MeCP2 and MBD2 expression during normal and pathological growth of the human mammary gland

Abstract

During the last years, a direct link between DNA methylation and repressive chromatin structure has been established. This structural modi®cation is mediated by histone deacetylases targeted to the methylated sequences by Methyl Binding Proteins (MBD). Human cancer cells exhibit both a global hypomethylation and some localized hypermethylations suggesting that the deregulation of the methylation machinery is a central event in tumorigenesis. Therefore, we have investigated in human tissues the expression of two major MBDs, MeCP2 and MBD2, during the proliferation of normal breast and in benign and neoplasic breast tumors. Quantitation of the transcripts indicates that MBD2 mRNAs are 20 ± 30-fold more abundant than MeCP2 transcripts in the adult and fetal human mammary gland. In pathological tissues samples MBD2 mRNA levels are signi®cantly higher (P=0.001) in benign tumors compared with normal breast tissues, whereas MeCP2 expression is not modi®ed in these specimens. In neoplasic samples a deregulation of the expression of both genes was found. The amounts of MBD2 and MeCP2 transcripts vary greatly between samples in cancer cells compared to normal breast tissues or benign tumors, and in invasive ductal carcinomas the amount of MBD2 mRNA is signi®cantly (P=0.03) associated with the tumor size. Taken together these data suggest that upregulation of MBD2 might be associated with breast cell proliferation. In line with this hypothesis MBD2 is also upregulated during the prenatal development of the human mammary gland, but in contrast to that observed in tumor cells, MeCP2 is also coordinately upregulated in the fetal breast tissues, suggesting that deregulation of MeCP2 and MBD2 occurs in human breast cancers.

Specific binding of the methyl binding domain protein 2 at the BRCA1-NBR2 locus

“…HeLa cells contain ∼20 times more MBD2 than MeCP2 transcripts (30). In addition, it has been shown that some methylated DNA regions are bound by multiple MBD proteins (15).…”

“…Although all the MBD proteins are ubiquitously expressed in somatic tissues, variations in their expression levels, depending on the cell type and the differentiation state, have been observed previously (35). For example, in mouse brain, Mecp2 and Mbd1 are highly expressed when compared with Mbd2 (2), while MBD2 transcripts are 20-fold more abundant than MeCP2 mRNA in breast tissues (30), suggesting that the relative MBD protein concentrations might be involved in the phenotypes associated with their experimental depletions. Therefore, their relative concentrations might be associated with a prominent binding of MBD2 to some methylated DNA segments.…”

“…After DNase I digestion (Ambion Inc.) and RNeasy purification (Qiagen), this competitor RNA was quantified by densitometry and then diluted in the presence of yeast tRNA as a carrier (40 ng/μl; Ambion). For BRCA1 and MBD2 quantitative RT–PCR, previously designed competitors were used (30,31). …”

Genotypes and haplotypes of the methyl-CpG-binding domain 2 modify breast cancer risk dependent upon menopausal status

“…For example, a recent study [16] showed that breast carcinomas exhibit alterations in MBD2 expression. One interesting finding from that study was that breast carcinomas can be divided into two groups, with one expressing very high levels of MBD2 and the other expressing a much lower level.…”

Reproductive medicine and inheritance of infertility by offspring: the role of fetal programming

“…[1] Methylation of DNA blocks the binding of transcriptional factors at their binding sites (28,29). [2] Methylation of DNA attracts methyl-CpG binding proteins, which recruit mediators of chromatin remodeling such as histone-modifying enzymes or other repressors of gene expression (30).…”