Nitric oxide inhibits capping in HL-60 cells

In the present study, we investigated the effect of nitric oxide (NO) on capping, which is associated with the actin polymerization in HL-60 cells (human promyelocytic leukemia cells). We first assessed the effect of NO on the patching and capping by using anti-human LFA-1 monoclonal antibody. Samples were analyzed by a fluorescence microscope. As expected, NO inhibited the percentage of capping dose dependently. We compared the effect of NO on capping with cytochalasin D (CD) and observed that CD also inhibits the capping in HL-60 cells. We next examined the effect of NO on the F-actin content. For assays of F-actin content, the FITC labelled phalloidin was permeabilized and stained in HL-60 cells. The bound fluorescence quantified by flow cytometry using a FACStar. There was a decrease in the F-actin formation in NO treated cells. Taken together, these data indicate that NO inhibits the capping on cellular membrane by decreasing the intracellular F-actin formation in HL-60 cells. We suggest that the formation of capping linked with actin polymerization at the inner leaflet of plasma membrane may be regulated by NO.