Abstracts
1997 Digestive Disease Week

Thrombospondin-1 and transforming growth factor-ß1 upregulate production of plasminogen activator inhibitor type 1 in pancreatic cancer.

D Albo, DH Berger J Vogel, H Chang, V Rothman, GP Tuszynski. Allegheny University of the Health Sciences, MCP*Hahnemann School of Medicine, Philadelphia, PA.

The urokinase plasminogen activator system (uPA) is important in malignant pericellular proteolysis and tumor cell invasion. A critical regulator of this system is PAI-1. We have previously shown that TSP-1 and TGF-ß1 promote uPA production in breast and oral squamous carcinomas. The aim of this study was to determine the role of TSP-1 and TGF-ß1 in the regulation of uPA and PAI-1 expression in human pancreatic cancer. ASPC-1 and COLO-357 human pancreatic cells were incubated either in control media, affinity purified TSP-1 (10, 20, 40, or 50 mg/ml), or TGF-ß1 (1, 2.5, 5, or 10 ng/ml) for 48 hours. The expression of uPA and PAI-1 in the cell extracts and the conditioned media was quantitated by ELISA assays. TSP-1 increased PAI-1 protein concentration in the conditioned media of both cell lines. TGF-ß1 increased PAI-1 concentration in the ASPC-1 conditioned media. However, TGF-ß1 did not increase PAI-1 concentration in the media of COLO-357 cells (Table 1).

Table 1.   PAI-1 Expression (ng/ml)
               Control         TSP-1           TGF-ß1
 ASPC-1       19.9±0.03       37.0±0.05*      35.0±0.15*
 Colo-357      0.5±0.03       62.7±0.06*       1.0±0.05
     *p < 0.01 by ANOVA & Students' t- test

Neither TSP-1 nor TGF-ß1 had an effect on PAI-1 expression in the tumor cell extracts (data not shown). uPA expression in both the tumor cell extracts and conditioned media was not effected by either TSP-1 or TGF-ß1 in either cell line (Table 2). These experiments show that TSP-1 and TGF-ß1 increase the concentration of PAI-1 secreted by human pancreatic cancer cells. This increase in secreted PAI-1 is not associated with an increase in secreted or cell associated uPA. Increased secretion of PAI-1 by these tumor cells could provide the means for controlling excessive degradation of the tumor-associated matrix which contributes to the dense stromal reaction seen in human pancreatic carcinomas.

Table 2. uPA Expression (ng/ml)
               Control         TSP-1           TGF-ß1
ASPC-1         4.90±0.05       5.10±0.16       4.93±0.14
Colo-357       0               0               0
*p < 0.01 by ANOVA & Students' t-test