IL-6 receptor availability and IL-6/STAT3 signal transduction is regulated by ALR through altered sheddase ADAM17

Interleukin 6 (IL-6), a key pleiotropic cytokine, plays a vital role for hepatic function and regeneration. Augmenter of Liver Regeneration (ALR) is a widely expressed co-mitogen with anti-apoptotic, anti-oxidative, and anti-inflammatory properties, often dysregulated in liver diseases. Application of ALR has been shown to dampen hepatic acute phase response (APR) triggered by IL-6. This study aimed to unveil the underlying molecular mechanism of how ALR affects IL-6 signaling pathway using in vitro experiments. Two hepatoma cell lines were treated with IL-6, in presence or absence of recombinant human ALR (rALR), and analyzed for expression as well as activation of IL-6 signaling cascade components by western blotting, qRT-PCR, protein activity assay and ELISA. Our findings demonstrate that rALR effectively reduces IL-6-induced STAT3 and JAK1/JAK2 phosphorylation, independent of IL-6 concentration. Expression and phosphorylation of SHP1, SHP2, SOCS1, SOCS3 and PIAS, all known negative regulators of STAT3 activity, remained unaffected by rALR. Furthermore, rALR treatment did not change IL-6 receptor-α (gp80) and IL-6R-β (gp130) mRNA expression. Western blot analysis of IL-6 receptor subunit expression was not conclusive due to low immune-signals. Nevertheless, we found elevated levels of soluble gp80 and gp130 receptor subunits in cell culture supernatants upon rALR treatment (with or without IL-6) by ELISA. Additionally, rALR enhances shedding activity of ADAM17 (TACE), which might be responsible for increased soluble and diminished membrane presence of IL-6 receptor. In conclusion, rALR attenuates hepatic IL-6 receptor availability and classical IL-6 signal transduction, but also may potentially affect IL-6 trans-signaling.

Publication History

Article published online:
23 January 2024