Molecular analyses of the mitotic checkpoint components hsMAD2, hBUB1 and hBUB3 in human cancer

During the metaphase-anaphase transition, the spindle checkpoint prevents s egregation of chromosomes if the spindle assembly is perturbed. Critical co mponents of this checkpoint are the MAD and BUB families of proteins, which prevent the proteolysis of Pds1 and B cyclins, producing mitotic arrest. I n the present study, we first intended to resolve the role of the hsMAD2 ge ne in human cancer by determining the potential presence of hsMAD2 mutation s in 44 primary bladder tumors, 42 soft-tissue sarcomas and 10 hepatocellul ar carcinomas. The entire coding region of the hsMAD2 gene was analyzed usi ng PCR-SSCP and sequencing. One of the bladder tumor samples showed a point mutation consisting of a transition, ATC --> GTC (Ile --> Val) in codon 19 0 of hsMAD2. However, no differences were found in the mitotic arrest betwe en cells transfected with mutant and wildtype MAD2 cDNA. We also identified mobility shifts in hsMAD2 in both normal and tumor DNA in 3 bladder tumors , 3 soft-tissue sarcomas and 1 hepatocellular carcinoma, consistent with a polymorphism at codon 143, CCA --> CCG (Pro --> Pro). Another polymorphism was identified in a hepatocellular carcinoma case at codon 22, GAG --> GAA (Glu --> Glu). In addition, a subgroup of 67 primary tumors was analyzed by Southern blot hybridization. No deletion or visible re-arrangements were d etected by comparing tumor and normal DNA band signals. Two other important components of the spindle mitotic checkpoint, hBUB1 and hBUB3, were also s creened for mutations: hBUB1 in 43 bladder tumors and 9 bladder cell lines and hBUB3 only in the cell lines. Two polymorphisms were found in hBUB1 at positions 144, CAG --> CAA (Gln --> Gln) in I primary tumor and 1 bladder c ell line, and 913 (ATC --> ATT, Ile --> Ile) in 1 primary tumor. We did not find sequence alterations in hBUB3. These results suggest that mutations o f the hsMAD2, hBUBI and hBUB3 genes are very rare in bladder tumors and tha t hsMAD2 alterations are also infrequent in soft-tissue sarcomas and hepato cellular carcinomas. (C) 2001 Wiley-Liss, Inc.