The IL-8 (or CXCL8) chemokine receptors, CXCR1 and CXCR2, activate protein kinase C (PKC) to mediate leukocyte functions. To investigate the roles of different PKC isoforms in CXCL8 receptor activation and regulation, human mononuclear phagocytes were treated with CXCL8 or CXCL1 (melanoma growth-stimulating activity), which is specific for CXCR2. Plasma membrane association was used as a measure of PKC activation. Both receptors induced time-dependent association of PKCα, -β1, and -β2 to the membrane, but only CXCR1 activated PKCε. CXCL8 also failed to activate PKCε in RBL-2H3 cells stably expressing CXCR2. ΔCXCR2, a cytoplasmic tail deletion mutant of CXCR2 that is resistant to internalization, activated PKCε as well as CXCR1. Expression of the PKCε inhibitor peptide εV1 in RBL-2H3 cells blocked PKCε translocation and inhibited receptor-mediated exocytosis, but not phosphoinositide hydrolysis or peak intracellular Ca2+ mobilization. εV1 also inhibited CXCR1-, CCR5-, and ΔCXCR1-mediated cross-regulatory signals for GTPase activity, Ca2+ mobilization, and internalization. Peritoneal macrophages from PKCε-deficient mice (PKCε-/-) also showed decreased CCR5-mediated cross-desensitization of G protein activation and Ca2+ mobilization. Taken together, the results indicate that CXCR1 and CCR5 activate PKCε to mediate cross-inhibitory signals. Inhibition or deletion of PKCε decreases receptor-induced exocytosis and cross-regulatory signals, but not phosphoinositide hydrolysis or peak intracellular Ca2+ mobilization, suggesting that cross-regulation is a Ca2+-independent process. Because ΔCXCR2, but not CXCR2, activates PKCε and cross-desensitizes CCR5, the data further suggest that signal duration leading to activation of novel PKC may modulate receptor-mediated cross-inhibitory signals.
ASJC Scopus subject areas
- Immunology and Allergy