Expression of protein kinase C isozymes in human basophils: Regulation by physiological and nonphysiological stimuli

The expression of protein kinase C (PKC) isozymes in human basophils and the regulation of PKC isozymes during basophil activation by phorbol 12- myristate 13-acetate (PMA) ± ionomycin, f-met-leu-phe (FMLP), and anti-IgE antibody were examined. In human basophils (> 98% purity), PKCβI, βII, δ, and ε were expressed, PKCα was difficult to detect, and PKCγ and η were undetectable. In unstimulated basophils, PKCβI and βII were found primarily in the cytosol fraction (95% ± 3% of total and 98% ± 1%, respectively). Within 5 minutes of stimulation with PMA (100 ng/mL), both PKCβI and βII were translocated to the membrane fraction (85% ± 4% and 83% ± 6%, respectively). In resting cells, 48% ± 3% and 61% ± 10% of PKCδ and ε, respectively, existed in the membrane fraction. Within 1 minute of stimulation with PMA, 90% ± 6% of PKCε was found in the membrane fraction, however, no translocation of PKCδ was apparent. Stimulation with FMLP caused modest translocation (≃20%) of all PKC isozymes by 1 minute, whereas stimulation with anti-IgE antibody led to no detectable changes in PKC location throughout a 15-minute period of measurement. However, concentrations of PMA and ionomycin that alone caused no PKC translocation and little histamine release, together caused significant histamine release but no apparent PKC translocation. Studies with bis-indolylmaleimide analogs showed inhibition of PMA-induced, but not anti-IgE-induced, histamine release. These pharmacological studies suggest that PKC does not play a prodegranulatory role in human basophil IgE-mediated secretion.