| Research Abstract |
Studies on induction of tumor differentiation in lung cancer may present the possibility of not only identifying the mechanism of malignant transformation, but also lead to development of new anti-tumor drugs. In this regard, to elucidate the molecules associated with tumor differentiation, we have been producing monoclonal antibodies which are able to induce tumor differentiation, and have been trying to identify the c-DNA of their epitope. One such antibody, KM43-2, changes the morphology of SBC- 1 , a human small cell lung cancer cell line, and inhibits the cell motility. We revealed that this antibody recognizes two transmembrane proteins, of 60K and 71K molecular weight, respectively. Genetic cloning demonstrated that the cDNA coding its epitope was of 560 base, and we named it differentiation inducing protein (DIP). However, there are substantial differences between the molecular weight measured by Western blot and base number of cDNA from genetic cloning. In addition, transfection of this cDNA into SBC- I did not cause a significant change in either biological function or morphology. These findings might be partly due to incomplete identification of the whole cDNA of the DIP gene. We tried to identify the entire structure of its protein using antibody affinity column, but to date have not succeed in identification of the DIP gene using this method. On the other hand, these results might be partly because the sugar chain of the transmembrane protein might chiefly regulate the function of DIP. Considering these reasons, we are performing further studies on DIP to identify its gene and to clarify its precise biological roles .
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