Dendritic cells regulate T-cell deattachment through the integrin-interacting protein CYTIP.

When T cells are primed by dendritic cells (DCs) to initiate antigen-specific immune responses screening for matching antigen receptor-MHC/peptide pairs takes place in DC-T-cell conjugates. For an immune response DC-T-cell conjugates formed during priming events need to dissolve. Although detailed knowledge on molecules involved in the conjugate formation is available, dissolving of them has not been considered to be an active process. Here, we identify CYTIP (cytohesin-interacting protein) to mediate DC-T-cell deattachment. CYTIP, which is induced during maturation of DCs, shortly accumulates to the contact zones with T cells within the first hour of coculture. Specific silencing of CYTIP results in stronger adhesion of DCs to T cells and to fibronectin. When a need for deattachment is created in a T-cell priming assay by only partially loading DCs with antigen, CYTIP silencing causes reduced priming capacity. Thus, CYTIP allows DCs to actively control DC-T-cell interactions.

In vitro treatment of dendritic cells with tacrolimus: impaired T-cell activation and IP-10 expression.

BACKGROUND: High doses (10(-6)-10(-8) M) of tacrolimus (FK506) were reported to induce a type-2 T-helper cell (Th2)-promoting function in developing dendritic cells (DC). We used a therapeutic dose (2.4 x 10(-9 )M) of tacrolimus to investigate its effect on human monocyte-derived DC. METHODS: Using untreated and treated immature and mature DC we compared T cell-activating capacity, surface marker expression, T cell and DC cytokine profile and transcription of genes coding for a panel of DC function-related molecules. RESULTS: Tacrolimus-treated mature DC had reduced T-cell stimulatory capacity. Although interleukin (IL)-12 production of DC was impaired, they did not promote Th2 development as T cells activated by tacrolimus-treated DC produced less interferon (IFN)-gamma, IL-4 and IL-10. The up-regulation of the T-cell activation marker CD69 and the production of IL-2 were impaired. In addition, tacrolimus-treated DC produced less IP-10 (CXCL10), which is known to be involved in allograft rejection. Other molecules related to DC function remained unchanged. CONCLUSIONS: Tacrolimus treatment reduces the ability of DC to stimulate T cells and the impaired production of DC-derived IP-10 (CXCL10) and IL-12 might play a role in the immunosuppressive action of tacrolimus.

Attenuation of cell adhesion in lymphocytes is regulated by CYTIP, a protein which mediates signal complex sequestration.

An important theme in molecular cell biology is the regulation of protein recruitment to the plasma membrane. Fundamental biological processes such as proliferation, differentiation or leukocyte functions are initiated and controlled through the reversible binding of signaling proteins to phosphorylated membrane components. This is mediated by specialized interaction modules, such as SH2 and PH domains. Cytohesin-1 is an intracellular guanine nucleotide exchange factor, which regulates leukocyte adhesion. The activity of cytohesin-1 is controlled by phospho inositide-dependent membrane recruitment. An interacting protein was identified, the expression of which is upregulated by cytokines in hematopoietic cells. This molecule, CYTIP, is also recruited to the cell cortex by integrin signaling via its PDZ domain. However, stimulation of Jurkat cells with phorbol ester results in re-localization of CYTIP to the cytoplasm, and membrane detachment of cytohesin-1 strictly requires co-expression of CYTIP. Consequently, stimulated adhesion of Jurkat cells to intracellular adhesion molecule-1 is repressed by CYTIP. These findings outline a novel mechanism of signal chain abrogation through sequestration of a limiting component by specific protein-protein interactions.