RESUMEN
The plasma membrane Ca2+-ATPase-2 (PMCA2) is expressed in stereocilia of hair cells of the inner ear, whereas PMCA1 is expressed in the basolateral plasma membrane of hair cells. Both extrude excess Ca2+ from the cytosol. They are predicted to contain ten membrane-spanning segments, two large cytoplasmic loops as well as cytosolic N- and C-termini. Several isoform variants are generated for both PMCA1 and PMCA2 by alternative splicing, affecting their first cytosolic loop (A-site) and their C-terminal tail. To understand how these isoforms are differentially targeted in hair cells, we investigated their targeting regions and expression in hair cells. Our results show that a Leu-Ile motif in 'b'-tail splice variants promotes PMCA1b and PMCA2b basolateral sorting in hair cells. Moreover, apical targeting of PMCA2 depends on the size of the A-site-spliced insert, suggesting that the conformation of the cytoplasmic loop plays a role in apical targeting.
Asunto(s)
Membrana Celular/metabolismo , Células Ciliadas Auditivas/citología , Células Ciliadas Auditivas/metabolismo , ATPasas Transportadoras de Calcio de la Membrana Plasmática/metabolismo , Secuencias de Aminoácidos , Secuencia de Aminoácidos , Animales , Células Cultivadas , Células Clonales , ADN Complementario/aislamiento & purificación , Perros , Células Epiteliales/citología , Células Ciliadas Auditivas/enzimología , Humanos , Isoleucina/metabolismo , Leucina/metabolismo , Datos de Secuencia Molecular , Peso Molecular , ATPasas Transportadoras de Calcio de la Membrana Plasmática/química , ATPasas Transportadoras de Calcio de la Membrana Plasmática/genética , Isoformas de Proteínas , Transporte de Proteínas , Ratas , PorcinosRESUMEN
Functional expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in cerebellar granule cells requires stargazin, a member of a large family of four-pass transmembrane proteins. Here, we define a family of transmembrane AMPA receptor regulatory proteins (TARPs), which comprise stargazin, gamma-3, gamma-4, and gamma-8, but not related proteins, that mediate surface expression of AMPA receptors. TARPs exhibit discrete and complementary patterns of expression in both neurons and glia in the developing and mature central nervous system. In brain regions that express multiple isoforms, such as cerebral cortex, TARP-AMPA receptor complexes are strictly segregated, suggesting distinct roles for TARP isoforms. TARPs interact with AMPA receptors at the postsynaptic density, and surface expression of mature AMPA receptors requires a TARP. These studies indicate a general role for TARPs in controlling synaptic AMPA receptors throughout the central nervous system.