Valla Fongchaiya, BSc *, Pichet Sampatanukul, MD, MSc*, and Kris Chatamra, MD, FRCS ** *Department of Pathology, Faculty of Medicine, Chulalongkorn University and
**Queen Sirikit Center for Breast Cancer, King Chulalongkorn Memorial Hospital, Thai Red Cross Society. Correspondence: Valla Fongchaiya, BSc., Department of Pathology, Faculty of Medicine, Chulalongkorn University. Email address: Valla.email@example.com Received 26 April 2013; Accepted 27 May 2013.
Introduction: From previous study with Methylation specific polymerase chain reaction (MSP), there were cases of DNA methylation showing positive protein expression. Some CpG sites of the primer were speculated to have no effect on protein expression.
Methods: Forty-six cases were selected including the two problem cases from our previous study samples of 88. The DNA extracts were sequenced after bisulfite conversion for the epigenetic part of the GSTP1 gene, 298 base pairs, which comprised 38 CpG sites. Methylation status at the sites 10-13 and 20-22 representing in the primer used in MSP study was correlated with the expression of protein to detect the active and inactive sites.
Result: The two problem cases revealed methylation of CpG sites no.11, 12, 13 and no. 21, 22, suggested that these were inactive sites. The sites no. 10 and 20 were regarded as active sites. The validity was confirmed on the methylation data of the rest of 44 cases. There were 11 cases showing methylated cytosine at either CpG site no. 10 or 20. All cases showed negative for the protein. On the other hand, of the 21 cases with positive protein, none elicited methylation at CpG sites no.10 and 20.
Conclusion: The impact of location of CpG sites on the silencing of the protein expression of GSTP1 is present. There are at least two active sites at no.10 and 20. Further studies to verify the other active sites are encouraging.