title: The forkhead transcription factor FOXO4 sensitizes cancer cells to doxorubicin-mediated cytotoxicity.
abstract: The forkhead superfamily of transcription factors, which play major roles in control of cellular proliferation, oxidative stress and apoptosis, are becoming more and more considered as crucial therapeutic targets in cancer. In this study, we addressed the contribution of class O of forkhead box transcription factor (FOXO) 4 transcription factor, a forkhead superfamily member, to cytotoxicity mediated by the anthracyclic drug doxorubicin. FOXO4 can be phosphorylated by phosphatidylinositol-3-kinase/AKT signaling resulting in its inactivation and nuclear exclusion. Under stress conditions, FOXO4 can be phosphorylated via jun N-terminal kinase (JNK) leading to increased transcriptional activation of the transcription factor. Our results show that doxorubicin incubation led to phosphorylation of AKT and concomitantly to AKT-dependent inactivation and nuclear exclusion of the tumor suppressor FOXO4 in Hct-116 cells. We found that inhibition of FOXO4 nuclear exclusion by blockage of AKT phosphorylation following overexpression of dominant-negative AKT enhanced doxorubicin-mediated cytotoxicity. Overexpression of wild-type FOXO4 led to an increase in doxorubicin-mediated cytotoxicity, which was further exacerbated by overexpression of a solely nuclear-localized FOXO4 mutant. In contrast, though doxorubicin resulted in JNK activation, modulation of JNK-dependent regulation of FOXO4 was of no effect to doxorubicin cytotoxicity. These results show for the first time that in Hct-116 cells sustained nuclear localization of FOXO4 seems to be one crucial point enhancing doxorubicin-induced cytotoxicity and apoptosis. Targeting FOXO4 or AKT may lead to new chances in sensitizing cancer cells to cytostatic drugs thereby allowing use of lower drug concentrations and minimizing drug-induced adverse effects in patients.
authors.affiliation: Institute of Toxicology, Heinrich Heine University of Düsseldorf, PO Box 10 10 07, D-40001 Düsseldorf, Germany.
authors.forename: Regine
authors.initials: R
authors.lastname: Lüpertz
authors.forename: Yvonni
authors.initials: Y
authors.lastname: Chovolou
authors.forename: Klaus
authors.initials: K
authors.lastname: Unfried
authors.forename: Andreas
authors.initials: A
authors.lastname: Kampkötter
authors.forename: Wim
authors.initials: W
authors.lastname: Wätjen
authors.forename: Regine
authors.initials: R
authors.lastname: Kahl
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D001483:Base Sequence; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D017931:DNA Primers; D004317:Doxorubicin / Q000494:pharmacology*; D051858:Forkhead Transcription Factors; D006801:Humans; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D018384:Oxidative Stress; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*
chemical_list: D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; D017931:DNA Primers; C108803:FOXO4 protein, human; D051858:Forkhead Transcription Factors; D017382:Reactive Oxygen Species; D014157:Transcription Factors; D004317:Doxorubicin; D051057:Proto-Oncogene Proteins c-akt; D048670:MAP Kinase Kinase 4