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    PTPRD is homozygously deleted and epigenetically downregulated in human hepatocellular carcinomas
    (Mary Ann Liebert Inc., 2015) Acun, T.; Demir, K.; Oztas, E.; Arango, D.; Yakicier, M.C.
    PTPRD (protein tyrosine phosphatase, receptor type, D) is a tumor suppressor gene, frequently inactivated through deletions or epigenetic mechanisms in several cancers with importance for global health. In this study, we provide new and functionally integrated evidence on genetic and epigenetic alterations of PTPRD gene in hepatocellular carcinomas (HCCs). Importantly, HCC is the sixth most common malignancy and the third most common cause of cancer-related mortality worldwide. We used a high throughput single nucleotide polymorphism (SNP) microarray assay (Affymetrix, 10K2.0 Assay) covering the whole genome to screen an extensive panel of HCC cell lines (N=14 in total) to detect DNA copy number changes. PTPRD expression was determined in human HCCs by Q-RT-PCR and immunohistochemistry. Promoter hypermethylation was assessed by combined bisulfite restriction analysis (COBRA). DNA methyl transferase inhibitor 5-azacytidine (5-AzaC) and/or histone deacetylase inhibitor Trichostain A (TSA) were used to restore the expression. We identified homozygous deletions in Mahlavu and SNU475 cells, in the 5′UTR and coding regions, respectively. PTPRD mRNA expression was downregulated in 78.5% of cell lines and 82.6% of primary HCCs. PTPRD protein expression was also found to be lost or reduced in HCC tumor tissues. We found promoter hypermethylation in 22.2% of the paired HCC samples and restored PTPRD expression by 5-AzaC and/or TSA treatments. In conclusion, PTPRD is homozygously deleted and epigenetically downregulated in HCCs. We hypothesize PTPRD as a tumor suppressor candidate and potential cancer biomarker in human HCCs. This hypothesis is consistent with compelling evidences in other organ systems, as discussed in this article. Further functional assays in larger samples may ascertain the contribution of PTPRD to hepatocarcinogenesis in greater detail, not to forget its broader importance for diagnostic medicine and the emerging field of personalized medicine in oncology. © Copyright 2015, Mary Ann Liebert, Inc. 2015.
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    SIP1 is downregulated in hepatocellular carcinoma by promoter hypermethylation
    (2011) Acun, T.; Oztas, E.; Yagci, T.; Yakicier, M.C.
    Background: Smad interacting protein-1 is a transcription factor that is implicated in transforming growth factor-β/bone morphogenetic protein signaling and a repressor of E-cadherin and human telomerase reverse transcriptase. It is also involved in epithelial-mesenchymal transition and tumorigenesis. However, genetic and epigenetic alterations of SIP1 have not been fully elucidated in cancers. In this study, we investigated mutations and promoter hypermethylation of the SIP1 gene in human hepatocellular carcinomas.Methods: SIP1 expression was analyzed in HCC cell lines and primary tumors in comparison to normal and non-tumor liver tissues by using semi-quantitative RT-PCR, quantitative real-time RT-PCR and immunohistochemistry. Mutation and deletion screening of the SIP1 gene were performed by direct sequencing in HCC-derived cells. Restoration of SIP1 expression was sought by treating HCC cell lines with the DNA methyl transferase inhibitor, 5-AzaC, and the histone deacetylase inhibitor, TSA. SIP1 promoter methylation was analyzed by the combined bisulfite restriction analysis assay in in silico-predicted putative promoter and CpG island regions.Results: We found that the expression of SIP1 was completely lost or reduced in five of 14 (36%) HCC cell lines and 17 of 23 (74%) primary HCC tumors. Immunohistochemical analysis confirmed that SIP1 mRNA downregulation was associated with decreased expression of the SIP1 protein in HCC tissues (82.8%). No somatic mutation was observed in SIP1 exons in any of the 14 HCC cell lines. Combined treatment with DNA methyl transferase and histone deacetylase inhibitors synergistically restored SIP1 expression in SIP1-negative cell lines. Analysis of three putative gene regulatory regions revealed tumor-specific methylation in more than half of the HCC cases.Conclusions: Epigenetic mechanisms contribute significantly to the downregulation of SIP1 expression in HCC. This finding adds a new level of complexity to the role of SIP1 in hepatocarcinogenesis. © 2011 Acun et al; licensee BioMed Central Ltd.