Novel Members of the Vesl/Homer Family of PDZ Proteins That Bind Metabotropic Glutamate Receptors

Abstract

Vesl-1S (186 amino acids, also called Homer) is a protein containing EVH1-and PDZ-like domains whose expression in the hippocampus is regulated during long term potentiation (LTP), one form of synaptic plasticity thought to underlie memory formation (Kato, A., Ozawa, F., Saitoh, Y., Hirai, K., and Inokuchi, K. (1997) FEBS Lett. 412, 183-189; Brakeman, P. R., Lanahan, A. A., O'Brien, R., Roche, K., Barnes, C. A., Huganir, R. L., and Worley, P. F. (1997) Nature 386, 284 -288). Here we report additional members of the Vesl/Homer family of proteins, Vesl-1L and Vesl-2. Vesl-1L (366 amino acids), a splicing variant of Vesl-1S, shares N-terminal 175 amino acids with Vesl-1S and contains additional amino acids at the C terminus. Vesl-2 (354 amino acids) was highly related to Vesl-1L in that both contain EVH1-and PDZlike domains at the N terminus (86% conservation) and an MCC (mutated in colorectal cancer)-like domain and a leucine zipper at the C terminus. In contrast to vesl-1S, we observed no changes in the levels of vesl-1L and vesl-2 mRNAs during dentate gyrus LTP. All these proteins interacted with metabotropic glutamate receptors (mGluR1 and mGluR5) as well as several hippocampal proteins in vitro. Vesl-1L and Vesl-2, but not Vesl-1S, interacted with each other through the C-terminal portion that was absent in Vesl-1S. Vesl-1L and Vesl-2 may mediate clustering of mGluRs at synaptic junctions. We propose that Vesl-1S may be involved in the structural changes that occur at metabotropic glutamatergic synapses during the maintenance phase of LTP by modulating the redistribution of synaptic components. Hippocampal long term potentiation (LTP),1 which is one form of synaptic plasticity thought to underlie cellular mechanisms of learning and memory (1), has two distinct phases. The early phase persists for several hours and does not require macromolecule synthesis, whereas the late phase lasts for weeks in vivo and depends on de novo protein and RNA synthesis for its maintenance (2-7). This indicates that a particular set of genes, up-regulated following LTP induction, play an important role in the maintenance of late LTP.vesl (VASP/Ena-related gene up-regulated during seizure and LTP)/homer was isolated as a synaptic plasticity-regulated gene from rat hippocampus (8,9). Hereafter, we denote the vesl cDNA that codes for a protein of 186 amino acids as vesl-1S. The expression of the vesl-1S transcript is induced in the granule cell layer of the dentate gyrus of both freely moving unanesthetized and urethane-anesthetized rats following a delivery of high frequency stimuli (HFS) to the perforant pathway, which elicits a persistent LTP lasting either several weeks or ϳ20 h, respectively. The induction is N-methyl-D-aspartate (NMDA) receptor-dependent. The Vesl-1S protein has significant homology to the EVH1 domain of VASP/Ena

Homers regulate drug-induced neuroplasticity: Implications for addiction

“…The Homer family of proteins is the product of three independent mammalian genes (Homer1-3), one Xenopus gene and one Drosophila gene [102][103][104][105]. In humans, Homer1, Homer2 and Homer3 are localized to chromosomes 5, 15 and 19, respectively [105] and Homer transcripts have been identified in many different tissues including: brain, retina, liver, kidney, spleen, testis, thymus, placenta, intestine, as well as cardiac, skeletal and smooth muscle [105][106][107].…”

“…In humans, Homer1, Homer2 and Homer3 are localized to chromosomes 5, 15 and 19, respectively [105] and Homer transcripts have been identified in many different tissues including: brain, retina, liver, kidney, spleen, testis, thymus, placenta, intestine, as well as cardiac, skeletal and smooth muscle [105][106][107]. First described in the late 1990's, the original family of Homer proteins consisted of Homer1a/b/c, Homer2a/b and 3 [102][103][104][105]. Since that time, 21 Homer mRNAs have been isolated from rat, mouse and human brain, however the proteins for some of these mRNAs have yet to be detected in mammalian brain tissue [107][108][109].…”

“…Since that time, 21 Homer mRNAs have been isolated from rat, mouse and human brain, however the proteins for some of these mRNAs have yet to be detected in mammalian brain tissue [107][108][109]. The mammalian genes encoding the Homer family of proteins have open reading frames that spread over 10 exons and can give rise to both constitutively expressed, as well as immediate early gene (IEG) products [102,104,110,111]. Exon 1 encodes the 5′ untranslated region (UTR) and contains the translational initiation codon ATG.…”

“…The EVH1 domain exhibits a high degree of similarity across Homer isoforms and is essential for Homer interactions with a proline-rich sequence (PPSPF) displayed by proteins regulating drug-induced alterations in neuronal morphology, synaptic architecture, and glutamate receptor signaling/intracellular calcium dynamics. Of particular relevance to drug-induced neuroplasticity [e.g., 20,73,74,[78][79][80][81][82][89][90][91][92][93][94][95][96][97][98][99][100][123][124][125][126][127][128][129][130], these proteins include the mGluR1a and mGluR5 subtypes of Group 1 metabotropic glutamate receptors (mGluRs) [34,102,104,107,[131][132][133][134][135][136][137], the NMDA glutamate receptor scaffolding protein Shank [38,132,138,139], the inositol-1,4,5-triphosphate (IP3) receptor, a down-stream mediator of Group1 mGluR signaling [133,[140]…”

“…Exons 6-10 encode the carboxy-tail of the majority of Homer proteins that consists of a coiled-coil (CC) domain, 2 leucine zipper motifs and encode also the 3′ UTR [104,105,107]. Homer proteins multimerize through CC/ leucine zipper motif interactions [104,105,107,133,143,144] and a recent elucidation of the quaternary structure of Homers indicate that these proteins form tetramers with each monomer oriented in parallel [143]. The tetrameric structure of Homer oligomers confers slower turnover rates and greater efficiency of localization to dendritic spines [143].…”