Pharmacological Targeting of the ER-Resident Chaperones GRP94 or Cyclophilin B Induces Secretion of IL-22 Binding Protein Isoform-1 (IL-22BPi1).

Of the three interleukin-22 binding protein (IL-22BP) isoforms produced by the human gene， IL-22BPi2 and IL-22BPi3 are capable of neutralizing IL-22. The longest isoform， IL-22BPi1， does not bind IL-22， is poorly secreted， and its retention within the endoplasmic reticulum (ER) is associated with induction of an unfolded protein response (UPR). Therapeutic modulation of IL-22BPi2 and IL-22BPi3 production may be beneficial in IL-22-dependent disorders. Recently， we identified the ER chaperones GRP94 and cyclophilin B in the interactomes of both IL-22BPi1 and IL-22BPi2. In this study， we investigated whether secretion of the IL-22BP isoforms could be modulated by pharmacological targeting of GRP94 and cyclophilin B， either by means of geldanamycin， that binds to the ADP/ATP pocket shared by HSP90 paralogs， or by cyclosporin A， which causes depletion of ER cyclophilin B levels through secretion. We found that geldanamycin and its analogs did not influence secretion of IL-22BPi2 or IL-22BPi3， but significantly enhanced intracellular and secreted levels of IL-22BPi1. The secreted protein was heterogeneously glycosylated， with both high-mannose and complex-type glycoforms present. In addition， cyclosporine A augmented the secretion of IL-22BPi1 and reduced that of IL-22BPi2 and IL-22BPi3. Our data indicate that the ATPase activity of GRP94 and cyclophilin B are instrumental in ER sequestration and degradation of IL-22BPi1， and that blocking these factors mobilizes IL-22BPi1 toward the secretory route.