Identification of different laminin binding proteins in basolateral cell membranes of human colorectal carcinomas and normal colonic mucosa.

The adhesive properties of tumour cells to laminin, the major glycoprotein of basement membranes, play a crucial part in the complex process of tumour invasion and metastasis. We therefore investigated the expression of laminin binding proteins in isolated basolateral cell membranes of human colorectal carcinomas and the adjacent normal colonic mucosa. Cell membrane binding assays and immunoblotting experiments showed appreciable quantitative and qualitative differences in the expression of these proteins in neoplastic and normal tissue. Epithelial basolateral cell membranes of colorectal carcinomas bound five to eight times more radioactive labelled laminin than basolateral cell membranes of the adjacent normal colonic epithelium. The expression of laminin binding proteins with Mr 66,000-69,000 daltons corresponding to the so called 'Mr 67,000 dalton laminin receptor' was three to four times higher in colorectal carcinomas than in normal colonic epithelium. In addition, laminin binding proteins with higher molecular weights, which may be related to the family of integrins, were also increased in colorectal carcinomas. In particular, laminin binding proteins with Mr 180,000 daltons were exclusively expressed on neoplastic epithelial cells of human colorectal carcinomas. Our data suggest that certain classes of laminin binding proteins may be selectively expressed on colonic tumour cells, leading to an increased capacity for migration, invasion, and metastasis.