title: Epigenetic regulation of MDR1 gene through post-translational histone modifications in prostate cancer.
abstract: BACKGROUND
  Multidrug resistance 1 (MDR1) gene encodes for an ATP binding cassette transporter--P-glycoprotein (P-gp)-- involved in chemoresistance to taxanes. MDR1 promoter methylation is frequent in prostate carcinoma (PCa), suggesting an epigenetic regulation but no functional correlation has been established. We aimed to elucidate the epigenetic mechanisms involved in MDR1 deregulation in PCa.
  
  
  RESULTS
  MDR1 promoter methylation and P-gp expression were assessed in 121 PCa, 39 high-grade prostatic intraepithelial neoplasia (HGPIN), 28 benign prostatic hyperplasia (BPH) and 10 morphologically normal prostate tissue (NPT) samples, using quantitative methylation specific PCR and immunohistochemistry, respectively. PCa cell lines were exposed to a DNA methyltransferases inhibitor 5-aza-2'deoxycytidine (DAC) and histone deacetylases inhibitor trichostatin A (TSA). Methylation and histone posttranscriptional modifications status were characterized and correlated with mRNA and protein expression. MDR1 promoter methylation levels and frequency significantly increased from NPTs, to HGPIN and to PCa. Conversely, decreased or absent P-gp immunoexpression was observed in HGPIN and PCa, inversely correlating with methylation levels. Exposure to DAC alone did not alter significantly methylation levels, although increased expression was apparent. However, P-gp mRNA and protein re-expression were higher in cell lines exposed to TSA alone or combined with DAC. Accordingly, histone active marks H3Ac, H3K4me2, H3K4me3, H3K9Ac, and H4Ac were increased at the MDR1 promoter after exposure to TSA alone or combined with DAC.
  
  
  CONCLUSIONS
  Our data suggests that, in prostate carcinogenesis, MDR1 downregulation is mainly due to histone post-translational modifications. This occurs concomitantly with aberrant promoter methylation, substantiating the association with P-gp decreased expression.
authors.forename: Rui
authors.initials: R
authors.lastname: Henrique
authors.forename: Ana Isabel
authors.initials: AI
authors.lastname: Oliveira
authors.forename: Vera L
authors.initials: VL
authors.lastname: Costa
authors.forename: Tiago
authors.initials: T
authors.lastname: Baptista
authors.forename: Ana Teresa
authors.initials: AT
authors.lastname: Martins
authors.forename: António
authors.initials: A
authors.lastname: Morais
authors.forename: Jorge
authors.initials: J
authors.lastname: Oliveira
authors.affiliation: Cancer Epigenetics Group, Research Center of the Portuguese Oncology Institute, Porto, Rua Dr, António Bernardino de Almeida, 4200-072 Porto, Portugal. carmenjeronimo@ipoporto.min-saude.pt.
authors.forename: Carmen
authors.initials: C
authors.lastname: Jerónimo
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics* / Q000378:metabolism; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001374:Azacitidine / Q000494:pharmacology; D045744:Cell Line, Tumor; D018899:CpG Islands; D019175:DNA Methylation; D044127:Epigenesis, Genetic / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006657:Histones / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D060787:Neoplasm Grading; D009367:Neoplasm Staging; D011401:Promoter Regions, Genetic; D011467:Prostate / Q000378:metabolism; D011470:Prostatic Hyperplasia / Q000235:genetics / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D011499:Protein Processing, Post-Translational
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D006657:Histones; D001374:Azacitidine