Attempts were made to identify the cellular and molecular changes associated with SV40-transformation of human fibroblasts, MRC-5. SV40-transformed human fibroblasts, MRC-5V1, displayed a polygonal to round morphology, grew slowly, had reduced plating efficiencies but high saturation densities. However, they could be propagated in low serum-containing medium and grew very efficiently in soft agar. These altered growth properties of MRC-5V1 suggested that SV40 induced changes in cell adhesion and growth factor requirements. Indeed, MRC-5V1 expressed markedly reduced levels of cellular fibronectin, high levels of tPA and the expression of procollagen alpha 2(I) and decorin were absent. Moreover, MRC-5V1 did not express HGF/SF, a paracrine effector of epithelial cells and expressed very low levels of EGF receptor. However, SV40 induced the expression of TGF alpha, one of the ligands of the EGF receptor, TGF beta 1 and TGF beta 2, all of which are associated with cellular transformation. Given the establishment of autocrine loops in MRC-5V1 and the fact that decorin interacts with fibronectin and collagens and negatively regulates the activity of TGF beta s, these changes could account for the altered growth and transformation properties of MRC-5V1. Several studies have provided a link between oncogenic transformation, transcriptional and translational control. SV40 markedly reduced the expression of junB but not c-jun in MRC-5V1 and the expression of EIF-4E and EF1 delta were not significantly affected. The data shows that SV40-transformation of human fibroblasts is associated with multiple genetic changes affecting the expression of genes involved in cell adhesion, signal transduction and transcription, hence suggesting the breakdown of several cellular control mechanisms.

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