargin blocked the increase in intracellular free calcium concentration induced by gastrin and diminished the ability of the peptide to stimulate Shc phosphorylation and recruitment of Grb2. In addition, removal of extracellular Ca2+ partially inhibited the effect of gastrin on Shc phosphorylation as well as its association with Grb2, indicating that the effects of gastrin are also mediated by Ca2+-dependent mechanisms. Furthermore, we show that blockage of the two major early signals generated by activation of PLC, which induced the activation of the Shc/Grb2 complex, also blocked gastrin-induced MAPK activation.
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Project description:Aldosterone in some tissues increases expression of the mRNA encoding the small monomeric G protein Ki-RasA. Renal A6 epithelial cells were used to determine whether induction of Ki-ras leads to concomitant increases in the total as well as active levels of Ki-RasA and whether this then leads to subsequent activation of its effector mitogen-activated protein kinase (MAPK/extracellular signal-regulated kinase) cascade. The molecular basis and cellular consequences of this action were specifically investigated. We identified the intron 1-exon 1 region (rasI/E1) of the mouse Ki-ras gene as sufficient to reconstitute aldosterone responsiveness to a heterologous promotor. Aldosterone increased reporter gene activity containing rasI/E1 threefold. Aldosterone increased the absolute and GTP-bound levels of Ki-RasA by a similar extent, suggesting that activation resulted from mass action and not effects on GTP binding/hydrolysis rates. Aldosterone significantly increased Ki-RasA and MAPK activity as early as 15 min with activation peaking by 2 h and waning after 4 h. Inhibitors of transcription, translation, and a glucocorticoid receptor antagonist attenuated MAPK signaling. Similarly, rasI/E1-driven luciferase expression was sensitive to glucocorticoid receptor blockade. Overexpression of dominant-negative RasN17, addition of antisense Ki-rasA and inhibition of mitogen-activated protein kinase kinase also attenuated steroid-dependent increases in MAPK signaling. Thus, activation of MAPK by aldosterone is dependent, in part, on a genomic mechanism involving induction of Ki-ras transcription and subsequent activation of its downstream effectors. This genomic mechanism has a distinct time course from activation by traditional mitogens, such as serum, which affect the GTP-binding state and not absolute levels of Ras. The result of such a genomic mechanism is that peak activation of the MAPK cascade by adrenal corticosteroids is delayed but prolonged.
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Project description:Radiation biodosimetry based on transcriptomic analysis of peripheral blood is a valuable tool to detect radiation exposure after a radiological/nuclear event and obtain useful biological information that could predict tissue and organismal injury. However, confounding factors, including inflammation, can potentially obscure the predictive power of the method. The mitogen-activated protein kinase (MAPK) p38 is normally regulated by the MAP3K-MAP2K pathway in mammalian cells. Members of the p38 MAPK family respond to pro-inflammatory signals and environmental stresses. However, in T cells there is an alternative pathway for p38MAPK activation. This pathway has been shown to play an important role in antigen-receptor-activated T cells and participate in immune and inflammatory responses. Radiation is known to induce a pro-inflammatory response. To examine the role of p38MAPK in response to radiation, we used two mouse models expressing either a p38αMAPK dominant negative (DN) mutation that would be expected to globally suppress p38MAPK signaling or a double knock-in (DKI) mutant, which would be expected to inhibit specifically T cell receptor activation. We exposed wild-type and p38MAPK mutant mice to 7 Gy x-rays and 24 h later we isolated whole blood and performed genome microarray and gene ontology analysis. Comparison between the two mutants (DN, DKI) suggest that the alternative p38MAPK pathway may have wider functions in the response to radiation exposure beyond its well established role as a downstream effector of activated T-cell receptor. Among the differentially enriched pathways, irradiation leads to a significant overrepresentation of pathways associated with morbidity and mortality as well as organismal cell death. In contrast, these pathways were significantly underrepresented in p38MAPKDN and p38MAPKDKI mutant mice, implying that p38MAPK suppression protects mice from the deleterious effects of radiation. Furthermore, radiation exposure resulted in an enrichment of a small number of phagocytosis-related pathways; however, considerably more phagocytosis-related pathways were overrepresented in the p38MAPK mutant mice, implying that p38MAPK signaling, normally, restricts phagocytosis of apoptotic cells after radiation and may, thus, contribute to persistent inflammation. Finally, despite the significant changes in gene expression, we were still able to identify a panel of genes that could accurately distinguish between irradiated and control mice, irrespective of p38MAPK status.
2022-05-06 | GSE184361 | GEO
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