Research

Research Interests of the Hepler Lab

Cell-cell communication is essential for all aspects of cell and organ physiology.  Cells communicate with one another by chemical messengers (e.g. hormones and neurotransmitters) that elicit their effects by recognizing and binding specific cell surface receptors to initiate cell signaling. The most prominent class of receptors is the family of G protein coupled receptors (GPCRs).  GPCRs and their linked signaling pathways are critically important for regulating cell and organ physiology, behavior and cognition. Accordingly, these signaling pathways are the targets of many existing drugs and for future drug development.  Research Image 1To exert their actions on cells, GPCR’s rely on linked protein partners (G proteins consisting of a three protein Gαβγ complex). G proteins sit at the inner surface of the plasma membrane of cells, and act as molecular switches to transmit GPCR signals from neurotransmitters/hormones on the outside of cells to the inside of cells.  G proteins are “turned on” by GTP in response to GPCR activation, where they regulate numerous downstream signaling pathways important for neurotransmitter and hormone actions (learn more link, PDF 1PDF 2, and link).

Recently, a class of signaling molecules known as the RGS proteins (regulators of Gprotein signaling) was discovered that regulates G protein signaling, in part, by limiting the lifetime of GPCR/G protein signaling events.  RGS proteins are a large, diverse family of multifunctional signaling proteins that bind a growing list of signaling proteins, thus indicating that RGS proteins play key roles as newly appreciated modulators and integrators of GPCR/G protein signaling (learn more link, PDF 1 and PDF 2). Research Image 2

The research focus of our laboratory is to understand how GPCRs, G proteins, RGS proteins, and newly discovered protein partners work together to propagate neurotransmitter signals to regulate brain cell functions.

RGS proteins as novel scaffolding proteins that integrate G protein pathways with other signaling pathways in neurons

Brown, N.E., Lambert, N.A and Hepler, J.R. (2016) RGS14 regulates the lifetime of Gα-GTP signaling but does not prolong Gβγ signaling following receptor activation in live cells. Pharmacol Res Perspectives. Aug 18;4(5):e00249

Brown, N.E., Goswami, D., Branch, M.R., Ramineni, S., Ortlund, E.A., Griffin, P.R. and Hepler, J.R. (2015) Integration of G protein alpha (Gα) Signaling by the Regulator of G protein Signaling 14 (RGS14). J. Biol. Chem., Apr 3;290(14):9037-49.

Brown, N.E., Blumer, J.B., and Hepler, J.R. (2015) Bioluminescence Resonance Energy Transfer to Detect Protein-Protein Interactions in Live Cells. In: Protein-Protein Interactions: Methods and Applications, Methods in Molecular Biology, 1278:457-65.

Vellano, C.P., Brown, N.E., Blumer, J.B. and Hepler, J.R. (2013) Assembly and function of the regulator of G protein signaling 14 (RGS14):H-Ras complex is regulated by Gαi1 and a Gi-linked GPCR. J. Biol. Chem., 288(5):3620-31. doi: 10.1074/jbc.M112.440057. Epub 2012 Dec 17. PMID: 23250758

Zhao, P., Nunn, C., Ramineni, S., Hepler, J.R. and Chidiac, P. (2013) The Ras-binding domain of RGS14 regulates its functional interactions with heterotrimeric G proteins. J. Cell. Biochem., 114(6): 1414-1423. doi: 10.1002/jcb.24483.

Vellano, C.P., Maher, E.M., Hepler, J.R. and Blumer, J.B. (2011) G protein coupled receptors and Ric-8A both regulate the Regulator of G protein Signaling 14 (RGS14):Gαi1 complex in living cells. J. Biol. Chem. 286(44): 38659-38669

Vellano CP, Shu FJ, Ramineni S, Yates CK, Tall GG, Hepler JR. (2011) Activation of the regulator of G protein signaling 14-Gαi1-GDP signaling complex is regulated by resistance to inhibitors of cholinesterase-8A.Biochemistry 50(5):752-62

Shu, F.J., Ramineni, S and Hepler, J.R. (2010) RGS14 is a multifunctional scaffold that integrates G protein and H-Ras/Raf/MAP kinase signaling pathways. Cellular Signalling, 22(3):366-76.

Shu F-J, Ramenini,S., Amyot, W.M., and Hepler, J.R.  (2007) Selective interactions between Giα1 and Giα3 and the GoLoco/GPR domain of RGS14 influence its dynamic subcellular localization. Cellular Signalling, 17: 383-389.

Hepler, J.R., Cladman, W. Ramenini, S. Hollinger, S. and Chidiac, P. (2005) Novel activity of RGS14 on Goα and Giα nucleotide binding and hydrolysis independent of its RGS domain and GDI activity.  Biochemistry, 44, 5495-5502.

Hollinger, S., Ramineni, S., and Hepler, J.R. (2003) Phosphorylation of RGS14 by protein kinase A modulates its activity toward Giα, Biochemistry, 42, 811-819.

Hollinger, S., Taylor, J.B.,  Hoag-Goldman, E.M., and Hepler, J.R. (2001) RGS14 is a  bifunctional regulator of Gai/o that exists in multiple populations in brain. J. Neurochem., 79, 941-949.

Rose, J.J., Taylor, J.B., Shi, J., Jones, P.G, Cockett, M.R. and Hepler, J.R.  (2000) RGS7 is palmitoylated and exists as biochemically distinct subpopulations in brain.  
J. Neurochem
. 75, 2103-2112. 

RGS protein regulation of hippocampal-based learning, memory and synaptic plasticity

Evans, P.R., Dudek, S. M., and Hepler, J.R. (2015) Regulator of G Protein Signaling 14: A Molecular Break on Synaptic Plasticity Linked to Learning and Memory. Prog Mol Biol Transl Sci., in press.

Evans, P.R., Lee, S.E., Smith, Y., and Hepler, J.R. (2014) Postnatal Developmental Expression of Regulator of G Protein Signaling 14 (RGS14) in the Mouse Brain. J. Comp. Neurol, 522 (1): 186-203. (DOI:10.1002/cne.23395 (online pub, Nov 26, 2013).

Vellano, C.P, Lee, S.E., Dudek, S.M. and Hepler, J.R. (2011) RGS14 at the interface of hippocampal signalling and synaptic plasticity.Trends in Pharmacological Sciences32(11):666-674.

Lee, S.E., Simons, S.B., Heldt, S.A., Zhou, M., Schroeder, J.P, Cowan, D.P., Vellano, C.P., Feng, Y., Sweatt, J.D., Weinshenkar, D., Ressler, K.J., Dudek, S.M. and Hepler, J.R. (2010) RGS14 is a natural suppressor both of synaptic plasticity in CA2 neurons and hippocampal-based learning and memory. Proceedings of the National Academy of Sciences, USA, 107(39):16994-8

RGS14 is dubbed “The Homer Simpson Gene”
RGS14 IN THE SPOTLIGHT
EMORY MAGAZINE
The DAILY MAIL
MEDICAL DAILY
SCIENCE DAILY
GIZMODO

Direct RGS protein regulation of GPCR/G protein signaling complexes

Brown, N.E., Blumer, J.B., and Hepler, J.R. (2015) Bioluminescence Resonance Energy Transfer to Detect Protein-Protein Interactions in Live Cells. In: Protein-Protein Interactions: Methods and Applications, Methods in Molecular Biology, 1278:457-65.

Ghil, SH, McCoy, K.L. and Hepler, J.R. (2014) RGS2 and RGS4 form distinct G protein-dependent complexes with protease activated recpetor-1 (PAR1) in live cells. PLoS onE, 9(4):e95355. Doi:10.1371.

Hepler, J.R. (2014) G protein coupled receptor signaling complexes in live cells. Cellular Logistics, 4(1):e29392

McCoy, K.L., and Hepler, J.R. (2009) RGS proteins as central components of the G protein coupled receptor signaling complex.   Progress in Mol. Biol. Translational. Sci, 86; 49-74.

Gu, S., He, J., Ho, W.T., Ramineni, S., Thal D.M., Natesh, R., Tesmer, J.J.G., Hepler, J.R. and Heximer, S.P. (2007). Unique hydrophobic extension of the RGS2 amphipathic helix domain imparts increased plasma membrane binding and function relative to other RGS R4/B subfamily members. J. Biol. Chem., 282: 33064-75.

Neitzel, K.L. and Hepler, J.R. (2006) Cellular mechanisms that determine selective regulation of G protein coupled receptor signaling by RGS proteins. Seminars in Developmental and Cellular Biology, 17: 383-389.

Roy, A.A., Baragli, A., Bernstein, L.S., Hepler, J.R., Hebert, T.E., and Chidiac, P. (2006) RGS2 interacts with adenylyl cyclase in living cells. Cellular Signalling., 18:336-48.

Hague, C., Bernstein, L.S., Ramenini, S., Chen, Z.J., Minneman, K.P. and Hepler, J.R. (2005) Selective inhibition of α1A-adrenergic receptor signaling by RGS2 association with the receptor third intracellular loop.  J .Biol Chem., 280, 27289-27295.

Bernstein, L.S., Ramineni, S., Chris Hague, Wendy Cladman, Peter Chidiac, Levey, A.I. and Hepler, J.R.  (2004) RGS2 binds directly and selectively to the M1 muscarinic cholinergic receptor third intracellular loop to modulate Gq/11α signaling.  J. Biol. Chem., 279, 21248-21256.

Hepler, J.R. (2003) RGS protein and G protein interactions: A little help from their friends.Molecular Pharmacology., 64, 547-549.

Cunningham, M., Waldo, G.L., Hollinger, S.,  Hepler, J.R. and Harden, T.K.  (2001) Protein  kinase C phosphorylates RGS2 and modulates its capacity for negative regulation of G11α signaling.  J. Biol. Chem., 276, 5438-5444.

Heximer, S. P., Srinivasa, S.P., Bernstein, L.S., Bernard, J.L., Linder, M.E., Hepler, J.R. and Blumer, K.J. (1999) G protein selectivity is a determinant of RGS2 function. J. Biol. Chem., 274, 34253-34259.

Saugstad, J.A., Marino, M.J., Folk, J.A., Hepler, J.R. and Conn, P.J.  (1998) RGS4 inhibits signaling by group I metabotropic glutamate receptors.  J. Neuroscience, 18: 905-913.

Heximer, S.P., Watson, N., Linder, M.E., Blumer, K.J. and Hepler, J.R. (1997) RGS2/GOS8 is a  selective inhibitor of Gqα function.  Proc. Natl. Acad. Sci. USA, 94: 14389-14393.

Diversity of protease activated receptor (PAR) signaling in brain (in collaboration with the Traynelis lab at Emory)

Ghil, SH, McCoy, K.L. and Hepler, J.R. (2014) RGS2 and RGS4 form distinct G protein-dependent complexes with protease activated recpetor-1 (PAR1) in live cells. PLoS ONE, 9(4):e95355. Doi:10.1371.

McCoy, K.L., Gyoneva, S., Vellano, C.P., Smrcka A.V., Traynelis, S.F. and Hepler, J.R. (2012) Protease-Activated Receptor 1 (PAR1) coupling to Gq/11 but not to Gi/o or G12/13 is mediated by discrete amino acids within the receptor second intracellular loop. Cellular Signalling, 24(6):1351-60).

McCoy, K.L., Traynelis, S.F. and Hepler, J.R. (2010) PAR1 and PAR2 couple to overlapping and distinct sets of G proteins and linked signaling pathways to regulate cell physiology.Molecular Pharmacology, 77(6):1005-15.

Mannaioni, G., Goldshmidt, A., Hamill, C., Yuan, H., Pedone, K. H., Junge, C. E., Lee, C.J., Yepes, M., Hepler, J.R. , and Traynelis, S.F. (2008) Plasmin potentiates synaptic NMDA receptor function in  rat hippocampal neurons through activation of PAR1. J. Biol. Chem.,  283(29): 20600-20611.

Nicole, O., Sorensen, S.D., Sastre, A. Hepler, J.R.. Brat, D., McKeon, R.,  and Traynelis, S.F. (2005)     Activation of protease activated receptor-1 (PAR-1) contributes to glial scar formation after brain injury.  J. Neuroscience, 25, 4319-4329.

Junge, C.E., Lee, J.C, Hubbard, K.B., Zhang, Z., Olsen, J.J., Hepler, J.R., Brat, D.J., Traynelis, S.F. (2004) Protease activated receptor-1 (PAR-1) in human brain: localization and functional expression in astrocytes.  Experimental Neurology, 188, 94-103.

Sorensen, S.D., Nicole, O., Peavy, R.D., Montoya, L.M., Lee, J.C., Murphy, T.J., Traynelis, S.,F. and Hepler, J.R. (2003) Common signaling pathways link activation of murine PAR-1, LPA and S1P receptors to  proliferation of astrocytes.  Molecular Pharmacology., 64, 1199-1209.

Cell signaling diversity of Gqα family members

Pedone, K.H. and Hepler, J.R. (2007) The importance of amino terminal polycysteine and polybasic sequences in determining G14α and G16α palmitoylation, plasma membrane targeting and signaling function.  J. Biol. Chem. 282(35): 25199-212.

Hubbard, K.B and Hepler, J.R (2005) Cell signaling diversity of the Gqα family of heterotrimeric G proteins. Cellular Signalling, 18:135-50.

Peavy, R.B., Hubbard, K.B., Lau, A.G., Fields, B., Lee, T.T., Gernert, K., Murphy, T. J., and Hepler, J.R.   (2005) Differential effects of Gqα, G14α and G15α on vascular smooth muscle cell survival and gene  expression profiles. Molecular Pharmacology, 67, 2102-2114.