Normal and tumor-derived myoepithelial cells differ in their ability to interact with luminal breast epithelial cells for polarity and basement membrane deposition

Abstract

The signals that determine the correct polarity of breast epithelial structures in vivo are not understood. We have shown previously that luminal epithelial cells can be polarized when cultured within a reconstituted basement membrane gel. We reasoned that such cues in vivo may be given by myoepithelial cells. Accordingly, we used an assay where luminal epithelial cells are incorrectly polarized to test this hypothesis. We show that culturing human primary luminal epithelial cells within collagen-I gels leads to formation of structures with no lumina and with reverse polarity as judged by dual stainings for sialomucin, epithelial specific antigen or occludin. No basement membrane is deposited, and β4-integrin staining is negative. Addition of purified human myoepithelial cells isolated from normal glands corrects the inverse polarity, and leads to formation of double-layered acini with central lumina. Among the laminins present in the human breast basement membrane (laminin-1, -5 and -10/11), laminin-1 was unique in its ability to substitute for myoepithelial cells in polarity reversal.Myoepithelial cells were purified also from four different breast cancer sources including a biphasic cell line. Three out of four samples either totally lacked the ability to interact with luminal epithelial cells, or conveyed only correction of polarity in a fraction of acini. This behavior was directly related to the ability of the tumor myoepithelial cells to produce α-1 chain of laminin. In vivo, breast carcinomas were either negative for laminin-1 (7/12 biopsies) or showed a focal, fragmented deposition of a less intensely stained basement membrane (5/12 biopsies). Dual staining with myoepithelial markers revealed that tumor-associated myoepithelial cells were either negative or weakly positive for expression of laminin-1, establishing a strong correlation between loss of laminin-1 and breast cancer. We conclude that the double-layered breast acinus may be recapitulated in culture and that one reason for the ability of myoepithelial cells to induce polarity is because they are the only source of laminin-1 in the breast in vivo. A further conclusion is that a majority of tumor-derived/-associated myoepithelial cells are deficient in their ability to impart polarity because they have lost their ability to synthesize sufficient or functional laminin-1. These results have important implications for the role of myoepithelial cells in maintenance of polarity in normal breast and how they may function as structural tumor suppressors.

Human Breast Extracellular Matrix Microstructures and Protein Hydrogel 3D Cultures of Mammary Epithelial Cells

“…The poor acini-formation capacity of the cancer cells is consistent with the nature and aggressiveness of the cancer cells, which have disrupted apicobasal polarity that is essential for a rotational movement of acini and the integrity of the acini architectures [ 61 , 62 ]. It is known that a laminin- and Col IV-rich basement membrane (BM) or a basement membrane-resembling hydrogel substratum, such as Matrigel, is necessary for normal mammary epithelial cells to form correctly polarized acinar structures in cultures [ 63 ], and Col I hydrogel alone does not support mammary epithelial cells to form properly polarized acinar structures [ 63 ]. However, both human breast ECM and porcine breast ECM are Col I-rich matrices [ 28 ], which contain minimum amount of laminin and Col IV, and yet their hydrogels are able to induce normal mammary epithelial cell acini formation and expression of laminin receptor β4 integrin on the surfaces of the cells contacting the ECM hydrogels, an indication of correct polarity of the acini.…”

Deletion of Col15a1 Modulates the Tumour Extracellular Matrix and Leads to Increased Tumour Growth in the MMTV-PyMT Mouse Mammary Carcinoma Model

“…Moreover, they mediate communication between luminal epithelial cells and the stroma and secure the polarity of luminal epithelial cells and prevent their dissemination to the surrounding tissue [34,36]. Interestingly, luminal epithelial cells are unable to polarise when cultured alone in a ColI matrix, but undergo polarisation when cultured in the BM extract Matrigel or together with myoepithelial cells in the ColI matrix [37]. The critical BM component for cell polarisation produced by myoepithelial cells was found to be the laminin subunit a1 [37], which is known to interact with ColXV in vitro [38].…”

“…Interestingly, luminal epithelial cells are unable to polarise when cultured alone in a ColI matrix, but undergo polarisation when cultured in the BM extract Matrigel or together with myoepithelial cells in the ColI matrix [37]. The critical BM component for cell polarisation produced by myoepithelial cells was found to be the laminin subunit a1 [37], which is known to interact with ColXV in vitro [38]. Based on these and our new findings, we speculate that myoepithelial cellderived ColXV could be involved in the regulation of mammary epithelial cell polarity by integrating signals from the collagenous matrix through laminin to luminal epithelial cells.…”

The Role of Extracellular Matrix Proteins in Breast Cancer

“…ECM is responsible for maintaining the proper polarity by the epithelial cells, and it should be mentioned that this function is realized mainly due to the presence of the aforementioned laminin 111. The appropriate biochemical dialogue between ECM components and lactogenic hormones is required for full differentiation of mammary epithelial cells [ 135 , 136 , 137 , 138 , 139 ]. Signal transducer and activator of transcription 5 (STAT5) participates in this differentiation and in the process of milk secretion from the breast [ 135 , 140 ].…”