[Expression of the human soluble interleukin 4 receptor in methylotropic yeast]

Interleukin-4 (IL-4) is a pleiotropic cytokine which plays a pivotal role in shaping immune responses. IL-4 mediates important proinflammatory functions in asthma, including the IgE isotype switch. IL-4 exerts its biological effects through binding to its receptor (IL-4R) complex, with the alpha chain as the high affinity binding subunit. Soluble IL-4R lacks the transmemberane and cytoplasmic domains, so it cannot induce cellular activation. By acting as a decoy to circulating IL-4 and neutralize its activity, its high specificity and affinity make it ideal as an IL-4 antagonist. Some companies have embarked the clinical research for asthma treatment with the sIL-4R and the result revealed well therapeutic effect. With RNA extracted from human monocyte as the template, The sIL-4R cDNA encoding the extracellular domain of IL-4R a chain was obtained by RT-PCR. Compared with the sIL-4R encoding sequence in GenBank, the nucleotide sequencing analysis indicated that there was a A-->G mutation at 148bp and the mutation caused Ile-->Val at 50th amino acid. According to the references, numerous polymorphisms have been identified in the IL-4R gene and the Ile50Val was the only known extracellular variant of human IL-4R. Then the recombinant vector pPIC9K/sIL-4R was constructed, linearized and introduced into Pichia pastoris GS115 by electroporation. The recombinant sIL-4R was identified by SDS-PAGE, Western blot and Ligand binding blot. The SDS-PAGE and Western blot analysis showed that the apparent molecular weight of expressed sIL-4R was about 30kD. And the Ligand binding blot analysis indicated the expressed sIL-4R had the biological activity. The sIL-4R, which had the biological activity, was successfully secretorily expressed in the Pichia pastoris (GS 115).