Activation of the Small GTPase Rac2 via the B Cell Receptor Regulates B Cell Adhesion and Immunological-Synapse Formation.
Arana, Eloisa 1,4; Vehlow, Anne 1,4; Harwood, Naomi E. 1; Vigorito, Elena 2; Henderson, Robert 3; Turner, Martin 2; Tybulewicz, Victor L.J. 3; Batista, Facundo D. 1,*
[Article]
Immunity.
28(1):88-99, January 2008.
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: The integrin leukocyte function-associated antigen-1 (LFA-1) is important in the promotion of B cell adhesion, thereby facilitating immunological synapse (IS) formation and B cell activation. Despite this significance, the associated signaling mechanisms regulating LFA-1 activation remain elusive. Here, we show that both isoforms of the small GTPase Rac expressed by primary B cells, Rac1 and Rac2, were activated rapidly downstream of Src-family kinases, guanine-nucleotide exchange factors Vav1 and Vav2, and phosphoinositide-3 kinase (PI3K) after BCR engagement. We identify Rac2, but not Rac1, as critical for B cell adhesion to intercellular adhesion molecule-1 (ICAM-1) and IS formation. Furthermore, B cells expressing constitutively active Rac2 are highly adhesive. We observe that Rac2-deficient B cells exhibit lower amounts of Rap1-GTP and severe actin polymerization defects, identifying a potential mechanism underlying their behavior. We postulate that this critical role for Rac2 in mediating B cell adhesion and IS formation might apply in all lymphocytes.
(C) 2008Elsevier, Inc.