Negative regulation of chemokine receptor signaling and B-cell chemotaxis by p66Shc.

Shc (Src homology 2 domain containing) adaptors are ubiquitous components of the signaling pathways triggered by tyrosine kinase-coupled receptors. In lymphocytes, similar to other cell types, the p52 and p66 isoforms of ShcA/Shc participate in a self-limiting loop where p52Shc acts as a positive regulator of antigen receptor signaling by promoting Ras activation, whereas p66Shc limits this activity by competitively inhibiting p52Shc. Based on the fact that many signaling mediators are shared by antigen and chemokine receptors, including p52Shc, we have assessed the potential implication of p66Shc in the regulation of B-cell responses to chemokines, focusing on the homing receptors CXCR4 (C-X-C chemokine receptor type 4) and CXCR5 (C-X-C chemokine receptor type 5). The results identify p66Shc as a negative regulator of the chemotactic responses triggered by these receptors, including adhesion, polarization and migration. We also provide evidence that this function is dependent on the ability of p66Shc to interact with the chemokine receptors and promote the assembly of an inhibitory complex, which includes the phosphatases SHP-1 (Src homology phosphatase-1) and SHIP-1 (SH2 domain-containing inositol 5'-phosphatase-1), that results in impaired Vav-dependent reorganization of the actin cytoskeleton. This function maps to the phosphorylatable tyrosine residues in the collagen homology 1 (CH1) domain. The results identify p66Shc as a negative regulator of B-cell chemotaxis and suggest a role for this adaptor in the control of B-cell homing.

Vav1 haploinsufficiency in a common variable immunodeficiency patient with defective T-cell function.

Common variable immunodeficiency (CVID) is a primary immune disorder characterized by impaired antibody production, which is in many instances secondary to defective T cell function (T-CVID). We previously identified a subset of T-CVID patients characterized by defective expression of Vav1, a guanine nucleotide exchanger which couples the T-cell antigen receptor to reorganization of the actin cytoskeleton. Here we have addressed the possibility that an intrinsic defect in the Vav1 gene might underlie the reduction in Vav protein observed in T cells from these patients. We report the identification in one T-CVID patient of a heterozygous deletion in Vav1. The gene deletion, spanning exons 2-27, accounts for the reduction in Vav1 mRNA and protein in T cells from this patient. The disease-related pedigree of this patient suggests a de novo origin of the Vav1 deletion. The findings highlights Vav1 as an autosomal dominant disease gene associated with CVID with defective T-cell function.

The Bcl-2 family as a rational target for the treatment of B-cell chronic lymphocytic leukaemia.

B-cell chronic lymphocytic leukaemia (B-CLL) is the most common lymphoid malignancy in the Western world, characterized by clonal growth and accumulation of monoclonal CD5+ B-cells in peripheral blood, bone marrow and peripheral lymphoid organs. Although the clinical course in B-CLL patients is highly variable, the most conserved feature is the prolonged survival of malignant B-cells, which has been associated to defects in the apoptotic machinery. The apoptosis defects are mainly determined by a defective balance among pro- and anti-apoptotic members of the Bcl-2 family, often related to resistance of CLL B-cells to chemotherapy. Purine nucleoside analogs or alkylating agents, alone or in combination, are the first-line treatment for B-CLL patients. Alternative, more specifically tailored therapeutics have been developed in recent years, including humanized monoclonal antibodies and kinase inhibitors. Here we shall review the drugs which are commonly used or are currently being assessed in clinical trials on B-CLL patients, their chemical structure, mechanisms of action, pharmacological properties, molecular targets, clinical efficacy and side effects, with a focus on drugs designed to promote apoptosis of malignant B-cells by targeting the Bcl-2 family.

A new cephalosporin derivative (ST-21) orally administered in laboratory animals.

The pivaloxymethyl ester of 7-(D-2-amino-2-phenylacetamido)-desacetoxicephalosporanic acid hydrochloride (ST-21) and cephalexin possess the same bacteridal activity. In fact, in the animal body ST-21 releases cephalexin. The acute toxicity study shows the good tolerance of both substances, whereas the tissue distribution is different, both after oral and i.v. administration. Cephalexin concentrations in some tissues of rats and rabbits, particularly in the lungs and kidneys, are higher and longer-lasting in the animals treated with ST-21 than in those receiving cephalexin, thus showing a different pattern of distribution in the body. For this reason ST-21 might be more suited for the treatment of lung and kidney infections.