Ectopic expression of PLC-β2 in non-invasive breast tumor cells plays a protective role against malignant progression and is correlated with the deregulation of miR-146a

Cells in non-invasive breast lesions are widely believed to possess molecular alterations that render them either susceptible or refractory to the acquisition of invasive capability. One such alteration could be the ectopic expression of the beta 2 isoform of phosphoinositide-dependent phospholipase C (PLC-beta 2), known to counteract the effects of hypoxia in low-invasive breast tumor-derived cells. Here, we studied the correlation between PLC-beta 2 levels and the propensity of non-invasive breast tumor cells to acquire malignant features. Using archival FFPE samples and DCIS-derived cells, we demonstrate that PLC-beta 2 is up-regulated in DCIS and that its forced down-modulation induces an epithelial-to-mesenchymal shift, expression of the cancer stem cell marker CD133, and the acquisition of invasive properties. The ectopic expression of PLC-beta 2 in non-transformed and DCIS-derived cells is, to some extent, dependent on the de-regulation of miR-146a, a tumor suppressor miRNA in invasive breast cancer. Interestingly, an inverse relationship between the two molecules, indicative of a role of miR-146a in targeting PLC-beta 2, was not detected in primary DCIS from patients who developed a second invasive breast neoplasia. This suggests that alterations of the PLC-beta 2/miR-146a relationship in DCIS may constitute a molecular risk factor for the appearance of new breast lesions. Since neither traditional classification systems nor molecular characterizations are able to predict the malignant potential of DCIS, as is possible for invasive ductal carcinoma (IDC), we propose that the assessment of the PLC-beta 2/miR-146a levels at diagnosis could be beneficial for identifying whether DCIS patients may have either a low or high propensity for invasive recurrence.