Band 4.1 proteins are expressed in the retina and interact with both isoforms of the metabotropic glutamate receptor type 8

Abstract

Abbreviations used: CTD, C-terminal domain; EF1a, elongation factor 1a; GCL, ganglion cell layer; GFP, green fluorescent protein; INL, inner nuclear layer; IPL, inner plexiform layer; MDB, membrane binding domain; mGluR, metabotropic glutamate receptor; ONL, outer nuclear layer; OPL, outer plexiform layer; PICK1, protein interacting with C-kinase; PRS, photoreceptor segments; SAB, spectrin/actin binding domain. AbstractThe function of the CNS depends on the correct regulation of neurotransmitter receptors by interacting proteins. Here, we screened a retinal cDNA library for proteins interacting with the intracellular C-terminus of the metabotropic glutamate receptor isoform 8a (mGluR8a). The band 4.1B protein binds to the C-termini of mGluR8a and mGluR8b, co-localizes with these glutamate receptors in transfected mammalian cells, facilitates their cell surface expression and inhibits the mGluR8 mediated reduction of intracellular cAMP concentrations. In contrast, no interaction with 4.1B was observed for other mGluRs tested. Amino acids encoded by exons 19 and 20 of 4.1B and a stretch of four basic amino acids present in the mGluR8 C-termini mediate the protein interaction. Besides binding to 4.1B, mGluR8 isoforms interact with 4.1G, 4.1N, and 4.1R. Because band 4.1 transcripts undergo extensive alternative splicing, we analyzed the splicing pattern of interacting regions and detected a 4.1B isoform expressed specifically in the retina. Within this tissue, mGluR8 and 4.1B, 4.1G, 4.1N, and 4.1R show a comparable distribution, being expressed in both synaptic layers and in somata of the ganglion cell layer. In summary, our studies identified band 4.1 proteins as new players for the mGluR8 mediated signal transduction.

Interaction of 4.1G and cGMP-gated channels in rod photoreceptor outer segments

“…Both these domains have been shown to be responsible for protein-protein interaction of 4.1 proteins. In particular the CTD domain appears to be associated with the binding of membrane receptors more frequently (Gibson et al, 2012;Lu et al, 2004a;Lu et al, 2004b;Rose et al, 2008). In contrast to the selective interaction of the SAB-less 4.1G with CNG channels observed in the retina, all of the three 4.1G variants in the mouse testis were coimmunoprecipitated with nectin-like 4 (NECL4) through binding of the FERM domain (Yang et al, 2011).…”

“…In the retina, 4.1G has been found in the neuronal synaptic layers, as well as in the photoreceptor layer (Rose et al, 2008), using immunofluorescence microscopy. An earlier proteomics study also detected the presence of 4.1G in bovine rod photoreceptor outer segment (ROS) preparations (Kwok et al, 2008).…”

“…The most widely expressed homolog, 4.1G, is abundantly expressed in many tissues including the nervous system (brain, spinal cord, Schwann cells, microglia and retina) (Ohno et al, 2005;Ohno et al, 2006;Rose et al, 2008), heart (Pinder et al, 2012), testis (Ohno et al, 2005;Terada et al, 2010) and adrenal gland (Wang et al, 2010). The gene encoding 4.1G has one translation initiation site but undergoes extensive, tissue-specific alternative splicing, giving rise to many isoforms, some of which lack the SAB domain (Wang et al, 2010;Yang et al, 2011).…”

Diversity of Metabotropic Glutamate Receptor–Interacting Proteins and Pathophysiological Functions

“…Thus, a-actinin-4 interacts with group I mGlu receptors (Cabello et al 2007;Francesconi et al 2009a); vimentin with mGlu1b (Francesconi et al 2009b); a/btubulin with mGlu1a/b and mGlu7 (Francesconi et al 2009b); band 4.1 proteins with mGlu1a and mGlu8 (Lu et al 2004;Rose et al 2008); filamin-A with mGlu5 (Enz 2002a), mGlu4, mGlu7, and mGlu8; and microtubule-associated protein 1B (MAP1B) with all group III mGlu subunits (Moritz et al 2009). …”

Glutamate Signaling in Alcohol Abuse and Dependence

“…Other proteins that have been characterized to interact with mGlu7 receptors include filamin A and syntenin (cf. Nicoletti et al, 2011), whereas Band 4.1 is demonstrated to facilitate the cell surface expression of, but inhibit, mGlu8 receptors (e.g., Rose, Dutting, & Enz, 2008). Thus a number of interacting proteins regulate the subcellular localization/function of both Group 1 and Group 3 mGluR subtypes, which renders them particularly attractive molecular candidates for therapeutic intervention in neuropsychiatric disease, including alcohol use disorders (see Bockaert, Perroy, Bucamel, Marin, & Fagni, 2010;Xu & Xia, 2006).…”