Sequence: apelin receptor [Homo sapiens]

Gene:APLNR     Conserved Domain     Related Protein 3D Structures

AID	Name	Type	Comment
2520	uHTS identification of small molecule agonists of the APJ receptor via a luminescent beta-arrestin assay	screening
2580	Summary assay for small molecule agonists of the APJ receptor	summary	Summary AID.

Data Source: Sanford-Burnham Center for Chemical Genomics (SBCCG)
Source Affiliation: Sanford-Burnham Medical Research Institute(SBMRI, San Diego)
Network: NIH Molecular Libraries Production Centers Network (MLPCN)
Grant Number: 1R21NS059422-01
Assay Provider: Dr. Layton Smith, Sanford-Burnham Medical Research Institute

Currently there are no small molecule tools to investigate the biological functions of apelin and its receptor. Apelin is the endogenous peptide ligand for the G-protein coupled receptor (GPCR) APJ (angiotensin II receptor-like 1, AGTRL-1 and APLNR). Until the discovery of apelin, APJ was an orphan GPCR. APJ is coupled to Gai, and has been shown in cell culture to inhibit adenylate cyclase. The APJ gene encodes a receptor that most closely resembles the angiotensin receptor AT1. However, the APJ receptor does not bind angiotensin II. Underscoring the emerging importance of the apelin/APJ system, recent studies have shown that apelin reduces the extent of atherosclerotic lesions in ApoE-/- mice, and opposes the development of abdominal aortic aneurysms. Additional research has revealed that APJ forms a heterodimer with the Ang II receptor AT1, and that this complex facilitates antagonism of Ang II signaling by apelin. Despite these exciting results, there remains a multitude of unanswered questions regarding the role of apelin and APJ in physiology and pathology.
The project goal is to identify a chemical probe of apelin receptor function that transiently and reversibly activates the receptor. An agonist or potentiator of this receptor would provide a novel research tool to evaluate the role of apelin in cardiovascular and metabolic disease pathology.
In this description we utilize enzyme-fragment complementation to directly measure GPCR activation. Unlike imaging or other second messenger assays, the DiscoveRx b-Arrestin assay allows for a direct measure of GPCR activation by detection of b-Arrestin binding to the APJ receptor. In this system, b-Arrestin is fused to an N-terminal deletion mutant of b-gal (termed the enzyme acceptor of EA) and the GPCR of interest is fused to a smaller (42 amino acids), weakly complementing fragment termed ProLink. In cells that stably express these fusion proteins, ligand stimulation results in the interaction of b-Arrestin and the Prolink-tagged GPCR, forcing the complementation of the two b-gal fragments and resulting in the formation of a functional enzyme that converts substrate to detectable signal.

This dose response assay is developed and performed to confirm hits originally identified in "uHTS identification of small molecule agonists of the APJ receptor via a luminescent beta-arrestin assay" (AID 2520) and to study the structure-activity relationship on analogs of the confirmed hits. Compounds are either acquired from commercial sources or synthesized internally.

A. Brief Description of the Assay:
The purpose of this assay is to detect agonists that cause the activation the Angiotensin II receptor-like 1 (Apelin receptor) in the CHO-K1 AGTRL-1 beta-Arrestin Cell Line in 1536-well plate format in uHTS mode.

B. Materials:
Angiotensin II receptor-like 1 (AGTRL-1) Cell Line (DiscoveRx, Cat# 93-0250C2)
F12 nutrient mix HAMs (Invitrogen, Cat# 11765)
Fetal Bovine Serum, heat-inactivated (Hyclone, Cat# SH30396)
100X Penicillin/Streptomycin Solution (Invitrogen, Cat#15140-122)
Hygromycin B (Roche, Cat# 10843555001)
Geneticin (MPBiomedicals, Cat# 1672548)
Trypsin-EDTA 0.25% (Invitrogen, Cat# 25200-056)
Cell Dissociation Buffer (Invitrogen, Cat# 13151)
DPBS (Hyclone, Cat# 30028.02)
T225 TC Flask (Nunc, Cat# 159934)
Cell strainer, 40 um (BD, Cat# 352340)
1536-well, white, solid-bottom, Kalypsys compatible, TC plate (Corning)
Apelin-13 (Sigma-Aldrich, Cat# A6469)
PathHunter Detection Reagents (DiscoveRx, Cat# 93-0001)
Galacton Star
Emerald 11
Cell Assay Buffer

D. Dose Response Procedures:
Day1 -Cell Seeding
1) Plate 1000 cells/well in 4 uL of assay media into columns 1-48 of a 1536-well assay plate, using straight tip dispense on a Kalypsys dispenser.
2) Centrifuge plates at 500 rpm for 1 minute on a Vspin centrifuge. Use Kalypsys metal lids.
3) Incubate overnight at 37 degrees, 100% relative humidity, 5% CO2 for 16-18 hours.
Day2 -Compound Addition
1) Centrifuge compound plates at 500 rpm for 1 minute on a Vspin centrifuge.
2) Using LabCyte Echo, transfer varying volumes from a 2 mM Echo qualified plate containing test compounds into assay plate Col. 5 - 48 to achieve the desired dose response concentrations and range. Backfill with DMSO to equalize final DMSO concentrations in all test wells. Transfer equal volume of DMSO to positive and negative control wells in Columns 1 - 4.
3) Immediately following compound/DMSO transfer via the Echo, using the Kalypsys Dispenser, transfer 2ul/well of Assay media to Col. 3-48 for the negative control and test compound wells.
4) Using the Kalypsys Dispenser, add 2ul/well of 30 nM Apelin-13 in assay media to Col. 1-2 for the positive control .
5) Centrifuge plates at 500 rpm for 1 minute on a Vspin centrifuge.
6) Incubate plates at 25 degrees in the dark for 90 minutes.
7) Following 90 minute incubation, deliver 3.0 uL of Detection Reagent solution to each assay plate (Columns 1 - 48) using a Kalypsys dispenser.
8) Centrifuge plates at 2000 rpm for 3 minute on a Vspin centrifuge.
9) Incubate plates for 60 minutes at 25 degrees in the dark.
10) Read plates using the Viewlux using a luminescence protocol.

E. Recipes:
Growth Media
F12 nutrient mix HAMs supplemented with 10% hi-FBS, 1X Penicillin/Streptomycin; selection reagents: 300ug/ml Hygromycin B, 800ug/ml Geneticin
Assay Media
Same as Growth Media without the selection reagents
Trypsin
Dilute 0.25% Trypsin/EDTA to 0.05% Trypsin/EDTA using DPBS
Positive Control
Growth Media with 30 nM Apelin-13
Detection Reagent
Use the following ratio to prepare the detection reagent:
Galacton Star : Emerald II : Assay Buffer = 1 : 5 : 19

Compounds with an EC50_Mean < 10 are considered to be active

Activity Scoring
Activity scoring rules were devised to take into consideration compound efficacy, its potential interference with the assay and the screening stage that the data was obtained. Details of the Scoring System will be published elsewhere. Briefly, the outline of the scoring system utilized for the assay is as follows:

1) First tier (0-40 range) is reserved for primary screening data and is not applicable in this assay.

2) Second tier (41-80 range) is reserved for dose-response confirmation data and is not applicable in this assay.

3) Third tier (81-100 range) is reserved for resynthesized true positives and their analogues.
a. Inactive compounds of the confirmatory stage are assigned a score value equal 81.
b. The score is linearly correlated with a compound potency and, in addition, provides a measure of the likelihood that the compound is not an artifact based on the available information.
c. The Hill coefficient is taken as a measure of compound behavior in the assay via an additional scaling factor QC:

QC = 2.6*[exp(-0.5*nH^2) - exp(-1.5*nH^2)]

This empirical factor prorates the likelihood of target-specific compound effect vs. its non-specific behavior in the assay. This factor is based on expectation that a compound with a single mode of action that achieved equilibrium in this assay demonstrates the Hill coefficient value of 1. Compounds deviating from that behavior are penalized proportionally to the degree of their deviation.
d. Summary equation that takes into account the items discussed above is

Score = 82 + 3*(pEC50 - 3)*QC,

where pEC50 is a negative log(10) of the EC50 value expressed in mole/L concentration units. This equation results in the Score values above 85 for compounds that demonstrate high potency and predictable behavior. Compounds that are inactive in the assay or whose concentration-dependent behavior are likely to be an artifact of that assay will generally have lower Score values.

Grant Number: 1R21NS059422-01