YEAST EXPRESSION OF THE CYTOKINE RECEPTOR DOMAIN OF THE SOLUBLE INTERLEUKIN-6 RECEPTOR

The complex of the soluble interleukin-6 receptor (sIL-6R) and IL-6 (I L-6) is a potent agonist on cells expressing the signal transducing pr otein gp130, In contrast, IL-6 alone only stimulates cells which expre ss a membrane bound form of the IL-6R and gp130. The natural occurring sIL-6R is generated by shedding of the membrane receptor and to a les ser extend by alternative splicing. We have inserted the coding sequen ce of the 323 amino acid residues of the human sIL-6R into an expressi on/secretion vector suitable for the methylotrophic yeast Pichia pasto ris. We obtained, however, no detectable expression and secretion of t he recombinant protein. When we used only the coding sequence of the c ytokine receptor domain of the sIL-6R for the construction of an expre ssion plasmid, this truncated version of the sIL-6R accumulated in the supernatant to 1-5 mg/1. The protein was purified by a single affinit y chromatography step using a monoclonal antibody directed against the human IL-6R. Following the same approach, we expressed a truncated sp lice variant of the sIL-6R. Both, the secreted truncated sIL-6R and th e splice variant showed full agonistic biological activity on human he patoma cells. The described expression strategy will be useful for lar ge scale production of biologically active sIL-6R and might be adapted for the expression of other members of the hematopoietic cytokine rec eptor family.