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 M_r=380 000 was identified by immunoprecipitation. Under non-reducing conditions only one M_r=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 M_r=380 000 polypeptide could be unrelated to the A chain of laminin.