Chromosomal changes and correspondingly altered proto-oncogene expression in human gliomas. Value of combined cytogenetic and molecular genetic analysis.
A combined cytogenetic and molecular genetic study was performed to analyze seven primary brain tumors: one oligoastrocytoma WHO-grade II, one anaplastic astrocytoma grade III, one anaplastic astrocytoma grade III/IV and four glioblastomas by G-banding and RNA dot blotting. A normal karyotype was found in the oligoastrocytoma. One of the two anaplastic astrocytomas (male) contained cells with a normal karyotype and cells with a Y-chromosomal loss, and the other one showed structural abnormalities too complex for complete analysis in mostly polyploid cells. Two of the four glioblastomas had few and the other two multiple chromosomal changes such as +7, +20, -8, -9 del(9)(p21), -10, del(10)(q24), -13,14, del(17)(p21), -22, add(3)(q13), double minutes and marker chromosomes. Compared to normal brain, all tumors had an increased EGFr and both anaplastic astrocytomas as well as three glioblastomas a decreased H-ras expression. The two glioblastomas with multiple chromosomal changes showed increased EGFr, Ki-ras, myb, mos and myc, decreased H-ras and N-ras and unchanged levels of abl, src and sis. Both the cytogenetic and molecular genetic findings are compatible even in the case of chromosomal losses, where the genes on the remaining allele may be responsible for dominant gene regulation mechanisms which result in a protooncogene overexpression. Our findings indicate that, apart from proto-oncogene overexpression, other mechanisms, e.g. tumor suppressor gene inactivation, are important for glial tumorigenesis. Karyotypic analysis makes it possible to search specifically for genetic events still unknown but arising from particular chromosomal changes.