Basal keratinocytes of the epidermis adhere to their underlying basement membrane through a specific interaction with laminin-5, which is composed by the association of ␣3, ␤3, and ␥2 chains. Laminin-5 has the ability to induce either stable cell adhesion or migration depending on specific processing of different parts of the molecule. One event results in the cleavage of the carboxyl-terminal globular domains 4 and 5 (LG4/5) of the ␣3 chain. In this study, we recombinantly expressed the human ␣3LG4/5 fragment in mammalian cells, and we show that this fragment induces adhesion of normal human keratinocytes and fibrosarcoma-derived HT1080 cells in a heparan-and chondroitin sulfate-dependent manner. Immunoprecipitation experiments with Na 2 35 SO 4 -labeled keratinocyte and HT1080 cell lysates as well as immunoblotting experiments revealed that the major proteoglycan receptor for the ␣3LG4/5 fragment is syndecan-1. Syndecan-4 from keratinocytes also bound to ␣3LG4/5. Furthermore we could show for the first time that unprocessed laminin-5 specifically binds syndecan-1, while processed laminin-5 does not. These results demonstrate that the LG4/5 modules within unprocessed laminin-5 permit its cell binding activity through heparan and chondroitin sulfate chains of syndecan-1 and reinforce previous data suggesting specific properties for the precursor molecule.Laminins (LNs) 1 are extracellular matrix glycoproteins composed of ␣, ␤, and ␥ chains assembled into a cross-shaped heterotrimer (␣␤␥) by forming a triple-stranded coiled-coil structure through their ␣-helical domains. At present, 15 heterotrimers termed LN-1 to LN-15 have been described with different subunit composition selected from five individual ␣ chains (␣1-␣5), three ␤ chains (␤1-␤3), and three ␥ chains (␥1-␥3) (1, 2). All LN ␣ chains comprise a large globular domain in their carboxylterminal region (G domain), which consists of five homologous globular subdomains of about 200 amino acids each (LG1-LG5). LN-5, with chain composition ␣3␤3␥2, is a component of basement membranes underlying specialized epithelia with secretory or protective function (3). In skin, LN-5 is synthesized by keratinocytes initially as a high molecular mass precursor protein of 460 kDa of which the ␣3 and ␥2 chains undergo specific processing to smaller forms after being secreted and deposited into the extracellular matrix (ECM) (4, 5). Processing of the ␣3 chain consists of cleavage of the carboxyl-terminal globular domains 4 and 5 (LG4/5) (6, 7). An additional cleavage within the aminoterminal domain IIIa of the ␣3 chain occurs subsequently and may also be important for LN-5 function (8, 9). Processing of the ␥2 chain occurs at the amino terminus with loss of a 50-kDa domain (9 -11). Processed LN-5 is the major component of anchoring filaments in skin (12) where it mediates cell adhesion via interaction of the ␣3 carboxyl-terminal LG1-3 triplet domain with both ␣ 3 ␤ 1 and ␣ 6 ␤ 4 integrins (13-16). Several studies have suggested that processed LN-5 functions both in the nuclea...

Matrilysin 1 [matrix metalloproteinase 7 (MMP7)] is one of the most important metalloproteinases expressed in human tissues. This enzyme is generally not expressed by normal differentiated epithelial colon cells, but has been shown to be up-regulated in human colon adenomas and adenocarcinomas. Little is known about the role of MMP7 in cell invasion and its involvement in proteolytic processes. By searching the ligands of MMP7 in the colonic carcinoma cells HT29, we identified laminin-5/laminin-332 (LN5) as a specific target for MMP7 enzymatic activity. LN5, composed of A3, B3, and ;2 chains, is an important component of epithelial basement membranes where it induces firm adhesion and hemidesmosome formation. In this study, we show that LN5 and MMP7 are coexpressed in HT29 cells as well as in HT29 xenograft tumors and human colorectal adenocarcinomas. We provide evidence that human LN5 is a ligand for MMP7 and that a specific cleavage occurs in its B3 chain, giving rise to a carboxyl-terminal B3 chain fragment of 90 kDa. We have identified the MMP7 cleavage site at position Ala 515 -Ile 516 in the B3 chain. Videomicroscopic analysis of HT29 cells plated on LN5 substrates reveals that the MMP7-processed LN5 significantly enhances cell motility. Moreover, the delayed migration of HT29 cells obtained after specific inhibition of MMP7 reinforces the hypothesis supporting its involvement in cell migration. Altogether, our results show that MMP7 is likely to play a crucial role in the regulation of carcinoma cell migration by targeting specific proteolytic processing of the LN5 B3 chain. (Cancer Res 2006; 66(23): 11228-37)

Laminin 5/laminin 332 (LN332) is an adhesion substrate for epithelial cells. After secretion of LN332, a regulated cleavage occurs at the carboxy-terminus of its alpha3 subunit, which releases a tandem of two globular modules named LG4/5. We show that the presence of the LG4/5 domain in precursor LN332 decreases its integrin-mediated cell adhesion properties in comparison with mature LN332. Whereas cell adhesion to the recombinant LG4/5 fragment relies solely on the heparan sulfate proteoglycan (HSPG) receptor syndecan-1, we reveal that both syndecan-1 and the alpha3beta1 integrin bind to precursor LN332. We further demonstrate that syndecan-1 mediated cell adhesion to the LG4/5 fragment and pre-LN332 allows the formation of fascin-containing protrusions, depending on the GTPases Rac and Cdc42 activation. Reducing syndecan-1 expression in normal keratinocytes prevents cell protrusions on pre-LN332 with subsequent failure of the peripheral localization of the alpha3beta1 integrin. We finally show that cell migration on pre-LN332 requires syndecan-1. Therefore, the LG4/5 domain in precursor LN332 appears to trigger intracellular signaling events, which participate in keratinocyte motility.