Overexpression of mutant Ptch in rhabdomyosarcomas is associated with promoter hypomethylation and increased Gli1 and H3K4me3 occupancy

Oncotarget. 2015 Apr 20;6(11):9113-24. doi: 10.18632/oncotarget.3272.

Abstract

Mice with heterozygous loss of the tumor suppressor Patched1 (Ptch) develop rhabdomyosarcoma (RMS)-like tumors. However, Ptch transcripts are consistently overexpressed in these tumors. We have recently shown that the upregulated transcripts are derived from the mutated Ptch allele thus leading to the hypothesis that the wild-type allele is repressed during RMS development. Here we describe epigenetic changes taking place at the Ptch locus during RMS development. We showed a lower degree of DNA-methylation in methylation-sensitive CpG regions of the Ptch promoter in RMS compared to normal muscle from heterozygous Ptch animals. In agreement with these results, treatment of heterozygous Ptch mice with the DNA demethylating agent 5-aza-2-deoxycytidine (5-aza-dC) between embryonic days E9.5-E11.5 significantly accelerated RMS formation. Since Ptch promoter methylation occurs after/around E13.5, the window for RMS initiation during embryogenesis, these results provide additional evidence that Ptch promoter hypomethylation may contribute to RMS formation. We have also demonstrated increased trimethylation of histone H3 lysine 4 (H3K4me3) and preferential binding of Gli1, a known Ptch activator, to the mutant locus in RMS. Together, these findings support an alternative model for RMS formation in heterozygous Ptch mice including loss of methylation and concomitant occupancy by activating histone marks of mutant Ptch.

Keywords: DNA hypomethylation; Gli1; H3K4me3; Ptch; RMS.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Azacitidine / analogs & derivatives
  • Azacitidine / pharmacology
  • CpG Islands
  • DNA Methylation* / drug effects
  • Decitabine
  • Embryonic Development / genetics
  • Gene Expression Regulation, Neoplastic / drug effects
  • Gene Expression Regulation, Neoplastic / genetics
  • Genes, Tumor Suppressor
  • Gestational Age
  • Heterozygote
  • Histones / metabolism*
  • Kruppel-Like Transcription Factors / metabolism*
  • Mice
  • Mice, Inbred BALB C
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Models, Genetic
  • Mutation
  • Neoplasm Proteins / biosynthesis
  • Neoplasm Proteins / genetics
  • Neoplasm Proteins / physiology*
  • Patched Receptors
  • Patched-1 Receptor
  • Polymorphism, Single Nucleotide
  • Promoter Regions, Genetic / genetics*
  • Protein Processing, Post-Translational*
  • Receptors, Cell Surface / biosynthesis
  • Receptors, Cell Surface / genetics
  • Receptors, Cell Surface / physiology*
  • Rhabdomyosarcoma / genetics*
  • Rhabdomyosarcoma / metabolism
  • Signal Transduction
  • Zinc Finger Protein GLI1

Substances

  • Gli1 protein, mouse
  • Histones
  • Kruppel-Like Transcription Factors
  • Neoplasm Proteins
  • PTCH protein, human
  • Patched Receptors
  • Patched-1 Receptor
  • Ptch1 protein, mouse
  • Receptors, Cell Surface
  • Zinc Finger Protein GLI1
  • Decitabine
  • Azacitidine