Cytokine receptor architecture, structure and genetic assembly

Urokinase receptor is associated with the components of the JAK1/STAT1 signaling pathway and leads to activation of this pathway upon receptor clustering in the human kidney epithelial tumor cell line TCL-598

The urokinase-type plasminogen activator (uPA) binds to cells via a specific receptor attached to the plasma membrane by a glycosylphosphatidylinositol (GPI) anchor. Despite the lack of a transmembrane domain, the urokinase receptor (uPAR) is capable of transducing extracellular signals affecting growth, migration, and adhesion. Several Tyr kinases of the src family as well as beta1, beta2, and beta3 integrins were found to be associated with the uPAR. We found that in the human kidney epithelial line TCL-598, also components of the JAK1/STAT1 signal transduction pathway including gp130, are associated with uPAR as revealed by coimmunoprecipitation and are co-localized in caveolae. Upon clustering of uPA.uPAR complex by a monoclonal antibody, JAK1 associates with uPAR, which in turn leads to STAT1 phosphorylation, dimerization, specific binding to DNA, and gene activation. To prove the dependence of STAT1 activation on the uPAR, TCL-598 cells were treated with sense and antisense uPAR oligonucleotides. In antisense-treated cells in which uPAR expression was reduced to less then one third, activation of STAT1 by the clustering antibody was abolished while STAT1 activation by interferon-gamma was unaffected. Therefore, in this cell line, uPA.uPAR also utilizes the JAK1/STAT1 pathway for signaling, and gp130 might be the transmembrane adapter for this signal transduction pathway.

A primer on cytokines: sources, receptors, effects, and inducers

Protection against pathogens is a prerequisite for survival of most organisms. To cope with this continuous challenge, complex defense mechanisms have evolved. The construction, adaptation, and maintenance of these mechanisms are under control of an extensive network of regulatory proteins called cytokines. A great number of cytokines have been described over the last 2 decades. This review consists of an overview of cytokines that are involved in immune responses and describes some historical and general aspects as well as prospective clinical applications. Major biological effects together with information on cytokine receptors, producers, inducers, and biochemical and molecular characteristics are listed in tables. In addition, some basic information is given on cytokine receptor signal transduction. Finally, the recent discoveries of cytokine receptors functioning as coreceptors in the pathogenesis of human immunodeficiency virus are summarized.

Interleukin-2 increases choline acetyltransferase activity in septal-cell cultures

Interleukin-2 (IL-2) is a potent modulator of in vitro acetylcholine release in hippocampal slices [Hanisch et al. (1993) J. Neurosci., 13:3368]. In order to further investigate the cellular nature of this effect, we used embryonic septal-cell cultures (E17), known to be enriched with the cholinergic phenotype. Septal cells were grown at different plating densities under serum-free conditions. The effect of IL-2 on the expression of the cholinergic phenotype was determined using choline acetyltransferase (ChAT) activity and acetylcholinesterase (AChE) cytochemistry. IL-2 significantly enhanced ChAT activity in 5-day-old cultures (5 days in vitro). The amplitude of increases correlated with plating density. At 5 x 10(5) cells/well, the increase in ChAT activity was 35-55% greater than control values in the presence of 10(-14)-10(-10) M IL-2, whereas at 7.5 x 10(5) cells/well, this increase was substantially lower (20%) and only observed at concentrations between 10(-13)-10(-11) M. At 10(6) cells/well, IL-2 had no effect on ChAT activity. The IL-2-induced increase in ChAT activity was significantly inhibited in the presence of an IL-2 receptor antibody. Moreover, this increase was not dependent upon trophic actions, as the number of AChE-positive cells or their morphological characteristics were not altered by IL-2. Taken together, these results suggest that IL-2 can stimulate, at pM concentrations, ChAT activity by acting via its own receptors expressed by septal neurons.