MOLECULAR MECHANISM OF CHEMOPREVENTION BY APIGENIN

Summary

Principal Investigator: Jill C Pelling
Abstract: DESCRIPTION: This is a competitive renewal application to investigate the molecular mechanisms involved in skin cancer chemoprevention by apigenin, a nontoxic and nonmutagenic bioflavonoid which inhibits UV-induced skin carcinogenesis when topically applied to mouse skin. During the previous funding period, the applicant investigated the effect of apigenin treatment on expression of the p53 tumor suppressor gene in mouse keratinocytes. In keratinocyte cell lines with wildtype p53 status, the applicant demonstrated that apigenin is extremely potent in elevating the level of wildtype p53 protein in keratinocytes (27-fold). This level of p53 induction is substantially higher than that induced in keratinocytes by UVB irradiation, for example (5-fold). The applicant further demonstrated that the increased level of p53 protein was due to protein stabilization, accompanied by increased phosphorylation of p53 at Ser15 and subsequent transcriptional activation of p53-responsive genes including p21WAF1. Interestingly, the applicant did not observe any increased accumulation of MDM2 protein in apigenin-treated cells, which is unexpected considering that the MDM2 gene is a downstream target of p53 transcriptional activation and generally responsible for feedback inhibition of p53 by promoting its degradation through ubiquitination. The applicant's results indicate that apigenin treatment of keratinocytes induces many of the same events in the p53 pathway that are normally triggered during the cellular UV DNA damage response, with the exception that the negative feedback MDM2 control loop appears to be absent. The lack of feedback inhibition by MDM2 may prolong the beneficial effects of p53 protein stabilization in apigenin-treated keratinocytes. The hypothesis to be tested in this renewal application is that apigenin's chemopreventive activity is derived from its ability to enhance the response of the normal cellular p53 pathway to UV-induced damage in keratinocytes. The applicant proposes four specific aims to test this hypothesis: (1) Investigate the mechanism(s) by which apigenin treatment induces posttranslational modification of p53, by identifying the p53 phosphorylation sites, the kinases involved in phosphorylation, and whether apigenin induces p53 acetylation in keratinocytes; (2) Having characterized p53 protein post-translational modification induced by apigenin treatment alone, investigate the combined effects of apigenin treatment plus UVB irradiation on p53 protein levels, stabilization, and post-translational modification; (3) Investigate the impact of apigenin treatment on MDM2 gene expression, on interaction of p53 and MDM2 protein, and whether apigenin treatment results in inhibition of MDM2-mediated p53 ubiquitination and degradation; (4) Investigate the combined effects of apigenin treatment plus UVB irradiation on MDM2 gene expression, MDM2/p53 protein interaction, and MDM2/p53 protein interaction, and MDM2-mediated p53 ubiquitination.
Funding Period: 1996-05-01 - 2008-01-31
more information: NIH RePORT

Top Publications

  1. ncbi Proteomic identification of 3-nitrotyrosine-containing rat cardiac proteins: effects of biological aging
    Jaroslaw Kanski
    University of Kansas, Department of Pharmaceutical Chemistry, 2099 Constant Ave, Lawrence, KS 66047, USA
    Am J Physiol Heart Circ Physiol 288:H371-81. 2005
  2. ncbi Proteomic analysis of protein nitration in aging skeletal muscle and identification of nitrotyrosine-containing sequences in vivo by nanoelectrospray ionization tandem mass spectrometry
    Jaroslaw Kanski
    Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, Kansas 66047, USA
    J Biol Chem 280:24261-6. 2005
  3. ncbi Inhibition of TPA-induced cyclooxygenase-2 (COX-2) expression by apigenin through downregulation of Akt signal transduction in human keratinocytes
    Rukiyah T van Dross
    Department of Pathology and Laboratory Medicine, University of Kansas Medical Center, Kansas City, KS 66160, USA
    Mol Carcinog 44:83-91. 2005
  4. ncbi Protein nitration in biological aging: proteomic and tandem mass spectrometric characterization of nitrated sites
    Jaroslaw Kanski
    Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, Kansas 66047, USA
    Methods Enzymol 396:160-71. 2005
  5. ncbi Enhancement of UVB-induced apoptosis by apigenin in human keratinocytes and organotypic keratinocyte cultures
    Adnan O Abu-Yousif
    Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City, Kansas, USA
    Cancer Res 68:3057-65. 2008
  6. pmc Enhancement of p53 expression in keratinocytes by the bioflavonoid apigenin is associated with RNA-binding protein HuR
    Xin Tong
    Department of Pathology and the Robert H Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
    Mol Carcinog 48:118-29. 2009

Detail Information

Publications6

  1. ncbi Proteomic identification of 3-nitrotyrosine-containing rat cardiac proteins: effects of biological aging
    Jaroslaw Kanski
    University of Kansas, Department of Pharmaceutical Chemistry, 2099 Constant Ave, Lawrence, KS 66047, USA
    Am J Physiol Heart Circ Physiol 288:H371-81. 2005
    ..Possibly the oxidative modifications of the identified proteins contribute to the age-dependent degeneration and functional decline of heart proteins...
  2. ncbi Proteomic analysis of protein nitration in aging skeletal muscle and identification of nitrotyrosine-containing sequences in vivo by nanoelectrospray ionization tandem mass spectrometry
    Jaroslaw Kanski
    Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, Kansas 66047, USA
    J Biol Chem 280:24261-6. 2005
    ..The latter experiments demonstrate that the in vitro exposure of an isolated protein to peroxynitrite may not always be a good model to mimic protein nitration in vivo...
  3. ncbi Inhibition of TPA-induced cyclooxygenase-2 (COX-2) expression by apigenin through downregulation of Akt signal transduction in human keratinocytes
    Rukiyah T van Dross
    Department of Pathology and Laboratory Medicine, University of Kansas Medical Center, Kansas City, KS 66160, USA
    Mol Carcinog 44:83-91. 2005
    ..These data show that apigenin inhibits TPA-mediated COX-2 expression by blocking signal transduction of Akt and that apigenin also blocks AA release, which may contribute to its chemopreventive activity...
  4. ncbi Protein nitration in biological aging: proteomic and tandem mass spectrometric characterization of nitrated sites
    Jaroslaw Kanski
    Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, Kansas 66047, USA
    Methods Enzymol 396:160-71. 2005
    ..Some examples for the MS/MS analysis of nitrated peptides obtained from aging rat heart and skeletal muscle are provided, such as nitration of Tyr105 of the mitochondrial electron-transfer flavoprotein and Tyr14 of creatine kinase...
  5. ncbi Enhancement of UVB-induced apoptosis by apigenin in human keratinocytes and organotypic keratinocyte cultures
    Adnan O Abu-Yousif
    Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City, Kansas, USA
    Cancer Res 68:3057-65. 2008
    ..The ability of apigenin to enhance UVB-induced apoptosis may explain, in part, the photochemopreventive effects of apigenin...
  6. pmc Enhancement of p53 expression in keratinocytes by the bioflavonoid apigenin is associated with RNA-binding protein HuR
    Xin Tong
    Department of Pathology and the Robert H Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
    Mol Carcinog 48:118-29. 2009
    ..Overall, these findings indicate that, in addition to modulating p53 protein stability, one of the mechanisms by which apigenin induces p53 protein expression is enhancement of translation through the RNA binding protein HuR...