A microfilament formation inhibitor, cytochalasin strongly enhances the low-affinity Fc epsilon receptor II (CD23) expression on the human monocyte-like cell line, U937

Enhancement of the low-affinity Fc epsilon receptor (CD23) expression by cy tochalasin was analyzed on the human monocytelike cell line, U937. The CD23 expression on the U937 cells was enhanced at 23 hr after culture with cyto chalasin B, D, or E, especially cytochalasin E having the most remarkable e ffect on it at the low concentration. This enhanced expression was found to be associated with a concomitant increase of a CD23 (about 45-kDa) protein on the U937 cells as assessed by Western blotting analysis. On the other h and, CD11a, CD18, CD31, CD49d, or CD53 was not markedly enhanced on the U93 7 cells by culture with cytochalasin E, although the mean fluorescence inte nsities (MFIs) of CD11a, CD18, and CD53 on U937 was partially up-regulated. Cell growth of U937 cultured with cytochalasin E was completely suppressed for 72 hr, but cell viability was sufficiently maintained (more than 958). Soluble-formed CD23 (sCD23) also was released from the U937 cells at 23 to 72 kr after culture with cytochalasin E. In addition, the protein tyrosine kinase activity was detected in the U937 cells cultured with cytochalasin E for 34 hr using the enzyme immunoassay. Enhancement of the CD23 expressio n on the U937 cells at 24 to 72 hr cultured with cytochalasin E was suffici ently blocked by protein tyrosine kinase inhibitors herbimycin A and genist ein, and a protein synthesis inhibitor, cychloheximide. On the other hand, protein kinase C inhibitors such as H-7 and H-8 had no effect on this CD23 expression. These results suggest that a mechanism underlying enhancement o f the CD23 expression on the U937 cells cultured with cytochalasin E is med iated through tyrosine phosphorylation and protein synthesis.