A folding switch regulates interleukin 27 biogenesis and secretion of its α-subunit as a cytokine

Abstract

A common design principle of heteromeric signaling proteins is the use of shared subunits. This allows encoding of complex messages while maintaining evolutionary flexibility. How cells regulate and control assembly of such composite signaling proteins remains an important open question. An example of particular complexity and biological relevance is the interleukin 12 (IL-12) family. Four functionally distinct αβ heterodimers are assembled from only five subunits to regulate immune cell function and development. In addition, some subunits act as independent signaling molecules. Here we unveil key molecular mechanisms governing IL-27 biogenesis, an IL-12 family member that limits infections and autoimmunity. In mice, the IL-27α subunit is secreted as a cytokine, whereas in humans only heterodimeric IL-27 is present. Surprisingly, we find that differences in a single amino acid determine if IL-27α can be secreted autonomously, acting as a signaling molecule, or if it depends on heterodimerization for secretion. By combining computer simulations with biochemical experiments, we dissect the underlying structural determinants: a protein folding switch coupled to disulfide bond formation regulates chaperone-mediated retention versus secretion. Using these insights, we rationally change folding and assembly control for this protein. This provides the basis for a more human-like IL-27 system in mice and establishes a secretion-competent human IL-27α that signals on its own and can regulate immune cell function. Taken together, our data reveal a close link between protein folding and immunoregulation. Insights into the underlying mechanisms can be used to engineer immune modulators.

The molecular basis of chaperone-mediated interleukin 23 assembly control

“…Engineered cytokines are a powerful tool to modulate immune functions, as previously reported e.g. for IL-2, IL-15, IL-27, and others 53–56 . Directly engineering folding and quality control of interleukins provides one possible avenue to obtain immune signaling molecules not present in nature, but with a low risk for off-target effects or immunogenicity 56 .…”

Decoding the Role of Interleukin-30 in the Crosstalk between Cancer and Myeloid Cells

“…Although human IL-30 essentially depends on assembly with a β-subunit for secretion, substitution of a single amino acid residue, and other molecular mechanisms can affect protein folding and regulate its secretion competence. It has been reported that polymorphisms in the human IL-30 gene can affect the regions identified to be important for its assembly-induced folding [72], which could lead to extracellular protein secretion with functional implications. Recent studies [73,74] suggest that common polymorphisms in the IL-30 gene are linked to cancer risk and might contribute to the progression of cancers and chronic inflammatory diseases in humans.…”

IL-17, IL-27, and IL-33: A Novel Axis Linked to Immunological Dysfunction During Sepsis

“…However, mice can produce IL-27p28 in the absence of EBI3, so it is unclear if the reported effects of IL-27 during sepsis are actually due to the full heterodimeric cytokine or merely to its alpha subunit. A group has recently reported the development of transgenic B57L/6J mice in which the IL-27p28 subunit cannot be produced independently of EBI3 (80). This animal model will be necessary to truly distinguish the effects of IL-27p28 from those of IL-27.…”