Cardiotrophin-like cytokine factor 1 forms a complex with IL12/IL23p40

Cardiotrophin-like cytokine factor 1 (CLCF1) is a cytokine of the IL6/IL12 superfamily with pro-neurotrophic and immune-modulating functions. Although the pro-neurotrophic activities of CLCF1 are mediated through the ciliary neurotrophic factor receptor (CNTFR), the α receptor chain of the CNTFR, CNTFRα, is not expressed by immune cells. This suggests the presence of an alternative receptor or protein complex that mediates the immune activities of CLCF1. Using the BioID2 proximity-dependent biotinylation assay, we identified p40, the β subunit of IL12/IL23, as a potential interaction partner for CLCF1. We confirmed the protein-protein interaction between CLCF1 and p40 using co-immunoprecipitation and a proximity ligation assay. We also observed that the CLCF1-p40 complex forms both intracellularly and in the extracellular space. Furthermore, secretion of the CLCF1-p40 heterodimer was induced by the cytokine receptor-like factor 1 (CRLF1), leading to the release of a tripartite CLCF1-CRLF1-p40 complex. Lastly, we showed that a CLCF1-p40 fusion protein binds to both CNTFRα and IL12Rβ1. Taken together, our results uncover a new putative composite cytokine of the IL6/IL12 superfamily, which might affect our understanding of both CLCF1 activities and p40-associated pathologies. Moreover, our results reinforce the connection between the IL6 and IL12 cytokine families, and suggest that other possible protein interactions between these two families should be further investigated.