The basement membrane protein laminin-5 acts as a soluble cell motility factor

One of the basement membrane (BM) proteins, laminin-5 (LN5), is known to support efficient cell adhesion and migration through interaction with integrins on the basal plasma membrane. Here, we show that a soluble form of LN5 induced migration of human epithelial cells and carcinoma cells by interacting with integrins on the apical cell surface. Although both LN5 and laminin-10/11 (LN10/11) promoted cell migration when coated onto a plastic surface as insoluble substrata, only LN5 stimulated cell migration in its soluble form on other substrata such as fibronectin (FN), vitronectin (VN) and collagen. Soluble LN5 interacted with integrins alpha3beta1 and alpha6beta1 on the apical cell surface and stimulated cell migration, while the cell morphology was largely dependent on the underlying substratum. Thus, integrin signals from the apical surface and the basal surface synergistically regulated cytoskeletal organization and cell motility. Soluble and insoluble LN5 induced cell motility by activating signal pathways via protein kinase C (PKC), phosphoinositide 3-OH kinase (PI3-K) and MAP kinase. The PKC dependency was more prominent for soluble LN5 than insoluble LN5, and was absent in the stimulation by insoluble LN10/11. In vitro scratch assays with keratinocytes, self-produced soluble LN5 bound to the apical cell surface of migrating cells at the scratched edges, suggesting that soluble LN5 may contribute to cell migration in pathological conditions such as wound healing and tumor invasion.