Laminin isoforms in non-tumoral and tumoral human livers -: Expression of α1, α2, β1, β2 and γ1 chain mRNA and an α chain homologous to the α2 chain

Background/Aims: Laminins, the major non-collagenous basement membrane components, are involved in various biological processes. Laminin isoforms have never been characterized in human livers. The expression of five laminin mRNA was investigated in livers with or without cancer and in hepatoma cells and, by comparison, in both rat hepatoma and hepatic stellate cells. Methods: Laminin alpha 1, alpha 2, beta 1, beta 2 and gamma 1 mRNA was detected by northern blot and/or RT-PCR in livers without chronic disease (n=5), in both tumoral and non-tumoral areas of livers with hepatocellular carcinomas (n=13) or metastases (n=18), in human HBGC2 and rat Faza-567 hepatoma cell lines, and in 6-day-old rat hepatic stellate cell cultures. Results: Laminin alpha 1, alpha 2 and beta 1 mRNA were found in 25-33% and gamma 1 mRNA in 58% of the livers, the signal for laminin beta 2 mRNA being faint in all the samples. Laminin alpha 2, beta 1, beta 2 and gamma 1 mRNA were expressed in hepatoma and stellate cells. The laminin alpha 2 cDNA probe recognized a 3.5 kb mRNA different from the expected 9 kb mRNA. Using degenerated oligonucleotides, RT-PCR products from both rat hepatoma and stellate cells revealed 90% identity with the alpha 2 chain sequence. Antibodies against peptide deduced from the conserved C-terminal domain of both al and alpha 2 chains recognized polypeptides corresponding to the degradation products of alpha 2 chain in liver extracts and both media and cell layers from hepatoma and stellate cells. In addition, a Mr=130000 polypeptide was revealed by these antibodies in liver extracts and cell layers, which was consistent with the expected size deduced from the 3.5 kb mRNA. Conclusions: This first report on laminin isoforms in human livers indicates that laminin 1 (alpha 1-beta 1-gamma 1), 2 (alpha 2-beta 1-gamma 1), 3 (alpha 1-beta 2-gamma 1) and 4 (alpha 2-beta 2-gamma 1) mRNA and a polypeptide homologous to the alpha 2 isoform, which could correspond to a truncated form of this chain, are usually expressed in non-tumoral and/or tumoral livers.