KCTD5, a putative substrate adaptor for cullin3 ubiquitin ligases

in FEBS Journal (2008), 275(15), 3900-3910

Potassium channel tetramerization domain (KCTD) proteins contain a bric-a-brac, tramtrak and broad complex (BTB) domain that is most similar to the tetramerization domain (T1) of voltage-gated potassium ... [more ▼]

Potassium channel tetramerization domain (KCTD) proteins contain a bric-a-brac, tramtrak and broad complex (BTB) domain that is most similar to the tetramerization domain (T1) of voltage-gated potassium channels. Some BTB-domain-containing proteins have been shown recently to participate as substrate-specific adaptors in multimeric cullin E3 ligase reactions by recruiting proteins for ubiquitination and subsequent degradation by the proteasome. Twenty-two KCTD proteins have been found in the human genome, but their functions are largely unknown. In this study, we have characterized KCTD5, a new KCTD protein found in the cytosol of cultured cell lines. The expression of KCTD5 was upregulated post-transcriptionally in peripheral blood lymphocytes stimulated through the T-cell receptor. KCTD5 interacted specifically with cullin3, bound ubiquitinated proteins, and formed oligomers through its BTB domain. Analysis of the interaction with cullin3 showed that, in addition to the BTB domain, some amino acids in the N-terminus of KCTD5 are required for binding to cullin3. These findings suggest that KCTD5 is a substrate-specific adaptor for cullin3-based E3 ligases. [less ▲]

Removal of C-terminal Src kinase from the immune synapse by a new binding protein

in Molecular and Cellular Biology (2005), 25(6), 2227-2241

The Csk tyrosine kinase negatively regulates the Src family kinases Lek and Fyn in T cells. Engagement of the T-cell antigen receptor results in a removal of Csk from the lipid raft-associated ... [more ▼]

The Csk tyrosine kinase negatively regulates the Src family kinases Lek and Fyn in T cells. Engagement of the T-cell antigen receptor results in a removal of Csk from the lipid raft-associated transmembrane protein PAG/Cbp. Instead, Csk becomes associated with an similar to72-kDa tyrosine-phosphorylated protein, which we identify here as G3BP, a phosphoprotein reported to bind the SH3 domain of Ras GTPase-activating protein. G3BP reduced the ability of Csk to phosphorylate Lek at Y505 by decreasing the amount of Csk in lipid rafts. As a consequence, G3BP augmented T-cell activation as measured by interleukin-2 gene activation. Conversely, elimination of endogenous G3BP by RNA interference increased Lek Y505 phosphorylation and reduced TCR signaling. In antigen-specific T cells, endogenous G3BP moved into a intracellular location adjacent to the immune synapse, but deeper inside the cell, upon antigen recognition. Csk colocalization with G3BP occurred in this "parasynaptic" location. We conclude that G3BP is a new player in T-cell-antigen receptor signaling and acts to reduce the amount of Csk in the immune synapse. [less ▲]

Lck dephosphorylation at Tyr-394 and inhibition of T cell antigen receptor signaling by Yersinia phosphatase YopH.

in Journal of Biological Chemistry (2004), 279(6), 4922-8

A key virulence factor for Yersinia pestis, the etiologic agent of plague, is the tyrosine phosphatase YopH, which the bacterium injects into host cells. We report that treatment of human T lymphocytes ... [more ▼]

A key virulence factor for Yersinia pestis, the etiologic agent of plague, is the tyrosine phosphatase YopH, which the bacterium injects into host cells. We report that treatment of human T lymphocytes with a recombinant membrane-permeable YopH resulted in severe reduction in intracellular tyrosine phosphorylation and inhibition of T cell activation. The primary signal transducer for the T cell antigen receptor, the Lck tyrosine kinase, was specifically precipitated by a substrate-trapping YopH mutant, and Lck was dephosphorylated at its positive regulatory site, Tyr-394, in cells containing active YopH. By turning off Lck, YopH blocks T cell antigen receptor signaling at its very first step, effectively preventing the development of a protective immune response against this lethal bacterium. [less ▲]

Protein tyrosine phosphatases in T cell physiology.

in Molecular Immunology (2004), 41(6-7), 687-700

The molecular mechanisms of signal transduction have been the focus of intense research during the last decade. In T cells, much of the work has centered on protein tyrosine kinase-mediated signaling from ... [more ▼]

The molecular mechanisms of signal transduction have been the focus of intense research during the last decade. In T cells, much of the work has centered on protein tyrosine kinase-mediated signaling from the TCR and cytokine receptors, while the study of protein tyrosine phosphatases has lagged behind. Nevertheless, it has now become clear that many protein tyrosine phosphatases play equally important roles in T cell physiology and that no kinase-regulated system would work without the counterbalancing participation of phosphatases. In fact, we have learned that many processes are regulated primarily on the phosphatase side. This minireview summarizes the current state-of-the art in our understanding of the regulation and biology of protein tyrosine phosphatases in T lymphocyte physiology. [less ▲]

Role of protein tyrosine phosphatases in T cell activation.

in Immunological Reviews (2003), 191

The last decade has seen an exponentially increasing interest in the molecular mechanisms of signal transduction. In T cells, much of the focus has been on protein tyrosine kinase (PTK)-mediated signaling ... [more ▼]

The last decade has seen an exponentially increasing interest in the molecular mechanisms of signal transduction. In T cells, much of the focus has been on protein tyrosine kinase (PTK)-mediated signaling from the T cell receptor (TCR) and cytokine receptors, while the study of protein tyrosine phosphatases (PTPases) has lagged behind. However, recent discoveries have revealed that several PTPases play important roles in many different aspects of T cell physiology. We predict that the phosphatases will become a 'hot topic' in the field within the next few years. This review summarizes the current understanding of the regulation and biology of PTPases in T lymphocyte activation. [less ▲]