Multimerization of the Protein-tyrosine Phosphatase (PTP)-like Insulin-dependent Diabetes Mellitus Autoantigens IA-2 and IA-2β with Receptor PTPs (RPTPs): INHIBITION OF RPTPα ENZYMATIC ACTIVITY

Steffen Gross,Christophe Blanchetot,Jan Schepens,Sabrina Albet,Reiner Lammers,Jeroen Den Hertog,Wiljan Hendriks

doi:10.1074/jbc.m208228200

Abstract

Most receptor-type protein-tyrosine phosphatases (RPTPs) contain two tandem PTP domains. For some RPTPs the enzymatically inactive membrane-distal phosphatase domains (D2) were found to bind enzymatically active membrane proximal PTP (D1) domains, and oligomerization has been proposed as a general regulatory mechanism. The RPTP-like proteins IA-2 and IA-2beta, major autoantigens in insulin-dependent diabetes mellitus, contain just a single enzymatically inactive PTP-like domain. Their physiological role is as yet enigmatic. To investigate whether the catalytically inactive cytoplasmic domains of IA-2 and IA-2beta are involved in oligomerization, we exploited interaction trap assay in yeast and glutathione S-transferase pull-down and co-immunoprecipitation strategies on lysates of transfected COS-1 cells. The results show that IA-2 and IA-2beta are capable of homo- and heterodimerization to which both the juxtamembrane region and the phosphatase-like segment can contribute. Furthermore, they can form heterodimers with some other RPTP members, most notably RPTPalpha and RPTPepsilon, and down-regulate RPTPalpha enzymatic activity. Thus, in addition to homo-dimerization, the enzymatic activity of receptor-type PTPs can be regulated through heterodimerization with other RPTPs, including the catalytically inactive IA-2 and IA-2beta.

Highlights

Most receptor-type protein-tyrosine phosphatases (RPTPs) contain two tandem PTP domains
Our findings indicate that the regulation of the enzymatic activity of RPTPs may in addition depend on the association with RPTP-like, catalytically inactive family members such as IA-2 and IA-2␤
These findings are specific, because both protein segments did not display binding to the protein encoded by the empty vector nor with phosphatase domain-containing segments of the unrelated PTP-SL/PTPBR7 [3] and PTP-BL [40]

Summary

Introduction

Most receptor-type protein-tyrosine phosphatases (RPTPs) contain two tandem PTP domains. Ily of PTPs can be classified into cytosolic and transmembrane or receptor-like PTPs (RPTPs) The latter consist of an ectodomain, which displays the use of a bewildering variety of protein modules, a single membrane-spanning region, and one (such as in PTPBR7 and DEP1 [1,2,3]) but in most cases two highly conserved intracellular tyrosine-specific phosphatase domains [4, 5]. RPTP-like proteins exist that have a single but inactive PTP domain, and it has been suggested that the inactive domain is used as a phosphotyrosine recognition/binding moiety [18] Two such proteins, IA-2 and IA-2␤, have drawn quite some attention because they were identified as the precursors of 40- and 37-kDa insulin-dependent diabetes mellitus-specific major auto-antigens, respectively [19]. Many investigations are focused on the role of IA-2 and IA-2␤ in autoimmune diabetes, but only limited information is avail-

Methods

Results

Conclusion