Figure 1

β1 and β4 integrins in normal mammary gland acini and in invasive breast tumors. (Left) Mammary gland acini consist of a polarized architecture with a pseudo-stratified epithelium, including a luminal epithelium and a myoepithelial layer covered by a basement membrane (BM). Epithelial cells display apico-basal polarity, a cobblestone-like morphology with cortical actin filaments and an apical lumen. In the myoepithelial cells, α6β4 integrin links the cytoskeleton intermediate filaments to the BM through the assembly of hemidesmosomes. β1 integrin heterodimers connect the extracellular matrix (ECM) components and their biochemical and physical cues to the actin cytoskeleton through the focal adhesion complex. (Right) Invasive breast tumors lose their organized architecture, bilayered epithelium and BM by upregulating matrix metalloproteinases. Tumor cells lack polarity, change cell shape and display actin protrusions, which mediate cell migration and invasion. α6β4 integrin is phosphorylated (P) following microenvironmental cues and relocates into an F-actin-rich protrusion after hemidesmosome disassembly. β1 heterodimers are localized in invasive protrusions assembled with focal adhesions.