Negative modulation of signal transduction via interleukin splice variation

Abstract

Interleukin 6 (IL-6) belongs to a large group of secreted proteins called cytokines functioning to mediate and regulate immunity, inflammation, and hematopoiesis with direct effects on cell proliferation, apoptosis, and differentiation. Along with the IL-6 protein, two of its splice variants, IL-6delta2 and IL-6delta4, were reported to be transcribed or expressed in vivo in human, and the mRNAs of IL-6delta3 and IL-6delta5 had been observed in mouse. While the existence of different splice variants of IL-6 has been shown, very little is known on how the structural modifications of IL-6 resulting from the formation of the different splice variants may alter cytokine functions. We have analyzed the potential effects splicing would have on interactions with the cell surface receptor complex. We (1) constructed three-dimensional structures of the IL-6 splice variants, IL-6delta2, IL-6delta3, and IL-6delta4, with the assumption that an interleukin splice variant as a folded protein should retain a functional hydrophobic core; (2) reconstructed the ternary structural complexes consisting of the modeled IL-6 splice variants, the IL-6 receptor molecule (IL-6R) and the dimeric signal-transducing protein, gp130, and (3) analyzed all complexes and made comparisons with the X-ray structure of the wild-type IL-6 complex. We identified three separate sites on IL-6 where interactions are made with IL-6R and with each of the two copies of gp130. The structural consequences of losing an exon lead to a unique pattern of lost interaction with different components of the receptor complex. Thus, in IL-6 and its splice variants, the exons appear to have compartmentalized roles contributing to the combined function of the cytokine. The modeled interactions suggest that splice variants could act as antagonists, and that IL-6delta2, missing the signal peptide, would be a cytoplasmic protein and be released and interact with nearby cell-surface receptors when cells are damaged. We argue that in the case of IL-6, helix E may act as a "silent secondary structure," which only has an active role when it substitutes for a part of the hydrophobic core, for example, replacing helix A in IL-6delta2.

Gene expression profiles reveal that chondrogenic progenitor cells and synovial cells are closely related

“…One notable exception to the concordance between microarrays and qPCR was that IL6 expression was substantially higher in chondrocytes than CPCs, SFCs and synoviocytes when measured by qPCR, but substantially lower when measured by microarray. This difference may reflect deficiencies in the ability of the probes used in the microarrays to detect IL6 mRNA splice variants expressed by chondrocytes …”

“…This difference may reflect deficiencies in the ability of the probes used in the microarrays to detect IL6 mRNA splice variants expressed by chondrocytes. 22…”

Evaluation of Zataria multiflora Boiss. (Shirazi Thyme) Hydro Alcoholic Extract Effect on Pro-Inflammatory Cytokine IL-6 Different Transcript Variants Expression Level in Mesenchymal Stem Cells (MSCs)

“…IL6 was implicated in some inflammation association disease such as obesity, diabetes, and arthritis rheumatoid (7). There are multiple splice variants reported for IL6, for which there is evidence from EST and cDNA clones (8). IL6 have six protein coding transcript variants NM-000600.3 IL6-201, IL6-202, IL6-004, IL6-005, IL6-006, and IL6-203 encoding proteins of sizes 212 aa, 252 aa, 136 aa, 189 aa, 198 aa, and 122 aa, respectively.…”

“…These alternate transcripts were characterized as follows: IL-6 (715 bp); IL6∆2 (568 bp, missing exon 2); IL6∆4 (523 bp, missing exon 4); IL6∆2, 4 (376 bp, missing both exon 2 and exon 4) (9)(10)(11). IL-6, as a cytokine, in its specific tissue could regulate immunity, inflammation, and hematopoiesis with direct effects on cell proliferation, apoptosis, and differentiation (8). It is recognized that naturally occurring splice variants of cytokines can perform various biological functions in different cells and positions (8).…”

Enhanced phagocytic capacity endows chondrogenic progenitor cells with a novel scavenger function within injured cartilage

“…The gene expression differences of ECM-forming and inflammation paralleled differences in SOX9 expression, a crucial chondrogenic transcriptional factor that was expressed at high, moderate, and low levels by chondrocytes, CPCs, and synoviocytes/SFCs, respectively. However, IL-6 expression in qPCR and microarray are quite different, which may reflect deficiencies in the probes used in the microarrays to detect IL-6 mRNA splice variants expressed by chondrocytes[76].…”