p14(ARF) Deletion and methylation in genetic pathways to glioblastomas

The CDKN2A locus on chromosome 9p21 contains the p14(ARF) and p16(INK4a) ge nes, and is frequently deleted in human neoplasms, including brain tumors. In this study, we screened 34 primary (de novo) glioblastomas and 16 second ary glioblastomas that had progressed from low-grade diffuse astrocytomas f or alterations of the p14(ARF) and p16(INK4a) genes, including homozygous d eletion by differential PCR, promoter hypermethylation by methylation-speci fic PCR, and protein expression by immunohistochemistry. A total of 29 glio blastomas (58%) had a p14(ARF) homozygous deletion or methylation, and 17 ( 34%) showed p16(INK4a) homozygous deletion or methylation. Thirteen gliobla stomas showed both p14(ARF) and p16(INK4a) homozygous deletion, while nine showed only a p14(ARF) deletion. Immunohistochemistry revealed loss of p14( ARF) expression in the majority of glioblastomas (38/50, 76%), and this cor related with the gene status, i.e. homozygous deletion or promoter hypermet hylation. There was no significant difference in the overall frequency of p 14(ARF) and p16(INK4a) alterations between primary and secondary glioblasto mas, The analysis of multiple biopsies from the same patients revealed hype rmethylation of p14(ARF) (5/15 cases) and p16(INK4a) (1/15 cases) already a t the stage of low-grade diffuse astrocytoma but consistent absence of homo zygous deletions. These results suggest that aberrant p14(ARF) expression d ue to homozygous deletion or promoter hypermethylation is associated with t he evolution of both primary and secondary glioblastomas, and that p14(ARF) promoter methylation is an early event in subset of astrocytomas that unde rgo malignant progression to secondary glioblastoma.