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p14ARF deletion and methylation in genetic pathways to glioblastomas
M Nakamura1, T Watanabe, U Klangby
1International Agency for Research on Cancer, Lyon, France.
Abstract:
The CDKN2A locus on chromosome 9p21 contains the p14ARF and p16INK4a genes, and is frequently deleted in human neoplasms, including brain tumors. In this study, we screened 34 primary (de novo) glioblastomas and 16 secondary glioblastomas that had progressed from low-grade diffuse astrocytomas for alterations of the p14ARF and p16INK4a genes, including homozygous deletion by differential PCR, promoter hypermethylation by methylation-specific PCR, and protein expression by immunohistochemistry. A total of 29 glioblastomas (58%) had a p14ARF homozygous deletion or methylation, and 17 (34%) showed p16INK4a homozygous deletion or methylation. Thirteen glioblastomas showed both p14ARF and p16INK4a homozygous deletion, while nine showed only a p14ARF deletion. Immunohistochemistry revealed loss of p14ARF expression in the majority of glioblastomas (38/50, 76%), and this correlated with the gene status, i.e. homozygous deletion or promoter hypermethylation. There was no significant difference in the overall frequency of p14ARF and p16INK4a alterations between primary and secondary glioblastomas. The analysis of multiple biopsies from the same patients revealed hypermethylation of p14ARF (5/15 cases) and p16INK4a (1/15 cases) already at the stage of low-grade diffuse astrocytoma but consistent absence of homozygous deletions. These results suggest that aberrant p14ARF expression due to homozygous deletion or promoter hypermethylation is associated with the evolution of both primary and secondary glioblastomas, and that p14ARF promoter methylation is an early event in subset of astrocytomas that undergo malignant progression to secondary glioblastoma.
Insights
Aberrant p14ARF expression, due to gene deletion or methylation, is linked to glioblastoma development. Promoter methylation of p14ARF is an early event in astrocytoma progression to secondary glioblastoma.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- The CDKN2A locus, housing p14ARF and p16INK4a genes, is frequently altered in human cancers, including brain tumors.
- Glioblastomas, aggressive brain tumors, arise either primarily or secondary from lower-grade astrocytomas.
Purpose of the Study:
- To investigate alterations in the p14ARF and p16INK4a genes in primary and secondary glioblastomas.
- To determine the frequency of homozygous deletion, promoter hypermethylation, and protein expression loss for p14ARF and p16INK4a.
- To assess if these alterations differ between primary and secondary glioblastomas and their role in astrocytoma progression.
Main Methods:
- Screening of 34 primary and 16 secondary glioblastomas for gene alterations.
- Utilized differential PCR for homozygous deletion detection.
- Employed methylation-specific PCR for promoter hypermethylation analysis.
- Conducted immunohistochemistry to assess protein expression.
Main Results:
- 58% of glioblastomas showed p14ARF homozygous deletion or methylation; 34% showed p16INK4a alterations.
- Loss of p14ARF protein expression occurred in 76% of glioblastomas, correlating with gene status.
- No significant difference in alteration frequency between primary and secondary glioblastomas.
- p14ARF promoter methylation was detected in early-stage astrocytomas, preceding homozygous deletions.
Conclusions:
- Aberrant p14ARF expression, via deletion or methylation, is associated with both primary and secondary glioblastoma evolution.
- p14ARF promoter methylation represents an early event in a subset of astrocytomas that progress to secondary glioblastoma.