Orally active angiotensin-converting enzyme inhibitor (SO 14,225) as a treatment for essential hypertension

Rasd1 interacts with Ear2 (Nr2f6) to regulate renin transcription

BACKGROUND

The Rasd1 protein is a dexamethasone induced monomeric Ras-like G protein that oscillates in the suprachiasmatic nucleus (SCN). Previous studies have shown that Rasd1 modulates multiple signaling cascades. However, it is still unclear exactly how Rasd1 carries out its function. Studying protein-protein interactions involving Rasd1 may provide insights into its biological functions in different contexts.

RESULTS

To further explore the molecular function of Rasd1, we performed a yeast two-hybrid screen and identified Ear2, a negative regulator of renin transcription, as an interaction partner of Rasd1. We validated the interaction in vitro and in transfected COS-7 cells. We further confirmed the interaction of endogenous Rasd1 and Ear2 from HEK293T cell and mouse brain extract. Rasd1 inhibited transcriptional repression by Ear2 on a renin promoter-luciferase reporter construct both in the presence and absence of all-trans-retinoic acid. Moreover, real-time RT-PCR showed upregulation of endogenous renin transcription in As4.1 cells over-expressing Rasd1. We demonstrated that the ligand binding domain of Ear2 is required for physical and functional interaction between the two proteins. In addition, we demonstrated that shRNA-mediated knockdown of Rasd1 results in further repression of Ear2-mediated renin transcription, whereas induction of Rasd1 by dexamethasone counteracts the effects of shRNA-mediated Rasd1 knockdown. Finally, our study showed that Rasd1 missense mutations not only attenuate their physical interaction with Ear2 but also abolish their ability to counteract repression of renin transcription mediated by Ear2.

CONCLUSIONS

Our study provides evidence for physical and functional interactions between Rasd1 and Ear2. The results suggest that their interactions are involved in renin transcriptional regulation. These findings not only reveal a novel role for Rasd1-medated signaling but also provide the basis for potential intervention of renin expression.

Captopril: a preliminary review of its pharmacological properties and therapeutic efficacy

Captopril is the first orally active inhibitor of angiotensin-converting enzyme to become available. It has been studied primarily in hypertension. In mild to moderate essential hypertension captopril is about as effective as usual doses of hydrochlorothiazide or propranolol, about one-half of such patients needing the addition of a diuretic to achieve satisfactory control of blood pressure. In severe hypertension captopril plus a diuretic (and in some patients a beta-blocker) usually reduced blood pressure significantly more than could be achieved with 'standard triple therapy' in patients not responding adequately to such a regimen, and often resulted in an improved feeling of well-being in severely hypertensive patients previously receiving intensive multiple drug therapy. Indeed, at the present stage of the drug's development, patients not responding to or not tolerating 'traditional' antihypertensive therapy represent the most suitable candidates for captopril treatment. While captopril has been well tolerated in most patients, some troublesome or potentially serious side effects have been reported, including agranulocytosis, dysgeusia and reduced renal function; although a clear causal relationship with captopril was not always established, it would appear that the final place of captopril in the treatment of hypertension may ultimately depend on further clarification of its adverse effects profile. In addition to studies in hypertension, captopril has produced encouraging improvement in a small number of patients with severe congestive heart failure resistant to conventional therapy. Captopril must be considered an exciting addition to the therapeutic armamentarium; it, and pharmacologically related compounds of the future, will continue to generate much interest as their final place in therapy becomes better defined through additional well designed studies and wider clinical experience.