| Research Abstract |
We have analyzed the status of candidate tumor suppressor p16 gene in 75 brain tumors (3 ependymomas, 9 oligodendrogliomas, 12 astrocytomas, 11 anaplastic astrosytomas, 1 medulloblastoma and 39 glioblastoma multiforms) from Japanese patients. With quantitative multiplex polymerase chain reaction (PCR) assay using the exon 2 primers of the p16 gene and control chromosome 9qSTS primers, we found homozygous deletion of the p16 gene in 7 cases; in 1 out of 11 anaplastic astrocytomas (HWO grade III), 6 out of 39 glioblastoma multiforms (gradeIV), but in none of the tumors of grade I or II. Using the single strand conformation polymorphism technique, mobility shift of PCR products were observed in 8 cases (1 astrocytoma, 1 anaplastic astrocytoma, 6 glioblastoma multiforms). DNA sequencing of the aberrantly migrated products revealed that 3 cases of glioblastoma multiform had mutations which caused amino acid substitutions in codon 66, 143 and 145.
Immunohistochemical analysis using polyclonal anti-p16 antibody revealed frequent loss of p16 expression. Of 45 cases analyzed (1 ependymoma, 4 oligodendrogliomas, 5 astrocytomas, 6 anaplastic astrocytomas, 29 glioblastoma multiforms), 1 astrocytoma, 2 anaplastic astrocytomas, 6 glioblastoma multiforms did not express p16 in over 70% of tumor cells. In conclusion, homozygous deletion, mutation and abnormal expression of p16 gene was frequent in high grade malignancy. In addition, the low frequency of homozygous deletions shown in this study is quite different from previous reports that demonstrated frequently deleted p16 gene in malignant gliomas from Caucasian patients and suggesting a possible racial difference in the mechanism of the tumorigenesis of gliomas.
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