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 Ca2+/Ca2+ -ionophore. In addition, Rap2 segregated and was selectively enriched into microvesicles released by Ca2+ -activated RBCs, suggesting a possible role for this GTPase in membrane shedding.
Department of Biochemistry, University of Pavia, Via Bassi 21, 27100 Pavia, Italy.
Fabio
F
Greco
Annarita
A
Ciana
Daniela
D
Pietra
Cesare
C
Balduini
Giampaolo
G
Minetti
Mauro
M
Torti
D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D022161:Transport Vesicles / Q000502:physiology*; D020668:rap GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D020827:rap1 GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism*
D012333:RNA, Messenger; C116756:RAP2A protein, human; D020668:rap GTP-Binding Proteins; D020827:rap1 GTP-Binding Proteins