Dual regulation of heat‐stable enterotoxin‐mediated cGMP accumulation in T84 cells by receptor desensitization and increased phosphodiesterase activity

Abstract

We report the regulation of cGMP accumulation induced by the heat-stable enterotoxin, STh, in the T84 human colonic cell line. STh binding to its receptor, guanylyl cyclase C (GCC), leads to elevated intracellular levels of cGMP. Prolonged exposure of T84 cells to STh induced refractoriness to further cGMP accumulation, without significant receptor internalization, but with reduced STh-induced cGMP synthesis by the receptor. Significantly, increased degradation of cGMP by a cGMP-specific phosphodiesterase was observed in desensitized cells. This is the first report on the desensitization of GCC, as well as the role of the Type V phosphodiesterase in inducing cellular refractoriness.

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

“…8-Br-cGMP, the cell-permeant analogue of cGMP, had identical effects on T84 and Caco2 proliferation compared with ST and uroguanylin, and inhibited the proliferation of SW480 cells stimulated by FBS. Finally, the effects of GC-C agonists on proliferation were mimicked and potentiated by zaprinast, a selective inhibitor of cGMP-regulated PDE5 that induces accumulation of [cGMP] i , potentiating ST stimulation of guanylyl cyclase activity in T84 cells (34,47). Taken together, these data support the hypothesis that ST and uroguanylin regulate proliferation of human intestinal cells by binding to and activating GC-C, inducing the accumulation of cGMP.…”

Interruption of Homologous Desensitization in Cyclic Guanosine 3′,5′-Monophosphate Signaling Restores Colon Cancer Cytostasis by Bacterial Enterotoxins

“…2, left). These temporal kinetics of desensitization and recovery of the antiproliferative effects of heatstable enterotoxins are nearly identical to those of induction and decline of PDE5 activity mediated by GCC and cGMP signaling (21,25). Of importance, linear regression analysis of the onset of cellular adaptation revealed two principle components characterized by rapid (tachyphylaxis) and slow (bradyphylaxis) rates of desensitization (Fig.…”

“…Moreover, GCC agonists have been proposed as novel cytostatic agents for targeted therapy for colorectal cancer metastases (13). However, receptor desensitization (21-23) and activation of phosphodiesterases (21,24) represent mechanisms by which colorectal cancer cells could develop resistance to cGMP-dependent cytostasis, limiting the therapeutic potential of GCC ligands.…”

The Regulation and Physiological Roles of the Guanylyl Cyclase Receptors.

“…GC-C GC-C may also undergo desensitization although specific mechanisms have not been clearly established. STa and uroguanylin, ligands for GC-C, cause attenuation of subsequent STa-induced cGMP generation in human colonic cell lines (T84 and Caco2 cells) [132,133]. A significant portion of the refractoriness seems to be caused by desensitization of GC-C. Homologous desensitization of GC-C occurs in a membrane preparation of HEK-293 cells stably transfected with GC-C cDNA [133], and after incubation of T84 cell membrane fractions with STa [132].…”

“…STa and uroguanylin, ligands for GC-C, cause attenuation of subsequent STa-induced cGMP generation in human colonic cell lines (T84 and Caco2 cells) [132,133]. A significant portion of the refractoriness seems to be caused by desensitization of GC-C. Homologous desensitization of GC-C occurs in a membrane preparation of HEK-293 cells stably transfected with GC-C cDNA [133], and after incubation of T84 cell membrane fractions with STa [132]. While the PKC pathway is able to desensitize GC-A and GC-B, STa-induced cGMP generation is augmented upon phosphorylation of the C-terminal tail of GC-C by PKC in T84 cells [134].…”