Rap2, but not Rap1 GTPase is expressed in human red blood cells and is involved in vesiculation.
Recent studies have suggested that Rap1 and Rap2 small GTP-binding proteins are both expressed in human red blood cells (RBCs). In this work, we carefully examined the expression of Rap proteins in leukocytes- and platelets-depleted RBCs, whose purity was established on the basis of the selective expression of the beta2 subunit of the Na(+)/K(+)-ATPase, as verified according to the recently proposed "beta-profiling test" [J.F. Hoffman, A. Wickrema, O. Potapova, M. Milanick, D.R. Yingst, Na pump isoforms in human erythroid progenitor cells and mature erythrocytes, Proc. Natl. Acad. Sci. U. S. A. 99 (2002) 14572-14577]. In pure RBCs preparations, Rap2, but not Rap1 was detected immunologically. RT-PCR analysis of mRNA extracted from highly purified reticulocytes confirmed the expression of Rap2b, but not Rap2a, Rap2c, Rap1a or Rap1b. In RBCs, Rap2 was membrane-associated and was rapidly activated upon treatment with Ca(2+)/Ca(2+)-ionophore. In addition, Rap2 segregated and was selectively enriched into microvesicles released by Ca(2+)-activated RBCs, suggesting a possible role for this GTPase in membrane shedding.[1]References
- Rap2, but not Rap1 GTPase is expressed in human red blood cells and is involved in vesiculation. Greco, F., Ciana, A., Pietra, D., Balduini, C., Minetti, G., Torti, M. Biochim. Biophys. Acta (2006) [Pubmed]
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