The Short Arm of the Laminin γ2 Chain Plays a Pivotal Role in the Incorporation of Laminin 5 into the Extracellular Matrix and in Cell Adhesion

Abstract

Laminin 5 is a basement membrane component that actively promotes adhesion and migration of epithelial cells. Laminin 5 undergoes extracellular proteolysis of the γ2 chain that removes the NH2-terminal short arm of the polypeptide and reduces the size of laminin 5 from 440 to 400 kD. The functional consequence of this event remains obscure, although lines of evidence indicate that cleavage of the γ2 chain potently stimulated scattering and migration of keratinocytes and cancer cells. To define the biological role of the γ2 chain short arm, we expressed mutated γ2 cDNAs into immortalized γ2-null keratinocytes. By immunofluorescence and immunohistochemical studies, cell detachment, and adhesion assays, we found that the γ2 short arm drives deposition of laminin 5 into the extracellular matrix (ECM) and sustains cell adhesion. Our results demonstrate that the unprocessed 440-kD form of laminin 5 is a biologically active adhesion ligand, and that the γ2 globular domain IV is involved in intermolecular interactions that mediate integration of laminin 5 in the ECM and cell attachment.

Integrin Regulation of Epidermal Functions in Wounds

“…Interestingly, this blistering phenotype was linked to reduced fibulin-2 levels in both neonatal skin and early wounds, and genetic deletion of fibulin-2 (i.e., in the presence of a 3 b 1 ) was sufficient to generate neonatal skin blisters. 91 Since fibulin-2 binds to the laminin-c 2 chain within the L4 module near the N-terminus, 128 and this interaction has been implicated in stable incorporation of laminin-332 into the developing BM, 129 these findings suggest an important role for a 3 b 1 -dependent fibulin-2 expression in BM maturation (Fig. 2).…”

“…58 Indeed, the L4 module to which fibulin-2 binds is lost upon proteolytic processing of c 2 , which might be an important step for BM maturation. 128,129,132 Interestingly, recent data from our laboratory indicates a role for epidermal a 3 b 1 in the regulation of laminin-c 2 chain processing, both in vivo during wound healing and in keratinocytes cultured under conditions of high calcium. 91 Thus, a 3 b 1 may have a dual role in BM assembly that involves both matrix protein deposition and proteolytic processing of matrix proteins (Fig.…”

C-terminal Truncation Impairs Glycosylation of Transmembrane Collagen XVII and Leads to Intracellular Accumulation

“…5A). Processing of laminin 5, which is needed for its integration in the basement membrane (25)(26)(27) was not altered in JEB keratinocytes, excluding the possibility that the scattered deposition of laminin 5 was caused by its deficient cleavage (not shown).…”

Laminin deposition in the extracellular matrix: a complex picture emerges

“…For example, the a3, a4, b3 and g2 laminin subunits have all been shown to undergo proteolytic cleavage, in vitro and in vivo (Giannelli et al, 1997;Talts et al, 2000;Tsubota et al, 2000;Udayakumar et al, 2003). With regard to the a3 and g2 laminin subunits, there is experimental evidence that only their unprocessed versions are properly incorporated into laminin-332 matrix (Gagnoux-Palacios et al, 2001;Sigle et al, 2004). One assumes that the domains that are released following cleavage 'encode' important matrix-assembly information.…”