Binding of soluble fibronectin and its subsequent incorporation into the extracellular matrix by early and late passage human skin fibroblasts

The specific binding of soluble 125I-labeled human plasma fibronectin (125I-HFN-P) to confluent cultures of early and late passage human skin fibroblasts was investigated. Previous studies of HFN-P bound to fibroblast cell layers indicated that HFN-P was present in the cultures in two separate pools, distinguishable on the basis of their solubility in 1% deoxycholate. Pool I contained deoxycholate-soluble fibronectin (cell-associated), whereas Pool II contained deoxycholate-insoluble fibronectin (matrix-associated). Time course studies indicated that HFN-P was initially incorporated into Pool I and then accumulated into Pool II (McKeown-Longo, P.J., and Mosher, D.F. (1983) J. Cell Biol. 97, 466-472). Examination of the kinetics of 125I-HFN-P binding to Pool I of early and late passage cultures revealed that both cultures required 2-4 h to approach steady-state conditions. Other kinetic studies showed that the rates of loss of 125I-HFN-P from either Pool I or Pool II were similar for both cultures. However, the late passage cultures bound greater than twice as much fibronectin into Pool I, per cell, than the early passage cultures. This difference was not related to a difference in the level of endogenously produced fibronectins accumulating in the medium. Late passage cultures incorporated 125I-HFN-P into the deoxycholate-insoluble Pool at an average rate 2.6 times greater than early passage cultures. The late passage cultures also chased a greater percent of their Pool I-bound fibronectin into Pool II and a lower percent into the chase medium. These results indicate that early and late passage cultures of human fibroblasts exhibit differences in the binding of soluble fibronectin and in the extent to which they incorporate soluble fibronectin into the extracellular matrix.