ISSN:
0021-9541
Keywords:
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
Protease nexin (PN) is a cell-secreted protein that links to thrombin (Th) and certain other serine proteases. PN mediates the binding, internalization, and degradation of these proteases by cells (Baker et al., 1980; Low et al., 1981). Here we show that binding of Th-PN complexes to human foreskin fibroblasts (HF cells) accounted for 90% of the specific cellular Th binding at certain mitogenic doses of the protease. However, cell-associated Th-PN complexes were likely to be inactive mitogenically because heparin (170 units/ml) inhibited cellular binding of 125-Th-PN by about 95% (a reduction from 1.3 × 105 to 6 × 103 125I-Th-PN complexes per cell) but did not influence Th-mediated mitogenic stimulation. In experiments with mouse embryo cells, heparin also markedly decreased cellular binding of 125I-Th-PN without changing the mitogenic response to Th. The lack of mitogenic activity of cell-associated Th-PN complexes suggested that PN might inhibit the mitogenically essential proteolytic activity of Th. This possibility is supported by the following findings. First, amounts of serum-free conditioned culture medium that contained enough PN to complex a large fraction of added Th inhibited the clotting activity of Th. Second, heparin increased the formation of 125I-Th-PN complexes and also increased this inhibitory effect of conditioned medium. We conclude that PN acts as a negative modulator of thrombin mitogenic activity.It is shown that like other fibroblastic cells HF cells bound free 125I-Th specifically (although with relatively low affinity, Kass 〈 108 M-1). Specific binding of free 125I-Th to HF cells increased fourfold in the presence of heparin (50 IU/ml).
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jcp.1041120220
