title: Transmembrane protein 88 (TMEM88) promoter hypomethylation is associated with platinum resistance in ovarian cancer.
abstract: Epigenetic alterations have been implicated in the development of platinum resistance in ovarian cancer (OC). In this study, we aimed to identify DNA methylation changes in platinum resistant tumors and their functional implications.
  
  
  
  To identify DNA methylation alterations we used the Illumina 450k DNA methylation array and profiled platinum sensitive and resistant OC xenografts. Validation analyses employed RT-PCR and immunohistochemistry (IHC).
  
  
  
  Genome-wide DNA methylation analysis of OC xenografts identified 6 genes (SSH3, SLC12A4, TMEM88, PCDHGC3, DAXX, MEST) whose promoters were significantly hypomethylated in resistant compared to sensitive (control) xenografts (p<0.001). We confirmed that TMEM88 and DAXX mRNA expression levels were increased in platinum resistant compared to control xenografts, inversely correlated with promoter methylation levels. Furthermore treatment of OC cells with SGI-110 (guadecitabine), a DNA methyl transferase (DNMT) inhibitor, increased TMEM88 mRNA expression levels, supporting that TMEM88 is transcriptionally regulated by promoter methylation. TMEM88 was detectable by IHC in all histological types of ovarian tumors and its knock-down by using siRNA promoted OC cell proliferation and colony formation and re-sensitized cells to platinum. Furthermore, TMEM88 knock down induced upregulation of cyclin D1 and c-Myc, known Wnt target genes, supporting that TMEM88 inhibits Wnt signaling.
  
  
  
  Overall, our results support that OC platinum resistance was correlated with TMEM88 overexpression regulated through decreased promoter methylation. Our data suggest that TMEM88 functions as an inhibitor of Wnt signaling, contributing to the development of platinum resistance.
authors.affiliation: Indiana University, Obstetrics and Gynecology Department, Division of Gynecologic Oncology, United States.
authors.forename: Maria
authors.initials: M
authors.lastname: de Leon
authors.affiliation: Northwestern University, Feinberg School of Medicine, Department of Obstetrics and Gynecology, United States.
authors.forename: Horacio
authors.initials: H
authors.lastname: Cardenas
authors.affiliation: Indiana University, Department of Medicine, United States.
authors.forename: Edyta
authors.initials: E
authors.lastname: Vieth
authors.affiliation: Indiana University, Department of Pathology, United States.
authors.forename: Robert
authors.initials: R
authors.lastname: Emerson
authors.affiliation: Indiana University, Department of Biostatics, United States.
authors.forename: Matthew
authors.initials: M
authors.lastname: Segar
authors.affiliation: Indiana University, Department of Biostatics, United States.
authors.forename: Yunlong
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Medical Sciences, Indiana University, Bloomington, United States.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Nephew
authors.affiliation: Northwestern University, Feinberg School of Medicine, Department of Obstetrics and Gynecology, United States; Robert H. Lurie Cancer Center, United States. Electronic address: daniela.matei@northwestern.edu.
authors.forename: Daniela
authors.initials: D
authors.lastname: Matei
mesh_terms: D000818:Animals; D000077216:Carcinoma, Ovarian Epithelial; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000235:genetics; D019175:DNA Methylation; D019008:Drug Resistance, Neoplasm; D005260:Female; D055785:Gene Knockdown Techniques; D006801:Humans; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009375:Neoplasms, Glandular and Epithelial / Q000188:drug therapy* / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D009944:Organoplatinum Compounds / Q000494:pharmacology*; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D011401:Promoter Regions, Genetic; D060449:Wnt Signaling Pathway; D023041:Xenograft Model Antitumor Assays
chemical_list: D008565:Membrane Proteins; D009944:Organoplatinum Compounds; C555652:TMEM88 protein, human
keywords: Cisplatin resistance; DNA methylation; Ovarian cancer; TMEM88; Wnt