Laminin isoforms in non-tumoral and tumoral human livers

Abstract 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 α1, α2, β1, β2 and γ1 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 α1, α2 and β1 mRNA were found in 25–33% and γ1 mRNA in 58% of the livers, the signal for laminin β2 mRNA being faint in all the samples. Laminin α2, β1, β2 and γ1 mRNA were expressed in hepatoma and stellate cells. The laminin α2 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 α2 chain sequence. Antibodies against peptide deduced from the conserved C-terminal domain of both α1 and α2 chains recognized polypeptides corresponding to the degradation products of α2 chain in liver extracts and both media and cell layers from hepatoma and stellate cells. In addition, a Mr=130 000 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 (α1-β1-γ1), 2 (α2-β1-γ1), 3 (α1-β2-γ1) and 4 (α2-β2-γ1) mRNA and a polypeptide homologous to the α2 isoform, which could correspond to a truncated form of this chain, are usually expressed in non-tumoral and/or tumoral livers.