A 'Field Effect' in Cancer Containing Breasts Results in an Altered Expression Profile of Myoepithelial Cells.

Abstract

Abstract Myoepithelial cells have an important role in controlling growth and differentiation of luminal epithelial cells and the myoepithelial cell has been described as a tumour suppressor, inhibiting proliferation and invasion. We have previously showed that non-involved tissue from cancer-containing breasts (NTCCB) has lower apoptotic indices and altered expression of myoepithelial proteins such as epidermal growth factor receptor and β4-integrin when compared to normal breast tissue from age matched women without cancer. In addition, using immunohistochemistry, we have found a significant difference in the expression of fibroblast growth factor-2 (FGF-2), a modulator of cell survival and inducer of mitogenic activity in epithelial cells, with greater staining observed in myoepithelial cells from NTCCB.The hypothesis tested is that due to a 'field effect' occurring in 'normal' tissue of breasts in which a cancer develops, the expression profile of myoepithelial cells is altered resulting in loss of their natural function and tumour suppressor properties.For this study, myoepithelial cells were isolated using positive selection from reduction mammoplasties and non-involved tissue from mastectomy/wide local excision specimens. Cells were cultured for up to 3 passages, purity assessed and RNA extracted. In order to compare the expression profiles between the two groups, 5 myoepithelial cell samples from NTCCB and 6 age-matching samples from normal breast were processed using the Illumina Whole-Genome Expression cDNA Microarray BeadChips. Results were analysed using a stepwise forward selection artificial neural network (ANN) modelling approach and validated using real time qPCR TaqMan assays.The ANN algorithm ranked the genes based on the difference of their expression levels and their predictive value on accurately differentiating samples from the two groups. The two top ranked genes were matrix metallopeptidase 23B (MMP23B) that was upregulated in myoepithelial cells from NTCCB and sprouty homolog 1 (SPRY1), a FGF signalling antagonist and inhibitor of the Ras/MAP kinase pathway, that was downregulated. Among the rest of the genes that showed differences in expression were proteins of the extracellular matrix, members of the tumour necrosis factor superfamily and RAB38 a GTPase, member of the ras oncogene family. Data from the real time qPCR showed a lesser degree of significance for the differences of MMP23B and SPRY1 expression but confirmed the higher expression of FGF-2 in myoepithelial cells from NTCCB (p=0.021). qPCR testing for the extended subset of genes identified by the microarray in conjunction with western blotting is underway to further evaluate these differences.In conclusion, these data confirm the existence of field changes in normal breast in which a cancer develops, where differences in expression could alter the natural properties and functions of myoepithelial cells. They also suggest FGF-2 as a potential molecular target for further study. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6120.