title: Suppression of Ser/Thr phosphatase 4 (PP4C/PPP4C) mimics a novel post-mitotic action of fostriecin, producing mitotic slippage followed by tetraploid cell death.
abstract: Fostriecin is a natural product purified from Sterptomyces extracts with antitumor activity sufficient to warrant human clinical trials. Unfortunately, difficulties associated with supply and stable drug formulation stalled further development. At a molecular level, fostriecin is known to act as a catalytic inhibitor of four PPP-family phosphatases, and reports describing the design of molecules in this class suggest derivatives targeting enzymes within the fostriecin-sensitive subfamily can be successful. However, it is not clear if the tumor-selective cytotoxicity of fostriecin results from the inhibition of a specific phosphatase, multiple phosphatases, or a limited subset of fostriecin sensitive phosphatases. How the inhibition of sensitive phosphatases contributes to tumor-selective cytotoxicity is also not clear. Here, high-content time-lapse imaging of live cells revealed novel insight into the cellular actions of fostriecin, showing that fostriecin-induced apoptosis is not simply induced following a sustained mitotic arrest. Rather, apoptosis occurred in an apparent second interphase produced when tetraploid cells undergo mitotic slippage. Comparison of the actions of fostriecin and antisense-oligonucleotides specifically targeting human fostriecin-sensitive phosphatases revealed that the suppression PP4C alone is sufficient to mimic many actions of fostriecin. Importantly, targeted suppression of PP4C induced apoptosis, with death occurring in tetraploid cells following mitotic slippage. This effect was not observed following the suppression of PP1C, PP2AC, or PP5C. These data clarify PP4C as a fostriecin-sensitive phosphatase and demonstrate that the suppression of PP4C triggers mitotic slippage/apoptosis.
  
  
  CONCLUSIONS
  Future development of fostriecin class inhibitors should consider PP4C as a potentially important target. Mol Cancer Res; 11(8); 845-55. ©2013 AACR.
authors.affiliation: Department of Biochemistry and Molecular Biology, MSB 2362, University of South Alabama, Mobile, AL 36688, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Theobald
authors.forename: Kathy
authors.initials: K
authors.lastname: Bonness
authors.forename: Alla
authors.initials: A
authors.lastname: Musiyenko
authors.forename: Joel F
authors.initials: JF
authors.lastname: Andrews
authors.forename: Gudrun
authors.initials: G
authors.lastname: Urban
authors.forename: Xizhong
authors.initials: X
authors.lastname: Huang
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Dean
authors.forename: Richard E
authors.initials: RE
authors.lastname: Honkanen
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D002453:Cell Cycle / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D006367:HeLa Cells; D006801:Humans; D008938:Mitosis / Q000187:drug effects*; D018716:Molecular Mimicry; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011090:Polyenes / Q000494:pharmacology*; D054645:Protein Phosphatase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D011753:Pyrones / Q000494:pharmacology*; D057891:Tetraploidy
chemical_list: D000970:Antineoplastic Agents; D009687:Nuclear Proteins; D011090:Polyenes; D011753:Pyrones; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; C089641:protein phosphatase 5; C040313:fostriecin