Expression and mutational analyses of the human MAD2L1 gene in breast cancer cells

Breast cancer is a heterogeneous disorder in which most tumors display some degree of aneuploidy, especially those at later stages of the disease. Aneuploidy and associated chromosome instability may be important in the progression of mammary tumorigenesis. Aneuploidy is prevented during normal cell division in part through regulation of a mitotic spindle checkpoint where mitotic arrest prevents segregation of misaligned chromosomes into daughter cells at anaphase. Mitotic arrest genes, including the MAD family, which was originally characterized in yeast, help regulate normal function of the mitotic spindle checkpoint. Decreased expression of the human gene MAD2L1 was previously reported in a breast cancer cell line exhibiting chromosome instability and aneuploidy. To explore further the potential role of MAD2L1 in breast cancer, we analyzed MAD2L1 gene expression in 13 minimally to grossly aneuploid human breast cancer cell lines and found significant differences of expression in three lines. Sequence analysis of MAD2L1 cDNA in these as well as nine additional aneuploid breast cancer and five immortalized normal human mammary epithelial cell lines revealed one heterozygous frameshift (572 del A) mutation in a cancer cell line that demonstrated a high level of transcript expression. In addition, two 3'UTR sequence variants were noted in breast cancer cell lines. The 572 del A mutation creates a truncated MAD2 protein product. Further functional studies in primary breast tumors are therefore warranted to determine the potential role MAD2L1 may play in breast cancer.