The Distribution and Function of Alternatively Spliced Insertions in hDlg

Margaret Mclaughlin,Robert Hale,Dawna Ellston,Suzanne Gaudet,Robert A Lue,Alain Viel

doi:10.1074/jbc.m108724200

Abstract

hDlg is the human homolog of the Drosophila Discs-large tumor suppressor. As a member of the MAGUK (membrane-associated guanylate kinase) family of scaffolding proteins, hDlg is composed of three PDZ (PSD-95, Dlg, and ZO-1) repeats, an SH3 (Src homology 3) motif, and a GUK (guanylate kinase-like) domain. Additionally, hDlg contains two regions of alternative splicing. Here we identify a novel insertion, I1B, located N-terminal to the PDZ repeats. We further analyze the tissue-specific combinations of insertions and correlate those results with the distribution of protein isoforms. We also identify the functions of the two alternatively spliced regions. The N-terminal alternatively spliced region is capable of binding several SH3 domains and also moderates the level of protein oligomerization. Insertions in the second region are responsible for determining the localization of hDlg, with insertion I3 targeting the protein to the membrane regions of cell-cell contact and insertion I2 targeting the protein to the nucleus.

Highlights

HDlg is the human homolog of the Drosophila Discslarge tumor suppressor
As a member of the MAGUK family of scaffolding proteins, hDlg is composed of three PDZ (PSD95, Dlg, and ZO-1) repeats, an SH3 (Src homology 3) motif, and a GUK domain
Dlg and hDlg are members of the MAGUK1 family of proteins typically involved in protein scaffolding and cell signaling

Summary

Introduction

As a member of the MAGUK (membrane-associated guanylate kinase) family of scaffolding proteins, hDlg is composed of three PDZ (PSD95, Dlg, and ZO-1) repeats, an SH3 (Src homology 3) motif, and a GUK (guanylate kinase-like) domain. First identified from human B lymphocyte cDNA, hDlg encodes a 100-kDa protein sharing ϳ60% similarity with Drosophila Dlg and 70% similarity with rat SAP90/PSD-95 [1]. An alternatively spliced insertion called I1 [1] is located between the unique N-terminal domain of hDlg (NAG) and the first PDZ repeat. The region between the SH3 and GUK domains of hDlg was first characterized as containing two alternatively spliced insertions, I2 and I3 [1]. A third alternatively spliced insertion, called I4, was described in a brain isoform of hDlg [9]. In keeping with our nomenclature, we have termed this region I5

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Conclusion