title: IC101 induces apoptosis by Akt dephosphorylation via an inhibition of heat shock protein 90-ATP binding activity accompanied by preventing the interaction with Akt in L1210 cells.
abstract: To find novel pharmacological tools useful for analyzing the molecular mechanism of apoptosis from natural resources, in the present study, we examined the activity of IC101, a cyclic depsipeptide isolated from Streptomyces sp. MJ202-72F3, to induce apoptosis in the L1210 cell line. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed that IC101 caused a concentration-dependent cell death with a 50% effective concentration value of 20 nM. Cell shrinkage, chromatin condensation, a typical DNA ladder pattern, and up-regulation of cleaved caspase-3 expression, which were biochemical characteristics of apoptosis, were induced by IC101. It also was observed that IC101 caused a concentration-dependent dephosphorylation of Akt and Bad without affecting phosphatidylinositol-3 kinase, an upstream molecule of Akt. IC101 dephosphorylated the 90-kDa protein, as assayed by immunblotting of the cell extract by using anti-phosphotyrosine antibody. To identify the 90-kDa protein, immunoprecipitation and direct nano-flow liquid chromatography-tandem mass spectrometry (LC-MS) were performed to demonstrate that this protein was heat shock protein 90 (HSP90). Consistently, it was observed that IC101 induced the HSP90 tyrosine dephosphorylation by immunoblot analysis of immunoprecipitates with anti-HSP90 antibody using anti-phosphotyrosine antibody. IC101 caused the degradation of Raf-1, which formed a complex with HSP90. The HSP90-ATP binding also was inhibited by IC101 in a noncompetitive manner. An interaction of HSP90 with Akt was shown to be inhibited by IC101 in a concentration-dependent manner. These results suggest that IC101 dephosphorylates Akt through an inhibition of HSP90 functions, resulting in the interaction with Akt to induce apoptotic cell death of L1210 cells.
authors.affiliation: Department of Pharmaceutical Molecular Biology, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan.
authors.forename: Hironori
authors.initials: H
authors.lastname: Fujiwara
authors.forename: Tohru
authors.initials: T
authors.lastname: Yamakuni
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Ueno
authors.forename: Masaaki
authors.initials: M
authors.lastname: Ishizuka
authors.forename: Takashi
authors.initials: T
authors.lastname: Shinkawa
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Isobe
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Ohizumi
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D017209:Apoptosis; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D053938:DNA Fragmentation / Q000187:drug effects; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D007939:Leukemia L1210 / Q000473:pathology*; D051379:Mice; D010455:Peptides / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism* / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000378:metabolism* / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D014407:Tumor Cells, Cultured; D051025:bcl-Associated Death Protein
chemical_list: D000255:Adenosine Triphosphate; D002352:Carrier Proteins; D053148:Caspase 3; D020169:Caspases; D018841:HSP90 Heat-Shock Proteins; D010455:Peptides; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf; D051025:bcl-Associated Death Protein; C494820:Bad protein, mouse; C085032:IC 101; C505409:Casp3 protein, mouse