Mutants of interleukin 13 with altered reactivity toward interleukin 13 receptors

Interleukin 13 (IL13) belongs to a family of cytokines whose members exhibi t structural homology, despite amino acid sequence dissimilarity. For examp le, while of limited sequence homology, IL13 and IL4 share a signaling rece ptor, IL13/4 receptor, on a variety of human normal cells. However, a subcl ass of II4-independent IL13 receptors is overexpressed on certain transform ed cells, including human malignant gliomas. We introduced mutations into h uman (h) IL13 to determine the site(s) involved in interaction with the sha red receptor and/or the glioma-associated receptor. This analysis identifie d at least three protein regions that are needed for signaling through the shared receptor. These regions were localized to alpha-helices A, C, and D and were mainly separate from the region(s) needed to interact with the gli oma-associated receptor. Glutamic acids at positions 13 and 16 in hIL13 alp ha-helix A, arginine and serine at positions 66 and 69 in helix C, and argi nine at position 109 in helix D were found to be important in inducing biol ogical signaling since their specific mutation resulted in loss and/or gain of function phenomena. We demonstrate that the molecular requirements of h IL13 to interact with its respective receptors are generally distinct and c an be controlled by mutagenesis of the cytokine.