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.

We thank Daniel McVicar, Debbie Hodge, and Franca Aiello for helpful discussions and critical review of the manuscript, John Wine for his technical assistance with the tail vein injections, Roberta Smith, Leslie Johnston, and Keith Rogers at the PHL, SAIC, Frederick, Md., for the histological analysis, Susan Reid and Eileen Southon for ES cell manipulations and blastocyst injections, and Hui-Fang Dong for isolation of the cells used in the chemotaxis studies.

This research was supported by the Intramural Research Program of the NIH, National Cancer Institute, Center for Cancer Research.