Modifications of tumor histology by point mutations in the v-fps oncogene: possible role of extracellular matrix.

Fujinami sarcoma virus (FSV) encodes a protein-tyrosine kinase, p130gag-fps, whose enzymatic activity and ability to transform cultured cells to a neoplastic phenotype are reduced by substitution of the major autophosphorylation site tyrosine-1073 with other amino acids. We compared the histopathology of tumors formed in syngeneic immunocompetent rats by Rat-2 cells and by Rat-2 cells transformed in culture with (a) wild type (wt) FSV, (b) mutant FSV where the codon for tyrosine-1073 of p130gag-fps had been changed to codons for phenylalanine or serine, and (c) a revertant FSV, genotypically identical to wt FSV, in which the codon for tyrosine-1073 had been restored. Latency periods from cell inoculation to tumor formation were 12-29 weeks with Rat-2 cells, 6-8 weeks with mutant-transformed Rat-2 cells, and 2-4 weeks with wt FSV- and revertant FSV-transformed Rat-2 cells. Untransfected Rat-2 cells formed tumors that histologically resembled low grade fibrosarcomas or fibromas and were characterized by uniform fusiform cells in parallel arrays with a prominent collagenous stroma. The growth pattern of tumors produced by mutant FSV-transformed cells was generally similar, although cellular forms and intercellular organization were less uniform. In contrast, Rat-2 cells transformed with either wt FSV or revertant FSV produced tumors that resembled highly malignant sarcomas and were composed of diffuse sheets of pleomorphic, disorganized cells and stroma rich in hyaluronate but poor in fibrous components. Local invasion occurred in 25% of tumors produced by Rat-2 cells and in 53 and 36% of tumors formed by mutant FSV- and wt FSV-transformed cells, respectively. In culture, Rat-2 cells and mutant FSV-transformed cells produced fibrillar pericellular matrices of collagen I and fibronectin. From 5 to 15% of protein secreted by these cells was collagen. Cultures of wt FSV- and revertant FSV-transformed cells lacked collagen and fibronectin matrices and collagen secretion was reduced to 0-2%. These results show that clinically relevant histological characteristics of malignant tumors can correlate with single amino acid substitutions previously shown to affect the enzymatic activity and transforming ability of an oncogenic protein tyrosine kinase. The mechanisms underlying some of the histological differences in this system may be related to differences in the production of extracellular matrix components among the transformed cells.