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Joshua D. Hoffman, Ping C. Mayo, Nathalie C. Schnetz-Boutaud, Douglas P. Mortlock, Margaret A. Pericak-Vance, Jonathan L. Haines; BAC-Based Small-Molecule Screen to Investigate Regulation of the Macular Degeneration Candidate Gene HTRA1. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3312.
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Age-Related Macular Degeneration (AMD) is one of the most common causes of visual impairment among the aging Caucasian population in the United States. Recent genome-wide association studies have implicated HtrA serine peptidase 1 (HTRA1) and age-related maculopathy susceptibility 2 (ARMS2) as being associated with AMD. Although these genes are located in close proximity to one another on chromosome 10, their individual roles in the pathogenesis of AMD are the subject of debate. We present a high-throughput small-molecule screen to characterize expression at the HTRA1 locus.
Screening was carried out using a bacterial artificial chromosome (BAC) due to the ability of BACs to capture the local and distant cis-regulatory elements that are necessary to recapitulate the endogenous cis-regulatory architecture. To measure expression from the HTRA1 locus in response to small molecules, a luciferase reporter cassette was inserted at the HTRA1 translational start site within the RP11-72B24 BAC clone. The BAC was transfected into HeLA cells and these were screened against a small molecule library of 2,000 compounds that have a mixture of known and unknown pharmacological effects. Compounds that gave a significant response in HeLA cells were examined in a retinal pigment epithelial (ARPE) cell line for changes in endogenous expression of HTRA1.
167 compounds gave a significant response as measured by greater than 3 standard deviations from the luciferase expression measured in a vehicle-only control, and were followed up with 4-point dose-response curve tests for further validation. At present, 7 of 16 compounds have been validated for repression of endogenous HTRA1 expression in wild-type HeLa cells using quantitative-PCR. Three compounds that repress HTRA1 mRNA include podophyllotoxin acetate, an antimitotic agent that inhibits tubulin polymerization; propargite, a pesticide with ATP-synthase inhibitory activity; and monensin sodium, a monovalent cation inhibitor. Menadione was also marginally able to repress HTRA1 transcripts. Menadione has vitamin-K-like properties, stimulates the ERK/MAPK pathway and can regulate connexins via interaction with EGFR signaling. We also confirmed previous reports that the proteasome inhibitor MG132 represses HTRA1 mRNA.
Analysis of the preliminary results is promising but requires further investigation and optimization.
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