title: Sp1 binding is inhibited by (m)Cp(m)CpG methylation.
abstract: Previously it has been found that binding of the Sp1 transcription factor is not significantly affected by methylation of the CpG dinucleotide within its binding site, 5'-GGGCGG (lower strand, 5'-CCGCCC). Since it has been established that mammalian cells also have the capacity to methylate cytosines (C) at CpNpG sites we examined the effect of methylation of the outer C of the CpCpG on Sp1 binding. We find that methylation of the outer C is inhibitory and in particular methylation of both cytosines (m)Cp(m)CpG inhibits binding by 95%. Furthermore, we have identified endogenous (m)Cp(m)CpG methylation of an Sp1 site in the CpG island promoter of the retinoblastoma (Rb) gene by genomic sequencing. This occurs in a proportion of retinoblastoma tumors which are extensively CpG methylated in the Rb promoter. The results raise the possibility that (m)Cp(m)CpG methylation could have a biological function in preventing Sp1 binding, thereby contributing to the subsequent abnormal methylation of CpG islands often observed in tumor cells.
authors.affiliation: Kanematsu Laboratories, Royal Prince Alfred Hospital, Camperdown, Australia. clark@pelican.dbe.csiro.au
authors.forename: S J
authors.initials: SJ
authors.lastname: Clark
authors.forename: J
authors.initials: J
authors.lastname: Harrison
authors.forename: P L
authors.initials: PL
authors.lastname: Molloy
mesh_terms: D001665:Binding Sites; D003596:Cytosine / Q000378:metabolism; D019175:DNA Methylation; D008969:Molecular Sequence Data; D009841:Oligonucleotides / Q000235:genetics / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism*
chemical_list: D009841:Oligonucleotides; D016160:Retinoblastoma Protein; D016329:Sp1 Transcription Factor; D003596:Cytosine