title: Epigenetic silencing of peroxisome proliferator-activated receptor γ is a biomarker for colorectal cancer progression and adverse patients' outcome.
abstract: The relationship between peroxisome proliferator-activated receptor γ (PPARG) expression and epigenetic changes occurring in colorectal-cancer pathogenesis is largely unknown. We investigated whether PPARG is epigenetically regulated in colorectal cancer (CRC) progression. PPARG expression was assessed in CRC tissues and paired normal mucosa by western blot and immunohistochemistry and related to patients' clinicopathological parameters and survival. PPARG promoter methylation was analyzed by methylation-specific-PCR and bisulphite sequencing. PPARG expression and promoter methylation were similarly examined also in CRC derived cell lines. Chromatin immunoprecipitation in basal conditions and after epigenetic treatment was performed along with knocking-down experiments of putative regulatory factors. Gene expression was monitored by immunoblotting and functional assays of cell proliferation and invasiveness. Methylation on a specific region of the promoter is strongly correlated with PPARG lack of expression in 30% of primary CRCs and with patients' poor prognosis. Remarkably, the same methylation pattern is found in PPARG-negative CRC cell lines. Epigenetic treatment with 5'-aza-2'-deoxycytidine can revert this condition and, in combination with trichostatin A, dramatically re-activates gene transcription and receptor activity. Transcriptional silencing is due to the recruitment of MeCP2, HDAC1 and EZH2 that impart repressive chromatin signatures determining an increased cell proliferative and invasive potential, features that can experimentally be reverted. Our findings provide a novel mechanistic insight into epigenetic silencing of PPARG in CRC that may be relevant as a prognostic marker of tumor progression.
authors.affiliation: Department of Biological and Environmental Sciences, University of Sannio, Benevento, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Pancione
authors.forename: Lina
authors.initials: L
authors.lastname: Sabatino
authors.forename: Alessandra
authors.initials: A
authors.lastname: Fucci
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Carafa
authors.forename: Angela
authors.initials: A
authors.lastname: Nebbioso
authors.forename: Nicola
authors.initials: N
authors.lastname: Forte
authors.forename: Antonio
authors.initials: A
authors.lastname: Febbraro
authors.forename: Domenico
authors.initials: D
authors.lastname: Parente
authors.forename: Concetta
authors.initials: C
authors.lastname: Ambrosino
authors.forename: Nicola
authors.initials: N
authors.lastname: Normanno
authors.forename: Lucia
authors.initials: L
authors.lastname: Altucci
authors.forename: Vittorio
authors.initials: V
authors.lastname: Colantuoni
mesh_terms: D000368:Aged; D014408:Biomarkers, Tumor / Q000235:genetics*; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism*; D019175:DNA Methylation; D018450:Disease Progression; D044127:Epigenesis, Genetic; D005260:Female; D020868:Gene Silencing; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D047495:PPAR gamma / Q000378:metabolism*; D011379:Prognosis; D011401:Promoter Regions, Genetic
chemical_list: D014408:Biomarkers, Tumor; D056572:Histone Deacetylase Inhibitors; D047495:PPAR gamma