Whether ␣6␤4 integrin regulates migration remains controversial. ␤4 integrin-deficient (JEB) keratinocytes display aberrant migration in that they move in circles, a behavior that mirrors the circular arrays of laminin (LM)-332 in their matrix. In contrast, wild-type keratinocytes and JEB keratinocytes, induced to express ␤4 integrin, assemble laminin-332 in linear tracks over which they migrate. Moreover, laminin-332-dependent migration of JEB keratinocytes along linear tracks is restored when cells are plated on wild-type keratinocyte matrix, whereas wild-type keratinocytes show rotation over circular arrays of laminn-332 in JEB keratinocyte matrix. The activities of Rac1 and the actin cytoskeleton-severing protein cofilin are low in JEB keratinocytes compared with wild-type cells but are rescued following expression of wild-type ␤4 integrin in JEB cells. Additionally, in wild-type keratinocytes Rac1 is complexed with ␣6␤4 integrin. Moreover, Rac1 or cofilin inactivation induces wild-type keratinocytes to move in circles over rings of laminin-332 in their matrix. Together these data indicate that laminin-332 matrix organization is determined by the ␣6␤4 integrin/actin cytoskeleton via Rac1/cofilin signaling. Furthermore, our results imply that the organizational state of laminin-332 is a key determinant of the motility behavior of keratinocytes, an essential element of skin wound healing and the successful invasion of epidermal-derived tumor cells.Migration of cells is an essential element of morphogenesis, remodeling following tissue damage and metastasis. For example, following wounding of the skin, epidermal cells migrate over a wound, a complex process involving changes in cytoskeleton organization, alterations in cell-cell and cell-matrix interactions, and modulation in gene and protein expression (1, 2).In particular, keratinocytes lose stable matrix adhesive structures called hemidesmosomes, migrate over exposed dermal collagen, and deposit a provisional matrix rich in laminin (LM) 3 -332 (old nomenclature: laminin-5), a heterotrimer consisting of ␣3, ␤3, and ␥2 subunits (1-5). This provisional matrix regulates the motility of keratinocytes (2-4). LM-332 is also believed to support tumor cell invasion (6 -12).Although cells in wounds and cancer cells migrate on a LM-332 substrate, LM-332 stabilizes epidermal cell adhesion in intact skin (3, 4,(12)(13)(14)(15)(16). These contradictory functions exhibited by LM-332, adhesion and motility, have been investigated by a number of laboratories, and results to date indicate that proteolytic processing of LM-332 has a profound impact on its functions. Specifically, in the extracellular matrix, the ␣3 and ␥2 subunits are processed from 190 to 160 kDa and from 140 to 100 kDa, respectively (4, 17-22). LM-332 containing an unprocessed ␣3 chain supports keratinocyte motility (20). Upon proteolytic cleavage of the ␣3 LM subunit within its G domain, LM-332 triggers hemidesmosome assembly, leading to decreased cell motility (3, 20 -24). However, further proteolysis of l...

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The ␣4 laminin subunit is a component of endothelial cell basement membranes. An antibody (2A3) against the ␣4 laminin G domain stains focal contact-like structures in transformed and primary microvascular endothelial cells (TrHBMECs and HMVECs, respectively), provided the latter cells are activated with growth factors. The 2A3 antibody staining colocalizes with that generated by ␣v and ␤3 integrin antibodies and, consistent with this localization, TrHBMECs and HMVECs adhere to the ␣4 laminin subunit G domain in an ␣v␤3-integrin-dependent manner. The ␣v␤3 integrin/2A3 antibody positively stained focal contacts are recognized by vinculin antibodies as well as by antibodies against plectin. Unusually, vimentin intermediate filaments, in addition to microfilament bundles, interact with many of the ␣v␤3 integrin-positive focal contacts. We have investigated the function of ␣4-laminin and ␣v␤3-integrin, which are at the core of these focal contacts, in cultured endothelial cells. Antibodies against these proteins inhibit branching morphogenesis of TrHBMECs and HMVECs in vitro, as well as their ability to repopulate in vitro wounds. Thus, we have characterized an endothelial cell matrix adhesion, which shows complex cytoskeletal interactions and whose assembly is regulated by growth factors. Our data indicate that this adhesion structure may play a role in angiogenesis.

Laminins are structural components of basement membranes. In addition, they are key extracellular-matrix regulators of cell adhesion, migration, differentiation and proliferation. This Commentary focuses on a relatively understudied aspect of laminin biology: how is laminin deposited into the extracellular matrix? This topic has fascinated researchers for some time, particularly considering the diversity of patterns of laminin that can be visualized in the matrix of cultured cells. We discuss current ideas of how laminin matrices are assembled, the role of matrix receptors in this process and how laminin-associated proteins modulate matrix deposition. We speculate on the role of signaling pathways that are involved in laminin-matrix deposition and on how laminin patterns might play an important role in specifying cell behaviors, especially directed migration. We conclude with a description of new developments in the way that laminin deposition is being studied, including the use of tagged laminin subunits that should allow the visualization of laminin-matrix deposition and assembly by living cells.

Abstract. The 180-kD bullous pemphigoid autoantigen (BP180) is a component of the hemidesmosome, a cellmatrix connector. This protein is oriented in a type II fashion in the membrane of the hemidesmosome and is a hybrid collagen (classified as type XVII). We have analyzed the fate of various mutant BP180 molecules transfected into several different cell types. A protein, D1, lacking the collagen-like extracellular domains of BP180 polarizes normally in 804G epithelial cells and colocalizes with other hemidesmosomal components in the plane of the basal cell surface. However, deletion of a stretch of 36 amino acids located at the NH2 terminus of D1 induces an apical polarization of the protein (D1-36N) in the cell surface of 804G cells. Deletion of the 27-amino acid noncollagenous extracellular domain that is located immediately after the membrane spanning domain of BP180 results in a failure of D1-27C protein to codistribute with other hemidesmosomal components despite its basal localization in transfected 804G cells. In FG cells, which lack their own BP180, transfected D1 protein localizes with the ot61~4 integrin heterodimer. In HT1080 cells, which do not possess BP180 or 64 integrin, D1 protein localizes with ot6131 integrin while both the D1-27C and D1-36N proteins do not. Moreover, D1 protein coprecipitates with et6 integrin from extracts of HT1080 transfectants. Taken together, these results suggest that the NH2-terminal domain of BP180 determines polarization of BP180 while the noncollagenous extracellular domain of BP180 stabilizes its interactions with other hemidesmosomal components, such as e~6 integrin. Perturbation of this latter domain by human bullous pemphigoid autoantibodies may explain the loss of epidermal cell-dermis attachment that characterizes the BP disease.