Heterotrimeric GTP-binding proteins in the lacrimal acinar cell endomembrane system.
Secretagogues accelerate traffic in the lysosomal and basal-lateral pathways, as well as in the regulated apical secretory pathway, of lacrimal acinar cells. It has been proposed that alterations of protein segregation in compartments where these traffic pathways intersect may influence autoimmune responses. Heterotrimeric GTP-binding proteins couple secretagogue receptor ligand binding to activation of intracellular signaling cascades, but they are also suggested to participate in endomembrane traffic phenomena. Distributions of G(o), G(i3), G(q), G(11), and two G(s)isoforms were mapped in reconstituted lacrimal acini by confocal immunofluorescence microscopy and in lysates of the reconstituted acini by analytical subcellular fractionation. All G proteins examined were detected at low levels in isolated compartments (blm(i,j)) believed to represent the basal-lateral plasma membrane. G(i3), G(11), and the G(s)isoforms were concentrated in a series of isolated compartments believed to be related to domains of a basal-lateral endosome with sorting and recycling functions (ble-s/r(i,j,k)), a distinct endosomal compartment with basal-lateral membrane-like composition (e-blml), and domains of the trans-Golgi network believed to be involved in traffic to and from the basal-lateral membrane (tgn-blmr). G(o)and G(q)were concentrated in compartments believed to represent a mixture of immature and mature secretory vesicle membranes (isvm and svm) and domains of the trans-Golgi network compartment believed to mediate traffic to secretory vesicles (tgn-svr) and to pre-lysosomes (tgn-lr). Confocal fluorescence microscopy confirmed the presence of both basal-lateral membrane and intracellular pools of the G proteins. Stimulation with 10 microM carbachol for 20min caused a component of the G(o)to redistribute away from the isvm+svm; components of the G(i3), G(q), and G(s)to redistribute away from the tgn-svr+tgn-lr; and a component of the G(i3)to redistribute away from the ble-blml+tgn-blmr. Thus, these proteins may participate in endomembrane traffic steps activated by cholinergic stimulation in addition to playing their classical roles in plasma membrane signal transduction.
Qian
Limin
L
Department of Physiology and Biophysics, University of Southern California, Los Angeles, CA 90033, USA.
Yang
Tao
T
Chen
Haishan
H
Xie
Jiansong
J
Zeng
Hongtao
H
Warren
Dwight W
DW
MacVeigh
Michaela
M
Meneray
Michele A
MA
Hamm-Alvarez
Sarah F
SF
Mircheff
Austin K
AK
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002458:Cell Fractionation / Q000379:methods; D002462:Cell Membrane / Q000737:chemistry / Q000187:drug effects; D002478:Cells, Cultured; D011992:Endosomes / Q000737:chemistry; D005260:Female; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019204:GTP-Binding Proteins / Q000032:analysis*; D020962:Heterotrimeric GTP-Binding Proteins / Q000032:analysis; D007765:Lacrimal Apparatus / Q000737:chemistry* / Q000166:cytology / Q000187:drug effects; D018613:Microscopy, Confocal; D009687:Nuclear Proteins / Q000032:analysis; D020033:Protein Isoforms / Q000032:analysis; D017346:Protein Serine-Threonine Kinases; D011817:Rabbits; D015398:Signal Transduction / Q000502:physiology; D021601:trans-Golgi Network / Q000737:chemistry
D009687:Nuclear Proteins; D020033:Protein Isoforms; D002217:Carbachol; D017346:Protein Serine-Threonine Kinases; C087996:STK19 protein, human; D019204:GTP-Binding Proteins; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins