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

The calcium-sensing receptor (CaSR) is a G protein-coupled receptor (GPCR) that signals through Gq/11and Gi/oto stimulate cytosolic calcium (Ca2+i) and mitogen-activated protein kinase (MAPK) signaling to control extracellular calcium homeostasis. Studies of loss- and gain-of-functionCASRmutations, 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+iresponses. 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 CaSRR680Gin HEK 293 cells showed that this mutation increased MAPK signaling without altering Ca2+iresponses. Moreover, this gain of function in MAPK activity occurred independently of Gq/11and Gi/oand was mediated instead by a noncanonical pathway involving β-arrestin proteins. Homology modeling and mutagenesis studies showed that the R680G CaSR mutation selectively enhanced β-arrestin signaling by disrupting a salt bridge formed between Arg680and Glu767, which are located in CaSR transmembrane domain 3 and extracellular loop 2, respectively. Thus, our results demonstrate CaSR signaling through β-arrestin and the importance of the Arg680-Glu767salt bridge in mediating signaling bias

Small molecules restore the function of mutant CLC5 associated with Dent disease

Dent disease type 1 is caused by mutations in the CLCN5 gene that encodes CLC5, a 2Cl−/H+ exchanger. The CLC5 mutants that have been functionally analysed constitute three major classes based on protein expression, cellular localization and channel function. We tested two small molecules, 4‐phenylbutyrate (4PBA) and its analogue 2‐naphthoxyacetic acid (2‐NOAA), for their effect on mutant CLC5 function and expression by whole‐cell patch‐clamp and Western blot, respectively. The expression and function of non‐Class I CLC5 mutants that have reduced function could be restored by either treatment. Cell viability was reduced in cells treated with 2‐NOAA. 4PBA is a FDA‐approved drug for the treatment of urea cycle disorders and offers a potential therapy for Dent disease

Sequence analysis and transcript expression of the MEN1 gene in sporadic pituitary tumours

The majority of pituitary tumours are monoclonal in origin and arise sporadically or occasionally as part of multiple endocrine neoplasia type 1 (MEN1). Whilst a multi-step aetiology involving both oncogenes and tumour suppressor genes has been proposed for their development, the target(s) of these changes are less clearly defined. Both familial and sporadic pituitary tumours have been shown to harbour allelic deletion on 11q13, which is the location of the recently cloned MEN1 gene. We investigated 23 sporadic pituitary tumours previously shown to harbour allelic deletion on 11q13 with the marker PYGM centromeric and within 50 kb of the MEN1 locus. In addition, the use of intragenic polymorphisms in exon 9 and at D11S4946, and of telomeric loci at D11S4940 and D11S4936, revealed that five of 20 tumours had loss of heterozygosity (LOH) telomeric to the menin gene. However, the overall pattern of loss in informative cases was indicative of non-contiguous deletion that brackets the menin gene. Sequence analysis of all MEN1 coding exons and flanking intronic sequence, in tumours and matched patient leucocyte DNA, did not reveal mutation(s) in any of the 23 tumours studied. A benign polymorphism in exon 9 was encountered at the expected frequency, and in seven patients heterozygous for the polymorphism the tumour showed retention of both copies of the menin gene. Reverse transcription polymerase chain reaction analysis of ten evaluable tumours and four normal pituitaries revealed the presence of the menin transcript. Whilst these findings suggest that gene silencing is unlikely to be mechanistic in sporadic pituitary tumorigenesis, they do not exclude changes in the level or stability of the transcript or translation to mature protein. Our study would support and extend very recent reports of a limited role for mutations in the MEN1 gene in sporadic pituitary tumours. Alternatively, these findings may point to an, as yet, unidentified tumour suppressor gene in this region

The role of the central stellar cluster in active galactic nuclei. I. Semi-analytical model

The subject of the paper is the role of the massive stellar cluster in the activity phenomenon and in the structure of active galactic nuclei. We introduce a simple model of stellar dynamics in the internal part of the cluster, which allows us to include both the star-disk and the star-star interactions. It is shown that the properties of the distribution of stars in the vicinity of the black hole are determined both by the interaction of the stars with the accretion disk and by the pair gravitational and contact interaction between the stars. We calculate the distribution of stars in the central parts of the cluster and we discuss possible effects of stellar mass-loss due to the star-disk interaction. Finally, we study the implications of the central cluster for active galactic nuclei activity. We model the broad line region assuming that the gaseous wakes, following stars after each disk crossing, play the role of the broad line region clouds, and we calculate the corresponding line profiles. We also analyze the contribution of star-star and star-disk collisions to active galactic nuclei variability.Comment: Accepted for publication in Astronomy and Astrophysic

A possible new syndrome with double endocrine tumors in association with an unprecedented type of familial heart-hand syndrome: a case report

<p>Abstract</p> <p>Introduction</p> <p>The combination of a pituitary prolactinoma and an aldosterone-producing adrenal adenoma is extremely rare. To the best of our knowledge, double endocrine tumors in association with heart-hand syndrome have not previously been reported.</p> <p>Case presentation</p> <p>A 21-year-old Japanese woman presented with galactorrhea and decreased visual acuity. A large pituitary adenoma with an increased level of serum prolactin was apparent by computed tomography. She additionally showed mild hypertension (136/90 mmHg) accompanied by hypokalemia. The plasma aldosterone concentration was increased. Computed tomography showed a mass in the right adrenal gland. No other tumors were found despite extensive imaging studies. Physical and radiographic examinations showed skeletal malformations of the hands and feet, including hypoplasia of the first digit in all four limbs. An atrial septal defect was demonstrated by echocardiography. Similar digital and cardiac abnormalities were detected in our patient's father, and a clinical diagnosis of hereditary heart-hand syndrome was made.</p> <p>Conclusion</p> <p>No established heart-hand syndrome was wholly compatible with the family's phenotype. Her father had no obvious endocrine tumors, implying that the parent of transmission determined variable phenotypic expression of the disease: heart-hand syndrome with multiple endocrine tumors from the paternal transmission or no endocrine tumor from the maternal transmission. This suggests that the gene or genes responsible for the disease may be under tissue-specific imprinting control.</p

A Novel Mutation in the Upstream Open Reading Frame of the CDKN1B Gene Causes a MEN4 Phenotype

PubMed ID: 23555276This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Somatic mutations of GNA11 and GNAQ in CTNNB1-mutant aldosterone-producing adenomas presenting in puberty, pregnancy or menopause.

Most aldosterone-producing adenomas (APAs) have gain-of-function somatic mutations of ion channels or transporters. However, their frequency in aldosterone-producing cell clusters of normal adrenal gland suggests a requirement for codriver mutations in APAs. Here we identified gain-of-function mutations in both CTNNB1 and GNA11 by whole-exome sequencing of 3/41 APAs. Further sequencing of known CTNNB1-mutant APAs led to a total of 16 of 27 (59%) with a somatic p.Gln209His, p.Gln209Pro or p.Gln209Leu mutation of GNA11 or GNAQ. Solitary GNA11 mutations were found in hyperplastic zona glomerulosa adjacent to double-mutant APAs. Nine of ten patients in our UK/Irish cohort presented in puberty, pregnancy or menopause. Among multiple transcripts upregulated more than tenfold in double-mutant APAs was LHCGR, the receptor for luteinizing or pregnancy hormone (human chorionic gonadotropin). Transfections of adrenocortical cells demonstrated additive effects of GNA11 and CTNNB1 mutations on aldosterone secretion and expression of genes upregulated in double-mutant APAs. In adrenal cortex, GNA11/Q mutations appear clinically silent without a codriver mutation of CTNNB1