Synthetic trimeric interleukin-6 receptor complexes with a STAT3 phosphorylation dominated activation profile

Area of Science:

• Molecular Biology
• Cellular Signaling
• Immunology

Background:

• Interleukin-6 (IL-6) signaling involves sequential binding of IL-6 to IL-6 receptor (IL-6R) and gp130, leading to hexameric complex formation and Janus kinase (JAK) activation.
• The intracellular domain (ICD) of IL-6R is not essential for STAT, ERK, and AKT pathway phosphorylation.
• Investigating chimeric receptors can elucidate the roles of specific domains in IL-6 signaling.

Purpose of the Study:

• To investigate the biological activity of a chimeric IL-6 receptor protein (IL-6R_ECD-gp130_TMD/ICD) by fusing the IL-6R extracellular domain (ECD) to the gp130 transmembrane domain (TMD) and ICD.
• To determine the conditions required for IL-6 signaling using these chimeric receptors.
• To explore the potential for creating customized synthetic IL-6 signaling pathways.

Main Methods:

• Co-expression of the chimeric IL-6R_ECD-gp130_TMD/ICD with signaling-deficient gp130 variants.
• Mimicking premature trimeric receptor complexes by using IL-6-mediated dimerization with gp130_ΔD1.
• Utilizing JAK-deficient and STAT/ERK/AKT-deficient gp130 variants to analyze signaling pathway dominance.

Main Results:

• Co-expression of IL-6R_ECD-gp130_TMD/ICD with signaling-deficient gp130 failed to induce IL-6 signaling, indicating impaired JAK dimerization.
• IL-6-mediated dimerization of IL-6R_ECD-gp130_TMD/ICD with gp130_ΔD1 induced signaling, predominantly activating the STAT3 pathway.
• Intracellular domain swapping from gp130 to IL-6R prevented effective ERK/AKT signaling, while STAT3 signaling remained dominant even with JAK deficiency.

Conclusions:

• The chimeric IL-6R_ECD-gp130_TMD/ICD receptor requires specific assembly conditions, such as dimerization with gp130_ΔD1, to confer biological activity.
• IL-6 signaling through these synthetic complexes exhibits a STAT3-dominated phosphorylation profile, independent of JAKs in certain configurations.
• Chimeric IL-6R/gp130 receptors offer a platform for developing customized synthetic IL-6 signaling pathways.