Functional Genetic Variations In HsMAD1 And HsMAD2 Are Associated With Lung Cancer Susceptibility

Background & Aims: The precision of the cell division process is enhanced by thespindle checkpoint. Human mitotic arrest deficient-1 (hsMADI) and -2 (hsMAD2) are twomajor proteins in the spindle checkpoint compound. The interactions of hsMAD2 withhsMAD1 are crucial. This study sought to identify functional polymorphisms in thehsMAD2 and evaluate their effects on hsMAD1-hsMAD2 interaction, spindle checkpointfunctions, and lung cancer risk, alone and in combination with hsMAD1 polymorphism.Methods: Thirty individual DNA samples were sequenced to search for singlenucleotide polymorphisms (SNPs), and the genotypes were analyzed in 1, 000 patients and1, 000 controls, and odds ratios (ORs) and 95% confidence intervals (CIs) were estimatedby logistic regression. The interactions of hsMAD1 and hsMAD2 variants in cells wereexamined by immunoprecipitation and immunoblotting analysis. The effects of thevariants on checkpoint function were evaluated by flow cytometry and mitotic index.Results: A SNP, Leu84Met, was identified in hsMAD2 and the frequency of Metallele was 0.05 in our study population. A case-control analysis showed that the hsMAD1558His/His and hsMAD2 84Leu/Met or Met/Met genotypes were associated with increasedsusceptibility to lung cancer (OR=1.43, 95% CI=1.10-1.84, P=0.007; OR=2.67, 95%CI=2.05-3.48, P＜0.001, respectively). Gene-gene interaction of hsMAD1 and hsMAD2polymorphisms increased the OR of lung cancer in a multiplicative manner (OR=3.84, 95% CI=2.30-6.40, P＜0.001). A supermultiplicative joint effect between the hsMAD2polymorphism and smoking was observed (OR=4.89, 95% CI=3.34-7.17, P＜0.001).Immunoprecipitation assays showed that the interactions between hsMAD2-84Leu andhsMAD1-558Arg or -558His were robust, but interactions between hsMAD2-84Met andeither hsMAD1-558Arg or-558His were weak. Cells transfected with hsMAD1-558Hisand hsMAD2-84Met had lower 4N-DNA content and mitotic index than cells transfectedwith hsMAD1-558Arg and hsMAD2-84Leu, suggesting impaired checkpoint function.Conclusions: The hsMAD1 and hsMAD2 polymorphisms confer host susceptibility tolung cancer, which might result from reduced hsMAD1-hsMAD2 interaction andattenuated spindle checkpoint function.