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The human laminin receptor was purified and molecularly cloned to investigate its biosynthetic regulation. Laminin receptor from normal and neoplastic tissue was preparatively affinity purified to homogeneity based on the high affinity of the receptor for laminin. The apparent molecular weight of the receptor from different carcinoma sources and from normal placental tissue is in the range of 68-72 kDa. Isoelectric focusing and two-dimensional gel electrophoresis indicated that the receptor protein consists of one major polypeptide chain with a pI value of 6.4 +/- 0.2. Laminin receptor cDNA clones were isolated after screening a human endothelial lambda gt11 cDNA library with a monoclonal antibody directed against a domain of the laminin receptor involved in ligand binding. Definitive identification of the cDNA clones was based on comparison of cDNA sequence with the amino acid sequence of a cyanogen bromide-generated octapeptide of purified placental laminin receptor. The laminin receptor mRNA is approximately 1700 bases long. The level of laminin receptor mRNA in a variety of human carcinoma-derived cell lines correlated with the number of laminin receptors on the cell surfaces of those cells. This suggests that the amount of laminin receptor mRNA may be a rate-limiting control step in the biosynthesis of the laminin receptor, and hence in the regulation of cellular attachment to basement membranes via laminin.
Wewer et al. (Wed,) studied this question.