Methylation Profile of the Promoter CpG Islands of Death Associated Protein-Kinase in Nephroblastoma

Abstract

Background : Nephroblastoma (Wilms Tumor) is the most common malignant, solid, extracranial tumor of childhood which has a complex etiology, displaying genetic and epigenetic changes, including loss of imprinting and tumor suppressor gene silencing. Methylation of promoter regions of CpG-rich sites is an important mechanism for silencing of tumor suppressor genes. Death Associated Protein Kinase (DAPK) is a pro-apoptotic, calcium/calmodulin-regulated protein kinase that methylation profile of the promoter CpG islands is a target for cancer. DAPK is not studied in nephroblastoma yet. The aim of this study is to establish the methylation profile of the promoter CpG islands of DAPK that might play role in tumorigenesis and chemotherapy effect of nephroblastoma. Patients and Methods : Methylation spesific PCR was performed to detect the methylation profile of the promoter CpG islands of DAPK in pre and post chemotherapy biopsy and operation tissues of the same cases of nephroblastoma (n=8), in persistant subcapsular nephrogenic zone (PSNZ) of kidney obtained from postnatal term autopsy cases (n=6). PSNZ is a blastic focus generally multifoca. It resembles nephroblastoma in morphology. This zone exists in embriology but differentiates to renal cortex after term delivery. Chi- square test was used in statistical analysis. Results : As detected by methylation specific PCR, DAPK methylation rate was low in nephroblastoma biopsy (25%) and after chemotherapy tissues (37.5%). It was 50% in PSNZ cases. The methylation status changed in only one case that became methylated after chemotherapy. There is no statistical difference between PSNZ and nephroblastoma cases. Conclusions : DAPK methylation does not seem to play a role in chemotherapy effect on nephroblastoma. It does not seem to play role in persistance of subcapsular nephrogenic zone in normal kidney. Further studies with large case series including nephroblastic rest tissue, chemotherapy resistant cases, normal renal cortical tissue and with wide panel of methylation status of genes are recommended.