Homer-3 regulates activation of serum response element in T cells via its EVH1 domain

Abstract

Drosophila enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) homology 1 (EVH1) domain proteins regulate signal transduction at the neuronal and immunologic synapse. Despite shared cell biologic machinery at these synapses, the regulation of client proteins that transmit synaptic activity to the nucleus is likely to be different. Homer-3, a member of the EVH1 family, is expressed in the thymus, suggesting a role for this protein in T-cell signal transduction. Upon T-cell receptor (TCR) engagement, Homer-3 was recruited to the contact area of Jurkat cells to anti-CD3 and CD28 antibodycoated beads prior to actin accumulation and was subsequently translocated into the nucleus. Overexpression of Homer-3 reduced transcriptional activation via the serum response element (SRE) in response to anti-CD3 antibody, phorbol ester, or dominant active Ha-Ras. Consistent with these results, knockdown of Homer-3 increased SRE activation. Homer-3 coprecipitated with CCAAT/enhancer binding protein ␤ (C/EBP␤), one of the transcription factors that binds to the SRE and has a consensus motif binding to EVH1 domain. Moreover, Homer-3 and its EVH1 domain fragment reduced transcriptional activation of C/EBP␤. These findings suggest that Homer-3 may be involved in the regulation of SRE activation in T cells via interaction between its EVH1 domain and C/EBP␤. IntroductionThe importance of compartmentalization in lymphocyte activation is only beginning to be appreciated. Early signaling events following T-cell receptor (TCR) ligation require lipid rafts and polymerization of the actin cytoskeleton, which serve to assemble signaling complexes. [1][2][3][4][5] Drosophila enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) homology 1 (EVH1) domaincontaining proteins can be divided into 4 subgroups: the Ena/VASP, Wiskott-Aldrich syndrome protein (WASP), Spred, and Homer families. 6 The EVH1 domain was first identified as a homologous region of about 110 amino acids present in the N-terminal region of the Ena/VASP family. Members of the Ena/VASP family are key adaptor molecules in regulating actin filament assembly. 7-9 WASP family proteins regulate actin dynamics through binding and activation of the actin-related protein 2/3 (Arp2/3) complex, which nucleates new actin filaments. [10][11][12] Spreds are Sprouty-related suppressors of Ras signaling. Spreds constitutively associate with Ras and suppress phosphorylation of Raf. 13 The Homer family was first identified as an immediate early gene expressed in rat brain after electroconvulsive seizures or electrical stimulation that leads to long-term potentiation of hippocampal glutamatergic synapses. 14,15 Members of the Homer family bind to a variety of proteins, including group I metabolic glutamate receptors (mGluR), inositol triphosphate receptors, ryanodine receptors, and Shank (Src homology 3 domain and ankyrin repeat-containing). 14,16-18 All of these interactions have been shown to be mediated by the EVH1 domain of the Homer molecule. The EVH1 domains of Homer family members re...

Identification of candidate target genes of genomic aberrations in esophageal squamous cell carcinoma

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Ca2+/Calmodulin-Dependent Protein Kinase II Is a Modulator of CARMA1-Mediated NF-κB Activation

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