EXPRESSION OF THE EXTRACELLULAR-MATRIX MOLECULE THROMBOSPONDIN INVERSELY CORRELATES WITH MALIGNANT PROGRESSION IN MELANOMA, LUNG AND BREAST-CARCINOMA CELL-LINES

Thrombospondin (TSP) is a member of a family of extracellular matrix glycoproteins that may participate in multiple aspects of the metastatic cascade. We report an inverse correlation of steady-state Thbs-1 mRNA and protein expression with malignant progression among murine melanoma and human lung and breast carcinoma cell lines. Murine K-1735 melanoma cell lines of low metastatic potential, including K-1735 lines transfected with the murine nm23-1 cDNA, expressed higher TSP levels than related highly metastatic lines. In a model system of lung carcinoma malignant progression, immortalized human branchial epithelial cells expressed higher TSP levels than v-Ki-ras, v-Ha-ras or n-ras transfectants, which in turn expressed higher TSP levels than tumor-derived, more aggressive variants. Among 3 unrelated breast carcinoma cell lines, Thbs-1 steady-state mRNA levels were greater in the 2 nonmetastatic lines than the metastatic line. Our data show that malignant progression in some cell lines is associated with reduced TSP expression. The suppressive effects of nm23-1 transfection an metastatic potential are also associated with increased TSP expression; ras transfection, which results in increased tumorigenesis, is associated with decreased TSP expression. (C) 1994 Wiley-Liss, Inc.*