Differential expression of laminin chains in hepatic lipocytes

The lipocyte is an important source of laminin in the normal liver. We have investigated the expression of the 3 chains of laminin in isolated rat lipocytes. Both B1 and B2 chains, but not A, were found in medium from 5-day-old lipocyte primary cultures by immunoblotting and immunoprecipitation of 35S-labeled proteins after reducing SDS-polyacrylamide gel electrophoresis. An additional polypeptide of Mr=380 000 was identified by immunoprecipitation. Under non-reducing conditions only one Mr=900 000 band was revealed. High levels of B1 and B2 mRNAs were also demonstrated in 5-day-old cultured lipocytes while at the time of seeding, only B2 chain mRNAs were clearly detectable. A chain mRNA was constantly absent. These results suggest that lipocytes produce a variant form of laminin in primary culture and that the Mr=380 000 polypeptide could be unrelated to the A chain of laminin.