Increased expression of mitotic checkpoint genes in breast cancer cells with chromosomal instability.
OBJECTIVE
Most breast cancers have chromosomal instability that seems related to defective mitotic spindle checkpoints. Because the molecular basis of this defect is unknown, we evaluated breast cancer cell lines and tissues for possible defects involving the major mitotic checkpoint genes responsible for maintaining chromosomal stability.


METHODS
We analyzed sequences and expression levels (RNA and protein) of eight major spindle checkpoint genes (MAD1L1, MAD2L1, MAD2L2, BUB1, BUB1B, BUB3, CDC20, and TTK) in a panel of 12 breast cancer cell lines, most with established genetic instability and defective spindle damage checkpoint response. mRNA levels of these genes were also measured in primary tumor samples, and immunohistochemical staining was used to evaluate BUB1B protein levels in a panel of 270 additional cases of breast cancer.


RESULTS
No functionally significant sequence variations were found for any of the eight genes in the breast cancer cell lines with chromosomal instability. More surprisingly, the mRNA and protein levels for these checkpoint genes are significantly higher in the genetically unstable breast cancer cell lines and in high-grade primary breast cancer tissues than in the stable (and checkpoint proficient) MCF-10A and normal mammary epithelial cells, or in normal breast tissues. In fact, overexpression of the BUB1B protein is a marker that recognizes nearly 80% of breast cancers in paraffin-embedded tissues.


CONCLUSIONS
Defective mitotic spindle checkpoints in breast cancer are most likely not caused by low expression or mutations of these eight checkpoint genes. High levels of these particular transcripts could represent a cellular compensation for defects in other molecular components of the mitotic spindle damage checkpoint, and increased expression of these genes might be markers of breast cancers with chromosomal instability.
Yuan
Bibo
B
Cancer Center, Johns Hopkins University School of Medicine, 417 North Caroline Street, Baltimore, MD 21231, USA.
Xu
Yi
Y
Woo
Ju-Hyung
JH
Wang
Yunyue
Y
Bae
Young Kyung
YK
Yoon
Dae-Sung
DS
Wersto
Robert P
RP
Tully
Ellen
E
Wilsbach
Kathleen
K
Gabrielson
Edward
E
D002288:Adenocarcinoma, Mucinous / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D018270:Carcinoma, Ductal, Breast / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002291:Carcinoma, Papillary / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002873:Chromosome Fragility; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D014644:Genetic Variation; D006801:Humans; D008938:Mitosis / Q000235:genetics; D009363:Neoplasm Proteins / Q000235:genetics* / Q000378:metabolism; D000075223:Poly-ADP-Ribose Binding Proteins; D011494:Protein Kinases / Q000235:genetics* / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D008941:Spindle Apparatus / Q000235:genetics*; D014407:Tumor Cells, Cultured
C489444:BUB3 protein, human; D018797:Cell Cycle Proteins; D009363:Neoplasm Proteins; D000075223:Poly-ADP-Ribose Binding Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D011494:Protein Kinases; C584277:BUB1 protein, human; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases