The intracellular precursor of IL-1 beta is associated with microtubules in activated U937 cells.

Treatment of the human histiocytic leukemia cell line U937 with PMA and LPS results in the induction of expression of IL-1. Rabbit polyclonal antibodies raised against mature rIL-1 have been used to investigate the intracellular location of the IL-1 beta precursor in U937 cells. The pattern of indirect immunofluorescence staining seen with these antibodies overlaps substantially with that seen by using a mAb raised against beta-tubulin. Depolymerization of tubulin by incubation of the cells at 0 degrees C before fixation results in the disruption of the pattern of IL-1 staining. IL-1 beta precursor in extracts of activated U937 cells is shown to co-cycle with exogenously added tubulin through two rounds of in vitro depolymerization/polymerization. In addition, immunoprecipitation of IL-1 from cell extracts at 30 degrees C but not at 0 degrees C results in co-precipitation of tubulin. Thus the IL-1 beta precursor is shown in vivo and in vitro to associate with the microtubules of the cytoskeleton.