title: miR-31 and its host gene lncRNA LOC554202 are regulated by promoter hypermethylation in triple-negative breast cancer.
abstract: BACKGROUND
  microRNAs have been established as powerful regulators of gene expression in normal physiological as well as in pathological conditions, including cancer progression and metastasis. Recent studies have demonstrated a key role of miR-31 in the progression and metastasis of breast cancer. Downregulation of miR-31 enhances several steps of the invasion-metastasis cascade in breast cancer, i.e., local invasion, extravasation and survival in the circulation system, and metastatic colonization of distant sites. miR-31 exerts its metastasis-suppressor activity by targeting a cohort of pro-metastatic genes, including RhoA and WAVE3. The molecular mechanisms that lead to the loss of miR-31 and the activation of its pro-metastatic target genes during these specific steps of the invasion-metastasis cascade are however unknown.
  
  
  RESULTS
  In the present report, we identify promoter hypermethylation as one of the major mechanisms for silencing miR-31 in breast cancer, and in the triple-negative breast cancer (TNBC) cell lines of basal subtype, in particular. miR-31 maps to the intronic sequence of a novel long non-coding (lnc)RNA, LOC554202 and the regulation of its transcriptional activity is under control of LOC554202. Both miR-31 and the host gene LOC554202 are down-regulated in the TNBC cell lines of basal subtype and over-expressed in the luminal counterparts. Treatment of the TNBC cell lines with either a de-methylating agent alone or in combination with a de-acetylating agent resulted in a significant increase of both miR-31 and its host gene, suggesting an epigenetic mechanism for the silencing of these two genes by promoter hypermethylation. Finally, both methylation-specific PCR and sequencing of bisulfite-converted DNA demonstrated that the LOC554202 promoter-associated CpG island is heavily methylated in the TNBC cell lines and hypomethylated in the luminal subtypes.
  
  
  CONCLUSIONS
  Loss of miR-31 expression in TNBC cell lines is attributed to hypermethylation of its promoter-associated CpG island. Together, our results provide the initial evidence for a mechanism by which miR-31, an important determinant of the invasion metastasis cascade, is regulated in breast cancer.
authors.affiliation: Department of Molecular Cardiology, Cleveland Clinic, Cleveland, OH, USA.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Augoff
authors.forename: Brian
authors.initials: B
authors.lastname: McCue
authors.forename: Edward F
authors.initials: EF
authors.lastname: Plow
authors.forename: Khalid
authors.initials: K
authors.lastname: Sossey-Alaoui
mesh_terms: D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D018899:CpG Islands; D019175:DNA Methylation; D015536:Down-Regulation / Q000235:genetics; D044127:Epigenesis, Genetic; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D023061:Gene Order; D020868:Gene Silencing; D006801:Humans; D007438:Introns; D035683:MicroRNAs / Q000235:genetics*; D011401:Promoter Regions, Genetic; D022661:RNA, Untranslated / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: C534612:MIRN31 microRNA, human; D035683:MicroRNAs; D022661:RNA, Untranslated