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Molecular analysis of alterations of the p18INK4c gene in human meningiomas
T Santarius1, M Kirsch, D C Nikas
1Neurosurgical Laboratories, Brigham, Women's Hospital, The Brain Tumor Center, Brigham and Women's Hospital, Children's Hospital, and Dana Farber Cancer Institute, Department of Surgery, Harvard Medical School, Boston, Massachusetts, USA.
Abstract:
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.
Insights
Researchers investigated the p18INK4c gene in meningiomas, common brain tumors. Despite frequent loss of heterozygosity at chromosome 1p32, the p18INK4c gene showed no significant genetic or epigenetic alterations, suggesting it does not play a key role in meningioma development.
Area of Science:
- Neuro-oncology
- Molecular genetics
- Cancer biology
Background:
- Meningiomas are common primary brain tumors often associated with NF2 gene alterations.
- Chromosome 1p deletions are frequently observed in meningiomas.
- The p18INK4c gene, a cyclin-dependent kinase inhibitor, is located on chromosome 1p and is a potential tumor suppressor.
Purpose of the Study:
- To investigate the role of the p18INK4c gene in the development of human meningiomas.
- To analyze genetic and epigenetic alterations of the p18INK4c gene in meningioma samples.
Main Methods:
- Analysis of loss of heterozygosity (LOH) at 1p32 using microsatellite markers.
- Mutation screening of the p18INK4c gene using single-stranded conformational polymorphism (SSCP) and direct sequencing.
- Analysis of p18INK4c gene methylation status.
- Immunohistochemical detection of p18 protein expression.
Main Results:
- Loss of heterozygosity (LOH) at 1p32 markers was detected in a significant proportion of meningioma samples (20-37%).
- No missense mutations were found; a single silent mutation was identified.
- No inactivating methylation of the p18INK4c gene was observed.
- p18 protein was expressed in most analyzed meningioma samples, with one exception showing homozygous deletion.
Conclusions:
- The high frequency of LOH at 1p32 in meningiomas does not correlate with genetic or epigenetic alterations in the p18INK4c gene.
- The presence of p18 protein in most tumors suggests that p18INK4c is unlikely to function as a critical tumor suppressor in meningioma development.