Myoepithelial Cells in DCIS Exhibit an Altered Phenotype and Promote Angiogenesis.

Abstract

Abstract In the breast, myoepithelial cells represent the interface between luminal cells and the stromal compartment. They have a regulatory function and exhibit broad tumour-suppressor activity, including an anti-angiogenic effect (Nguyen et al., 2000). It is becoming evident that normal 'host' cells frequently exhibit changes in cancer, and in the breast phenotypic alterations have been described in myoepithelial cells in DCIS (Allinen et al., 2004). We have identified frequent up-regulation of the integrin αvβ6 in myoepithelial cells of DCIS. A major ligand for αvβ6 is Latency Associated Peptide (LAP) through which interaction αvβ6 can activate TGFβ, a recognised pro-angiogenic molecule. We therefore hypothesised that expression of αvβ6 integrin on myoepithelial cells of DCIS would alter myoepithelial function and lead to enhanced angiogenesis.We investigated the relationship between myoepithelial-associated αvβ6 and angiogenesis by immunohistochemistry on 64 cases of DCIS for αvβ6 and CD31. Ducts were positive for αvβ6 in 57% of cases. The angiogenic pattern was scored as rim pattern, where the vessels are adjacent to the basement membrane of the ducts with DCIS, and a diffuse stromal pattern (Guidi et al., 1994). In the αvβ6 positive cases, the rim pattern of vessels was more prominent than in the αvβ6 negative cases. Assesment of microvessel density within 100μm of the myoepithelial border showed a significantly higher count in cases with αvβ6 positive myoepithelial cells compared to those lacking αvβ6 (p=0.0007).To investigate the functional relationship between myoepithelial-associated αvβ6 and angiogenesis, we used an immortalised myoepithelial cell line (1089) and an αvβ6 over-expressing counterpart (β6-1089). We show that β6-1089 myoepithelial cells express significantly higher levels of VEGF than the normal 1089 myoepithelial cells (p=0.0005). This was reversed by knock-down of αvβ6 using siRNA (p=0.0007). In an aortic ring assay, β6-1089 cells promoted more vascular sprouting than their normal counterparts (p=0.05).Together these data indicate that up-regulation of αvβ6 integrin on myoepithelial cells in DCIS can mediate the angiogenic switch in cancer progression. This emphasises the importance of myoepithelial changes in DCIS and suggests that targeting these cells could influence progression of DCIS to invasive disease.