Honors & Awards

  • 30 Under 30: Healthcare, Forbes Magazine (2016)
  • 1st place, Collegiate Inventors Competition, Invent Now (2013)
  • Paul Sigler Memorial Award, Yale Dept. of Molecular Biophysics and Biochem (2008)
  • Barry M Goldwater Scholarship, Barry M. Goldwater Foundation (2007-2008)
  • Beckman Scholar, Arnold and Mabel Beckman Foundation (2006-2007)

Education & Certifications

  • Master of Science, Yale University, Molecular Biophysics & Biochem (2008)
  • Bachelor of Science, Yale University, Molecular Biophysics & Biochem (2008)

Research & Scholarship

Lab Affiliations


All Publications

  • Antibodies to Interleukin-2 Elicit Selective T Cell Subset Potentiation through Distinct Conformational Mechanisms IMMUNITY Spangler, J. B., Tomala, J., Luca, V. C., Jude, K. M., Dong, S., Ring, A. M., Votavova, P., Pepper, M., Kovar, M., Garcia, K. C. 2015; 42 (5): 815-825


    Interleukin-2 (IL-2) is a pleiotropic cytokine that regulates immune cell homeostasis and has been used to treat a range of disorders including cancer and autoimmune disease. IL-2 signals via interleukin-2 receptor-β (IL-2Rβ):IL-2Rγ heterodimers on cells expressing high (regulatory T cells, Treg) or low (effector cells) amounts of IL-2Rα (CD25). When complexed with IL-2, certain anti-cytokine antibodies preferentially stimulate expansion of Treg (JES6-1) or effector (S4B6) cells, offering a strategy for targeted disease therapy. We found that JES6-1 sterically blocked the IL-2:IL-2Rβ and IL-2:IL-2Rγ interactions, but also allosterically lowered the IL-2:IL-2Rα affinity through a "triggered exchange" mechanism favoring IL-2Rα(hi) Treg cells, creating a positive feedback loop for IL-2Rα(hi) cell activation. Conversely, S4B6 sterically blocked the IL-2:IL-2Rα interaction, while also conformationally stabilizing the IL-2:IL-2Rβ interaction, thus stimulating all IL-2-responsive immune cells, particularly IL-2Rβ(hi) effector cells. These insights provide a molecular blueprint for engineering selectively potentiating therapeutic antibodies.

    View details for DOI 10.1016/j.immuni.2015.04.015

    View details for Web of Science ID 000354827400009

  • Cytokine therapy reverses NK cell anergy in MHC-deficient tumors JOURNAL OF CLINICAL INVESTIGATION Ardolino, M., Azimi, C. S., Iannello, A., Trevino, T. N., Horan, L., Zhang, L., Deng, W., Ring, A. M., Fischer, S., Garcia, K. C., Raulet, D. H. 2014; 124 (11): 4781-4794

    View details for DOI 10.1172/JCI74337

    View details for Web of Science ID 000344203300015

  • Activation and allosteric modulation of a muscarinic acetylcholine receptor. Nature Kruse, A. C., Ring, A. M., Manglik, A., Hu, J., Hu, K., Eitel, K., Hübner, H., Pardon, E., Valant, C., Sexton, P. M., Christopoulos, A., Felder, C. C., Gmeiner, P., Steyaert, J., Weis, W. I., Garcia, K. C., Wess, J., Kobilka, B. K. 2013; 504 (7478): 101-106


    Despite recent advances in crystallography and the availability of G-protein-coupled receptor (GPCR) structures, little is known about the mechanism of their activation process, as only the β2 adrenergic receptor (β2AR) and rhodopsin have been crystallized in fully active conformations. Here we report the structure of an agonist-bound, active state of the human M2 muscarinic acetylcholine receptor stabilized by a G-protein mimetic camelid antibody fragment isolated by conformational selection using yeast surface display. In addition to the expected changes in the intracellular surface, the structure reveals larger conformational changes in the extracellular region and orthosteric binding site than observed in the active states of the β2AR and rhodopsin. We also report the structure of the M2 receptor simultaneously bound to the orthosteric agonist iperoxo and the positive allosteric modulator LY2119620. This structure reveals that LY2119620 recognizes a largely pre-formed binding site in the extracellular vestibule of the iperoxo-bound receptor, inducing a slight contraction of this outer binding pocket. These structures offer important insights into the activation mechanism and allosteric modulation of muscarinic receptors.

    View details for DOI 10.1038/nature12735

    View details for PubMedID 24256733

  • Adrenaline-activated structure of ß2-adrenoceptor stabilized by an engineered nanobody. Nature Ring, A. M., Manglik, A., Kruse, A. C., Enos, M. D., Weis, W. I., Garcia, K. C., Kobilka, B. K. 2013; 502 (7472): 575-579


    G-protein-coupled receptors (GPCRs) are integral membrane proteins that have an essential role in human physiology, yet the molecular processes through which they bind to their endogenous agonists and activate effector proteins remain poorly understood. So far, it has not been possible to capture an active-state GPCR bound to its native neurotransmitter. Crystal structures of agonist-bound GPCRs have relied on the use of either exceptionally high-affinity agonists or receptor stabilization by mutagenesis. Many natural agonists such as adrenaline, which activates the β2-adrenoceptor (β2AR), bind with relatively low affinity, and they are often chemically unstable. Using directed evolution, we engineered a high-affinity camelid antibody fragment that stabilizes the active state of the β2AR, and used this to obtain crystal structures of the activated receptor bound to multiple ligands. Here we present structures of the active-state human β2AR bound to three chemically distinct agonists: the ultrahigh-affinity agonist BI167107, the high-affinity catecholamine agonist hydroxybenzyl isoproterenol, and the low-affinity endogenous agonist adrenaline. The crystal structures reveal a highly conserved overall ligand recognition and activation mode despite diverse ligand chemical structures and affinities that range from 100 nM to ∼80 pM. Overall, the adrenaline-bound receptor structure is similar to the others, but it has substantial rearrangements in extracellular loop three and the extracellular tip of transmembrane helix 6. These structures also reveal a water-mediated hydrogen bond between two conserved tyrosines, which appears to stabilize the active state of the β2AR and related GPCRs.

    View details for DOI 10.1038/nature12572

    View details for PubMedID 24056936

  • Engineered SIRPa variants as immunotherapeutic adjuvants to anticancer antibodies. Science Weiskopf, K., Ring, A. M., Ho, C. C., Volkmer, J., Levin, A. M., Volkmer, A. K., Ozkan, E., Fernhoff, N. B., van de Rijn, M., Weissman, I. L., Garcia, K. C. 2013; 341 (6141): 88-91


    CD47 is an antiphagocytic signal that cancer cells employ to inhibit macrophage-mediated destruction. Here, we modified the binding domain of human SIRPα, the receptor for CD47, for use as a CD47 antagonist. We engineered high-affinity SIRPα variants with approximately 50,000-fold increased affinity for human CD47 relative to wild-type SIRPα. As high-affinity SIRPα monomers, they potently antagonized CD47 on cancer cells but did not induce macrophage phagocytosis on their own. Instead, they exhibited remarkable synergy with all tumor-specific monoclonal antibodies tested by increasing phagocytosis in vitro and enhancing antitumor responses in vivo. This "one-two punch" directs immune responses against tumor cells while lowering the threshold for macrophage activation, thereby providing a universal method for augmenting the efficacy of therapeutic anticancer antibodies.

    View details for DOI 10.1126/science.1238856

    View details for PubMedID 23722425

  • Regulatory T cells control NK cells in an insulitic lesion by depriving them of IL-2 JOURNAL OF EXPERIMENTAL MEDICINE Sitrin, J., Ring, A., Garcia, K. C., Benoist, C., Mathis, D. 2013; 210 (6): 1153-1165


    Regulatory T (T reg) cells control progression to autoimmune diabetes in the BDC2.5/NOD mouse model by reining in natural killer (NK) cells that infiltrate the pancreatic islets, inhibiting both their proliferation and production of diabetogenic interferon-γ. In this study, we have explored the molecular mechanisms underlying this NK-T reg cell axis, following leads from a kinetic exploration of gene expression changes early after punctual perturbation of T reg cells in BDC2.5/NOD mice. Results from gene signature analyses, quantification of STAT5 phosphorylation levels, cytokine neutralization experiments, cytokine supplementation studies, and evaluations of intracellular cytokine levels collectively argue for a scenario in which T reg cells regulate NK cell functions by controlling the bioavailability of limiting amounts of IL-2 in the islets, generated mainly by infiltrating CD4(+) T cells. This scenario represents a previously unappreciated intertwining of the innate and adaptive immune systems: CD4(+) T cells priming NK cells to provoke a destructive T effector cell response. Our findings highlight the need to consider potential effects on NK cells when designing therapeutic strategies based on manipulation of IL-2 levels or targets.

    View details for DOI 10.1084/jem.20122248

    View details for Web of Science ID 000319807800010

    View details for PubMedID 23650440

  • Mechanistic and structural insight into the functional dichotomy between IL-2 and IL-15 NATURE IMMUNOLOGY Ring, A. M., Lin, J., Feng, D., Mitra, S., Rickert, M., Bowman, G. R., Pande, V. S., Li, P., Moraga, I., Spolski, R., Oezkan, E., Leonard, W. J., Garcia, K. C. 2012; 13 (12): 1187-?

    View details for DOI 10.1038/ni.2449

    View details for Web of Science ID 000311217900012

  • Exploiting a natural conformational switch to engineer an interleukin-2 'superkine' NATURE Levin, A. M., Bates, D. L., Ring, A. M., Krieg, C., Lin, J. T., Su, L., Moraga, I., Raeber, M. E., Bowman, G. R., Novick, P., Pande, V. S., Fathman, C. G., Boyman, O., Garcia, K. C. 2012; 484 (7395): 529-U159


    The immunostimulatory cytokine interleukin-2 (IL-2) is a growth factor for a wide range of leukocytes, including T cells and natural killer (NK) cells. Considerable effort has been invested in using IL-2 as a therapeutic agent for a variety of immune disorders ranging from AIDS to cancer. However, adverse effects have limited its use in the clinic. On activated T cells, IL-2 signals through a quaternary 'high affinity' receptor complex consisting of IL-2, IL-2R? (termed CD25), IL-2R? and IL-2R?. Naive T cells express only a low density of IL-2R? and IL-2R?, and are therefore relatively insensitive to IL-2, but acquire sensitivity after CD25 expression, which captures the cytokine and presents it to IL-2R? and IL-2R?. Here, using in vitro evolution, we eliminated the functional requirement of IL-2 for CD25 expression by engineering an IL-2 'superkine' (also called super-2) with increased binding affinity for IL-2R?. Crystal structures of the IL-2 superkine in free and receptor-bound forms showed that the evolved mutations are principally in the core of the cytokine, and molecular dynamics simulations indicated that the evolved mutations stabilized IL-2, reducing the flexibility of a helix in the IL-2R? binding site, into an optimized receptor-binding conformation resembling that when bound to CD25. The evolved mutations in the IL-2 superkine recapitulated the functional role of CD25 by eliciting potent phosphorylation of STAT5 and vigorous proliferation of T cells irrespective of CD25 expression. Compared to IL-2, the IL-2 superkine induced superior expansion of cytotoxic T cells, leading to improved antitumour responses in vivo, and elicited proportionally less expansion of T regulatory cells and reduced pulmonary oedema. Collectively, we show that in vitro evolution has mimicked the functional role of CD25 in enhancing IL-2 potency and regulating target cell specificity, which has implications for immunotherapy.

    View details for DOI 10.1038/nature10975

    View details for Web of Science ID 000303200400054

    View details for PubMedID 22446627

  • WNK2 Kinase Is a Novel Regulator of Essential Neuronal Cation-Chloride Cotransporters JOURNAL OF BIOLOGICAL CHEMISTRY Rinehart, J., Vazquez, N., Kahle, K. T., Hodson, C. A., Ring, A. M., Gulcicek, E. E., Louvi, A., Bobadilla, N. A., Gamba, G., Lifton, R. P. 2011; 286 (34): 30171-30180


    NKCC1 and KCC2, related cation-chloride cotransporters (CCC), regulate cell volume and ?-aminobutyric acid (GABA)-ergic neurotranmission by modulating the intracellular concentration of chloride [Cl(-)]. These CCCs are oppositely regulated by serine-threonine phosphorylation, which activates NKCC1 but inhibits KCC2. The kinase(s) that performs this function in the nervous system are not known with certainty. WNK1 and WNK4, members of the WNK (with no lysine [K]) kinase family, either directly or via the downstream SPAK/OSR1 Ste20-type kinases, regulate the furosemide-sensitive NKCC2 and the thiazide-sensitive NCC, kidney-specific CCCs. What role the novel WNK2 kinase plays in this regulatory cascade, if any, is unknown. Here, we show that WNK2, unlike other WNKs, is not expressed in kidney; rather, it is a neuron-enriched kinase primarily expressed in neocortical pyramidal cells, thalamic relay cells, and cerebellar granule and Purkinje cells in both the developing and adult brain. Bumetanide-sensitive and Cl(-)-dependent (86)Rb(+) uptake assays in Xenopus laevis oocytes revealed that WNK2 promotes Cl(-) accumulation by reciprocally activating NKCC1 and inhibiting KCC2 in a kinase-dependent manner, effectively bypassing normal tonicity requirements for cotransporter regulation. TiO(2) enrichment and tandem mass spectrometry studies demonstrate WNK2 forms a protein complex in the mammalian brain with SPAK, a known phosphoregulator of NKCC1. In this complex, SPAK is phosphorylated at Ser-383, a consensus WNK recognition site. These findings suggest a role for WNK2 in the regulation of CCCs in the mammalian brain, with implications for both cell volume regulation and/or GABAergic signaling.

    View details for DOI 10.1074/jbc.M111.222893

    View details for Web of Science ID 000294046600074

    View details for PubMedID 21733846

  • Angiotensin II signaling increases activity of the renal Na-Cl cotransporter through a WNK4-SPAK-dependent pathway PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA San-Cristobal, P., Pacheco-Alvarez, D., Richardson, C., Ring, A. M., Vazquez, N., Rafiqi, F. H., Chari, D., Kahle, K. T., Leng, Q., Bobadilla, N. A., Hebert, S. C., Alessi, D. R., Lifton, R. P., Gamba, G. 2009; 106 (11): 4384-4389


    Mutations in the kinase WNK4 cause pseudohypoaldosteronism type II (PHAII), a syndrome featuring hypertension and high serum K(+) levels (hyperkalemia). WNK4 has distinct functional states that regulate the balance between renal salt reabsorption and K(+) secretion by modulating the activities of renal transporters and channels, including the Na-Cl cotransporter NCC and the K(+) channel ROMK. WNK4's functions could enable differential responses to intravascular volume depletion (hypovolemia) and hyperkalemia. Because hypovolemia is uniquely associated with high angiotensin II (AngII) levels, AngII signaling might modulate WNK4 activity. We show that AngII signaling in Xenopus oocytes increases NCC activity by abrogating WNK4's inhibition of NCC but does not alter WNK4's inhibition of ROMK. This effect requires AngII, its receptor AT1R, and WNK4, and is prevented by the AT1R inhibitor losartan. NCC activity is also increased by WNK4 harboring mutations found in PHAII, and this activity cannot be further augmented by AngII signaling, consistent with PHAII mutations providing constitutive activation of the signaling pathway between AT1R and NCC. AngII's effect on NCC is also dependent on the kinase SPAK because dominant-negative SPAK or elimination of the SPAK binding motif in NCC prevent activation of NCC by AngII signaling. These effects extend to mammalian cells. AngII increases phosphorylation of specific sites on SPAK and NCC that are necessary for activation of each in mpkDCT cells. These findings place WNK4 in the signaling pathway between AngII and NCC, and provide a mechanism by which hypovolemia maximizes renal salt reabsoprtion without concomitantly increasing K(+) secretion.

    View details for DOI 10.1073/pnas.0813238106

    View details for Web of Science ID 000264278800060

    View details for PubMedID 19240212

  • Molecular physiology of the WNK kinases ANNUAL REVIEW OF PHYSIOLOGY Kahle, K. T., Ring, A. M., Lifton, R. P. 2008; 70: 329-355


    Mutations in the serine-threonine kinases WNK1 and WNK4 cause a Mendelian disease featuring hypertension and hyperkalemia. In vitro and in vivo studies have revealed that these proteins are molecular switches that have discrete functional states that impart different effects on downstream ion channels, transporters, and the paracellular pathway. These effects enable the distal nephron to allow either maximal NaCl reabsorption or maximal K+ secretion in response to hypovolemia or hyperkalemia, respectively. The related kinase WNK3 has reciprocal actions on the primary mediators of cellular Cl(-) influx and efflux, effects that can serve to regulate cell volume during growth and in response to osmotic stress as well as to modulate neuronal responses to GABA. These findings define a versatile new family of kinases that coordinate the activities of diverse ion transport pathways to achieve and maintain fluid and electrolyte homeostasis.

    View details for DOI 10.1146/annurev.physiol.70.113006.100651

    View details for Web of Science ID 000254489400015

    View details for PubMedID 17961084

  • An SGK1 site in WNK4 regulates Na+ channel and K+ channel activity and has implications for aldosterone signaling and K+ homeostasis PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Ring, A. M., Leng, Q., Rinehart, J., Wilson, F. H., Kahle, K. T., Hebert, S. C., Lifton, R. P. 2007; 104 (10): 4025-4029


    The steroid hormone aldosterone is secreted both in the setting of intravascular volume depletion and hyperkalemia, raising the question of how the kidney maximizes NaCl reabsorption in the former state while maximizing K(+) secretion in the latter. Mutations in WNK4 cause pseudohypoaldosteronism type II (PHAII), a disease featuring increased renal NaCl reabsorption and impaired K(+) secretion. PHAII-mutant WNK4 achieves these effects by increasing activity of the Na-Cl cotransporter (NCC) and the Na(+) channel ENaC while concurrently inhibiting the renal outer medullary K(+) channel (ROMK). We now describe a functional state for WNK4 that promotes increased, rather than decreased, K(+) secretion. We show that WNK4 is phosphorylated by SGK1, a mediator of aldosterone signaling. Whereas wild-type WNK4 inhibits the activity of both ENaC and ROMK, a WNK4 mutation that mimics phosphorylation at the SGK1 site (WNK4(S1169D)) alleviates inhibition of both channels. The net result of these effects in the kidney would be increased K(+) secretion, because of both increased electrogenic Na(+) reabsorption and increased apical membrane K(+) permeability. Thus, modification at the PHAII and SGK1 sites in WNK4 impart opposite effects on K(+) secretion, decreasing or increasing ROMK activity and net K(+) secretion, respectively. This functional state for WNK4 would thus promote the desired physiologic response to hyperkalemia, and the fact that it is induced downstream of aldosterone signaling implicates WNK4 in the physiologic response to aldosterone with hyperkalemia. Together, the different states of WNK4 allow the kidney to provide distinct and appropriate integrated responses to intravascular volume depletion and hyperkalemia.

    View details for DOI 10.1073/pnas.0611728104

    View details for Web of Science ID 000244972400064

    View details for PubMedID 17360471

  • WNK4 regulates activity of the epithelial Na+ channel in vitro and in vivo PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Ring, A. M., Cheng, S. X., Leng, Q., Kahle, K. T., Rinehart, J., Lalioti, M. D., Volkman, H. M., Wilson, F. H., Hebert, S. C., Lifton, R. P. 2007; 104 (10): 4020-4024


    Homeostasis of intravascular volume, Na(+), Cl(-), and K(+) is interdependent and determined by the coordinated activities of structurally diverse mediators in the distal nephron and the distal colon. The behavior of these flux pathways is regulated by the renin-angiotensin-aldosterone system; however, the mechanisms that allow independent modulation of individual elements have been obscure. Previous work has shown that mutations in WNK4 cause pseudohypoaldosteronism type II (PHAII), a disease featuring hypertension with hyperkalemia, due to altered activity of specific Na-Cl cotransporters, K(+) channels, and paracellular Cl(-) flux mediators of the distal nephron. By coexpression studies in Xenopus oocytes, we now demonstrate that WNK4 also inhibits the epithelial Na(+) channel (ENaC), the major mediator of aldosterone-sensitive Na(+) (re)absorption, via a mechanism that is independent of WNK4's kinase activity. This inhibition requires intact C termini in ENaC beta- and gamma-subunits, which contain PY motifs used to target ENaC for clearance from the plasma membrane. Importantly, PHAII-causing mutations eliminate WNK4's inhibition of ENaC, thereby paralleling other effects of PHAII to increase sodium balance. The relevance of these findings in vivo was studied in mice harboring PHAII-mutant WNK4. The colonic epithelium of these mice demonstrates markedly increased amiloride-sensitive Na(+) flux compared with wild-type littermates. These studies identify ENaC as a previously unrecognized downstream target of WNK4 and demonstrate a functional role for WNK4 in the regulation of colonic Na(+) absorption. These findings support a key role for WNK4 in coordinating the activities of diverse flux pathways to achieve integrated fluid and electrolyte homeostasis.

    View details for DOI 10.1073/pnas.0611727104

    View details for Web of Science ID 000244972400063

    View details for PubMedID 17360470