Distribution of a tumor cell surface protein common to several murine lung carcinomas

In previous work with line 1, a spontaneous BALB/c alveolar carcinoma, we identified a surface protein with a molecular weight of 180,000 (TSP-180) on tumor cells but not on normal mouse cells. This protein was not identical to known cell surface proteins or any C-type virus protein. In this report, we have continued to characterize TSP-180. It can be labeled metabolically with [3 H]leucine or [3 H]glucosamine, confirming that it is a glycoprotein synthesized by line 1 cells. In addition, a competition radioimmunoassay using radioiodinated TSP-180 from line 1 cells was used to measure the amount of TSP-180 in tissues of tumor-bearing animals as well as in other tissues and cells. It was found that during tumor growth, TSP-180 accumulates in the area of primary tumor to a plateau level. It is not detected in other organs except that small amounts are detected in serum when the primary tumor exceeds 1 cm in diameter. No evidence of cross-reactive material was found using BALB/c fibroblasts, mouse mammary tumor cells, BALB/c embryonic tissues, rat tracheal tumor cells, or human alveolar tumor cells. Complete competition was obtained using line 1 tissue culture cell or extracted tumor proteins. Carcinomas from two other mouse strains were also good competitors while adenomas of BALB/c lung competed weakly. Proteins from six other BALB/c lung carcinoma cell lines derived from radiation or chemically-induced tumors as well as tumors of spontaneous origin were also found to compete efficiently in the radioimmunoassay. The presence of TSP-180 on the surfaces of these lung carcinoma cell lines was confirmed using radioiodination catalyzed by lactoperoxidase. Partial protease digests of TSP-180 isolated from four of these lines showed identical molecular weight patterns indicating a highly conserved sequence homology. These results strongly suggest that TSP-180 represents a cell surface protein common to several tumors of the lung carcinoma class. The feasibility of using TSP-180 antigenic determinants for early detection of radiation or chemically-induced tumors, for monitoring progression of metastases, or as targets for directed drug delivery is discussed.