The Scaffold Protein Cybr Is Required for Cytokine-Modulated Trafficking of Leukocytes In Vivo

Abstract

Trafficking and cell adhesion are key properties of cells of the immune system. However, the molecular pathways that control these cellular behaviors are still poorly understood. Cybr is a scaffold protein highly expressed in the hematopoietic/immune system whose physiological role is still unknown. In vitro studies have shown it regulates LFA-1, a crucial molecule in lymphocyte attachment and migration. Cybr also binds cytohesin-1, a guanine nucleotide exchange factor for the ARF GTPases, which affects actin cytoskeleton remodeling during cell migration. Here we show that expression of Cybr in vivo is differentially modulated by type 1 cytokines during lymphocyte maturation. In mice, Cybr deficiency negatively affects leukocytes circulating in blood and lymphocytes present in the lymph nodes. Moreover, in a Th1-polarized mouse model, lymphocyte trafficking is impaired by loss of Cybr, and Cybr-deficient mice with aseptic peritonitis have fewer cells than controls present in the peritoneal cavity, as well as fewer leukocytes leaving the bloodstream. Mutant mice injected with Moloney murine sarcoma/leukemia virus develop significantly larger tumors than wild-type mice and have reduced lymph node enlargement, suggesting reduced cytotoxic T-lymphocyte migration. Taken together, these data support a role for Cybr in leukocyte trafficking, especially in response to proinflammatory cytokines in stress conditions. Leukocytes are extremely mobile cells capable of controlling their interactions with other cells or with the extracellular matrix in a fast and efficient manner (25). How the signal received from the extracellular environment is transduced intracellularly to coordinate the appropriate cell response is a major question in leukocyte biology. Scaffold proteins, containing various protein-protein interaction domains, are emerging as molecules able to rapidly integrate signals from different pathways through the interaction with multiple partners, especially in situations of rapid cellular response to an external stimulus (21).Cybr (also known as B3-1/36.3K zipper-containing protein [8], CBP [12], Cytip [3], and CASP [14]) is a 359-amino-acid (aa) scaffold protein containing two adjacent protein-protein interacting domains: a 90-aa PDZ (postsynaptic density protein-95/discs-large/ZO-1) domain and a 20-aa leucine-rich domain. In particular, the leucine-rich domain is responsible for Cybr interaction with cytohesin-1, a guanine exchange factor (GEF) for the ARF (ADP-ribosylation factors) GTPase family members (3,27

Cybr, CYTIP or CASP: An attempt to pinpoint a molecule's functions and names

“…Lymphocytes show a deficit in their trafficking behaviour and the CD8-mediated immune response to Moloney murine sarcoma virus (M-MSV) is delayed significantly. This is attributed to the impaired trafficking capacity of lymphocytes (Coppola et al, 2006), but is also in accordance with the finding that human dendritc cells silenced for CYTIP show a reduced stimulatory capacity for antigen-specific CD8 positive T-cells (Hofer et al, 2006). With the latter mouse model Watford and colleagues, in accordance with the first mouse model, found no effect of lack of Cybr on the development of the immune system.…”

“…For in vivo characterization of the multinamed molecule two Cybr-deficient mice were created, one by the removal of exon 1 using the cre-lox system (Coppola et al, 2006), the other by replacing parts of exon 2 and exon 3 by enhanced EGFP-encoding sequence (Watford et al, 2006). Using the first mouse model, Coppola and colleagues found that Cybr deletion does not seem to affect the development of the immune system.…”

Infection of dendritic cells with herpes simplex virus type 1 induces rapid degradation of CYTIP, thereby modulating adhesion and migration

“…Subsequently, the complex translocates from the plasma membrane to the cytosol, thereby interrupting the activation of LFA-1. 14 Recently, it was shown that CYTIP regulates leukocyte trafficking 15 and the adherence of DCs to fibronectin 16 as well as T-cell detachment and T-cell priming. 16,17 Herpes simplex virus type 1 (HSV-1) is the prototypic member of the large and diverse family of herpesviridae, including several human pathogens.…”

Cytip regulates dendritic‐cell function in contact hypersensitivity

“…Cytip-deficient mice [7] were kindly provided by Antonio Rosato (Department of Oncology and Surgical Sciences, University of Padova, Italy).…”