tautomycin and Leukemia--Myeloid

Tautomycin, a protein serine/threonine phosphatase inhibitor, was chemically degraded, and five derivatives were investigated for their biological activities. None of them exerted any inhibitory effects on the activity of protein phosphatase types 1 and 2A. However, one derivative, named TM2a, induced a significant morphological change (bleb-formation) of human myeloid leukemia K562 cells. TM2b, the trimethyl ester of TM2, did not induce bleb-formation. Thus, the maleic anhydride structure played an important role in the biological activity. The biological properties of TM2a toward K562 cells resembled those of a phorbol ester, rather than of tautomycin. The phorbol ester-induced bleb formation was abrogated by a non-specific inhibitor of protein kinases, staurosporine, and by an inhibitor of protein kinase C (PKC), H-7, but TM2a-induced bleb formation was abrogated only by staurosporine. Enhanced phosphorylation of the two proteins was observed after their exposure to TM2a. This suggest that the effect was not due to any inhibition of protein phosphatase 1 or 2A, but rather to the activation of an unidentified kinase, possibly of the PKC family, or to inhibition of a protein phosphatase other than type 1 or 2A.

Topics: Antifungal Agents; Biodegradation, Environmental; Humans; Leukemia, Myeloid; Phorbol Esters; Phosphoprotein Phosphatases; Phosphorylation; Platelet Aggregation Inhibitors; Protein Phosphatase 1; Pyrans; Spiro Compounds; Structure-Activity Relationship; Tumor Cells, Cultured

A protein phosphatase inhibitor, tautomycin induces blebs on the surface of human myeloid leukemia K562 cells within 10 min. In this paper we examined the cytoskeleton of tautomycin-treated cells. In the presence of tautomycin, cells with blebs turned into segmented forms with smooth surfaces after 15 min and into smooth round shapes without microprotuberance after 60 min. Observation with fluorescence microscopy showed 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 electron dense ring-structure was detected at the segmentation center. Tautomycin did not induce major changes of the microtubule network although F-actin accumulated near the microtubule organizing center. The amount of F-actin increased in tautomycin-treated cells. These results indicate that the morphological changes are induced by reorganization of actinfilaments.

Topics: Actin Cytoskeleton; Actins; Antifungal Agents; Cell Membrane; Cytochalasin D; Humans; Intermediate Filaments; Leukemia, Myeloid; Microscopy, Electron; Microscopy, Fluorescence; Microtubules; Phosphoprotein Phosphatases; Pyrans; Spiro Compounds; Tumor Cells, Cultured

A novel antibiotic tautomycin induced many blebs on the surface of K562 human chronic myeloid leukemia cells, similar to the morphological changes induced by phorbol esters. However, tautomycin did not induce nitroblue tetrazolium reducing activity, when HL60 human promyelocytic leukemia cells were caused to differentiate by quinomycin into mature granulocytes. It did not induce spread of HL60 cells, one of the phenotypes of mature macrophages. In addition, it did not compete with phorbol dibutyrate to bind to the cell surface of K562 cells. However, tautomycin significantly activated protein kinase C (PKC) extracted from K562 cells. These results indicate that tautomycin is a new activator of PKC, distinct from phorbol esters.

Topics: Anti-Bacterial Agents; Antifungal Agents; Cell Differentiation; Cytochalasin D; Cytochalasins; Enzyme Activation; Humans; Leukemia, Myeloid; Phorbol 12,13-Dibutyrate; Phorbol Esters; Protein Kinase C; Pyrans; Spiro Compounds; Tumor Cells, Cultured