DNA methylation, nuclear structure, gene expression and cancer

DNA methylation, chromatin structure, transcription, and cancer have traditionally been studied as separate phenomena. Recent data provide now direct physical and functional links between these processes revealing a complex network of interactions and mutual dependences. Methylated DNA is bound by methyl-CpG binding protein (MeCP) complexes that include histone deacetylases (HDACs). This recruitment of HDACs is suggested to promote local chromatin condensation and thereby repress gene expression. Most recently, also complexes of DNA methyltransferase (Dnmt1) with transcriptional repressors, DMAP1 and pRB, have been described providing a direct link to transcriptional regulation and tumor suppression. Inactivation of the DNA methyltransferase genes (Dnmt1, 3a, and 3b) was found to be lethal in mice and several human diseases (ICF and Rett syndrome) turned out to be linked to DNA methylation. In particular, global hypomethylation has been found in tumor samples together with cancer-type-specific, local hypermethylation. Taken together, these lines of evidence clearly underscore the central role of DNA methylation in the regulation of gene expression and chromatin structure during normal development and diseases like cancer. (C) 2001 Wiley-Liss, Inc.