DNA Methylation Pathway Alterations in an Autochthonous Murine Model of Prostate Cancer

Abstract

We examined the DNA methylation pathway in an autochthonous murine prostate cancer model, transgenic adenocarcinoma of mouse prostate (TRAMP). We observed that, compared with strain-matched normal prostates, primary and metastatic TRAMP tumors display increased cytosine DNA methyltransferase (Dnmt) activity, Dnmt1 and Dnmt3b protein expression, and Dnmt1, Dnmt3a, and Dnmt3b mRNA expression. Increased expression of Dnmt genes correlates with increased expression of cyclin A and E2F target genes, implicating increased cell proliferation and Rb inactivation in Dnmt overexpression. We analyzed DNA methylation in TRAMP and found that global levels of 5-methyl-2 ¶-deoxycytidine are unaltered, whereas specific tumors display centromeric repeat hypomethylation. To interrogate locus-specific methylation, we did restriction landmark genomic scanning (RLGS) on normal prostates and primary tumors. In primary tumors, 2.3% of f1,200 analyzed loci display aberrant DNA hypermethylation, whereas a considerably smaller number of events show hypomethylation. The pattern of RLGS changes was nonrandom, indicating a coordinated methylation defect. Two specific genes identified by RLGS were studied in detail. Surprisingly, methylation of a downstream exon of p16(INK4a) (p16) was the highest frequency hypermethylation event identified in TRAMP, where it is associated with increased p16 mRNA and protein expression. In contrast, hypermethylation of the 5 ¶ CpG island region of the homeobox gene Irx3 in TRAMP is associated with reduced gene expression. In summary, our data reveal a systemic DNA methylation pathway defect in TRAMP reminiscent of human prostate cancer, supporting the use of this model to investigate the functional role of DNA methylation pathway alterations in prostate cancer development. (Cancer Res 2006; 66(24): 11659-67)

Side population cells have the characteristics of cancer stem-like cells/cancer-initiating cells in bone sarcomas

“…NR4A2 belongs to the steroid nuclear hormone receptor superfamily and has a role in cell transformation in cervical cancer (Ke et al, 2004). IRX3 is epigenetically inactivated by methylation in CpG islands in brain tumours (Ordway et al, 2006) and prostate cancer (Morey et al, 2006). NLRP12, also known as RNO2/monarch-1, is reported to activate inflammation in humans (Ye et al, 2008).…”

Phenotype-Specific CpG Island Methylation Events in a Murine Model of Prostate Cancer

“…This RLGS spot has been identified in the 3 ¶ end of the Cdkn2a locus. We have previously shown that the promoter region of p19 and p16 were not methylated in TRAMP tumors, and the 3 ¶ end methylation detected by RLGS was associated with overexpression (11).…”

“…A region of the profile containing 1,445 spots was found to be resolvable in all tumor gels and was analyzed in all 90 TRAMP tumor RLGS profiles compared with a single benign prostate tissue DNA RLGS profile. Any spot absent or greatly reduced in intensity in the tumor profile was considered lost and, therefore, methylated as previously shown (11,33,34). The numbers of RLGS spots lost for each of the three groups of 30 tumors studied is shown in Supplementary Table S3 and analyzed in Fig.…”

“…Dnmts were found to be overexpressed in late-stage TRAMP primary tumors and metastases to liver, kidney, and lymph node. Furthermore, nonrandom hypermethylation of CpG islands in late-stage TRAMP primary tumors was also reported (11).…”

“…Hypomethylation of repetitive elements is frequently seen and hypermethylation of specific CpG islands in promoter regions of several tumor suppressor genes are commonly observed to be associated with the transcriptional silencing of the gene (4)(5)(6)(7)(8). Although less wellstudied, methylation of nonpromoter CpG islands in the 3 ¶ ends or bodies of genes has been associated with ectopic, or overexpression of genes such as PAX6 (9, 10), p16 (11), and others (12).…”