Contributions of the LG modules and furin processing to laminin-2 functions.
The alpha2-laminin subunit contributes to basement membrane functions in muscle, nerve, and other tissues, and mutations in its gene are causes of congenital muscular dystrophy. The alpha2 G-domain modules, mutated in several of these disorders, are thought to mediate different cellular interactions. To analyze these contributions, we expressed recombinant laminin-2 (alpha(2)beta(1)gamma(1)) with LG4-5, LG1-3, and LG1-5 modular deletions. Wild-type and LG4-5 deleted-laminins were isolated from medium intact and cleaved within LG3 by a furin-like convertase. Myoblasts adhered predominantly through LG1-3 while alpha-dystroglycan bound to both LG1-3 and LG4-5. Recombinant laminin stimulated acetylcholine receptor (AChR) clustering; however, clustering was induced only by the proteolytic processed form, even in the absence of LG4-5. Furthermore, clustering required alpha(6)beta(1) integrin and alpha-dystroglycan binding activities available on LG1-3, acting in concert with laminin polymerization. The ability of the modified laminins to mediate basement membrane assembly was also evaluated in embryoid bodies where it was found that both LG1-3 and LG4-5, but not processing, were required. In conclusion, there is a division of labor among LG-modules in which (i) LG4-5 is required for basement membrane assembly but not for AChR clustering, and (ii) laminin-induced AChR clustering requires furin cleavage of LG3 as well as alpha-dystroglycan and alpha(6)beta(1) integrin binding.
Smirnov
Sergei P
SP
Department of Pathology & Laboratory Medicine, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
McDearmon
Erin L
EL
Li
Shaohua
S
Ervasti
James M
JM
Tryggvason
Karl
K
Yurchenco
Peter D
PD
D001483:Base Sequence; D002448:Cell Adhesion; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000378:metabolism; D017931:DNA Primers; D049030:Dystroglycans; D045683:Furin; D006801:Humans; D016023:Integrins / Q000378:metabolism; D007797:Laminin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000378:metabolism; D009154:Mutation; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D011950:Receptors, Cholinergic / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013381:Subtilisins / Q000378:metabolism*; D014162:Transfection
D003598:Cytoskeletal Proteins; C483081:DAG1 protein, human; D017931:DNA Primers; D016023:Integrins; D007797:Laminin; D008562:Membrane Glycoproteins; D011950:Receptors, Cholinergic; D011994:Recombinant Proteins; D049030:Dystroglycans; D013381:Subtilisins; D045683:Furin