Bioflavonoid Effects on EGF Signaling and Cell Cycle Pathways in Prostate Cancer

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DESCRIPTION (provided by applicant): The plant bioflavonoid, luteolin (L or LUT), and two synthetic ligands (BMHPC and ZN-2) interact with type II [3H]estradiol binding sites with high affinity (Kd" 5nM) and inhibit normal and malignant prostate cell proliferation in vivo and in vitro. The identification of type II sites as a ligand-binding domain on histone H4 (and/or histone H3/H4 dimers) suggests that ligand occupancy of this site modulates post-translational modifications (acetylation, methylation, phosphorylation, etc.) of histones H3 or H4 that regulate gene transcription. This represents a novel epigenetic mechanism for controlling gene transcription by these ligands. Microarray and real time PCR (qPCR) studies demonstrate that L, BMHPC or ZN-2 regulate cell cycle gene (CCNA2, CCNE2, CDKN1B, CDC25A, PCNA, PLK1) expression in PC-3 human prostate cancer cells in addition to a number of genes involved in the EGF Signaling Pathway (EGFR, GRB2, SOS, RasGAP, MKK4, c-Fos, JNK1). L modulation of EGF Signaling and Cell Cycle Pathway genes was also confirmed in DU-145 prostate cancer cells. Chromatin immunoprecipitation (ChIP) studies revealed that L reduced the acetylation state of histone H4 (at Lys 5, 8, 12, 16) associated with the PLK1 (but not RB1) gene promoter, supporting the epigenetic control hypothesis. We suspect this will be the case for a number of genes in the EGF Signaling and Cell Cycle Pathways controlled by L, BMHPC and ZN-2. The goal of the proposed studies is to define the mechanism of action of these type II site ligands. Specific Aim 1 will define temporal relationships between L, BMHPC or ZN-2 effects on gene expression (mRNA and protein) in the EGF Signaling and Cell Cycle Pathways and cell proliferation. The effects of EGFR agonists (EGF) and antagonists (Gefitinib) on L, BMHPC and ZN-2 regulation of EGF Signaling and cell cycle gene expression (Specific Aim 2) will be studied. Specific Aim 3 will consist of ChIP studies on preparations from PC-3 or DU-145 cells treated with L, BMHPC or ZN-2. We will determine if post-translational modifications (acetylation) of histones H3 and/or H4 associated with EGF Signaling (EGFR, c-Fos) or cell cycle (PLK1, CDKN1B) gene promoters are responsible for the regulation of gene transcription by these ligands in these cell lines. Specific coregulators (histone acetyl transferases; HAT's and histone deacetylases; HDAC's) recruited to EGFR, c-Fos, PLK1 and CDKN1B promoters will be identified (via re-ChIP assays) and L, BMHPC or ZN-2 effects on the association of these coregulators with the promoters will be studied. Lastly, Specific Aim 4 will define the effects of L, BMHPC and ZN-2 on EGF Signaling and cell cycle gene expression (mRNA, protein) and cell proliferation in normal prostate tissue and in PC-3 or DU-145 cell xenografts in nude mice. The studies should define the mechanism of action of L, BMHPC and ZN-2 in the regulation of histone function, gene expression and prostate cancer cell proliferation and could lead to the development of new type II site ligand based drugs for the control of gene expression in EGF Signaling and Cell Cycle Pathways responsible for the proliferation of normal and malignant cells. PUBLIC HEALTH RELEVANCE: The studies described in this research proposal indicate that diet-derived plant bioflavonids influence the activity of genes in the epidermal growth factor (EGF) Signaling and cell cycle pathways. These molecular pathways contains a number of genes encoding proteins that determine how slow or fast normal and malignant prostate cells divide. This is because bioflavonoids like luteolin mimic a biological agent (methyl p- hydroxyphenyllactate; MeHPLA) that normally controls the growth of non-malignant cells. The experiments proposed in this grant application will define the mechanism of action of luteolin, and two drugs (BMHPC and ZN-2) designed to act like MeHPLA, in the control of the activity of the EGF Signaling Pathway genes and normal and malignant prostate cell division. These studies may lead to the development of new drugs and/or dietary components for use in cancer prevention or treatment.