Laminin-5 (LN5) is a matrix component of epithelial tissue basement membranes and plays an important role in the initiation and maintenance of epithelial cell anchorage to the underlying connective tissue. Here we show that two distinct LN5 function-inhibitory antibodies, both of which bind the globular domain of the ␣3 subunit, inhibit proliferation of epithelial cells. These same antibodies also induce a decrease in mitogenactivated protein kinase activity. Inhibition of proliferation by the function-perturbing LN5 antibodies is reversed upon removal of the antibodies and can be overcome by providing the antibody-treated cells with exogenous LN5 and rat tail collagen. Because epithelial cells use the integrin receptor ␣31 to interact with both LN5 and rat tail collagen, we next investigated the possibility that integrin ␣31 is involved in mediating the proliferative impact of LN5. Proliferation of human epithelial cells is significantly inhibited by a function-perturbing ␣3 integrin antibody. In addition, antibody activation of 1 integrin restores the proliferation of epithelial cells treated with LN5 functionperturbing antibodies. These data indicate that a complex comprising LN5 and ␣31 integrin is multifunctional and contributes not only to epithelial cell adhesion but also to the regulation of cell growth via a signaling pathway involving mitogen-activated protein kinase. We discuss our study in light of recent evidence that LN5 expression is up-regulated at the leading tips of tumors, where it may play a role in tumor cell proliferation.
INTRODUCTIONCell interaction with elements of the extracellular matrix impacts their adherence, motility, as well as protein and gene expression (for example, see Adams and Watt, 1993;Roskelly et al., 1995). In intact normal tissue epithelial cells bind to extracellular matrix molecules, which are organized into a complex multiprotein structure called the basement membrane. The major components of the latter include type IV collagen, proteoglycans, and laminins. One laminin isoform, laminin-5 (LN5), 1 in particular plays an important role in establishing firm adherence of epithelial cells to the basement membrane, because it is necessary for the assembly and maintenance of stable anchorage devices between epithelial cells and matrix called hemidesmosomes (Baker et al., 1996;Green and Jones, 1996). However, recent reports also indicate that LN5 is expressed at the budding tips of invading tumor cells, i.e., at sites where cancer cells are undergoing cell division but where there are most likely no hemidesmosomes (Pyke et al., 1994(Pyke et al., , 1995. This provides an indication § Corresponding author. E-mail address: j-jones3@nwu.edu. 1 Abbreviations used: BrdU, bromodeoxyuridine; DAPI, 4,6-diamidino-2-phenylindole; EGF, epidermal growth factor; FN, fibronectin; hLN5, human laminin-5; Ig, immunoglobulin; LN, laminin; MAP, mitogen-activated protein; MAPK, MAP kinase; RTC, rat tail collagen; rtLN5, rat laminin-5.© 1999 by The American Society for Cell Biology 259 that L...