Interleukins 19, 20, and 24 Signal through Two Distinct Receptor Complexes

Abstract

Reporter, proliferation, and direct STAT activation assays using cell lines expressing transfected receptors revealed differences between the receptor complexes. IL-19 and IL-24 also exhibited growth inhibition on a cell line endogenously expressing all three receptor subunits, an effect that was seen at cytokine levels two orders of magnitude above those required for STAT activation or proliferation. These results demonstrate that, although this subclass exhibits receptor complex redundancy, there are differences in ligand/receptor interactions and in signal transduction that may lead to specificity and a distinct biology for each cytokine.

Characterization of the Recombinant Extracellular Domains of Human Interleukin-20 Receptors and Their Complexes with Interleukin-19 and Interleukin-20

“…We thus conclude that any trace amounts of the binary complexes (IL-19/sIL-20R1, IL-20/sIL-20R1) are very likely artifacts of the particular experimental conditions, such as high protein concentration, but are not biologically relevant. Our results agree with the data showing that sIL-20R1 cannot inhibit the activity of IL-19 or IL-20 in competition luciferase assays (27).…”

“…The IL-19/sIL-20R1/sIL-20R2 complex was prepared with the excess of the ligand; the sample yielded the second peak with two absorption maxima at 75 and 77 mL (Figure 5a) corresponding mostly to the heavier, glycosylated species of IL-19 and the mixture of glycosylated and nonglycosylated molecules. An excess of the free soluble receptors in the IL-20/sIL-20R1/sIL-20R2 sample gave two usual peaks at 67.5 and 71 mL corresponding to the first and the second receptor (Figure 5b Our results are in good agreement with previous experiments aimed at the determination of which soluble receptors were capable of blocking ligand activity (27). In this set of experiments, BHK570 cells were stably transfected with IL-20R1/IL-20R2 and a reporter construct consisting of the firefly luciferase gene driven by promoter/enhancer sequences comprised of tandem STAT-binding elements.…”

“…Overexpression of IL-20 in transgenic mice resulted in neonatal lethality with skin abnormalities, similar to those found in psoriatic skin (2). By contrast, it was reported that IL-19-overexpressing transgenic mice had no overt skin phenotype (27).…”

“…The major part of the binary complexes eluted from the column as fractions corresponding to molecular mass 45-50 kDa. In addition, SDS-PAGE of the binary complex fractions showed similar intensity of the bands representing the ligand and the receptor, suggesting an equimolar ratio of the individual components of the sample (Figure 2 Competition luciferase assays performed on BHK570 cells with stably transfected receptors showed that a >1000-fold excess of sIL-20R2 is capable of blocking IL-19 activity, suggesting that sIL-20R2 competes for IL-19 with the fulllength receptor on the cell surface (27). However, sIL-20R2 had no effect on the activity of IL-20 at any concentration that was tried in the same cells transfected with the same receptors.…”

“…In this set of experiments, BHK570 cells were stably transfected with IL-20R1/IL-20R2 and a reporter construct consisting of the firefly luciferase gene driven by promoter/enhancer sequences comprised of tandem STAT-binding elements. Cells (27). We are not sure how to interpret the latter result, particularly since sIL-20R1 also did not affect the activity of IL-20, although one possibility could be that sIL-20R2 affinity toward IL-20 is lower than that of the membrane-bound full-length IL-20R2.…”