Inhibition of an endogenous growth‐related proteinase enhances the recovery of a negative growth regulator from cultured human cells.

Abstract

The possibility that a growth-related proteinase may act by degrading a negative growth regulatory protein has been investigated. Proteinase inhibitors which inhibit the enzyme also enhance the accumulation of the growth regulator by human fibroblasts. The negative growth regulator shows a similar specificity of inhibition of cellular growth to inhibitors of the growth-related proteinase.

Partial identification by site-directed mutagenesis of a cell growth inhibitory site on the human galectin-1 molecule

“…The endpoint of the haemagglutination titration was 1 μg/ml for the hexahis-galectin-1, compared to 1.3 μg/ml for the GST-galectin 1 fusion protein. It should also be noted that the growth-inhibitory activity seen here (I 50 = 5 μg/ml) was about 12–15 times greater than with the recombinant galectin-1 cleaved from a GST-galectin 1 fusion protein by thrombin [10], and roughly comparable with that of natural human galectin-1 [9]. It is still, however, about tenfold less active than recombinant mouse or human galectin expressed in COS-1 cells [4,22].…”

“…Our original interest in galectin-1 was as a putative substrate for a growth-regulatory, cell-surface proteinase [9]. Inhibition of the proteinase led to an accumulation of endogenous galectin-1 in the culture medium.…”

“…In fact, evidence for a growth-inhibitory phase could be seen in several earlier reports of the mitogenic activity of galectins from other species [6-8]. There was some evidence for a similar activity associated with human galectin-1, and it was suggested that proteolysis of secreted galectin-1 could account in part for the action of a growth-related cell-surface proteinase [9]. …”

Thrombin Receptor and Endogenous Growth‐related Proteolysis in Human Fibroblasts

“…The possibility that growth-related proteinases may exert a direct intracellular effect on cell growth has already been discussed, but an indirect effect is also a possibility, perhaps mediated by a secreted negative growth regulator (Wells and Mallucci, 1991), wlich is apparently susceptible to degradation by the GRP 645 (Manilal et a\., 1993). If this is so, then addition of his growth regulator to fibroblast cultures should affect protein phosphorylation in the same way as does GRP inhibition.…”

Changes in sensitivity of human tumour cells to growth inhibition by proteinase inhibitors.

“…Recently we have shown that an autocrine or paracrine fibroblast growth inhibitor, known also to be a galactose-binding protein (GBP; Wells and Malluchi, 1991), may also be a substrate for the fibroblast GRP. Continuous degradation of the GBP by the GRP may be necessary for normal growth (Manilal et al, 1993).…”