Immunology

Biography

Biography: Charles J Malemud

Abstract

Interleukin-6 (IL-6) is a potent pro-inflammatory cytokine which is elevated in patients with the diagnosis of rheumatoid arthritis. We have previously shown that recombinant human (rh) IL-6 stimulated the production of matrix metalloproteinase-9 (MMP-9) in the T/C28a2 and C-28/I2 lines of immortalized juvenile human chondrocytes. IL-6 is known to activate the Janus Kinase/Signal Transducers and Activators of Transcription (JAK/STAT) signaling pathway through the interaction of IL-6 with the IL-6 receptor-α (IL-6Rα)/gp130 complex, with membrane-bound IL-6R or with soluble IL-6R. STAT3 is a major STAT protein activated by IL-6. Importantly, the production of MMP-9 by C-28/I2 chondrocytes was inhibited by tocilizumab (TCZ), a fully humanized monoclonal antibody which neutralizes IL-6-mediated JAK/STAT signaling. To begin a systematic analysis of rhIL-6-mediated STAT3 protein activation by human chondrocytes, C-28/I2 chondrocytes were employed to determine the repertoire of STAT3 proteins produced by these cells. Western blot analysis showed that C-28/I2 chondrocytes produced 2 STAT3 isoforms; one STAT3 isoform migrated on 10% SDS-PAGE at a position similar to STAT3α (~75kDa) reported in other cell types. A second STAT3 isoform migrated somewhat faster than STAT3α which we presume to be a truncated isoform of STAT3 and thus may be STAT3β. The 2 STAT3 isoforms were detected in C-28/I2 chondrocytes without any additions or after incubation with rhIL-6 or with rhIL-6 plus TCZ for up to 60 min. Of note, a protein extract produced from HeLa cells which were supplied by the manufacturer of the anti-STAT3 antibody used in this study showed that HeLa produced only STAT3α. Thus, it will be of interest to determine whether or not both STAT3 isoforms produced by C-28/I2 chondrocytes are differentially phosphorylated by rhIL-6 as well as the extent to which TCZ differentially inhibits these STAT3 isoforms.