Molecular analysis of alterations of the p18INK4c gene in human meningiomas.

Meningiomas are common primary brain tumours frequently presenting with deleted and/or mutated NF2 gene located on 22q.1p has been reported as the second most commonly deleted chromosomal region in these neoplasms. A new member of the INK4 family of CDK inhibitors, the p18INK4c gene, has recently been mapped to this chromosomal arm. By virtue of its structural and functional similarities with the p16 gene, p18 has been implicated as a tumour suppressor gene in a variety of cancers. In this paper 40 human meningiomas were analysed for loss of heterozygosity (LOH) at the p18 locus, mutations and inactivating methylation of the p18 gene. LOH at D1S193, D1S463 and D1S211 microsatellite marker loci mapped to 1p32 was detected in 13 of 35 (37%), four of 20 (20%), and six of 24 (25%) tumour samples, respectively. One sample presented with homozygous deletion at D1S193. Mutational analysis using single stranded conformational polymorphism (SSCP) and direct sequencing did not detect any missense mutation but revealed a novel silent mutation, G to T, at coding nucleotide 435. Analysis of HgaI, BsaHI, ScrFI and Eco0109I restriction sites of p18 exon 1 revealed absence of inactivating methylation. Immunohistochemistry with p18 monoclonal antibody detected presence of cytoplasmic p18 staining in 21 of 22 examined samples. One sample did not stain and was shown to carry homozygous deletion at D1S193. Despite the high frequency of LOH at 1p32 microsatellite markers, the lack of genetic and epigenetic aberrations in the p18 gene together with the presence of p18 protein in all but one meningioma samples argues against the role of p18 as a tumour suppressor gene important for meningioma development.