Dataset Information

A calcium-sensing receptor mutation causing hypocalcemia disrupts a transmembrane salt bridge to activate ?-arrestin-biased signaling.

ABSTRACT: The calcium-sensing receptor (CaSR) is a G protein-coupled receptor (GPCR) that signals through Gq/11 and Gi/o to stimulate cytosolic calcium (Ca2+i) and mitogen-activated protein kinase (MAPK) signaling to control extracellular calcium homeostasis. Studies of loss- and gain-of-function CASR mutations, which cause familial hypocalciuric hypercalcemia type 1 (FHH1) and autosomal dominant hypocalcemia type 1 (ADH1), respectively, have revealed that the CaSR signals in a biased manner. Thus, some mutations associated with FHH1 lead to signaling predominantly through the MAPK pathway, whereas mutations associated with ADH1 preferentially enhance Ca2+i responses. We report a previously unidentified ADH1-associated R680G CaSR mutation, which led to the identification of a CaSR structural motif that mediates biased signaling. Expressing CaSRR680G in HEK 293 cells showed that this mutation increased MAPK signaling without altering Ca2+i responses. Moreover, this gain of function in MAPK activity occurred independently of Gq/11 and Gi/o and was mediated instead by a noncanonical pathway involving ?-arrestin proteins. Homology modeling and mutagenesis studies showed that the R680G CaSR mutation selectively enhanced ?-arrestin signaling by disrupting a salt bridge formed between Arg680 and Glu767, which are located in CaSR transmembrane domain 3 and extracellular loop 2, respectively. Thus, our results demonstrate CaSR signaling through ?-arrestin and the importance of the Arg680-Glu767 salt bridge in mediating signaling bias.

SUBMITTER: Gorvin CM

PROVIDER: S-EPMC6166785 | biostudies-literature | 2018 Feb

REPOSITORIES: biostudies-literature

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A calcium-sensing receptor mutation causing hypocalcemia disrupts a transmembrane salt bridge to activate β-arrestin-biased signaling.

Gorvin Caroline M CM Babinsky Valerie N VN Malinauskas Tomas T Nissen Peter H PH Schou Anders J AJ Hanyaloglu Aylin C AC Siebold Christian C Jones E Yvonne EY Hannan Fadil M FM Thakker Rajesh V RV

Science signaling 20180220 518

The calcium-sensing receptor (CaSR) is a G protein-coupled receptor (GPCR) that signals through Gq/11 and Gi/o to stimulate cytosolic calcium (Ca2+i) and mitogen-activated protein kinase (MAPK) signaling to control extracellular calcium homeostasis. Studies of loss- and gain-of-function CASR mutations, which cause familial hypocalciuric hypercalcemia type 1 (FHH1) and autosomal dominant hypocalcemia type 1 (ADH1), respectively, have revealed tha ...[more]

PMID: 29463778

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Project description:Neuroblastoma is the most common extracranial solid childhood tumor with clinical manifestations ranging from benign tumors that spontaneously regress to highly aggressive metastatic disease. Unfortunately, there is no therapy known to be curative for high-risk neuroblastoma. The calcium-sensing receptor (CaSR) is a G protein-coupled receptor that senses plasmatic fluctuation in the extracellular concentration of calcium and plays a key role in maintaining calcium homeostasis. We have previously reported that this receptor exhibits tumor suppressor properties in neuroblastoma. The activation of CaSR with cinacalcet, a positive allosteric modulator of CaSR, reduces neuroblastoma tumor-growth by promoting differentiation, ER stress and apoptosis. However, these promising results came with an associated side effect, since cinacalcet exposure resulted in hypocalcemia. Based on the biased signaling shown by calcimimetics, we aimed to identify a new drug that might exert tumor-growth inhibition similar to cinacalcet without affecting plasma calcium levels. We identified a structurally different calcimimetic AC-265347 as a promising therapeutic agent for neuroblastoma, since it reduced tumor-growth by induction of differentiation, without affecting plasma calcium levels. Microarrays analysis suggested biased allosteric modulation of the CaSR signaling by both calcimimetics towards distinct intracellular pathways since no upregulation of genes involved in calcium signaling and ER stress were observed in PDX models exposed to AC-265347. Moreover, the most significant upregulated biological pathways promoted by AC-265347 were linked to RHO GTPases signaling. AC-265347 also up-regulated cancer testis antigens (CTAs), thus providing new opportunities for CTA-based immunotherapies. Taken together, this study helps to shed light about the importance of the biased allosteric modulation when targeting GPCRs in cancer. More importantly, the capacity of AC-265347 to promote differentiation of malignant neuroblastoma cells provides new opportunities, alone or in combination with other drugs, to control minimal residual disease and to prevent relapse in patients affected with neuroblastoma.

Project description:Halophilic proteins have greater abundance of acidic over basic and very low bulky hydrophobic residues. Classical electrostatic stabilization was suggested as the key determinant for halophilic adaptation of protein. However, contribution of specific electrostatic interactions (i.e. salt-bridges) to overall stability of halophilic proteins is yet to be understood. To understand this, we use Adaptive-Poison-Boltzmann-Solver Methods along with our home-built automation to workout net as well as associated component energy terms such as desolvation energy, bridge energy and background energy for 275 salt-bridges from 20 extremely halophilic proteins. We then perform extensive statistical analysis on general and energetic attributes on these salt-bridges. On average, 8 salt-bridges per 150 residues protein were observed which is almost twice than earlier report. Overall contributions of salt-bridges are -3.0 kcal mol-1. Majority (78%) of salt-bridges in our dataset are stable and conserved in nature. Although, average contributions of component energy terms are equal, their individual details vary greatly from one another indicating their sensitivity to local micro-environment. Notably, 35% of salt-bridges in our database are buried and stable. Greater desolvation penalty of these buried salt-bridges are counteracted by stable network salt-bridges apart from favorable equal contributions of bridge and background terms. Recruitment of extensive network salt-bridges (46%) with a net contribution of -5.0 kcal mol-1 per salt-bridge, seems to be a halophilic design wherein favorable average contribution of background term (-10 kcal mol-1) exceeds than that of bridge term (-7 kcal mol-1). Interiors of proteins from halophiles are seen to possess relatively higher abundance of charge and polar side chains than that of mesophiles which seems to be satisfied by cooperative network salt-bridges. Overall, our theoretical analyses provide insight into halophilic signature in its specific electrostatic interactions which we hope would help in protein engineering and bioinformatics studies.

Dataset Information

A calcium-sensing receptor mutation causing hypocalcemia disrupts a transmembrane salt bridge to activate ?-arrestin-biased signaling.

Publications

A calcium-sensing receptor mutation causing hypocalcemia disrupts a transmembrane salt bridge to activate β-arrestin-biased signaling.

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