ROLE OF THE C-TERMINUS OF THE INTERLEUKIN-8 RECEPTOR IN SIGNAL-TRANSDUCTION AND INTERNALIZATION

Interleukin 8 (IL-8) is a potent neutrophil chemoattractant and activa tor. Two IL-8 receptor subtypes, A and B, are expressed in neutrophils . In this work, we analyzed the role of the C terminus domain of the I L-8 receptor on the signal transduction and receptor internalization m echanisms, The IL-8 receptor A was tagged with an epitope correspondin g to the monoclonal antibody 1D4 to monitor the, localization of the I L-8 receptor, We demonstrated IL-S-dependent. receptor internalization by monitoring tile density of surface I-125-labeled IL-8 binding site s and by immunofluorescence microscopy, Truncation of the last 27 amin o acids of the IL-8 receptor A severely impaired the IL-8-induced inte rnalization of the receptor. Of importance was tire observation that b inding of IL-8 to receptors A and B triggered a dramatically faster ra te of internalization of receptor B than receptor A, suggesting that t he heterologous C termini among receptor subtypes modulate the rate of internalization of IL-8 receptors. However, substitution of the C ter minus of the receptor subtype A for the C terminus of receptor B reduc ed the internalization rate of receptor A. Furthermore, we found that the rate of internalization of IL-8 receptor B triggered by IL-8 was f aster than the one induced by the IL-S-related peptide, melanoma growt h stimulatory activity, Studies with human neutrophils pretreated with 100 nM IL-8 for 5 min revealed a positive and a negative calcium resp onse mediated by receptors A and B, respectively. In contrast, neutrop hils pretreated with melanoma growth stimulatory activity showed posit ive calcium responses to both receptors A and B. These data suggest th at the neutrophil responses mediated by IL-8 are modulated by the rate of internalization of receptors.