An endothelial cell inhibitor was purified from supernatant of an Epstein-Barr virus–immortalized cell line and identified as fragments of calreticulin. The purified recombinant NH2-terminal domain of calreticulin (amino acids 1–180) inhibited the proliferation of endothelial cells, but not cells of other lineages, and suppressed angiogenesis in vivo. We have named this NH2-terminal domain of calreticulin vasostatin. When inoculated into athymic mice, vasostatin significantly reduced growth of human Burkitt lymphoma and human colon carcinoma. Compared with other inhibitors of angiogenesis, vasostatin is a small, soluble, and stable molecule that is easy to produce and deliver. As an angiogenesis inhibitor that specifically targets proliferating endothelial cells, vasostatin has a unique potential for cancer treatment.

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 Xgtll 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 lamiin.Laminin, a high molecular weight glycoprotein, is a prominent component of basement membranes from all types of tissues. It appears to play a significant role in a variety of biologic phenomena including cell attachment, cell spreading, morphogenesis, differentiation, mitogenesis, neurite outgrowth, cell migration, and cancer metastases (1). Many of these biologic functions may be mediated through highaffinity binding of laminin to a specific cell surface protein called the laminin receptor. A laminin receptor (Mr 68-72,000) has been isolated from both murine and human neoplastic cells and from bovine myocytes (2-5). In the present study, we describe a modified purification procedure that has allowed us to obtain preparative amounts of homogeneous laminin receptor for biochemical analysis and amino acid sequence determination. The amino acid sequences were used to definitively identify a cDNA clone encoding the COOH-terminal half of the laminin receptor. Hybridization studies suggest that pretranslational events in the biosynthesis of laminin receptor may play an important role in the regulation of the laminin-mediated cellular attachment to basement membrane. MATERIALS AND METHODSTissue. Tissues from liver metastases derived from human breast and colon carcinoma were obtained from the

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