Centrosome abnormalities in human carcinomas of the gallbladder and intrahepatic and extrahepatic bile ducts

Centrosome abnormalities, genomic instability and carcinogenic progression

Centrosome abnormalities are a frequent finding in various malignant tumors. Since centrosomes form the poles of the mitotic spindle, these abnormalities have been implicated in chromosome missegregation and the generation of aneuploid cells which is commonly found in many human neoplasms. It is a matter of debate, however, whether centrosome alterations can drive cells into aneuploidy or simply reflect loss of genomic integrity by other mechanisms. Since these two models have fundamentally different implications for the diagnostic and prognostic value of centrosome abnormalities, we will discuss the relevance of abnormal centrosomes in the context of different oncogenic events as exemplified by high-risk human papillomavirus-associated carcinogenesis.

Correlation between centrosome abnormalities and chromosomal instability in human pancreatic cancer cells

Chromosomal instability, characterized by abnormal numbers or structures of chromosomes, is a common feature of human cancers, but the mechanisms behind these changes are still unclear. Since centrosomes play a pivotal role in balanced chromosomal segregation during mitosis, we attempted to investigate the association between centrosome abnormalities and chromosomal instability in a large number of human pancreatic cancer cell lines. Immunofluorescence microscopy revealed centrosomes that were highly atypical with respect to their size, shape, and number in most cell lines. These abnormal centrosomes contributed to the assembly of multipolar spindles, resulting in defective mitosis and chromosome mis-segregation. Interestingly, a high frequency of centrosome defects inversely correlated with the growth rate of cells in culture. Fluorescence in situ hybridization revealed a dramatic variation of chromosome numbers in cell lines with the defective centrosome phenotype. Furthermore, a significant positive correlation existed between the level of centrosome defects and the level of chromosomal imbalances. These results indicate that centrosome abnormalities can lead to spindle disorganization and chromosome segregation errors, which may drive the accumulation of chromosomal alterations. Thus, defects in centrosome function may be an underlying cause of genetic instability in human pancreatic cancers.

A possible role for centrosome overduplication in radiation-induced cell death

Radiotherapy plays a key role in the treatment of many tumors; however, the precise mechanisms responsible for radiation-induced cell death remain uncertain. We have reported previously that ionizing radiation induces centrosome overduplication in human tumor cells. The present study was designed to elucidate a possible link between centrosome dysregulation and radiation-induced cell death. Exposure to 10 Gy gamma-radiation resulted in a substantial increase in cells containing an abnormally high number of centrosomes in a variety of cell lines derived from different types of human solid tumors. These aberrant centrosomes contribute to the assembly of multipolar spindles, thereby causing an unbalanced division of chromosomes and mitotic cell death characterized by the appearance of multi- or micronucleated cells. An extensive analysis of a panel of 10 tumor cell lines revealed a positive correlation between the fraction of cells with multiple centrosomes and the fraction with these nuclear abnormalities after irradiation. When the centrosome overduplication was blocked by enforced expression of p21Waf1/Cip1, the radiation-induced lethality was drastically rescued. Taken together, these results indicate that centrosome overduplication may be a critical event leading to mitotic failure and subsequent cell death following exposure to ionizing radiation.