Assembly-induced folding regulates interleukin 12 biogenesis and secretion

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Interleukin-12 (IL-12) family cytokines are crucial for immune regulation, linking innate and adaptive immunity.
• Their unique heterodimeric structures, formed from shared subunits, present challenges in understanding their cellular assembly and regulation.
• IL-12 and related cytokines are significant therapeutic targets in various diseases.

Purpose of the Study:

• To investigate the fundamental principles governing the biogenesis and assembly of the IL-12 heterodimer.
• To identify the role of disulfide bonds in the folding, secretion, and biological activity of IL-12α.
• To determine if assembly-induced folding is a general mechanism for the IL-12 cytokine family.

Main Methods:

• Cell-biological approaches were employed to study protein folding and assembly.
• Expression and co-expression of IL-12 subunits (IL-12α and IL-12β) were analyzed.
• Disulfide bond formation and its impact on protein structure, secretion, and activity were assessed.

Main Results:

• IL-12α, when expressed alone, misfolds and forms incorrect disulfide bonds.
• Co-expression with IL-12β subunit prevents IL-12α misfolding, enabling the secretion of active heterodimeric IL-12.
• Two of the three disulfide bridges in IL-12α are dispensable for secretion, stability, and activity, while others are critical.
• Similar misfolding issues were observed for IL-23α, another IL-12 family member.

Conclusions:

• Assembly-induced folding is a key mechanism for the biogenesis and secretion of IL-12 family cytokines.
• The identification of essential disulfide bonds provides insights into controlling IL-12 cytokine function.
• This understanding may facilitate the development of simplified and functional IL-12-based therapeutics.