The propensity of cancer cells to spread in the body and produce metastases is the major cause of death from cancer. Recognition and adhesion among circulating tumor cells, and between tumor and normal host cells, lead to the formation of multicell emboli, a process directly related to the development of metastases. The molecular nature of the cell surface proteins, including carbohydrate-binding-proteins, i.e. endogenous lectins, mediating such cognitive cellular interactions is now being unveiled. The fundamental role of a 34 KDa galactoside-binding-lectin (mL-34) in cell transformation and metastasis of mouse cells has been demonstrated. This mL-34 lectin is expressed in a wide range of neoplasms and among related tumor cell variants of K-1735 melanoma, the UV-2237 fibrosarcoma and the A31-angiosarcoma, expression correlates with metastatic capability. We have cloned and characterized the gene encoding mL-34 and reported it to be a chimeric gene product, formed by fusion of the 5'-end of a -14 KDa gal- lectin with the internal domain of the collagen & gene. Comparison of the mL-34 sequence with that of the cloned murine 14.5 KDa gal-lectin (mL-14.5) led to the identification of the putative galactoside-binding-domain. Recently, we have identified and cloned the human homologue to mouse mL-34; a 31 Kd polypeptide (hL-31). The gene coding for the hL-31 was mapped to the chromosomal band 1p13 and provided preliminary evidence that the mouse and the human homologue have similar functional properties.
The aim of this project is to continue to investigate the functional role of tumor cell surface lectin in vitro (cellular recognition and interaction) and in vivo (hematogenous spread). In particular, we propose the following to continue to identify and establish the role of gal-lectins in metastasis: 1) To establish the membrane spacial orientation of gal-lectin, to determine the number of gal-lectins and ligand molecules on the cell surface, and the affinity of lectin-ligand binding in relation to their cell-cell interaction and metastasis properties; 2) To generate peptides derived from the mL-14.5 and mL-34 sequences and study their effects on cellular interactions and hematogenous spread; 3) To generate antibodies against the effective peptide(s) and test them, and Fab derived from them, for ability to affect tumor cell metastasis and growth; 4) To identify, characterize the natural ligand(s) for mL-14.5 and mL-34, and to study their effect on cellular interaction and metastasis; 5) To clone the promoters of the mL-14.5 and mL-34 for studies on the regulatory mechanisms that direct their expression in high- and low-metastatic cells. It is expected that such studies will broaden our knowledge of the role of gal- lectins in transformation and metastasis, will allow a critical evaluation of their function in the various intracellular interactions which are relevant to metastatic spread, and will lead to the development of diagnostic reagents for the detection of metastatic circulating tumor cells.
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