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Alternative splicing of the p15 cdk inhibitor in glioblastoma multiforme
1Neurochirurgische Klinik, Universitätskliniken Bonn, Germany. Matthias.Simon@ukb.uni-bonn.de
Abstract:
Thirty-four to fifty-six percent of malignant gliomas harbor homozygous co-deletions of the INK4a(p16-p14ARF) and INK4b(p15) tumor suppressor genes. Recently, an alternatively spliced form of p15 has been cloned and termed p10 based on the presumed molecular weight of the protein. In this study, we have investigated the role of p10 expression in human glioblastomas. Both, wild-type p15 and p10 were detected in three of nine glioblastoma cell lines. Sixteen of twenty-nine (55%) glioblastoma tumor samples contained INK4b transcripts, but only nine (31%) tumors expressed p15 protein. Three p15 protein-negative tumors expressed only p10 mRNA. Preferential expression of p10 was not due to splice site mutations. Strong suppression of tumorigenicity was seen in four glioblastoma cell lines after transfection with p15 but not with p10. Loss of p15 protein expression was almost always accompanied by loss of p16 expression. p1 6/p15-negative tumors commonly lacked p14ARF expression. These results suggest that differential splicing of the INK4b gene may result in the expression of p10 at the expense of p15, which would lead to loss of p15-mediated growth suppression. This novel mechanism of loss of p15 might complement alterations of the INK4a tumor suppressor gene in some glioblastomas, resulting in combined loss of p16, p15 and p14ARF.
Insights
Malignant gliomas often lose tumor suppressor genes INK4a and INK4b. A new form, p10, may replace p15 via alternative splicing, potentially contributing to glioblastoma growth.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Malignant gliomas frequently exhibit homozygous co-deletions of INK4a (p16-p14ARF) and INK4b (p15) tumor suppressor genes.
- An alternatively spliced form of p15, termed p10, has been identified.
Purpose of the Study:
- To investigate the role and expression of p10 in human glioblastomas.
- To understand the implications of p10 expression on glioblastoma tumorigenicity and its relationship with p15 and INK4a alterations.
Main Methods:
- Detection of wild-type p15 and p10 in glioblastoma cell lines and tumor samples using molecular techniques.
- Analysis of p15 protein expression and its correlation with p16 and p14ARF expression.
- Tumorigenicity assays following transfection with p15 and p10 in glioblastoma cell lines.
Main Results:
- Both wild-type p15 and p10 were detected in some glioblastoma cell lines.
- INK4b transcripts were found in 55% of tumors, but only 31% expressed p15 protein, with three tumors expressing only p10 mRNA.
- Transfection with p15, but not p10, strongly suppressed glioblastoma cell line tumorigenicity.
- Loss of p15 protein expression correlated with loss of p16 and often p14ARF expression.
Conclusions:
- Differential splicing of the INK4b gene can lead to p10 expression at the expense of functional p15, contributing to glioblastoma growth.
- This novel mechanism of p15 loss complements INK4a alterations, resulting in a combined loss of p16, p15, and p14ARF in some glioblastomas.