Aberrant p27Kip1 promoter methylation in malignant melanoma

p27(Kip1) is a regulator of the mammalian cell cycle and a putative tumor suppressor. Distinct altered patterns of p27(Kip1) protein expression are found in a variety of human carcinomas, and p27(Kip1) expression levels usually correlate directly with disease-free survival. The mechanism(s) by which p27(Kip1) expression is reduced or lost during tumorigenesis remains unclear, Specific alterations of the p27(Kip1) gene, including mutations and homozygous deletions, are exceedingly rare in human cancers. We have used methylation-specific PCR and bisulfite genomic sequencing to examine the methylation status of p27(Kip1) in 61 primary and metastatic tumors and 35 cell lines from patients with malignant melanoma, Dense methylation of a CpG island in the promoter region of p27(Kip1) was detected in four of 45 metastatic tumors (9%) and three of the cell lines (9%), including two cell lines established from two different metastases from the same patient. Examination of a naturally occurring, allele-specific sequence variant demonstrated that p27(Kip1) methylation is associated with transcriptional silencing in situ, Cell lines with p27(Kip1) methylation showed retention of the wild-type allele and detectable p27(Kip1) protein whose abundance was reduced compared with normal melanocytes, Collectively, our data suggest that DNA methylation may be a cause of monoallelic p27(Kip1) silencing in malignant melanoma, which would support a role for p27(Kip1) haploinsuffciency in human cancer.