| 1. |
- Dib, Karim, et al.
(author)
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beta 2 Integrins target Rap GTPases to the plasma membrane by means of degranulation
- 2008
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In: Biochemical and Biophysical Research Communications. - : Elsevier BV. - 1090-2104 .- 0006-291X. ; 376:4, s. 642-646
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Journal article (peer-reviewed)abstract
- We report the novel observation that engagement of beta 2 integrins on human neutrophils is accompanied by increased levels of the small GTPases Rap1 and Rap2 in a membrane-enriched fraction and a concomitant decrease of these proteins in a granule-enriched fraction. In parallel, we observed a similar time-dependent decrease of gelatinase B (a marker of specific and gelatinase B-containing granules) but not myeloperoxidase (a marker of azurophil granules) in the granule fraction, and release of lactoferrin (a marker of specific granules) in the extracellular medium. Furthermore, inhibition of Src tyrosine kinases, or phosphoinositide 3-kinase with PP1 or LY294002, respectively, blocked 02 integrin-induced degranulation and the redistribution of Rap1 and Rap2 to a membrane-enriched fraction. Consequently, the 02 integrin-dependent exocytosis of specific and gelatinase B-containing granules occurs via a Src tyrosine kinase/phosphoinositide 3-kinase signaling pathway and is responsible for the translocation of Rap1 and Rap2 to the plasma membrane in human neutrophils. (C) 2008 Elsevier Inc. All rights reserved.
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| 2. |
- Jenei, V, et al.
(author)
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E3B1, a human homologue of the mouse gene product Abi-1, sensitizes activation of Rap1 in response to epidermal growth factor
- 2005
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In: Experimental Cell Research. - : Elsevier BV. - 1090-2422 .- 0014-4827. ; 310:2, s. 463-473
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Journal article (peer-reviewed)abstract
- E3B1, a human homologue of the mouse gene product Abi-1, has been implicated in growth-factor-mediated regulation of the small GTPases p21(Ras) and Rac. E3b1 is a regulator of Rac because it can form a complex with Sos-1 and eps8, and such a Sos-1-e3B1-eps8 complex serves as a guanine nucleotide exchange factor for Rac. In the present study, we found that overexpression of e3B1 in NIH3T3/ EGFR cells sensitized EGF-induced activation of Rac1, whereas it had no impact on EGF-induced activation of p21(Ras). Remarkably, we found that EGF-induced activation of the p21(Ras)-related GTPase Rapt was also sensitized in NIH3T3/EGFR-e3B1 cells. Thus, in NIH3T3/ EGFR-e3B1 cells, maximal EGF-induced activation of Rap1 occurs with a dose of EGF much lower than in NIH3T3/EGFR cells. We also report that overexpression of e3B1 in NIH3T3/EGFR cells renders EGF-induced activation of Rapt completely dependent on Src tyrosine kinases but not on c-Abl. However, EGF-induced tyrosine phosphorylation of the Rap GEF C3G occurred regardless of whether e3B1 was overexpressed or not, and this did not involve Src tyrosine kinases. Accordingly, we propose that overexpression of e3B1 in NIH3T3/EGFR cells leads to mobilization of Src tyrosine kinases that participate in EGF-induced activation of Rap1 and inhibition of cell proliferation.
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| 3. |
- Jenei, Veronika, et al.
(author)
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Nitric oxide produced in response to engagement of beta 2 integrins on human neutrophils activates the monomeric GTPases Rap1 and Rap2 and promotes adhesion
- 2006
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In: Journal of Biological Chemistry. - 1083-351X. ; 281:46, s. 35008-35020
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Journal article (peer-reviewed)abstract
- We found that engagement of beta 2 integrins on human neutrophils increased the levels of GTP-bound Rap1 and Rap2. Also, the activation of Rap1 was blocked by PP1, SU6656, LY294002, GF109203X, or BAPTA-AM, which indicates that the downstream signaling events in Rap1 activation involve Src tyrosine kinases, phosphoinositide 3-kinase, protein kinase C, and release of calcium. Surprisingly, the beta 2 integrin-induced activation of Rap2 was not regulated by any of the signaling pathways mentioned above. However, we identified nitric oxide as the signaling molecule involved in beta 2 integrin-induced activation of Rap1 and Rap2. This was illustrated by the fact that engagement of beta 2 integrins increased the production of nitrite, a stable end-product of nitric oxide. Furthermore, pretreatment of neutrophils with N-omega-mono-methy1-L-arginine, or 1400W, which are inhibitors of inducible nitric- oxide synthase, blocked beta 2 integrin-induced activation of Rap1 and Rap2. Similarly, R-P-8pCPT-cGMPS, an inhibitor of cGMP-dependent serine/threonine kinases, also blunted the beta 2 integrin-induced activation of Rap GTPases. Also nitric oxide production and its downstream activation of cGMP-dependent serine/threonine kinases were essential for proper neutrophil adhesion by beta 2 integrins. Thus, we made the novel findings that beta 2 integrin engagement on human neutrophils triggers production of nitric oxide and its downstream signaling is essential for activation of Rap GTPases and neutrophil adhesion.
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