Pisiferdiol and pisiferic acid isolated from Chamaecyparis pisifera activate protein phosphatase 2C in vitro and induce caspase-3/7-dependent apoptosis via dephosphorylation of Bad in HL60 cells

Abstract 

Protein phosphatase 2C (PP2C) dephosphorylates a broad range of substrates and regulates apoptosis, stress response and growth-related pathways. In the course of screening for PP2C activators from natural sources, we isolated abietane-type diterpenes, pisiferdiol and pisiferic acid from Chamaecyparis pisifera. Pisiferdiol having a unique seven-membered ring showed more specific PP2C activation activity (1.3-fold at 100μM) than pisiferic acid having a normal six-membered ring and oleic acid, which is known to activate PP2C. Pisiferdiol and pisiferic acid showed mixed-type activation with respect to α-casein, and this differed from the non-competitive activation of oleic acid in vitro. In vivo, the cytotoxicity of pisiferdiol toward human promyelocytic leukemia cell line HL60 with an IC₅₀ value of 18.3μM was 2-fold and 7-fold stronger than those of pisiferic acid and oleic acid, and pisiferdiol induced apoptosis through a caspase 3/7-dependent mechanism involving the dephosphorylation of Bad¹, which is a PP2C substrate. We thus conclude that pisiferdiol and pisiferic acid are novel PP2C activators, and the more specific activator, pisiferdiol, may be a useful chemical probe to study PP2C-mediated signaling pathways, and a lead compound for pharmaceutical agents.

Keywords: PP2C activator, Chamaecyparis pisifera, Pisiferdiol, Pisiferic acid, Bad, Apoptosis

Abbreviations: PP, protein phosphatase, MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide

• 1 Bad is a proapoptotic member of the Bcl-2 family.