Endostatin expression in pancreatic tissue is modulated by elastase

Abstract

Pancreatic tumours are scirrhous, avascular tumours, suggesting that they may produce angiogenesis inhibitors that suppress the growth of the vasculature to the tumour and metastases. We have sought evidence for the angiogenesis inhibitor, endostatin, in normal and cancerous pancreatic tissue. Using Western blotting, we found mature 20 kDa endostatin in cancer tissue but not in normal tissue. Several endostatin-related peptides of higher mol wt were present in both tissues. Extracts from normal tissue were able to degrade exogenous endostatin, whereas extracts from cancer were without effect. Although the exocrine pancreas secretes inactive proenzymes of trypsin, chymotrypsin and elastase, their possible role in this degradation was examined. The trypsin/ chymotrypsin inhibitor, Glycine max, did not prevent the degradation of endostatin by normal pancreatic extracts but elastatinal, a specific inhibitor of elastase, reduced the rate of degradation. Extracts of pancreatic tumours did not express any detectable elastase activity, but an elastase (K m 1.1 mM) was expressed by extracts of normal pancreas. We conclude that endostatin is present and stable in pancreatic cancer tissues, which may explain their avascular nature, but that normal pancreatic tissue expresses enzymes, including elastase, which rapidly degrade endostatin. The stability of endostatin may have implications for its therapeutic use.

Endostatin expression in a pancreatic cell line is modulated by a TNFα-dependent elastase

“…This compares with the Km of 1.1 mM for an elastase we identified in human pancreas (Brammer et al, 2005) and human leukocyte elastase where the Km is reported to be 0.14 mM (Castillo et al, 1979). Effect of TNFa on endostatin production from SUIT-2 cells Figure 6 shows the effect of incubation of SUIT-2 cells with TNFa for 48 h on endostatin secretion.…”

“…Although they may have a role in endostatin generation , they may also be important in endostatin degradation. We previously implicated elastase in the degradation of endostatin in extracts of normal pancreas (Brammer et al, 2005). The release of intracellular proteases that degrade endostatin following tissue injury, may be a means to reduce local endostatin levels.…”

“…The cell layer proteins were also analysed by SDS -PAGE to allow comparison between secreted and nonsecreted endostatin-related fragments. Detection was as described previously (Brammer et al, 2005) using enhanced chemiluminescence with rabbit polyclonal antisera to human endostatin (Chemicon, Hampshire, UK) diluted 1 : 100. The specificity of the antisera was shown by preabsorption of the antibody with an excess of recombinant endostatin.…”

“…We have previously identified endostatin in human pancreatic cancer tissue and showed that it was susceptible to degradation by elastase (Brammer et al, 2005). We sought to identify a pancreatic cell line capable of endostatin production in order to examine the regulation of endostatin production.…”

Endostatin in the pancreas

“…Now that at least one inhibitor of endostatin is known, it may also be possible to modify the amino-acid sequence of endostatin to create analogues, which retain antiangiogenic activity but which are more resistant to degradation by pancreatic elastase. One issue which was not addressed by the study by Brammer et al (2005) is whether any products of endostatin resulting from elastase digestion retain activity as inhibitors of angiogenesis. Adenocarcinoma of the pancreas has largely frustrated the efforts of oncologists to modify its behaviour.…”