PTPRO is methylated in breast cancer cell lines but not in normal breast epithelial cells. (a) Expression of PTPRO in normal human mammary epithelial cells (48R) and human breast cancer cell lines Hs578t, MCF-7, and MDA-MB-231. Total RNA isolated from cell lines was subjected to RT-PCR analysis using PTPRO-specific primers. 18S rRNA was used as an internal loading control. (b) MSP analysis of PTPRO methylation status in breast cancer cell lines. HMESC48R was used as a normal control. M, methylated; U, unmethylated. (c) PTPRO CpG island from randomly selected breast tumor tissue and its matched normal tissue; also shown are HMEC 48R and MCF-7 cells, all of which were subjected to BS genomic sequencing. Each solid square represents a methylated cytosine and an open square represents unmethylated cytosine in a CpG dinucleotide. Each row corresponds to a single clone. N, normal corresponding adjacent non-cancerous tissue; T, tumor tissue.