PHORBOL ESTER-INDUCED MODULATION OF CELL-SURFACE ANTIGENS ON U-937 CELLS IN PROTEIN-FREE MEDIUM - EFFECT OF PROTEIN-KINASE AND CALMODULIN INHIBITORS

Phorbol ester (PMA) induced decrease in cell surface expression of CD4 antigen was potentiated on human monoblastoid cell line U-937 culture d and induced in protein-free culture medium. Down-regulation of the C D4 antigen was partially inhibited by the isoquinoline protein kinase inhibitor H7 and unaffected by the calmodulin inhibitor R24571 (calmid azolium). PMA-induced increase of the monocyte-associated CD14 antigen was dependent the presence of fetal bovine serum (FBS) in culture med ium and partially abolished by calmodulin inhibitor R24571. H7 inhibit or partially abrogated this up-regulation in 4 out of 8 induction expe riments. PMA-induced down-regulation of MHC class I antigen was found in both FBS-supplemented and protein-free culture media. This effect w as partially inhibited by both H7 and R24571 inhibitors.