Whitehead, Clark M.

Abstract The centrosome is the major microtubule organizing center in most mammalian cells, and as such it determines the number, polarity, and spatial distribution of microtubules (MTs). Interphase MTs, together with actin and intermediate filaments, constitute the cell's cytoskeleton, which dynamically maintains cell polarity and tissue architecture. Interphase cells begin Gl of the cell cycle with one centrosome. During S phase, the centrosome duplicates concomitantly with DNA replication. Duplicated centrosomes usually remain in close proximity to one another until late G2, at which time they separate and then move during prophase to become the poles that organize the bipolar mitotic spindle. During the G2/M transition, interphase MTs depolymerize and a new population of highly dynamic mitotic MTs are nucleated at the spindle poles. The bipolar mitotic spindle apparatus constitutes the machinery that partitions and separates sister chromatids equally between two daughter cells.

Earlier studies of invasive breast tumors have shown that 60–80% are aneuploid and ≈80% exhibit amplified centrosomes. In this study, we investigated the relationship of centrosome amplification with aneuploidy, chromosomal instability, p53 mutation, and loss of differentiation in human breast tumors. Twenty invasive breast tumors and seven normal breast tissues were analyzed by fluorescence in situ hybridization with centromeric probes to chromosomes 3, 7, and 17. We analyzed these tumors for both aneuploidy and unstable karyotypes as determined by chromosomal instability. The results were then tested for correlation with three measures of centrosome amplification: centrosome size, centrosome number, and centrosome microtubule nucleation capacity. Centrosome size and centrosome number both showed a positive, significant, linear correlation with aneuploidy and chromosomal instability. Microtubule nucleation capacity showed no such correlation, but did correlate significantly with loss of tissue differentiation. Centrosome amplification was detected in in situ ductal carcinomas, suggesting that centrosome amplification is an early event in these lesions. Centrosome amplification and chromosomal instability occurred independently of p53 mutation, whereas p53 mutation was associated with a significant increase in centrosome microtubule nucleation capacity. Together, these results demonstrate that independent aspects of centrosome amplification correlate with chromosomal instability and loss of tissue differentiation and may be involved in tumor development and progression. These results further suggest that aspects of centrosome amplification may have clinical diagnostic and/or prognostic value and that the centrosome may be a potential target for cancer therapy.