The interaction of the tumor cell with its extracellular matrix may play an important role in determining its metastatic and invasive properties. We have identified, isolated, and characterized three laminin binding proteins that are present in both normal and neoplastic tissues. All three proteins share a common epitope, and specifically bind to the poly-N-acetyllactosamine chains of laminin. The 67 kDa high affinity laminin receptor has been previously characterized as a nonintegrin binding protein and has been molecularly cloned. It is expressed to a greater degree in metastatic tissues than in benign conditions in a variety of tissue-specific neoplasms. Recently, we have shown that expression of both the laminin receptor protein and the mRNA are significantly increased in human colorectal carcinomas. In addition to its ability to bind to the carbohydrate structures on laminin, the 67 kDa laminin receptor apparently also has the ability to bind to specific amino acid sequences on the laminin molecule. we have recently established that the 67 kDa laminin receptor is synthesized from a cytoplasmic precursor with an approximate molecular mass of 37 kDa. we recently purified two other nonintegrin laminin binding proteins, HLBP31 and HLBP12, from both human placenta and human cancer cell lines. HLBP31 and HLBP12 have apparent molecular masses of 31 kDa and 12 kDa, respectively. Protein microsequencing identified HLBP31 as a previously characterized protein that has been called a beta-galactoside binding lectin, the low affinity IgE binding protein, or Mac-2 by different groups. HLBP12 has been previously identified as a soluble beta- galactoside binding lectin. we isolated a cDNA clone of HLBP31. The level of HLBP31 mRNA is inversely modulated with the 67 kDa laminin receptor in human colorectal carcinomas. Future studies will determine if the selective use of different laminin binding proteins by colonic cancer cells may play a functional role in the disease process.
