Microsatellite instability during the immortalization and transformation of human breast epithelial cells in vitro

The objective of this study was to determine whether microsatellite instability (MSI) and loss of heterozygosity (LOH) are involved in the immortalization of human breast epithelial cells (HBECs) in vitro and in the early stages of their transformation by benzo[a]pyrene (BP) and 7,12-dimethylbenz[a]anthracene (DMBA). We performed a genome-wide analysis of a total of 466 microsatellite DNA polymorphism loci along the X chromosome and the 22 pairs of human autosomes. MSI was found in the immortalized MCF-10F cells at the following loci: D11S1392 (on chromosome 11p13) and D17S849 (at 17p13.3), D17S796 (at 17p13.1), D17S513 (at 17p13.1), TP53 (at 17p13.1), D17S786 (at 17p13.1), and D17S520 (at 17p12) on chromosome 17. The BP-transformed cells exhibited MSI in the same loci and also in locus D11S912 (at 11q25). The more transformed BP1E cells also exhibited MSI on chromosome 13q12-13 at D13S260 and D13S289, markers known to flank the breast cancer susceptibility gene BRCA2. In the DMBA-transformed D3 and D3-1 cells, MSI was observed at the locus D13S260 in addition to the previously reported locus D16S285 (at 16q12.1). No LOH was observed on any of the chromosomes tested in these cells. These observations led us to conclude that the immortalization and transformation of HBECs may involve defects in mechanisms responsible for the cell's genomic stability, such as DNA replication and DNA mismatch repair.