title: Derangement of a factor upstream of RARalpha triggers the repression of a pleiotropic epigenetic network.
abstract: BACKGROUND
  Chromatin adapts and responds to extrinsic and intrinsic cues. We hypothesize that inheritable aberrant chromatin states in cancer and aging are caused by genetic/environmental factors. In previous studies we demonstrated that either genetic mutations, or loss, of retinoic acid receptor alpha (RARalpha), can impair the integration of the retinoic acid (RA) signal at the chromatin of RA-responsive genes downstream of RARalpha, and can lead to aberrant repressive chromatin states marked by epigenetic modifications. In this study we tested whether the mere interference with the availability of RA signal at RARalpha, in cells with an otherwise functional RARalpha, can also induce epigenetic repression at RA-responsive genes downstream of RARalpha.
  
  
  RESULTS
  To hamper the availability of RA at RARalpha in untransformed human mammary epithelial cells, we targeted the cellular RA-binding protein 2 (CRABP2), which transports RA from the cytoplasm onto the nuclear RARs. Stable ectopic expression of a CRABP2 mutant unable to enter the nucleus, as well as stable knock down of endogenous CRABP2, led to the coordinated transcriptional repression of a few RA-responsive genes downstream of RARalpha. The chromatin at these genes acquired an exacerbated repressed state, or state "of no return". This aberrant state is unresponsive to RA, and therefore differs from the physiologically repressed, yet "poised" state, which is responsive to RA. Consistent with development of homozygosis for epigenetically repressed loci, a significant proportion of cells with a defective CRABP2-mediated RA transport developed heritable phenotypes indicative of loss of function.
  
  
  CONCLUSIONS
  Derangement/lack of a critical factor necessary for RARalpha function induces epigenetic repression of a RA-regulated gene network downstream of RARalpha, with major pleiotropic biological outcomes.
authors.affiliation: Cancer Genetics Program, Roswell Park Cancer Institute, Buffalo, New York, USA.
authors.forename: Francesca
authors.initials: F
authors.lastname: Corlazzoli
authors.forename: Stefano
authors.initials: S
authors.lastname: Rossetti
authors.forename: Gaia
authors.initials: G
authors.lastname: Bistulfi
authors.forename: Mingqiang
authors.initials: M
authors.lastname: Ren
authors.forename: Nicoletta
authors.initials: N
authors.lastname: Sacchi
mesh_terms: D000483:Alleles; D001692:Biological Transport; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D015536:Down-Regulation / Q000235:genetics*; D044127:Epigenesis, Genetic; D020868:Gene Silencing; D006720:Homozygote; D006801:Humans; D008957:Models, Genetic; D010641:Phenotype; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D000072482:Retinoic Acid Receptor alpha; D014158:Transcription, Genetic; D014212:Tretinoin / Q000378:metabolism
chemical_list: D002843:Chromatin; C000607071:RARA protein, human; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; C082928:retinoic acid binding protein II, cellular; C082925:retinoic acid receptor beta; D014212:Tretinoin