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Patients with the multiple endocrine neoplasia type 1 (MEN1) syndrome carry germline heterozygous loss-of-function mutations in the MEN1 gene which predisposes them to develop various endocrine and non-endocrine tumors. Over 90% of the tumors show loss of heterozygosity (LOH) at chromosome 11q13, the MEN1 locus, due to somatic loss of the wild-type MEN1 allele. Thymic neuroendocrine tumors (NETs) or thymic carcinoids are uncommon in MEN1 patients but are a major cause of mortality. LOH at the MEN1 locus has not been demonstrated in thymic tumors. The goal of this study was to investigate the molecular aspects of MEN1-associated thymic tumors including LOH at the MEN1 locus and RNA-sequencing (RNA-Seq) to identify genes associated with tumor development and potential targeted therapy. A retrospective chart review of 294 patients with MEN1 germline mutations identified 14 patients (4.8%) with thymic tumors (12 thymic NETs and 2 thymomas). LOH at the MEN1 locus was identified in 10 tumors including the 2 thymomas, demonstrating that somatic LOH at the MEN1 locus is also the mechanism for thymic tumor development. Unsupervised principal component analysis and hierarchical clustering of RNA-Seq data showed that thymic NETs formed a homogenous transcriptomic group separate from thymoma and normal thymus. KSR2 (kinase suppressor of Ras 2), that promotes Ras-mediated signaling, was abundantly expressed in thymic NETs, a potential therapeutic target. The molecular insights gained from our study about thymic tumors combined with similar data from other MEN1-associated tumors may lead to better surveillance and treatment of these rare tumors.

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) may occur in 30% to 90% of patients with multiple endocrine neoplasia type 1 (MEN1). However, only 1% of GEP-NETs are grade 3 (G3). Given the rarity of these aggressive tumors, treatment of advanced G3 GEP-NETs in MEN1 is based on the treatment guidelines for sporadic GEP-NETs. We report a 43-year-old male with germline MEN1 followed at our institution, with clinical features including hyperparathyroidism, a nonfunctional pancreatic NET, and Zollinger–Ellison syndrome. On routine surveillance imaging at age 40, computed tomography/positron emission tomography imaging showed 2 arterially enhancing intraluminal masses on the medial aspect of the gastric wall. Anatomical imaging confirmed 2 enhancing masses within the pancreas and a rounded mass-like thickening along the lesser curvature of the stomach. The gastric mass was resected, and pathology reported a well-differentiated G3 NET with a Ki-67 >20%. The patient continued active surveillance. Eighteen months later cross-sectional imaging studies showed findings consistent with metastatic disease within the right hepatic lobe and bland embolization was done. On follow-up scans, including 68Ga-DOTATATE (68Ga-DOTA(0)-Tyr(3)-octreotate) imaging, interval increase in number and avidity of metastatic lesions were compatible with disease progression. Given a paucity of treatment recommendations for G3 tumors in MEN1, the patient was counseled based on standard NET treatment guidelines and recommended 177Lu-DOTATATE treatment. PRRT (peptide receptor radionuclide therapy) with 177Lu-DOTATATE (177Lu-tetraazacyclododecanetetraacetic acid-octreotide) is an important therapeutic modality for patients with somatostatin receptor–positive NETs. However, prospective studies are needed to understand the role of PRRT in G3 NETs.

Protein-protein interaction (PPI) networks are known to be valuable targets for therapeutic intervention; yet the development of PPI modulators as next-generation drugs to target specific vertices, edges, and hubs has been impeded by the lack of structural information of many of the proteins and complexes involved. Building on recent advancements in cross-linking mass spectrometry (XL-MS), we describe an effective approach to obtain relevant structural data on R7BP, a master regulator of itch sensation, and its interfaces with other proteins in its network. This approach integrates XL-MS with a variety of modeling techniques to successfully develop antibody inhibitors of the R7BP and RGS7/Gβ5 duplex interaction. Binding and inhibitory efficiency are studied by surface plasmon resonance spectroscopy and through an R7BP-derived dominant negative construct. This approach may have broader applications as a tool to facilitate the development of PPI modulators in the absence of crystal structures or when structural information is limited., Adikaram et al perform protein cross-linking coupled with mass spectrometry and structural modelling to obtain a structure of R7BP, a master regulator of itch. They identify domains interacting with R7BP partners RGS7 and Gβ5 and develop R7BP antibodies that obstruct its binding to the RGS7/Gβ5 duplex.

Mutation of the CDC73 gene, which encodes parafibromin, has been linked with parathyroid cancer. However, no correlation between genotypes of germline CDC73 mutations and the risk of parathyroid cancer has been known. In this study, subjects with germline CDC73 mutations were identified from the participants of two clinical protocols at National Institutes of Health (Discovery Cohort) and from the literature (Validation Cohort). The relative risk of developing parathyroid cancer was analyzed as a function of CDC73 genotype, and the impact of representative mutations on structure of parafibromin was compared between genotype groups. A total of 419 subjects, 68 in Discovery Cohort and 351 in Validation Cohort, were included. In both cohorts, percentages of CDC73 germline mutations that predicted significant conformational disruption or loss of expression of parafibromin (referred as ‘high-impact mutations’) were significantly higher among the subjects with parathyroid cancers compared to all other subjects. The Kaplan–Meier analysis showed that high-impact mutations were associated with a 6.6-fold higher risk of parathyroid carcinoma compared to low-impact mutations, despite a similar risk of developing primary hyperparathyroidism between two groups. Disruption of the C-terminal domain (CTD) of parafibromin is directly involved in predisposition to parathyroid carcinoma, since only the mutations impacting this domain were associated with an increased risk of parathyroid carcinoma. Structural analysis revealed that a conserved surface structure in the CTD is universally disrupted by the mutations affecting this domain. In conclusion, high-impact germline CDC73 mutations were found to increase risk of parathyroid carcinoma by disrupting the CTD of parafibromin.

Background: Here we describe a patient who presented with symptomatic hypocalcemia and a biochemical picture suggestive of PTH resistance. PTH resistance is a hallmark of pseudohypoparathyroidism, a heterogeneous group of rare disorders caused by genetic or epigenetic alterations of PTH/PTHrP signaling. However, PTH receptor-related autoimmune etiology has not been identified as the underlying mechanism for PTH resistance. Here we describe the first case of acquired autoimmune PTH resistance that is secondary to PTH1R autoantibodies. Clinical Case: A 60-year-old African-American woman, who previously had normal calcium homeostasis, presented with acute, symptomatic hypocalcemia, hyperphosphatemia and markedly elevated serum PTH, consistent with parathyroid hormone resistance. She did not have other hormone resistance or a clinical phenotype suggestive of pseudohypoparathyroidism. Whole-exome sequencing and GNAS methylation analysis revealed no genetic or epigenetic defects of the PTH/PTHrP signaling pathway. Treatment with Calcitriol and Calcium supplements was initiated with good clinical response. Within 10 years of follow-up, the patient developed autoimmune hypothyroidism, alopecia and an unusual form of membranous glomerulonephritis, raising the suspicion for an autoimmune etiology for PTH resistance. Luciferase immunoprecipitation system assay identified antibodies against PTH1R with mapping to the N-terminal extracellular ligand-binding domain (amino acids 1- 178). Using an in vitro biological assay in GP-2.3 cells, we found that the antibodies derived from the patient’s serum blocked PTH downstream signaling via Gsalpha/cAMP/protein kinase A pathway in a concentration-dependent manner. The patient’s autoantibody profile led to the diagnosis of additional autoimmune diseases, including atrophic gastritis and Sjogren syndrome. Lymphocyte immunophenotyping using flow cytometry revealed an overall normal B and T cell profile, but with decreased frequencies and numbers of switched and non-switched memory B cell subsets and an increased frequency and number of the CD8+ naïve cell population. Genes associated with autoimmune inflammatory disorders were sequenced but no pathologic changes were detected. Conclusions: Identification of the first case of autoimmune PTH resistance secondary to PTH1R autoantibodies extends the etiologic spectrum of hypoparathyroidism and should be considered when a patient presents with findings consistent with pseudohypoparathyroidism, especially in the presence of additional autoimmune diseases.

Background: Neuroendocrine neoplasms (NEN) are a heterogenous group of tumors. Patients with the multiple endocrine neoplasia type 1 (MEN1) syndrome often manifest with simultaneous functional and non-functional NEN in various endocrine glands. In MEN1, nuclear medicine plays an important role in the diagnostic work-up and localization of NEN. Little is known about the comparative efficacy of 68Ga-Dotatate PET/CT (DOTA) versus 18F-FDOPA PET/CT (FDOPA) and both versus non-nuclear medicine imaging (CT and MRI) in the identification of primary and metastatic NEN. Methods: This prospective MEN1 cohort study evaluated 15 germline MEN1 mutation-positive patients. Subjects were imaged using CT, MRI, DOTA and 18F-FDOPA. Radiological review with a multidisciplinary team was performed for each patient. Results: One-hundred twenty-nine total lesions were identified using any of the four scans. DOTA sensitivity was 69% (89/129; 95% CI 61% to 76%) with a mean standardized uptake value (SUV) of 33.9 ± 30.1, FDOPA sensitivity was 18% (23/129; 95% CI 12% to 25%) with mean SUV of 12.1 ± 15.16. DOTA identified an additional 50 lesions not seen on CT (of which MRI detected 8 lesions with an average size 0.95 cm ± 0.48; 3 pancreatic, 2 duodenal, 2 liver, and 1 lymph node) and identified 55 lesions not seen on MRI (of which CT identified 13 with a mean size of 1.1 cm ± 0.45; 1 lung, 4 pancreatic, 2 duodenal, 1 liver, and 5 lymph nodes). Overall, CT detected 51.2% (66/129) of lesions (mean 0.61 cm ± 0.73; 95% CI 43% to 60%) and MRI detected 39.5% (51/129; 0.47 cm ± 0.71; 95% CI 32% to 48%), and there was no significant difference in the size of lesions detected (p=0.18). Analysis by organ NEN revealed equal sensitivity between FDOPA and DOTA for lung carcinoid, detecting 33% (4/12) of lesions, while CT detected 92% (11/12) of lesions. In the duodenum, DOTA identified 100% (11 /11) of lesions, while FDOPA had poor sensitivity (9%) in this location. Within the pancreas, DOTA has a sensitivity of 81% (31/38), while FDOPA had a sensitivity of 21% (8/38). CT localized 42% (16/38) of pancreatic lesions, of which MRI missed 6. Interestingly, DOTA missed 7 pancreatic lesions all approximately 1cm or larger, which is previously unrecognized (range 0.9 - 1.8cm). Twenty-three liver metastases were detected on anatomic imaging (CT identified 14, while MRI detected 15, with only 9 overlapping lesions). DOTA identified 60% (14/23) of lesions, of which 3 lesions were missed by CT and MRI. However, DOTA was more sensitive in the liver than FDOPA which only detected 2 lesions. FDOPA detected one lesion in the adrenal (0.9cm) that was not seen on DOTA. Conclusion: DOTA imaging proved to be superior to FDOPA, CT and MRI overall in detecting NENs in MEN1, specifically in the duodenum. Pancreatic NEN missed by DOTA may represent higher grade tumors and may benefit from 18FDG PET/CT imaging.

Context: Germline gain-of-function variants in the transcription factor GCM2 were found in 18% of kindreds with familial isolated hyperparathyroidism (FIHP). These variants [c.1136T>A (p.Leu379Gln) and c.1181A>C (p.Tyr394Ser)] were located in a 17-amino acid transcriptional inhibitory domain named C-terminal conserved inhibitory domain (CCID). Objective: We investigated the ethnicity of individuals with germline variants in the GCM2 CCID in our primary hyperparathyroidism (PHPT) patient samples and in the Genome Aggregation Database. Design: Ethnicity information was obtained from an in-house clinical database and genetic counseling. Sanger sequencing of blood DNA was used to determine the genotype of the GCM2 CCID region. Luciferase reporter assays were performed to determine the functional impact of GCM2 variants. Setting and Patients: National Institute of Diabetes and Digestive and Kidney Diseases endocrine clinic is a service that accepts PHPT referral patients. Results: The GCM2 p.Tyr394Ser variant was found in 41% [95% confidence interval (CI), 22% to 64%] of Ashkenazi Jewish (AJ) kindreds with FIHP and in 27% (95% CI, 17% to 40%) of AJ patients with sporadic PHPT. The p.Tyr394Ser variant was also found in sporadic PHPT patients of European ancestry, but at a lower prevalence. The p.Leu379Gln variant was found in 8% (95% CI, 1% to 26%) of European kindreds with FIHP and 0.5% (95% CI, 0% to 3.0%) of sporadic PHPT cases of European ancestry. The sporadic PHPT patients with GCM2-activating variants often had multigland involvement or postoperative recurrent or persistent disease. Conclusions: Specific GCM2-activating variants enriched among various ethnic backgrounds could contribute to a large number of cases with FIHP or sporadic PHPT., Specific GCM2 activating variants enriched in various ethnic backgrounds could contribute to a large number of cases with familial isolated hyperparathyroidism or sporadic primary hyperparathyroidism.

Background: Further characterization of insulinomas from MEN1 patients versus sporadic cases may help elucidate pathophysiological differences and improve future diagnostic algorithms. Methods A retrospective analysis of all patients with insulinoma were included (MEN1 between 1971-2019; sporadic between 1997-2019). Demographic, clinical, laboratory results including a supervised fast, imaging and intra-arterial calcium stimulation (CaStim) data were retrieved when available. Categorical and continuous variables were compared using Fisher’s exact test and Mann-Whitney U-test, respectively. Results One hundred and thirteen patients were identified with insulinoma (69 women, median 44 years, range 13-78 years); of these, 27 patients had MEN1 (11 women, median 37 years, range 18-64 years). Patients with MEN1-related insulinomas sustained a significantly longer duration of the fast and had larger surgically resected tumors (29.73±15.32 vs 15.4±10.8 hours, p

Patients with the multiple endocrine neoplasia 1 (MEN1) syndrome develop various tumors during their lifetime. One of the rare manifestations observed in MEN1 patients is thymic neuroendocrine tumor (Th-NET) or thymic carcinoid, which is a major cause of death due to its aggressive nature, frequent recurrence, and lack of effective treatment. The goal of this study was to analyze the clinical presentation and outcome of Th-NETs in MEN1 patients at our institution and to investigate the correlation between genotype and phenotype. We evaluated the clinical characteristics of MEN1 patients with Th-NETs from a cohort of 350 patients with a MEN1 germline mutation and identified 13 patients (3.7%) with Th-NETs: 11 with thymic carcinoid, 1 with a thymoma demonstrating a neuroendocrine phenotype, and 1 with a non-neuroendocrine thymoma. Thymic carcinoid occurred exclusively in men and was the first tumor identified in 2 of the patients, while the 2 patients with thymoma were both females. Median age of diagnosis for Th-NETs was 43 years (range: 29-65 years). Mean tumor largest diameter was 7.18 cm (range: 2.5-15 cm). ACTH production was not detected in any of the thymic carcinoid cases. Seven patients died, 4 of them are still followed, and 2 of them were lost to follow-up. Th-NETs recurred following surgical resection in 7 patients. Family history of thymic carcinoid was identified in 6 patients. Smoking history was found in 6 patients. MEN1-associated tumors in our cohort included parathyroid adenoma (n=13), pancreatic NET (n=11), pituitary adenoma (n=8), Zollinger-Ellison syndrome (n=7), and lung carcinoid (n=1). In archived tumor samples obtained from 11 patients, chromogranin-A and synaptophysin immunohistochemistry confirmed the neuroendocrine phenotype in thymic carcinoids and showed neuroendocrine differentiation in one of the thymomas. Tumor grade analysis was performed using Ki-67 staining. Genomic DNA was isolated from peripheral blood leukocytes and the following MEN1 germline heterozygous mutations were identified: 8 frameshift, 3 nonsense, 1 in-frame deletion, and 1 missense mutation (found in a thymoma sample). The mutations were scattered throughout the entire MEN1 coding region without specific clustering. Moreover, the only genotype-phenotype correlation observed was a preponderance of protein truncating mutations (frameshift and nonsense) in the Th-NET cohort. Th-NETs are uncommon in MEN1 syndrome. Our Th-NET cohort showed a male predominance. MEN1 mutations in the Th-NET patients did not show any specific clustering, but a preponderance of protein truncating mutations was observed in the MEN1 gene. Further analysis of Th-NET samples for genetic alterations and gene expression profiles will help to uncover the yet to be determined modifying factors in the pathophysiology of Th-NETs.

Background Because chronic kidney disease is an important comorbidity associated with primary hyperparathyroidism, we sought to evaluate the prevalence of chronic kidney disease and effects of parathyroidectomy on kidney function in patients with multiple endocrine neoplasia type 1–associated primary hyperparathyroidism. Methods We performed a retrospective analysis of 112 patients with multiple endocrine neoplasia type 1–associated primary hyperparathyroidism who had at least 1 operation for primary hyperparathyroidism at 2 tertiary referral centers. The preoperative and postoperative estimated glomerular filtration rates were compared. The prevalence of chronic kidney disease stage 3 or worse (estimated glomerular filtration rates less than 60 mL/min/1.73m2) in this cohort was compared to the rates in the US population reported by the Centers for Disease Control and Prevention. Results The median age at the time of parathyroidectomy was 36.5 years (range: 12–76 years). A total of 99 patients had biochemical remission. The rate of chronic kidney disease stage 3 or worse in patients with multiple endocrine neoplasia type 1–associated primary hyperparathyroidism was greater than that observed in the US population for ages 20–39 and 40–59 (5% [n = 2/44] vs 0.39% [n = 18/4565], P = .015 and 10% [n = 4/40] vs 2.31% (n = 89/3848), P = .015, respectively). We observed improved estimated glomerular filtration rates in those with chronic kidney disease stage 3 or worse postoperatively (48 vs 57 mL/min/1.73m2, P = .047). A successful parathyroidectomy normalized all 24-hour urine calcium excretion. Conclusion An indication for early parathyroidectomy should include estimated glomerular filtration rates less than 60mL/min/1.73m2 in patients with multiple endocrine neoplasia type 1–associated primary hyperparathyroidism.

We report here the identification of a gene associated with the hyperparathyroidism-jaw tumor (HPT-JT) syndrome. A single locus associated with HPT-JT (HRPT2) was previously mapped to chromosomal region 1q25-q32. We refined this region to a critical interval of 12 cM by genotyping in 26 affected kindreds. Using a positional candidate approach, we identified thirteen different heterozygous, germline, inactivating mutations in a single gene in fourteen families with HPT-JT. The proposed role of HRPT2 as a tumor suppressor was supported by mutation screening in 48 parathyroid adenomas with cystic features, which identified three somatic inactivating mutations, all located in exon 1. None of these mutations were detected in normal controls, and all were predicted to cause deficient or impaired protein function. HRPT2 is a ubiquitously expressed, evolutionarily conserved gene encoding a predicted protein of 531 amino acids, for which we propose the name parafibromin. Our findings suggest that HRPT2 is a tumor-suppressor gene, the inactivation of which is directly involved in predisposition to HPT-JT and in development of some sporadic parathyroid tumors.

GNB5 encodes the G protein β subunit 5 and is involved in inhibitory G protein signaling. Here, we report mutations in . GNB5 that are associated with heart-rate disturbance, eye disease, intellectual disability, gastric problems, hypotonia, and seizures in nine individuals from six families. We observed an association between the nature of the variants and clinical severity; individuals with loss-of-function alleles had more severe symptoms, including substantial developmental delay, speech defects, severe hypotonia, pathological gastro-esophageal reflux, retinal disease, and sinus-node dysfunction, whereas related heterozygotes harboring missense variants presented with a clinically milder phenotype. Zebrafish . gnb5 knockouts recapitulated the phenotypic spectrum of affected individuals, including cardiac, neurological, and ophthalmological abnormalities, supporting a direct role of GNB5 in the control of heart rate, hypotonia, and vision.

Genomic engineering by the guide RNA (gRNA)-directed CRISPR/CAS9 is rapidly becoming a method of choice for various biological systems. However, pressing concerns remain regarding its off-target activities and wide variations in efficacies. While next generation sequencing (NGS) has been primarily used to evaluate the efficacies and off-target activities of gRNAs, it only detects the imperfectly repaired double strand DNA breaks (DSB) by the error-prone non-homologous end joining (NHEJ) mechanism and may not faithfully represent the DSB activities because the efficiency of NHEJ-mediated repair varies depending on the local chromatin environment. Here we describe a reporter system for unbiased detection and comparison of DSB activities that promises to improve the chance of success in genomic engineering and to facilitate large-scale screening of CAS9 activities and gRNA libraries. Additionally, we demonstrated that the tolerances to mismatches between a gRNA and the corresponding target DNA can occur at any position of the gRNA, and depend on both specific gRNA sequences and CAS9 constructs used.

Objective To describe the clinical management of menorrhagia in a woman with hyperparathyroidism–jaw tumor syndrome (HPT-JT). Design Case report. Setting Large translation research hospital. Patient(s) A 26-year-old nulligravid woman with familial HPT-JT presented with life-long menorrhagia resistant to progesterone intrauterine device (IUD) therapy and a desire for fertility. Intervention(s) Aromatase inhibitor therapy. Main Outcome Measure(s) Clinical response to therapy and pregnancy. Result(s) Imaging demonstrated an enlarged endometrial lining and thickening of the junctional zone. At operative hysteroscopy, multiple atypical endometrial polyp-like lesions filled the entire uterine cavity and were removed. Histologic evaluation demonstrated the lesions to be adenomyomas with an abundance of aromatase expression. Postoperative treatment included an aromatase inhibitor. The patient's menorrhagia, which had previously been resistant to progesterone IUD therapy, resolved with the aromatase inhibitor. After 10 months of this treatment, the aromatase inhibitor was discontinued and a repeated hysteroscopy revealed a markedly improved uterine cavity. The patient subsequently became pregnant on her first natural cycle and delivered a healthy term infant. Conclusion(s) Aromatase inhibitors may represent a novel treatment for benign uterine pathology in HPT-JT.

Due to frequent multiplicity of tumors in multiple endocrine neoplasia type 1, it may be difficult to decide when to stop a parathyroid exploration. A fall of intraoperative serum PTH by a certain percentage during parathyroid surgery is often used as one criterion for ending the operation.We report two patients with primary hyperparathyroidism due to multiple endocrine neoplasia type 1 who had their first parathyroidectomy at the National Institutes of Health. In both cases, two and a half glands were removed, an extensive search was done for an occult parathyroid tumor, and intraoperative PTH decreased markedly to the lower limits of normal, suggesting a successful operation. Despite this, both patients became hypercalcemic within 3 d after the operation and showed persistent primary hyperparathyroidism. Detailed findings suggest the following course: chronic hypercalcemia had caused near total suppression of PTH secretion by an undiscovered parathyroid tumor (sleeping parathyroid tumor). When the hypercalcemia decreased after surgery due to the removal of the dominant parathyroid tumor(s), the abnormal yet previously suppressed tumor rapidly began to oversecrete PTH and thus caused postoperative hypercalcemia.Even a fall of the intraoperative PTH to the lower limits of the normal range cannot guarantee that removal of all parathyroid tumors has been complete in cases with multiple tumors. These findings likely reflect strikingly differing PTH secretory functions among distinct tumors in the same patient, with hypercalcemia at least from a dominant tumor suppressing PTH secretion by one or more other parathyroid tumors.

Background We reviewed reoperations for persistent or recurrent sporadic parathyroid adenoma to evaluate and compare our current results and outcomes to our previous experience. Methods From 1996 to 2008, 237 patients with persistent or recurrent hyperparathyroidism after failed operation underwent reoperation. Patients were re-explored with the assistance of non-invasive and sometimes invasive imaging. Results A missed adenoma was suspected pre-operatively in 163 patients. Reoperation resulted in long-term resolution of hypercalcemia in 92%. Adenomas were in entopic locations in 32%; the most frequent ectopic location was the thymus (20%). Sestamibi scanning and ultrasonography were the most successful non-invasive imaging studies (96% positive predictive value (PPV) and 84% PPV respectively). Forty-four percent of patients had a reoperation based solely on non-invasive imaging. Of the invasive procedures performed, arteriography resulted in the best localization (92% PPV). Permanent recurrent laryngeal nerve injury occurred in 1.8%. Conclusion Compared to our prior experience (1982–1995), outcomes remained similar (92% resolution of hypercalcemia and 1.8% recurrent nerve injury currently versus 96% and 1.3% previously). Fewer patients received invasive studies for pre-operative localization (56% vs 73%, respectively). The decreased use of invasive imaging is due to technical improvements and greater confidence in the combination of ultrasonography and sestamibi scanning.

A structurally divergent G-protein beta subunit expressed in brain and retina, Gbeta5, exhibits functional specialization in its protein-protein interactions in vitro. In retina, Gbeta5 has been isolated in a soluble complex with regulator of G-protein signaling RGS7. The function and molecular associations of Gbeta5 in brain are unknown. To identify tightly bound proteins associated with Gbeta5 in the brain, it was immunoaffinity-purified from a nonionic detergent extract of washed mouse brain membranes using an antibody directed against its N terminus. Elution with cognate peptide revealed a broad band of 55 kDa that coeluted with Gbeta5 on SDS-PAGE. The copurifying 55 kDa band was identified as an approximately 1:1 mixture of RGS6 and RGS7 by matrix-assisted laser desorption ionization mass spectroscopic analysis of tryptic peptides. Gbeta5 and RGS7 could be reciprocally coimmunoprecipitated from unfractionated brain membrane extracts confirming the tight association of native proteins. In contrast, immunoblotting of the peptide eluate revealed no copurifying Galphaq/11, Galphai1/2, Ggamma2, Ggamma3, or Ggamma7. These findings implicate RGS6 and RGS7 in the function of Gbeta5 in the brain and suggest that a large fraction of membrane-targeted Gbeta5 has no associated G subunit and therefore functions outside the canonical framework of G(beta)(gamma) interactions.

Antibodies generated to a synthetic decapeptide, RMHLRQYELL, representing the carboxyl-terminus of G s -α have been characterized in immunoblots and functional studies. This antibody, designated RM, reacts exclusively with a doublet of proteins of 52 and 45 kDa in immunoblots of bovine brain and wild-type S49 murine lymphoma cell membranes. No such reactivity is seen in membranes from cyc − S49 cells, which lack G s . RM blocks receptor-mediated activation of G s and adenylyl cyclase in membranes from wild-type S49 cells. RM could also immunoprecipitate adenylyl cyclase activity in detergent extracts from GTP[γ]S- or fluoride-preactivated bovine brain membranes; thus binding of α s to effector and carboxyl-terminal antibody was mutually compatible. Such experiments provide an approach for the elucidation of functionally relevant interactions of G-proteins with receptors and electors in the membrane.

Opiate receptors from NG108-15 neuroblastoma-glioma hybrid cell membranes were purified to apparent homogeneity in a form covalently labeled with the opiate affinity ligand 3-methylfentanylisothiocyanate (super-FIT). The purification procedure consists of five steps: quantitative labeling of opiate receptors in membranes with super-FIT; solubilization in a lubrol/3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate mixture; adsorption to and elution from a wheat germ agglutinin-Sepharose column; immunoaffinity chromatography on columns of immobilized anti-fentanyl; preparative gel electrophoresis in the presence of NaDodSO4. The protein was purified approximately 30,000-fold in 3% overall yield to a state in which there is 1 mol of super-FIT bound per mol of protein, corresponding to 21,000 pmol per mg of protein, the theoretically expected specific activity. The protein is glycosylated and migrates on NaDodSO4 gel electrophoresis with a Mr near 58,000. It has a strong tendency to dimerize, even in the presence of denaturing detergents, and it exists primarily as an oligomer in nondenaturing detergents.

Background Germline and somatic inactivating mutations in the HRPT2 gene occur in the inherited hyperparathyroidism-jaw tumor syndrome, in some cases of parathyroid cancer and in some cases of familial hyperparathyroidism. HRPT2 encodes parafibromin. To identify parafibromin interacting proteins we used the yeast two-hybrid system for screening a heart cDNA library with parafibromin as the bait. Results Fourteen parafibromin interaction positive preys representing 10 independent clones encoding actinin-2 were isolated. Parafibromin interacted with muscle alpha-actinins (actinin-2 and actinin-3), but not with non-muscle alpha-actinins (actinin-1 and actinin-4). The parafibromin-actinin interaction was verified by yeast two-hybrid, GST pull-down, and co-immunoprecipitation. Yeast two-hybrid analysis revealed that the N-terminal region of parafibromin interacted with actinins. In actin sedimentation assays parafibromin did not dissociate skeletal muscle actinins from actin filaments, but interestingly, parafibromin could also bundle/cross-link actin filaments. Parafibromin was predominantly nuclear in undifferentiated proliferating myoblasts (C2C12 cells), but in differentiated C2C12 myotubes parafibromin co-localized with actinins in the cytoplasmic compartment. Conclusion These data support a possible contribution of parafibromin outside the nucleus through its interaction with actinins and actin bundling/cross-linking. These data also suggest that actinins (and actin) participate in sequestering parafibromin in the cytoplasmic compartment.