title: Spontaneous Mn2+ entry is specifically inhibited by calyculin A in human leukemic HL-60 cells.
abstract: The effects of calyculin A and other agents which enhance protein Ser/Thr phosphorylation, on the cytosolic free Ca2+ concentration ([Ca2+]i) and spontaneous Mn2+ entry were investigated in fura-2-loaded human leukemic HL-60 cells. Calyculin A (30 nM), a specific inhibitor of protein Ser/Thr phosphatase (PP) 1 and 2A, significantly decreased [Ca2+]i. By contrast, another structurally unrelated inhibitor of PP1 and 2A, okadaic acid (1 microM), caused a slight elevation in [Ca2+]i. Forskolin (30 microM), which could enhance protein kinase A activity by raising cAMP concentration, also caused a rise in [Ca2+]i. Phorbol myristate acetate (PMA, 300 nM), an activator of protein kinase C, did not have a significant effect on [Ca2+]i. Spontaneous entry of Mn2+ (a surrogate ion for Ca2+) was strongly inhibited by calyculin A, but not okadaic acid, forskolin or phorbol myristate acetate. Such inhibition was not significantly affected by staurosporine (300 nM), a non-specific inhibitor of protein Ser/Thr kinases. Our results suggest that calyculin A inhibited a plasmalemmal leak pathway to Mn2+ (and Ca2+), probably leading to a decrease in [Ca2+]i. Inhibition of spontaneous Mn2+ entry by calyculin A may depend on a specific protein phosphorylation pattern induced by staurosporine-insensitive protein kinase(s).
authors.affiliation: Department of Physiology, Faculty of Medicine, The University of Hong Kong. leungy@fhs.mcmaster.ca
authors.forename: Y M
authors.initials: YM
authors.lastname: Leung
authors.forename: C Y
authors.initials: CY
authors.lastname: Kwan
authors.forename: T T
authors.initials: TT
authors.lastname: Loh
mesh_terms: D002118:Calcium / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D003864:Depression, Chemical; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018922:HL-60 Cells; D006801:Humans; D008345:Manganese / Q000378:metabolism*; D008387:Marine Toxins; D019319:Okadaic Acid / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D008387:Marine Toxins; D010080:Oxazoles; D005576:Colforsin; D019319:Okadaic Acid; D008345:Manganese; C059041:calyculin A; D010749:Phosphoprotein Phosphatases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D004121:Dimethyl Sulfoxide