Aberrant p27(Kip1) promoter methylation in malignant melanoma

p27(Kip1) is a regulator of the mammalian cell cycle and a putative tumor s uppressor. Distinct altered patterns of p27(Kip1) protein expression are fo und in a variety of human carcinomas, and p27(Kip1) expression levels usual ly correlate directly with disease-free survival. The mechanism(s) by which p27(Kip1) expression is reduced or lost during tumorigenesis remains uncle ar, Specific alterations of the p27(Kip1) gene, including mutations and hom ozygous deletions, are exceedingly rare in human cancers. We have used meth ylation-specific PCR and bisulfite genomic sequencing to examine the methyl ation status of p27(Kip1) in 61 primary and metastatic tumors and 35 cell l ines from patients with malignant melanoma, Dense methylation of a CpG isla nd in the promoter region of p27(Kip1) was detected in four of 45 metastati c tumors (9%) and three of the cell lines (9%), including two cell lines es tablished from two different metastases from the same patient. Examination of a naturally occurring, allele-specific sequence variant demonstrated tha t p27(Kip1) methylation is associated with transcriptional silencing in sit u, Cell lines with p27(Kip1) methylation showed retention of the wild-type allele and detectable p27(Kip1) protein whose abundance was reduced compare d with normal melanocytes, Collectively, our data suggest that DNA methylat ion may be a cause of monoallelic p27(Kip1) silencing in malignant melanoma , which would support a role for p27(Kip1) haploinsuffciency in human cance r.