DNA methylation of the cytosine in the CpG dinucleotide is typically associated with gene silencing. Genomic analyses have identified low CpG promoters that are both methylated and transcriptionally active, but the mechanism underlying the activation of these methylated promoters remains unclear. Here we show that CpG methylation of the CRE sequence (TGACGTCA) enhances the DNA binding of the C/EBPα transcription factor, a protein critical for activation of differentiation in various cell types. Transfection assays also show that C/EBPα activates the CRE sequence only when it is methylated. The biological significance of this observation was seen in differentiating primary keratinocyte cultures from newborn mice where certain methylated promoters are both bound by C/EBPα and activated upon differentiation. Experimental demethylation by either 5-azacytidine treatment or DNMT1 depletion diminished both C/EBPα binding and activation of the same methylated promoters upon differentiation suggesting that CpG methylation can localize C/EBPα. Transfection studies in cell cultures using methylated tissue-specific proximal promoters identified half-CRE (CGTCA) and half-C/EBP (CGCAA) sequences that need to be methylated for C/EBPα mediated activation. In primary dermal fibroblasts, C/EBPα activates a different set of methylated tissue-specific promoters upon differentiation into adipocytes. These data identify a new function for methyl CpGs: producing DNA binding sites at half-CRE and half-C/EBP sequences for C/EBPα that are needed to activate tissue-specific genes.

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Human papillomavirus (HPV) DNA in cervical scrape samples of married women from Manipur (n= 692) and Sikkim (n= 415) in northeast India was determined and compared with that of women from West Bengal (n= 1112) in eastern India by polymerase chain reaction. HPV prevalence was lower in Manipur (7.4%) than in Sikkim (12.5%), which was closely followed by West Bengal (12.9%). HPV18 was predominant in Manipur (2.03%) and strikingly lower (0.2%) in Sikkim and West Bengal (0.9%), while the reverse was true for HPV16. The proportion of HPV16/18 infections in Manipur (3.3%, 22/672) and Sikkim (3.89%, 14/359) were comparable and significantly lower compared to that in West Bengal (7.8%, 79/1007) among women having normal cervical cytology. Such prevalence was similar among all age groups in Manipur: increased with age for women in Sikkim and dropped with age for those in West Bengal similar to that reported previously. At age < or =30 years, HPV16/18 prevalence in Manipur (3.3%) and Sikkim (2.5%) was comparable but was significantly lower (P < 0.05) in contrast to that in West Bengal (8.8%). Among abnormal cytologic lesions, HPV16/18 infections were significantly higher than in normals (P= 0.000) both in Sikkim (14.3%) and West Bengal (20.9%) and absent in Manipur. Such prevalence was noted among women in Sikkim aged >30 years and equally among those in West Bengal aged < or =30 or >30 years. Thus, women from northeast India, particularly from Manipur, appear less susceptible to HPV16/18 infection and related cervical lesions compared to those from West Bengal, where such proneness was prominently evident at age < or =30 years.