Cloning and expression of the mouse laminin gamma 2 (B2t) chain, a subunit of epithelial cell laminin.

We have isolated and sequenced the full-length cDNA for the mouse laminin gamma 2 chain and mapped it to mouse Chromosome 1 proximal to laminin gamma 1. The mRNA for the mouse gamma 2 spans 5.2 kb and codes for a 1192-residue amino acid polypeptide. The gamma 2 chain (formerly termed laminin B2t), a homologue of gamma 1 (formerly B2), lacks an N-terminal domain and has a shorter domain III in comparison to the laminin gamma 1 chain. The expression of the laminin gamma 2 and gamma 1 chains in both newborn and fetal mice was examined by both Northern analysis and in situ hybridization. mRNA for the laminin gamma 2 chain was expressed specifically by epithelial cells in many tissues with a particularly high level of expression in the tongue, hair follicles, lung and kidney. In contrast, a high level of expression of the laminin gamma 1 chain mRNA was seen in both epithelial and endothelial cells in these tissues. In addition, gamma 1 mRNA was expressed in other tissues such as the nasal septum, blood vessels, and the muscle of the tongue. Immunohistochemistry with an anti-gamma 2 IgG detected strong expression of the laminin gamma 2 chain in the basement membrane of the collecting tubules of the kidney and of the pancreas. Immunoprecipitation studies with antibodies to the gamma 2 chain detected three species at 165, 155 and 140 kDa in HT-1080 cell-conditioned media. This protein complex is characteristic of the kalinin (nicein/epiligrin) complex, and provides further evidence that these proteins are identical and that the gamma 2 chain is the subunit of the epithelial-cell-specific laminin.