Expression of the p210BCR-ABL oncoprotein drives centrosomal hypertrophy and clonal evolution in human U937 cells.

Centrosomes play fundamental roles in mitotic spindle organization, chromosome segregation and maintenance of genetic stability. Recently, we have shown that centrosome aberrations occur early in chronic myeloid leukemia (CML) and are induced by imatinib in normal fibroblasts in vitro. To investigate the influence of BCR-ABL on centrosomes, we performed long-term in vitro experiments employing the conditionally p210BCR-ABL-expressing (tetracycline-inducible promoter) human monocytic cell line U937p210BCR-ABL/c6 as a model of CML chronic phase. Centrosome hypertrophy was detectable after 4 weeks of transgene expression onset, increasing up to a rate of 25.7% aberrant cells within 13 weeks of propagation. This concurred with clonal expansion of aneuploid cells displaying a hyperdiploid phenotype with 57 chromosomes. Partial reversibility of centrosome aberrations (26-8%) was achieved under prolonged propagation (14 weeks) after abortion of induction and bcr-abl silencing using small interfering RNA. Therapeutic doses of imatinib did not revert the aberrant phenotype, but counteracted the observed reverting effect of bcr-abl gene expression switch off. Suggesting a mechanistic model that features distinct abl-related tyrosine kinase activity levels as essential determinants of centrosomal integrity, this is the first report mechanistically linking p210BCR-ABL oncoprotein activity to centrosomal hypertrophy.