Maria de Leon1, Horacio Cardenas2, Edyta Vieth3, Robert Emerson4, Matthew Segar5, Yunlong Liu5, Kenneth Nephew6, Daniela Matei7. 1. Indiana University, Obstetrics and Gynecology Department, Division of Gynecologic Oncology, United States. 2. Northwestern University, Feinberg School of Medicine, Department of Obstetrics and Gynecology, United States. 3. Indiana University, Department of Medicine, United States. 4. Indiana University, Department of Pathology, United States. 5. Indiana University, Department of Biostatics, United States. 6. Medical Sciences, Indiana University, Bloomington, United States. 7. 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.
Abstract
OBJECTIVES: 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. METHODS: 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). RESULTS: 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. CONCLUSIONS: 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. Published by Elsevier Inc.
OBJECTIVES: 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. METHODS: 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). RESULTS: 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. CONCLUSIONS: 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. Published by Elsevier Inc.
Entities:
Keywords:
Cisplatin resistance; DNA methylation; Ovarian cancer; TMEM88; Wnt
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