María del Carmen Rodríguez

KCTD5, a putative substrate adaptor for cullin3 ubiquitin ligases

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.

Characterization of New Substrates Targeted By Yersinia Tyrosine Phosphatase YopH

YopH is an exceptionally active tyrosine phosphatase that is essential for virulence of Yersinia pestis, the bacterium causing plague. YopH breaks down signal transduction mechanisms in immune cells and inhibits the immune response. Only a few substrates for YopH have been characterized so far, for instance p130Cas and Fyb, but in view of YopH potency and the great number of proteins involved in signalling pathways it is quite likely that more proteins are substrates of this phosphatase. In this respect, we show here YopH interaction with several proteins not shown before, such as Gab1, Gab2, p85, and Vav and analyse the domains of YopH involved in these interactions. Furthermore, we show that Gab1, Gab2 and Vav are not dephosphorylated by YopH, in contrast to Fyb, Lck, or p85, which are readily dephosphorylated by the phosphatase. These data suggests that YopH might exert its actions by interacting with adaptors involved in signal transduction pathways, what allows the phosphatase to reach and dephosphorylate its susbstrates.

Platelet-activating factor : the effector of protein-rich plasma extravasation and nitric oxide synthase induction in rat immune complex peritonitis

1 The involvement of platelet‐activating factor (PAF) in immune complex‐induced/polymorphonuclear‐mediated tissue injury was studied by use of a reverse passive Arthus (RPA) model in the peritoneal cavity of rats. 2 Extravasation of protein‐rich plasma, accumulation of polymorphonuclear leukocytes (PMN), and the production of nitric oxide (NO) by resident peritoneal mononuclear phagocytes were assayed. 3 Treatment of rats with either UR‐12460 or BB‐823, two compounds which possess different chemical structures, but elicit the same antagonistic effect on the PAF receptor, abrogated protein‐rich plasma extravasation. In contrast, they did not show any effect on the accumulation of PMN. 4 Inhibition of NO production with both NG‐mono methyl‐l‐arginine and NG‐nitro‐l‐arginine failed to prevent protein‐rich plasma extravasation. 5 The production of NO by peritoneal adherent cells following RPA was measured in cells maintained for 2 to 28 h in culture, and it was significantly increased in cells removed as early as 15 min after RPA induction, as compared to controls. 6 Addition of 10 nm PAF to the culture medium reduced the generation of NO by peritoneal cells from RPA rats, whereas this mediator enhanced NO production in cells from naive control animals. 7 Treatment with either UR‐12460 or BB‐823 prior to the induction of RPA produced an almost complete inhibition of NO production. 8 Assay of nitric oxide synthase activity in cell homogenates from peritoneal cells showed that the activity was due to the inducible form of the enzyme. 9 Study by Northen blotting of mRNA coding for the inducible NO synthase (iNOS) showed transcription at 6 and 18 h after the induction of RPA, which was inhibited in UR‐12460‐treated rats. 10 These data indicate that PAF is the main mediator of the early plasma leakage observed in RPA, and also that PAF is implicated in the triggering of long‐term changes via induction of specific genes, as judged from its ability to promote the expression of iNOS.

A functional water channel protein in the pathogenic bacterium Brucella abortus

The gene for a new bacterial aquaporin, AqpX, was cloned from the pathogenic Gram-negative bacterium Brucella abortus. The gene was mapped on the large chromosome of B. abortus. It is flanked by one upstream and two downstream copies of the Brucella repeated sequence Bru-RS. Prediction from the nucleotide sequence indicated that the protein is a member of the MIP family, which comprises channels for water and/or solute transport. Expression in Xenopus oocytes and cryoelectron microscopy of Escherichia coli cells transformed with the aqpX gene confirmed that the protein is an efficient water channel. Glycerol uptake experiments in E. coli also showed that the protein is not able to transport glycerol.

Proline-serine-threonine phosphatase interacting protein 1 inhibition of T-cell receptor signaling depends on its SH3 domain

Proline‐serine‐threonine phosphatase interacting protein 1 (PSTPIP1) is an adaptor protein associated with the cytoskeleton that is mainly expressed in hematopoietic cells. Mutations in PSTPIP1 cause the rare autoinflammatory disease called pyogenic arthritis, pyoderma gangrenosum, and acne. We carried out this study to further our knowledge on PSTPIP1 function in T cells, particularly in relation to the phosphatase lymphoid phosphatase (LYP), which is involved in several autoimmune diseases. LYP–PSTPIP1 binding occurs through the C‐terminal homology domain of LYP and the F‐BAR domain of PSTPIP1. PSTPIP1 inhibits T‐cell activation upon T‐cell receptor (TCR) and CD28 engagement, regardless of CD2 costimulation. This function of PSTPIP1 depends on the presence of an intact SH3 domain rather than on the F‐BAR domain, indicating that ligands of the F‐BAR domain, such as the PEST phosphatases LYP and PTP‐PEST, are not critical for its negative regulatory role in TCR signaling. Additionally, PSTPIP1 mutations that cause the pyogenic arthritis, pyoderma gangrenosum and acne syndrome do not affect PSTPIP1 function in T‐cell activation through the TCR.

The Autoimmunity Risk Variant LYP-W620 Cooperates with CSK in the Regulation of TCR Signaling

The protein tyrosine phosphatase LYP, a key regulator of TCR signaling, presents a single nucleotide polymorphism, C1858T, associated with several autoimmune diseases such as type I diabetes, rheumatoid arthritis, and lupus. This polymorphism changes an R by a W in the P1 Pro rich motif of LYP, which binds to CSK SH3 domain, another negative regulator of TCR signaling. Based on the analysis of the mouse homologue, Pep, it was proposed that LYP and CSK bind constitutively to inhibit LCK and subsequently TCR signaling. The detailed study of LYP/CSK interaction, here presented, showed that LYP/CSK interaction was inducible upon TCR stimulation, and involved LYP P1 and P2 motifs, and CSK SH3 and SH2 domains. Abrogating LYP/CSK interaction did not preclude the regulation of TCR signaling by these proteins.

In vivo site-specific recombination using the β-rec/six system

The prokaryotic beta serine recombinase (beta-rec) catalyzes site-specific recombination between two directly oriented six sites (93 bp) in mammalian cells, both in episomal and in chromosomally integrated substrates. The beta-rec/six exclusive intramolecular site-specific recombination (SSR) system has been proposed as a suitable approach when several independently controlled recombination events are needed in a single cell. Here we explored the use of the beta-rec/six system for selective induction of genome-targeted modifications. We generated and analyzed mouse transgenic lines (Tgbeta) expressing beta-rec under the control of the Lck promoter. beta-rec activity was demonstrated, and there was no evidence of alterations to thymic or peripheral T cell development. We developed two transgenic mouse lines harboring different target sequences (Tgrec and KOsix) and analyzed the effect of beta-rec expression on these animals. The results indicate that the beta-rec/six SSR system is functional for in vivo gene-targeting applications.