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  • Title: Biological activities of homologous loop regions in the laminin alpha chain G domains.
    Author: Suzuki N, Nakatsuka H, Mochizuki M, Nishi N, Kadoya Y, Utani A, Oishi S, Fujii N, Kleinman HK, Nomizu M.
    Journal: J Biol Chem; 2003 Nov 14; 278(46):45697-705. PubMed ID: 12933811.
    Abstract:
    Laminin alpha chains (alpha1-alpha5 chains) have diverse chain-specific biological functions. The LG4 modules of laminin alpha chains consist of a 14-stranded beta-sheet (A-N) sandwich structure. Several biologically active sequences have been identified in the connecting loop regions. Here, we evaluated the biological activities of the loop regions of the E and F strands in the LG4 modules using five homologous peptides from each of the mouse alpha chains (EF-1: DYATLQLQEGRLHFMFDLG, alpha1 chain 2747-2765; EF-2: DFGTVQLRNGFPFFSYDLG, alpha2 chain 2808-2826; EF-3: RDSFVALYLSEGHVIFALG, alpha3 chain 2266-2284; EF-4: DFMTLFLAHGRLVFMFNVG, alpha4 chain 1511-1529; EF-5: SPSLVLFLNHGHFVAQTEGP, alpha5 chain 3304-3323). These homologous peptides showed chain-specific cell attachment and neurite outgrowth activities. Well organized actin stress fibers and focal contacts with vinculin accumulation were observed in fibroblasts attached on EF-1, whereas fibroblasts on EF-2 and EF-4 showed filopodia with ruffling. Fibroblast attachment to EF-2 and EF-4 was mediated by syndecan-2. In contrast, EF-1 promoted alpha2beta1 integrin-mediated fibroblast attachment and inhibited fibroblast attachment to a recombinant laminin alpha1 chain LG4-5. The receptors for EF-3 and EF-5 are unknown. Further, when the active core sequence of EF-1 was cyclized, utilizing two additional cysteine residues at both the N and C termini through a disulfide bridge, the cyclic peptide significantly enhanced integrin-mediated cell attachment. These results indicate that integrin-mediated cell attachment to the EF-1 sequence is conformation-dependent and that the loop structure is important for the activity. The homologous peptides, which promote either integrin- or syndecan-mediated cell attachment, may be useful for understanding the cell type- and chain-specific biological activities of the laminins.
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