Late stage counterscreen for the probe development effort to identify selective agonists of the Transient Receptor Potential Channels 3 (TRPML3): fluorescence-based cell-based dose response assay for TRPN1 agonists.
Name: Late stage counterscreen for the probe development effort to identify selective agonists of the Transient Receptor Potential Channels 3 (TRPML3): fluorescence-based cell-based dose response assay for TRPN1 agonists. ..more
Source (MLPCN Center Name): The Scripps Research Institute Molecular Screening Center (SRIMSC)
Center Affiliation: The Scripps Research Institute (TSRI)
Assay Provider: Stefan Heller, Stanford University
Network: Molecular Libraries Probe Production Centers Network (MLPCN)
Grant Proposal Number 1 R03 MH083077-01
Grant Proposal PI: Stefan Heller, Stanford University
External Assay ID: TRPN1_AG_FLUO8_1536_3XEC50_LATE STAGE CS DRUN
Name: Late stage counterscreen for the probe development effort to identify selective agonists of the Transient Receptor Potential Channels 3 (TRPML3): fluorescence-based cell-based dose response assay for TRPN1 agonists.
Cell signaling pathways that mediate osmosensation, photosensation, and thermosensation depend on a family of diverse transient receptor potential (TRP) cation channels, which are activated by agonist-receptor coupling (1-5). A role for these channels in inner ear hair cell mechanotransduction was gleaned from TRP channel mutations identified in flies, worms, and lower vertebrates with defective balance and impaired sensitivity to touch (1-5). TRPML3 (mucolipin 3; MCOLN3) is a TRP channel expressed in inner ear hair cells and stereocilia (5-7), suggesting it may play a role in hearing and mechanotransduction. Reports that mice with mutations in TRPML3 (known as varitint-waddler mutants) exhibit early-onset hearing loss accompanied by head-bobbing and circling behaviors (8-10), provide further support for a role of TRPML3 in hearing and vestibular function. As a result, the identification of selective probes for TRPML3 would be useful to investigate the function of TRPML3 in inner ear mechanotransduction and hearing biology (11).
1. Clapham, D.E., TRP channels as cellular sensors. Nature. 2003. 426(6966): p. 517-24.
2. Cuajungco, M.P., C. Grimm, and S. Heller, TRP channels as candidates for hearing and balance abnormalities in vertebrates. Biochim Biophys Acta. 2007. 1772(8): p. 1022-7.
3. Gillespie, P.G. and R.G. Walker. Molecular basis of mechanosensory transduction. Nature. 2001. 413(6852): p. 194-202.
4. Eberl, D.F., R.W. Hardy, and M.J. Kernan. Genetically similar transduction mechanisms for touch and hearing in Drosophila. J Neurosci. 2000. 20(16): p. 5981-8.
5. Gong, Z., W. Son, Y.D. Chung, J. Kim, D.W. Shin, C.A. McClung, Y. Lee, H.W. Lee, D.J. Chang, B.K. Kaang, H. Cho, U. Oh, J. Hirsh, M.J. Kernan, and C. Kim. Two interdependent TRPV channel subunits, inactive and Nanchung, mediate hearing in Drosophila. J Neurosci. 2004. 24(41): p. 9059-66.
6. Kim, J., Y.D. Chung, D.Y. Park, S. Choi, D.W. Shin, H. Soh, H.W. Lee, W. Son, J. Yim, C.S. Park, M.J. Kernan, and C. Kim. A TRPV family ion channel required for hearing in Drosophila. Nature. 2003. 424(6944): p. 81-4.
7. Walker, R.G., A.T. Willingham, and C.S. Zuker. A Drosophila mechanosensory transduction channel. Science. 2000. 287(5461): p. 2229-34.
8. Corey, D.P. What is the hair cell transduction channel? J Physiol. 2006. 576(Pt 1): p. 23-8.
9. Shin, J.B., D. Adams, M. Paukert, M. Siba, S. Sidi, M. Levin, P.G. Gillespie, and S. Grunder. Xenopus TRPN1 (NOMPC) localizes to microtubule-based cilia in epithelial cells, including inner-ear hair cells. Proc Natl Acad Sci U S A. 2005. 102(35): p. 12572-7.
10. Sidi, S., R.W. Friedrich, and T. Nicolson. NompC TRP channel required for vertebrate sensory hair cell mechanotransduction. Science. 2003. 301(5629): p. 96-9.
11. Small molecule activators of TRPML3. Grimm C, Jors S, Saldanha SA, Obukhov AG, Pan B, Oshima K, Cuajungco MP, Chase P, Hodder P, Heller S. Chem Biol. 2010 Feb 26;17(2):135-148.
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The purpose of this assay is to determine dose response curves for powder samples of compounds identified as active in a previous set of experiments entitled, "Primary cell-based high-throughput screening assay to identify agonists of the transient receptor potential channel ML3" (PubChem AID 1448), and "Dose response cell-based high-throughput screening assay for agonists of the transient receptor potential channel ML3 (TRPML3)" (AID 1562), and that were inactive in a set of experiments entitled, "Fluorescence counterscreen assay for TRPML3 agonists: dose response cell-based high-throughput screening assay to identify agonists of the transient receptor potential channel N1 (TRPN1)" (AID 1682). This assay serves as a counterscreen to determine whether these compounds were nonselective due to activation of TRPN1. This assay may also have tested analogs of the above compounds. This assay employs a HEK293 cell line that stably expresses the zebrafish TRPN1-YFP cation channel. The cells are treated with test compounds followed by measurement of intracellular calcium as monitored by a fluorescent, cell permeable calcium indicator dye. As designed, compounds that act as TRPN1 agonists will increase calcium mobilization, resulting in increased relative fluorescence of the indicator dye, and thus increase well fluorescence. Compounds were tested in triplicate using a 10-point, 1:3 dilution series starting at a nominal concentration of 29.9 micromolar.
The TRPN1 HEK293 cell line was routinely cultured in T-175 sq cm flasks at 37 degrees C and 95% relative humidity (RH). The growth media consisted of Minimum Essential Medium with GlutaMAX and supplemented with 10% v/v heat-inactivated qualified fetal bovine serum, 800 micrograms/mL Geneticin, and 1X antibiotic mix (penicillin, streptomycin, and neomycin). The day before the assay 1500 cells in 3 microliters of growth media were seeded into each well of 1536 well microtiter plates and allowed to incubate at 37 degrees C, 5% CO2, and 95 % RH for 23 hours. Next, 2 microliters of the fluorogenic Fluo-8 intracellular calcium indicator mixture with 1 mM trypan red plus (prepared according to the manufacturer's protocol) was added to each well. After a 1 hour incubation at 37 degrees C, 5% CO2, and 95 % RH followed by a 30 minute incubation at room temperature, the assay was started by performing a basal read of plate fluorescence (470-495 nm excitation and 515-575 nm emission) for 5 seconds on the FLIPR Tetra (Molecular Devices). Next, 15 nL of test compound in DMSO, DMSO alone (0.3% final concentration), or the cholinergic agonist carbachol (87 micromolar final concentration) in DMSO were dispensed to the appropriate wells. Then a real time fluorescence measurement was immediately performed for the remaining 120 seconds of the assay.
A ratio for each well was calculated to normalize assay data, according to the following mathematical expression:
Ratio = I_Max / I_Min
I_Max represents the maximum measured fluorescence emission intensity over the 125 second read and;
I_Min represents the minimum (basal) measured fluorescence emission intensity before compound was added.
Percent activation was calculated from the median ratio as follows:
%Activation = ( ( Ratio_Test_Compound - Median_Ratio_Low_Control ) / ( Median_Ratio_High_Control - Median_Ratio_ Low_Control ) ) * 100
Test_Compound is defined as wells containing test compound.
High_Control is defined as wells containing carbachol.
Low_Control is defined as wells containing DMSO.
For each test compound, percent activation was plotted against compound concentration. A four parameter equation describing a sigmoidal dose-response curve was then fitted with adjustable baseline using Assay Explorer software (Symyx Technologies Inc). The reported EC50 values were generated from fitted curves by solving for the X-intercept value at the 50% activation level of the Y-intercept value. In cases where the highest concentration tested (i.e. 29.9 micromolar) did not result in greater than 50% activation, the EC50 was determined manually as greater than 50 micromolar. Compounds with an EC50 greater than 10 micromolar were considered inactive. Compounds with an EC50 equal to or less than 10 micromolar were considered active.
PubChem Activity Outcome and Score:
Any compound with a percent activity value <50% at all test concentrations was assigned an activity score of zero. Any compound with a percent activity value >50% at any test concentration was assigned an activity score greater than zero. Activity score was then ranked by the potency, with the most potent compounds assigned the highest activity scores.
The PubChem Activity Score range for inactive compounds is 0-0, there are no actives.
List of Reagents:
TRPN1 HEK293 cell line (provided by Prof. Stefan Heller)
Fluo-8 No Wash Calcium Assay Kit (ABD Bioquest, part 36316)
Trypan red plus (ABD Bioquest, part 2456)
MEM with GlutaMAX (Invitrogen, part 41090-101)
Geneticin (Invitrogen, part 10131-027)
Trypsin-EDTA solution (Invitrogen, part 25200-056)
Fetal Bovine Serum (Invitrogen, part 16140-071)
Carbachol (Sigma, part C4382)
100X Penicillin-Streptomycin-Neomycin mix (Invitrogen, part 15640-055)
T-175 tissue culture flasks (Corning, part 431080)
1536-well plates (Greiner, part 789072)
This assay may have been run as two or more separate campaigns, each campaign testing a unique set of compounds. In this case the results of each separate campaign were assigned "Active/Inactive" status based upon that campaign's specific compound activity cutoff value. Possible artifacts of this assay can include, but are not limited to: dust or lint located in or on wells of the microtiter plate, compounds that non-specifically modulate calcium levels or channel activity, and compounds that quench or emit fluorescence within the well. All test compound concentrations reported are nominal; the specific concentration for a particular test compound may vary based upon the actual sample provided.
Categorized Comment - additional comments and annotations
Assay Format: Cell-based
Assay Cell Type: HEK293
Assay Format: Cell-based
Assay Type: Functional
* Activity Concentration. ** Test Concentration.
Data Table (Concise)