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Escherichia coli heat-stable toxin receptors in human colonic tumors
S L Carrithers1, S J Parkinson, S Goldstein
1Department of Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania.
Background/Aims:
Escherichia coli heat-stable enterotoxins (ST) are small peptides of 18 or 19 amino acids that bind to specific cell surface receptors located on the intestinal brush border and activate guanylate cyclase, resulting in an increase in the intracellular cyclic guanosine 3',5'-monophosphate content of the cell. The present study examined whether receptors for ST are expressed by primary and metastatic human colonic tumors in vivo.
Methods:
Plasma membranes prepared from surgical tissue samples from normal colon, liver and lung, primary colonic adenocarcinomas, and colon carcinomas metastatic to lung and liver were analyzed for the structural and functional characteristics of constituent ST receptors.
Results:
All primary and metastatic colonic tumors examined bound ST, showing receptors of high (pmol/L) and low (nmol/L) affinity with densities that were similar to those in normal colon. Also, affinity cross-linking of labeled ST to membranes showed similar binding proteins in primary and metastatic tumors and normal colon. ST binding and affinity-labeled proteins were not detected in normal extraintestinal tissues. Guanylate cyclase was activated by ST in membranes from all colonic tumors studied, with efficacies and potencies that were similar to those in normal colon. ST did not activate this enzyme in normal extraintestinal tissues.
Conclusions:
Receptors for ST are expressed by primary and metastatic human colonic tumors in vivo, with structural and functional characteristics that are similar to those in normal human colon.
Insights
Human colonic tumors, both primary and metastatic, express receptors for Escherichia coli heat-stable enterotoxins (ST). These ST receptors function similarly to those found in normal colon tissue.
Area of Science:
- Gastroenterology
- Oncology
- Molecular Biology
Background:
- Escherichia coli heat-stable enterotoxins (ST) are peptides that bind to intestinal receptors, activating guanylate cyclase.
- Understanding ST receptor expression in colorectal cancer is crucial for potential therapeutic strategies.
Purpose of the Study:
- To investigate the presence and characteristics of ST receptors on human colonic tumors.
- To compare ST receptor expression in primary and metastatic colorectal tumors versus normal colon tissue.
Main Methods:
- Analysis of plasma membranes from normal colon, primary tumors, and metastatic tumors (liver, lung).
- Assessment of ST receptor binding affinity, density, and associated proteins via cross-linking.
- Functional assay of guanylate cyclase activation by ST in tumor and normal tissues.
Main Results:
- ST receptors were detected in all primary and metastatic colonic tumors, with similar affinities and densities to normal colon.
- Binding proteins for ST were consistent across tumor types and normal colon, but absent in normal extraintestinal tissues.
- ST activated guanylate cyclase in colonic tumors and normal colon similarly, but not in extraintestinal tissues.
Conclusions:
- Receptors for heat-stable enterotoxins (ST) are present on human colorectal tumors.
- These receptors exhibit similar structural and functional properties in both cancerous and normal colonic tissues.
