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Hana Itani

Mentor: Curt D. Sigmund, Ph.D.
Lab Phone: 335-8926

Functional Characterization of Polymorphisms in the Kidney Enhancer of the Human Renin Gene

Our lab is interested in studying the Renin Angiotensin system (RAS) that plays a significant role in the regulation of blood pressure and electrolyte homeostasis. My project focuses on the renin (REN) enhancer (E) which is a highly conserved transcriptional regulatory element required for high level expression in renin-expressing As4.1 cells. We hypothesized that sequence variation in the E; particularly in transcription-factor (TF) binding sites may alter its function and may be associated with hypertension. We based this on our data showing that: 1) the mouse E (mE) is much stronger than the human E (hE) in transfection assays, and 2) there are sequence differences between the hE and mE that map to the response element (HRE) for members of the steroid hormone family of TF. We next asked whether there is natural variation in the renin E in humans. We sequenced the kidney enhancer from 90 samples derived from the Coriell Polymorphism Discovery Resource and 95 severely hypertensive Caucasian and African American individuals. A single relatively frequent polymorphism (7%, 2% and 7%, respectively in the Coriell, African American and Caucasian) was identified in the enhancer, one nucleotide downstream of the promoter distal half site of the RARE. This variant was transcriptionally silent in transfection assays performed in renin expressing As4.1 cells, a model of renal juxtaglomerular cells. A singleton polymorphism in the promoter was also identified in a single African American individual. This polymorphism was located between binding sites for CBF1 and HoxD10 but was also transcriptionally silent either in the presence or absence of the enhancer. Results demonstrate the presence of silent polymorphisms in the renin promoter and enhancer thus underscoring the critical importance of performing functional analyses before initiating expensive clinical studies seeking association between polymorphisms and complex diseases such as hypertension.

My current project focuses on the Regulation of Renin Gene Expression by Oxidative Stress. Angiotensin-II (AII) is involved in the pathogenesis of hypertension and mediates its effects in part by causing oxidative stress. AII feedback inhibits renin (REN) gene expression. We hypothesize that the effect of AII on REN expression is due to oxidative stress. Our results illustrate that Hydrogen peroxide (HP) caused a dose dependent decrease in steady state REN mRNA levels, yet, there was no difference in the level of cyclophilin (control) mRNA in response to the treatment. Also, HP caused a dose-dependent reduction in transcriptional activity of the REN promoter. Importantly, there was no effect of HP on the renilla internal control, and no effect on the transcriptional activity of the SV40 promoter driving firefly luciferase indicating the selectivity of the response.

Itani H, Liu X, Sarsour EH, Goswami PC, Born E, Keen HL, Sigmund CD. Regulation of renin gene expression by oxidative stress. Hypertension. 2009 Jun;53(6):1070-6. Epub 2009 May 11. PubMed PMID: 19433777; PubMed Central PMCID: PMC2740736.

Weatherford ET, Itani H, Keen HL, Sigmund CD. Is peroxisome proliferator-activated receptor-gamma a new "pal" of renin? Hypertension. 2007 Nov;50(5):844-6. Epub 2007 Sep 4. PubMed PMID: 17785627.

Itani HA, Liu X, Pratt JH, Sigmund CD. Functional characterization of polymorphisms in the kidney enhancer of the human renin gene. Endocrinology. 2007 Mar;148(3):1424-30. Epub 2006 Dec 7. PubMed PMID: 17158202.


Itani, H.A., Widmer, N. and Sigmund, C.D. Identification of a Single Nucleotide Polymorphism Near a Transcriptional Regulatory Element of the Renin Enhancer in Humans. FASEB Journal, 18:A1217, 2004.

Itani, H.A., Sigmund C.D. Identification and Function of Polymorphisms in the Human Renin Enhancer. Council for High Blood Pressure Research, AHA 2005.

Itani, H.A. , Liu X , Sigmund C.D. Regulation of rennin Gene Expression by Oxidative Stress. Council for High Blood Pressure Research, AHA 2007.

Honors and Awards

  • Experimental Biology "FASEB" 2004, Washington, DC.