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Guanylyl cyclase C agonists regulate progression through the cell cycle of human colon carcinoma cells
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Edited by Robert F. Furchgott, State University of New York Downstate Medical Center, Brooklyn, NY, and approved May 8, 2001 (received for review March 13, 2001)

Abstract
The effects of Escherichia coli heat-stable enterotoxin (ST) and uroguanylin were examined on the proliferation of T84 and Caco2 human colon carcinoma cells that express guanylyl cyclase C (GC-C) and SW480 human colon carcinoma cells that do not express this receptor. ST or uroguanylin inhibited proliferation of T84 and Caco2 cells, but not SW480 cells, in a concentration-dependent fashion, assessed by quantifying cell number, cell protein, and [3H]thymidine incorporation into DNA. These agonists did not inhibit proliferation by induction of apoptosis, assessed by TUNEL (terminal deoxynucleotidyl transferase-mediated dNTP-biotin nick end labeling of DNA fragments) assay and DNA laddering, or necrosis, assessed by trypan blue exclusion and lactate dehydrogenase release. Rather, ST prolonged the cell cycle, assessed by flow cytometry and [3H]thymidine incorporation into DNA. The cytostatic effects of GC-C agonists were associated with accumulation of intracellular cGMP, mimicked by the cell-permeant analog 8-Br-cGMP, and reproduced and potentiated by the cGMP-specific phosphodiesterase inhibitor zaprinast but not the inactive ST analog TJU 1-103. Thus, GC-C agonists regulate the proliferation of intestinal cells through cGMP-dependent mechanisms by delaying progression of the cell cycle. These data suggest that endogenous agonists of GC-C, such as uroguanylin, may play a role in regulating the balance between epithelial proliferation and differentiation in normal intestinal physiology. Therefore, GC-C ligands may be novel therapeutic agents for the treatment of patients with colorectal cancer.
Footnotes
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↵‡ To whom reprint requests should be addressed at: Division of Clinical Pharmacology, Thomas Jefferson University, 1100 Walnut Street, 811 Medical Office Building, Philadelphia, PA 19107. E-mail: gmpitari{at}yahoo.com.
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This paper was submitted directly (Track II) to the PNAS office.
Abbreviations
- [cGMP]i, intracellular cGMP,
- GC-C, guanylyl cyclase C;
- IBMX,
- 3-isobutyl-1-methylxanthine;
- PI,
- propidium iodide;
- PDE,
- phosphodiesterase;
- PKG II,
- cGMP-dependent protein kinase II;
- ST,
- Escherichia coli heat-stable enterotoxin;
- TUNEL,
- terminal deoxynucleotidyltransferase-mediated dNTP-biotin nick end labeling of DNA fragments;
- EMEM,
- Eagle's minimal essential medium
- Received March 13, 2001.
- Copyright © 2001, The National Academy of Sciences