Coordinate Down-regulation of Adenylyl Cyclase Isoforms and the Stimulatory G Protein (Gs) in Intestinal Epithelial Cell Differentiation

Abstract

The intestinal epithelium is dynamic, with proliferation of undifferentiated crypt cells balanced by terminal differentiation and cell death at the colon surface or small intestinal villus tips. Cyclic AMP, induced by agonists such as prostaglandin E 2 and vasoactive intestinal polypeptide, promotes proliferation and ion secretion and suppresses apoptosis in intestinal epithelial cells. Here, we show that cell differentiation in a model intestinal epithelium leads to attenuation of cAMP production in response to G protein-coupled receptor and receptor-independent agonists. Concomitantly, key components of the cAMP cascade, the ␣ subunit of the stimulatory G protein, G s , and adenylyl cyclase (AC) isoforms 3, 4, 6, and 7 are down-regulated. By contrast, AC1, AC2, AC8, and AC9, and the receptors for prostaglandin E 2 and vasoactive intestinal polypeptide, are not expressed or not affected by differentiation. We confirmed key findings in normal murine colon epithelium, in which the major AC isoforms and G s ␣ are markedly down-regulated in differentiated surface cells. Suppression of AC isoforms and G s ␣ is functionally important, because their constitutive expression completely reverses differentiation-induced cAMP attenuation. Thus, down-regulation of AC isoforms and G s ␣ is an integral part of the intestinal epithelial differentiation program, perhaps serving to release cells from cAMP-promoted anti-apoptosis as a prerequisite for cell death upon terminal differentiation.The intestinal epithelium, a single-cell layer that separates and protects the body from microbes and toxins in the intestinal lumen, is critical for digestion and uptake of nutrients and is characterized by rapid turnover and spatial specialization. Epithelial cells at the bottom of crypts proliferate and migrate upwards toward the tips of the villi in the small intestine or the surface in the colon, where they die and slough off or are taken up by underlying phagocytic cells.

Adenylyl cyclase 3 haploinsufficiency confers susceptibility to diet-induced obesity and insulin resistance in mice

“…In the present study, the HFD-induced decrease in total Adcy activity observed in visceral adipose tissue of both WT and Adcy3 +/ − mice was accompanied by downregulation of Adcy1 , Adcy2 , Adcy3 , and Adcy8 mRNA expression. This finding is in line with previous reports indicating that expression of Adcy isoforms in a specific cell or tissue type can be selectively changed in response to pathophysiologic stimuli 25 26 . Choi et al observed that treatment of human colon epithelial cells with butyrate, which induced cell differentiation, downregulated mRNA expression of Adcy3 , Adcy4 , Adcy6, and Adcy7 by 70–90%, while mRNA levels of the other three isoforms, including Adcy1 , Adcy5 , and Adcy9 , were unchanged 25 .…”

“…This finding is in line with previous reports indicating that expression of Adcy isoforms in a specific cell or tissue type can be selectively changed in response to pathophysiologic stimuli 25 26 . Choi et al observed that treatment of human colon epithelial cells with butyrate, which induced cell differentiation, downregulated mRNA expression of Adcy3 , Adcy4 , Adcy6, and Adcy7 by 70–90%, while mRNA levels of the other three isoforms, including Adcy1 , Adcy5 , and Adcy9 , were unchanged 25 . Furthermore, Suzuki et al reported that among four isoforms of Adcys (Adcy2 , Adcy6 , Adcy7 , and Adcy 9) detected in the gastrocnemius muscle, Adcy 2 and Adcy 9 mRNA were selectively downregulated after denervation carried out by excision of the left sciatic nerve at the midthigh region 26 .…”

Role of adenylyl cyclase 6 in the development of lithium-induced nephrogenic diabetes insipidus

“…Thus, the combined effect of Li + and AC6 deletion could have a positively additive effect on the IC-to-PC ratio. Whether AC6 in the kidney is an indicator/modulator of differentiation as described in the mouse colon (44), in which AC6 is downregulated in the most differentiated surface cells, remains to be determined. However, based on the current data, it is plausible that AC6 plays distinctive roles in epithelial cell proliferation and may even be a determinant of the conversion of PC to IC (45).…”

Cyclic nucleotide signaling in intestinal epithelia: getting to the gut of the matter

“…Activation of PR2/4 increase cAMP production which promotes cell growth and inhibits apoptosis . Downregulation of adenylyl cyclase isoforms and G α s, is an integral part of the intestinal epithelial differentiation program, perhaps serving to release cells from a cAMP‐promoted antiapoptotic state that could be a prerequisite for cell death upon terminal differentiation.…”