BeWo choriocarcinoma cells produce laminin 10

BeWo is a choriocarcinoma cell line that generates an extracellular matrix (ECM) rich in laminin and is a useful model for human trophoblast. Immunofluorescence with monoclonal antibodies demonstrates that BeWo ECM contains laminin subunits β1 and γ1. Immunoprecipitation from conditioned medium shows that the cells secrete two distinct laminin trimers both containing β1 and γ1 but with α subunits of approx. 400 and 450 kDa. The culture medium also contains a species thought to be β1γ1 dimer. Immunoprecipitation with monoclonal antibody 4C7, previously thought to recognize the α1 subunit, isolates complexes containing only the smaller α subunit. A second complex containing the larger α subunit along with β1, γ1 and a 150 kDa polypeptide is precipitated from 4C7-depleted medium with an anti-(laminin 1) polyclonal antibody. Peptide sequencing demonstrates that the 4C7-reactive species is α5, which is present as two similarly sized polypeptides. mRNA species encoding laminin subunits α1, α5, β1, β2 and γ1 are all present in the cells. These results demonstrate the secretion of a novel laminin isoform, laminin 10, the subunit composition of which is α5β1γ1. Laminin 1 is also produced. No evidence for the secretion of β2-containing laminin isoforms could be derived despite the presence of β2 mRNA. Analysis with reverse transcriptase-mediated PCR also showed the presence of laminin α5 in first-trimester placenta and decidua.