Human N-terminal analogs of interleukin 1 beta demonstrate altered binding and function in hematopoiesis

This study describes the structure-function relationship of interleukin 1 beta (IL-1 beta) using two amino-terminal muteins of human IL-1 beta. One mutein, clone 18, which substitutes a threonine and methionine for the alanine and proline at positions 1 and 2 of the N-terminus of fully processed and active IL-1 beta, demonstrated similar activity to that of native IL-1 beta in inducing granulocyte-macrophage colony-stimulating activity (GM-CSA) from cultured fibroblasts. Clone 18 also demonstrated similar binding to IL-1 beta receptors on fibroblasts when using a competitive binding assay. The second mutein was GLU-4, which in addition to substituting alanine and proline by threonine and methionine also substituted glutamine for arginine at position 4 of the processed IL-1 beta molecule. GLU-4 required a 3-log increase in concentration to obtain the same GM-CSA release from fibroblasts and to produce the same amount of competitive binding inhibition as clone 18 and native IL-1 beta. In addition, preincubation of bone marrow cells with clone 18 and native IL-1 beta demonstrated a greater ability to protect early hematopoietic progenitors from the lethal effects of 4-hydroperoxycyclophosphamide when compared to similar concentrations of GLU-4. A greater number of large granulocyte-macrophage, erythroid, and mixed colonies as well as blast cell colonies were observed when bone marrow cells were preincubated for 20 h with clone 18 or native IL-1 beta as compared to preincubation with GLU-4 or medium alone. Therefore, arginine at position 4 of the processed IL-1 beta molecule was shown to be a key residue in the function of IL-1 beta as a hematopoietic regulator. These results also suggest that minor changes in the N-terminal sequence of IL-1 beta result in decreased interaction with its receptor and a subsequent reduction in biological activity.