Isolation of the CXC chemokines ENA-78, GRO alpha and GRO gamma from tumorcells and leukocytes reveals NH2-terminal heterogeneity - Functional comparison of different natural isoforms

Chemokines are a family of chemotactic peptides affecting leukocyte migrati on during the inflammatory response. Post-translational modification of che mokines has been shown to affect their biological potency. Here, the isolat ion and identification of natural isoforms of the neutrophil chemoattractan ts GRO alpha and GRO gamma and the epithelial-cell-derived neutrophil attra ctant-78 (ENA-78), is reported. Cultured tumor cells produced predominantly intact chemokine forms, whereas peripheral blood monocytes secreted mainly NH2-terminally truncated forms. The order of neutrophil chemotactic potenc y of these CXC chemokines was GRO alpha > GRO gamma > ENA-78 both for intac t and truncated forms. However, truncated GRO alpha(4,5,6-73), GRO gamma(5- 73) and ENA-78(8,9-78) were 30-fold, fivefold and threefold more active tha n the corresponding intact chemokine. As a consequence, truncated GRO alpha (4,5,6-73) was 300-fold more potent than intact ENA-78 indicating that both the type of chemokine and its mode of processing determine the chemotactic potency. Similar observations were made when intact and truncated GRO alph a, GRO gamma and ENA-78 were compared for their capacity to induce an incre ase in the intracellular calcium concentration in neutrophilic granulocytes , and to desensitize the calcium response towards the CXC chemokine granulo cyte chemotactic protein-2. (GCP-2). It must be concluded that physiologica l proteolytic cleavage of CXC chemokines in general enhances the inflammato ry response, whereas for CC chemokines NH2-terminal processing mostly resul ts in reduced chemotactic potency.