MORPHOLOGICAL-CHANGES AND REORGANIZATION OF ACTINFILAMENTS IN HUMAN MYELOID-LEUKEMIA CELLS INDUCED BY A NOVEL PROTEIN PHOSPHATASE INHIBITOR, TAUTOMYCIN

A protein phosphatase inhibitor, tautomycin induces blebs on the surfa ce of human myeloid leukemia K562 cells within 10 min. In this paper w e examined the cytoskeleton of tautomycin-treated cells. In the presen ce of tautomycin, cells with blebs turned into segmented forms with sm ooth surfaces after 15 min and into smooth round shapes without microp rotuberance after 60 min. Observation with fluorescence microscopy sho wed that F-actin detached from the plasma membrane at the site of the blebs. Further treatment with tautomycin induced the accumulation of F -actin at the segmentation centers. Under electron microscopy, an elec tron dense ring-structure was detected at the segmentation center. Tau tomycin did not induce major changes of the microtubule network althou gh F-actin accumulated near the microtubule organizing center. The amo unt of F-actin increased in tautomycin-treated cells. These results in dicate that the morphological changes are induced by reorganization of actinfilaments.