WW Domains Provide a Platform for the Assembly of Multiprotein Networks
Journal - Molecular and Cellular Biology
WW domains are protein modules that mediate protein-protein interactions through recognition of proline-rich peptide motifs and phosphorylated serine/threonine-proline sites. To pursue the functional properties of WW domains, we employed mass spectrometry to identify 148 proteins that associate with 10 human WW domains. Many of these proteins represent novel WW domain-binding partners and are components of multiprotein complexes involved in molecular processes, such as transcription, RNA processing, and cytoskeletal regulation. We validated one complex in detail, showing that WW domains of the AIP4 E3 protein-ubiquitin ligase bind directly to a PPXY motif in the p68 subunit of pre-mRNA cleavage and polyadenylation factor Im in a manner that promotes p68 ubiquitylation. The tested WW domains fall into three broad groups on the basis of hierarchical clustering with respect to their associated proteins; each such cluster of bound proteins displayed a distinct set of WW domain-binding motifs. We also found that separate WW domains from the same protein or closely related proteins can have different specificities for protein ligands and also demonstrated that a single polypeptide can bind multiple classes of WW domains through separate proline-rich motifs. These data suggest that WW domains provide a versatile platform to link individual proteins into physiologically important networks.
The Epstein-Barr Virus Protein, Latent Membrane Protein 2A, Co-opts Tyrosine Kinases Used by the T Cell Receptor*
Journal - Journal of Biological Chemistry
Epstein-Barr virus (EBV) is the causative agent of infectiousmononucleosis and is associated with several human malignancies.The EBV protein latent membrane protein 2A (LMP2A) promotesviral latency in memory B cells by interfering with B cell receptorsignaling and provides a survival signal for mature B cellsthat have lost expression of surface immunoglobulin. The latterfunction has suggested that LMP2A may enhance the survival ofEBV-positive tumors. EBV is associated with several T cell malignanciesand, since LMP2A has been detected in several of these disorders,we examined the ability of LMP2A to transmit signals and interferewith T cell receptor signaling in T cells. We show that LMP2Ais tyrosine-phosphorylated in Jurkat TAg T cells, which requiresexpression of the Src family tyrosine kinases, Lck and Fyn.Lck and Fyn are recruited to the tyrosine-phosphorylated Tyr112site in LMP2A, whereas phosphorylation of an ITAM motif in LMP2Acreates a binding site for the ZAP-70/Syk tyrosine kinases.LMP2A also associates through its two PPPPY motifs with AIP4,a NEDD4 family E3 ubiquitin ligase; this interaction resultsin ubiquitylation of LMP2A and serves to regulate the stabilityof LMP2A and LMP2A-kinase complexes. Furthermore, stable expressionof LMP2A in Jurkat T cells down-regulated T cell receptor levelsand attenuated T cell receptor signaling. Thus, through recruitingtyrosine kinases involved in T cell receptor activation, LMP2Amay provide a survival signal for EBV-positive T cell tumors,whereas LMP2A-associated NEDD4 E3 ligases probably titer thestrength of this signal.* This work was supported by grants from the Canadian Institutesfor Health Research (to T. P.) and the Swedish Cancer Society(to I. E.). The costs of publication of this article were defrayedin part by the payment of page charges. This article must thereforebe hereby marked "advertisement" in accordance with 18 U.S.C.Section 1734 solely to indicate this fact.1 Recipient of a postdoctoral fellowship from the National CancerInstitute of Canada (supported by Funds from the Terry Fox Run)and a Fellow of the Leukemia and Lymphoma Society. Present address:Dept. of Biology, University of Victoria, Petch Bldg. 053, 3800Finnerty Rd., Victoria, British Columbia V8P 5C2, Canada.2 Recipient of Swedish Research Council Grant K2002-16X-14227-01Aand Swedish Children's Cancer Foundation Grant PROJ01/18.