DNA methylation and histone modification regulate silencing of OPG during tumor progression.
The identification of molecules that are down-regulated in malignant phenotype is important for understanding tumor biology and their role in tumor suppression. We compared the expression profile of four normal nasal mucosal (NNM) epithelia and a series of nasopharyngeal cancinoma (NPC) cell lines using cDNA microarray and confirmed the actual expression of the selected genes, and found osteoprotegerin (OPG) to be ubiquitously deficient in NPC cells. We also found OPG to be down-regulated in various cancer cell lines, including oral, cervical, ovarian, lung, breast, pancreas, colon, renal, prostate cancer, and hepatoma. Administration of recombinant OPG (rOPG) brought about a reduction in cancer cell growth through apoptotic mechanism. We generated eleven monoclonal antibodies (MAbs) against OPG to study OPG's expression and biological functions in cancer cells. OPG was detected in the tumor stromal regions, but not in the cancer cell per se in surgical specimens of liver cancer. Quantitative reverse transcription-polymerase chain reaction (Q-RT-PCR) revealed that OPG was down-regulated in NPC tissues compared with normal nasal polyp (NNP) tissues. In addition, we showed OPG silencing to be associated with promoter methylation as well as histone modifications. In OPG-silenced cancer cell lines, the OPG gene promoter CpG dinucleotides were highly methylated. Compared to normal cells, silenced OPG gene in cancer cells were found to have reduced histone 3 lysine 4 tri-methylation (H3K4me3) and increased histone 3 lysine 27 tri-methylation (H3K27me3). Taken together, these results suggest that OPG silencing in carcinoma cancer cells occurs through epigenetic repression.
Lu
Tung-Ying
TY
Institute of Cellular and Organismic Biology, Academia Sinica, Taipei 115, Taiwan.
Kao
Cheng-Fu
CF
Lin
Chin-Tarng
CT
Huang
Dah-Yeou
DY
Chiu
Chien-Yu
CY
Huang
Yu-Shin
YS
Wu
Han-Chung
HC
D045744:Cell Line, Tumor; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006657:Histones / Q000378:metabolism*; D006801:Humans; D008297:Male; D008745:Methylation; D009369:Neoplasms / Q000235:genetics* / Q000473:pathology; D053244:Osteoprotegerin / Q000235:genetics* / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology
D006657:Histones; D053244:Osteoprotegerin