Guanylyl cyclase C agonists regulate progression through the cell cycle ofhuman colon carcinoma cells

The effects of Escherichia coli heat-stable enterotoxin (ST) and uroguanyli n were examined on the proliferation of T84 and Caco2 human colon carcinoma cells that express guanylyl cyclase C (GC-C) and SW480 human colon carcino ma cells that do not express this receptor. ST or uroguanylin inhibited pro liferation of T84 and Caco2 cells, but not SW480 cells, in a concentration- dependent fashion, assessed by quantifying cell number, cell protein, and [ H-3]thymidine incorporation into DNA. These agonists did not inhibit prolif eration by induction of apoptosis, assessed by TUNEL (terminal deoxynucleot idyl transferase-mediated dNTP-biotin nick end labeling of DNA fragments) a ssay and DNA laddering, or necrosis, assessed by trypan blue exclusion and lactate dehydrogenase release. Rather, ST prolonged the cell cycle, assesse d by flow cytometry and [H-3]thymidine incorporation into DNA. The cytostat ic effects of CC-C agonists were associated with accumulation of intracellu lar cGMP, mimicked by the cell-permeant analog 8-Br-cGMP, and reproduced an d potentiated by the cGMP-specific phosphodiesterase inhibitor zaprinast bu t not the inactive ST analog TJU 1-103. Thus, CC-C agonists regulate the pr oliferation of intestinal cells through cCMP-dependent mechanisms by delayi ng progression of the cell cycle. These data suggest that endogenous agonis ts of GC-C, such as uroguanylin, may play a role in regulating the balance between epithelial proliferation and differentiation in normal intestinal p hysiology. Therefore, GC-C ligands may be novel therapeutic agents for the treatment of patients with colorectal cancer.