title: Rap1 up-regulation and activation on plasma membrane regulates T cell adhesion.
abstract: Rap1 and Ras are closely related GTPases that share some effectors but have distinct functions. We studied the subcellular localization of Rap1 and its sites of activation in living cells. Both GFP-tagged Rap1 and endogenous Rap1 were localized to the plasma membrane (PM) and endosomes. The PM association of GFP-Rap1 was dependent on GTP binding, and GFP-Rap1 was rapidly up-regulated on this compartment in response to mitogens, a process blocked by inhibitors of endosome recycling. A novel fluorescent probe for GTP-bound Rap1 revealed that this GTPase was transiently activated only on the PM of both fibroblasts and T cells. Activation on the PM was blocked by inhibitors of endosome recycling. Moreover, inhibition of endosome recycling blocked the ability of Rap1 to promote integrin-mediated adhesion of T cells. Thus, unlike Ras, the membrane localizations of Rap1 are dynamically regulated, and the PM is the principle platform from which Rap1 signaling emanates. These observations may explain some of the biological differences between these GTPases.
authors.affiliation: Deparment of Cell Biology, New York University School of Medicine, 550 First Ave., New York, NY 10016, USA.
authors.forename: Trever G
authors.initials: TG
authors.lastname: Bivona
authors.forename: Heidi H
authors.initials: HH
authors.lastname: Wiener
authors.forename: Ian M
authors.initials: IM
authors.lastname: Ahearn
authors.forename: Joseph
authors.initials: J
authors.lastname: Silletti
authors.forename: Vi K
authors.initials: VK
authors.lastname: Chiu
authors.forename: Mark R
authors.initials: MR
authors.lastname: Philips
mesh_terms: D000818:Animals; D002448:Cell Adhesion / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology; D006056:Golgi Apparatus / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D008934:Mitogens / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013347:Subcellular Fractions / Q000737:chemistry / Q000378:metabolism; D013601:T-Lymphocytes / Q000378:metabolism*; D015854:Up-Regulation; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D008934:Mitogens; D011993:Recombinant Fusion Proteins; D004815:Epidermal Growth Factor; D006160:Guanosine Triphosphate; D020827:rap1 GTP-Binding Proteins