Laminin N-terminus α31 is upregulated in invasive ductal breast cancer and changes the mode of tumour invasion.
Laminin N-terminus 31 (LaNt 31) is an alternative splice isoform derived from the laminin 3 gene. The LaNt 31 protein is enriched around the terminal duct lobular units in normal breast tissue. In the skin and cornea the protein influences epithelial cell migration and tissue remodelling. However, LaNt 31 has never been investigated in a tumour environment. Here we analysed LaNt 31 in invasive ductal carcinoma and determined its contribution to breast carcinoma invasion. LaNt 31 expression and distribution were analysed by immunohistochemistry in human breast tissue biopsy sections and tissue microarrays covering 232 breast cancer samples. This analysis revealed LaNt 31 to be upregulated in 56 % of invasive ductal carcinoma specimens compared with matched normal tissue, and further increased in nodal metastasis compared with the tumour mass in 45 % of samples. 65.8 % of triple negative cases displayed medium to high LaNt 31 expression. To study LaNt 31 function, an adenoviral system was used to induce expression in MCF-7 and MDA-MB-231 cells. Metabolic activity, 2D cell migration, and invasion into collagen hydrogels were not significantly different between LaNt 31 overexpressing cells and control treated cells. However, LaNt 31 overexpressing MDA-MB-231 cells displayed a striking change in their mode of invasion into laminin-containing Matrigel; changing from multicellular streaming to individual cellular-invasion. In agreement with these results, 66.7% of the tumours with the highest LaNt 31 expression were non-cohesive. Together these findings indicate that breast cancer-associated changes in LaNt 31 expression could directly contribute to tumour invasiveness, and that this little-studied protein may become a therapeutic target.