Changes in fibronectin synthesis and binding distribution in SV40-transformed human keratinocytes

We have studied the synthesis and distribution of fibronectin in human epidermal keratinocytes infected by SV40, a system in which the acquisition of transformed properties occurs in a sequential and progressive manner. Immunofluorescence studies showed that cultured uninfected keratinocytes do not exhibit fibronectin on the superficial cell surface, but that virus-infected cells come to display superficial fibronectin-containing cables in a density-dependent manner after a certain point in the transformation process. In contrast, organized arrays of fibronectin-containing fibrils associated with the cell-substrate attachment complex were seen in uninfected keratinocytes and in virus-infected cells at all stages of the transformation process. Studies of fibronectin synthesis using metabolic labelling of cell proteins with 35S methionine showed that viral infection caused a striking increase in overall fibronectin synthesis, although with a much higher proportion of newly synthesized fibronectin being secreted into the cell culture medium than in the case of the uninfected cells.