Cyclooxygenase-2 expression induces genomic instability in MCF10A breast epithelial cells

Background. Cyclooxygenase-2 (COX-2) is induced in many breast cancers and COX-2 expression correlates with a worse outcome in the clinic. We hypothesized that the induction of genomic instability is a major mechanism through which COX-2 contributes to breast cancer progression. Methods. We transfected a normal immortalized breast epithelial cell line of Basal B subtype, MCF10A, with the pSG5-COX-2 vector and established the stably transfected cell line MCF10A/COX-2. We analyzed the genomic instability phenotype by chromosomal analysis of metaphase-arrested MCF10A and MCF10A/ COX-2 cells after Giemsa staining. Groups were compared using chi(2) tests. To investigate the DNA damage checkpoint signaling, we analyzed the phosphorylation status of CHK1. protein with a phospho-specific antibody. Results. Cytogenetic analysis of early passage transfected cells showed that COX-2 expression increased genomic instability compared with the MCF10A cells transfected with a luciferase vector alone. COX-2 overexpression was associated with a significant increase in chromosomal aberrations (fusions, breaks, and tetraploidy). There was a statistically significant increase in the number of polyploid cells in the COX-2 transfected cells versus the control (P = 0.004). We also found that an inhibitory CHK1. phosphorylation at Ser-280 was dramatically increased upon COX-2 overexpression in MCF10A cells, thus explaining the mechanism of inactivation of an important cell cycle checkpoint. Further analysis of the MCF10A/COX-2 cells showed that these cells have acquired a premalignant phenotype characterized by a morphological transformation, a resistance to anoikis, a reduced requirement of epidermal growth factor for growth in culture, but their inability to establish tumors in a nude mouse model of malignancy. Conclusion. We found that COX-2 expression in MCF10A breast epithelial cells confers a premalignant phenotype that includes enhanced genomic instability and altered cell-cycle regulation. (C) 2007 Elsevier Inc. All rights