Mutation analysis of hBUB1, hBUBR1 and hBUB3 genes in glioblastomas

Glioblastomas, the most malignant human brain tumors, are characterized by marked aneuploidy, suggesting chromosomal instability which may be caused b y a defective mitotic spindle checkpoint. We screened 22 glioblastomas for mutations in the mitotic spindle checkpoint genes hBUB1, hBUBR1 and hBUB3. DNA sequencing revealed a silent mutation at codon 144 of hBUB1 (CAG-->CAA, Gln-->Gln) in one glioblastoma, a silent mutation at codon 952 of hBUBR1 ( GAC-->GAT, Asp-->Asp) in another glioblastoma, and a silent mutation at cod on 388 of the hBUBR1 gene (GCG-->GCA, Ala-->Ala) in 8 glioblastomas. We als o observed a known polymorphism at hBUBR1 codon 349 (CAA/CGA, Gln/Arg), wit h an allelic frequency of 0.75 for Gln and 0.25 for Arg, which is similar t o that among healthy Caucasian individuals (0.73 vs 0.27). The coding seque nce of the hBUB3 gene did not contain any mutation, but in 4 glioblastomas (18%), a C-->T point mutation was detected at position -6 (6 nucleotides up stream of the ATG initiator codon). Analysis of blood DNA of these patients showed identical sequence alterations, indicating that this is a polymorph ism. Again, the frequency in glioblastomas was similar to that in healthy C aucasians (15%). We further screened hBUB1 in 18 cases of giant cell gliobl astoma, a variant characterized by a predominance of bizarre, multinucleate d giant cells. There were no changes, except for a silent mutation at codon 144 in two cases. These results suggest that mutations in these mitotic sp indle checkpoint genes do not play a significant role in the causation of c hromosomal instability in glioblastomas.