Subunit Assembly of Laminin Variants in Cultured Animal Cells

Abstract

Bovine aortic endothelial cells (BAEC) produce two variant forms of laminin with a subunit composition of AB₁B₂ and A’B₁B₂. Analyses of the intracellular assembly of these subunits revealed that the B₁B₂ dimer formed first, and that A or A’ joined to form the AB₁B₂ or A’B₁B₂ trimer. Angiostatic steroids shifted the relative size of the A and A’ monomer pool in BAEC, and competition between the A and A’ subunits in joining the B₁B₂ dimer produced AB₁B₂ and A’B₁B₂ in different ratios. This result suggests that subunit replacement is the general mechanism for producing laminin variants by various cells for tissue morphogenesis. When laminin subunits in BAEC were cross-linked with dithio-bis-(succinimidylpropionate)(DSP) and immunoprecipitated with anti-laminin antiserum, monomeric A, A’, B₁ and B₂ monomers and the B₁B₂ dimer migrated as extremely large molecules in sodium dodecyl sulfate gel electrophoresis under non-reducing conditions. When the crosslinking disulfide bonds were cleaved under reducing conditions, they migrated as the usual subunits. This result suggests that molecular chaperones were involved in the process of the assembly and replacement of laminin subunits.