Adaptation of a Commercial NAD+ Quantification Kit to Assay the Base-Exchange Activity and Substrate Preferences of SARM1

Here, we report an adapted protocol using the Promega NAD/NADH-Glo™ Assay kit. The assay normally allows quantification of trace amounts of both oxidized and reduced forms of nicotinamide adenine dinucleotide (NAD) by enzymatic cycling, but we now show that the NAD analog 3-acetylpyridine adenine dinucleotide (AcPyrAD) also acts as a substrate for this enzyme-cycling assay. In fact, AcPyrAD generates amplification signals of a larger amplitude than those obtained with NAD. We exploited this finding to devise and validate a novel method for assaying the base-exchange activity of SARM1 in reactions containing NAD and an excess of the free base 3-acetylpyridine (AcPyr), where the product is AcPyrAD. We then used this assay to study competition between AcPyr and other free bases to rank the preference of SARM1 for different base-exchange substrates, identifying isoquinoline as a highly effect substrate that completely outcompetes even AcPyr. This has significant advantages over traditional HPLC methods for assaying SARM1 base exchange as it is rapid, sensitive, cost-effective, and easily scalable. This could represent a useful tool given current interest in the role of SARM1 base exchange in programmed axon death and related human disorders. It may also be applicable to other multifunctional NAD glycohydrolases (EC 3.2.2.6) that possess similar base-exchange activity.

Deregulated mitochondrial quality control, the heel of Achilles in elucidating the role of autophagy in SARM1-mediated axon degeneration

Autophagic dysfunction in neurodegenerative diseases is being extensively studied, yet the exact mechanism of macroautophagy/autophagy in axon degeneration is still elusive. A recent study by Kim et al. links autophagic stress to the sterile α and toll/interleukin 1 receptor motif containing protein 1 (SARM1)-dependent core axonal degeneration program, providing a new insight into the role of autophagy in axon degeneration. In the classical Wallerian axon degeneration model of axotomy, disruption of axonal transport destroys the coordinated activity of pro-survival and pro-degenerative factors in the axoplasm and activates the NADase activity of SARM1, thus triggering the axonal self-destruction program. However, the mechanism for SARM1 activation in the chronic neurodegenerative disorders is more complex. Mitochondrial defects and oxidative stress contribute to the activation of SARM1, while mitophagy can inhibit mitochondrial dysfunction and promote the clearance of SARM1 on mitochondria, thus protecting against neuronal degeneration. Therefore, in-depth elucidation of the underlying mechanisms of mitophagy during axonal degeneration can help develop promising strategies for the prevention and treatment of various neurodegenerative disorders.

High prevalence of adrenal cortical adenomas in patients with cerebral meningiomas

PURPOSE

Adrenal cortical adenomas (ACAs) represent one of the most common endocrine neoplasms. Recently, a genetic syndrome, characterized by tumor-suppressor ARMC5-gene mutations and causing primary macronodular bilateral adrenal hyperplasia with concomitant meningiomas of the central nervous system, has been described. Apart from this rare disorder and despite the well-known influence of steroid hormones on meningiomas, no data are available about the association between ACAs and meningiomas.

METHODS

We investigated the prevalence of ACAs in a group of patients with cerebral meningioma undergoing unenhanced chest CT scans before attending surgical treatment. Patients with meningioma were age- and sex-matched in a 1:3 ratio with hospitalized patients for COVID-19.

RESULTS

Fifty-six patients with meningioma were included and matched with 168 control patients with COVID-19. One-hundred forty-four (66.1%) were female and the median age was 63 years. Twenty ACAs were detected in the overall population (8.9% of the subjects): 10 in patients with meningioma (18%) and the remaining 10 (6%) in the control group (p = 0.007). Multivariate analysis showed that age and presence of meningioma were statistically associated with the presence of ACAs (p = 0.01, p = 0.008).

CONCLUSION

We report, for the first time, a higher prevalence of ACAs in patients with meningioma as compared to age- and sex-matched controls. Larger studies are needed to confirm our data and to clarify the characteristics of the ACAs in patients with meningioma. Whether the detection of ACAs should prompt a neuroimaging evaluation to exclude the presence of meningiomas needs also to be considered.

The expression and prognostic significance of PIK3CB in lung adenocarcinoma

OBJECTIVE

The aim of this study was to explore the expression and prognostic significance of PIK3CB in lung adenocarcinoma (LUAD) and to analyse the possible molecular mechanism that promotes LUAD development.

METHODS

Differences of PIK3CB expression at transcriptional level between LUAD and normal tissues were analysed with the Timer and UALCAN databases. Then, immunohistochemical staining was performed to investigate PIK3CB expression at the protein level, and relationships between PIK3CB and clinical characteristics were accessed. Univariate and multivariate Cox regression were performed to identify the independent prognostic risk factors for LUAD. Genetic alterations were analysed using the cBioPortal database. The main coexpressed genes and enrichment pathways of PIK3CB were estimated with the LinkedOmics database.

RESULTS

Compared with normal tissues, PIK3CB was higherly expressed in LUAD at the transcriptional level and protein level, respectively. PIK3CB expression was closely related to prognosis of LUAD patients, and PIK3CB protein expression was associated with lymph node metastasis and pathological differentiation, but not related to sex, age, pleural invasion, vascular invasion, tumour site, tumour size or clinical stage. PIK3CB and tumour size were independent risk factors for LUAD patients. The expression of PIK3CB was negatively correlated with AKT1 and AKT2, but there was no significant correlation with AKT3, and strong positive correlations with ARMC8, DNAJC13 and PIK3R4. The main enrichment pathways of PIK3CB and related genes included adherens junctions and the phosphatidylinositol signalling pathways, ErbB signalling pathways, Hedgehog signalling pathways, and C-type lectin receptor signalling pathways. Therefore, we hypothesized that PIK3CB expression did not promote LUAD development through the classical PI3K/AKT pathway.

CONCLUSION

High PIK3CB expression was associated with the development of LUAD and worse prognosis. PIK3CB was an independent risk factor for LUAD patients. Therefore, this study provides a reliable reference for the prognostic assessment and targeted therapy for LUAD patients.

cADPR induced calcium influx mediates axonal degeneration caused by paclitaxel

Activation of the NAD hydrolase domain of Sarm1 mediates axonal degeneration caused by chemotherapy drugs, but the downstream events are unknown. In this issue, Li and colleagues (2021. J. Cell Biol.https://doi.org/10.1083/jcb.202106080) demonstrate that cADPR, a breakdown product of NAD, mediates paclitaxel-induced axonal degeneration by promoting influx of calcium into the axons.

Enrichment of SARM1 alleles encoding variants with constitutively hyperactive NADase in patients with ALS and other motor nerve disorders

SARM1, a protein with critical NADase activity, is a central executioner in a conserved programme of axon degeneration. We report seven rare missense or in-frame microdeletion human SARM1 variant alleles in patients with amyotrophic lateral sclerosis (ALS) or other motor nerve disorders that alter the SARM1 auto-inhibitory ARM domain and constitutively hyperactivate SARM1 NADase activity. The constitutive NADase activity of these seven variants is similar to that of SARM1 lacking the entire ARM domain and greatly exceeds the activity of wild-type SARM1, even in the presence of nicotinamide mononucleotide (NMN), its physiological activator. This rise in constitutive activity alone is enough to promote neuronal degeneration in response to otherwise non-harmful, mild stress. Importantly, these strong gain-of-function alleles are completely patient-specific in the cohorts studied and show a highly significant association with disease at the single gene level. These findings of disease-associated coding variants that alter SARM1 function build on previously reported genome-wide significant association with ALS for a neighbouring, more common SARM1 intragenic single nucleotide polymorphism (SNP) to support a contributory role of SARM1 in these disorders. A broad phenotypic heterogeneity and variable age-of-onset of disease among patients with these alleles also raises intriguing questions about the pathogenic mechanism of hyperactive SARM1 variants.

Armadillo-repeat kinesin1 interacts with Arabidopsis atlastin RHD3 to move ER with plus-end of microtubules

In living cells, dynamics of the endoplasmic reticulum (ER) are driven by the cytoskeleton motor machinery as well as the action of ER-shaping proteins such as atlastin GTPases including RHD3 in Arabidopsis. It is not known if the two systems interplay, and, if so, how they do. Here we report the identification of ARK1 (Armadillo-Repeat Kinesin1) via a genetic screen for enhancers of the rhd3 mutant phenotype. In addition to defects in microtubule dynamics, ER organization is also defective in mutants lacking a functional ARK1. In growing root hair cells, ARK1 comets predominantly localize on the growing-end of microtubules and partially overlap with RHD3 in the cortex of the subapical region. ARK1 co-moves with RHD3 during tip growth of root hair cells. We show that there is a functional interdependence between ARK1 and RHD3. ARK1 physically interacts with RHD3 via its armadillo domain (ARM). In leaf epidermal cells where a polygonal ER network can be resolved, ARK1, but not ARK1ΔARM, moves together with RHD3 to pull an ER tubule toward another and stays with the newly formed 3-way junction of the ER for a while. We conclude that ARK1 acts together with RHD3 to move the ER on microtubules to generate a fine ER network.

High expression of adrenal P450 aromatase (CYP19A1) in association with ARMC5-primary bilateral macronodular adrenocortical hyperplasia

Primary bilateral macronodular adrenocortical hyperplasia (PBMAH) is a rare cause of ACTH-independent Cushing syndrome (CS), which has been associated with ectopic G-protein coupled receptors (GPCRs) in the adrenal cortex. We recently studied a 51-year-old male with PBMAH who presented with severe CS and hyperestronemia, manifesting clinically with a Cushingoid appearance, gynecomastia, and telangiectasias. Analysis of adrenal tissues following bilateral adrenalectomy showed high expression of P450 aromatase (CYP19A1). The patient carried a germline non-sense pathogenic variant in ARMC5 (p.R173*), with two independent somatic pathogenic variants identified in the right (p.S571*) and left (p.Q235*) adrenal tissues, respectively. The expression of ARMC5 was drastically decreased in the hyperplastic regions when compared to either the adjacent non-hyperplastic regions and samples from PBMAH without pathogenic variants in ARMC5. We found expression of CYP19A1 in other cases of PBMAH, although there were no differences in aromatase expression between ARMC5-mutant and ARMC5-non-mutant cases. We conclude that in select cases, PBMAH can be associated with aromatase expression resulting in elevated estrogens, irrespective of sex. Additionally, CYP19A1 expression does not appear to depend on the ARMC5 variant status.

Genetics of Hypertension in African Americans and Others of African Descent

Hypertension is the leading cause of cardiovascular disease in the United States, affecting up to one-third of adults. When compared to other ethnic or racial groups in the United States, African Americans and other people of African descent show a higher incidence of hypertension and its related comorbidities; however, the genetics of hypertension in these populations has not been studied adequately. Several genes have been identified to play a role in the genetics of hypertension. They include genes regulating the renin-aldosterone-angiotensin system (RAAS), such as Sodium Channel Epithelial 1 Beta Subunit (SCNN1B), Armadillo Repeat Containing 5 (ARMC5), G Protein-Coupled Receptor Kinase 4 (GRK4), and Calcium Voltage-Gated Channel Subunit Alpha1 D (CACNA1D). In this review, we focus on recent genetic findings available in the public domain for potential differences between African Americans and other populations. We also cover some recent and relevant discoveries in the field of low-renin hypertension from our laboratory at the National Institutes of Health. Understanding the different genetics of hypertension among various groups is essential for effective precision-guided medical therapy of high blood pressure.

Whole-genome sequencing revealed armadillo repeat containing 5 (ARMC5) mutation in a Chinese family with ACTH-independent macronodular adrenal hyperplasia

Primary macronodular adrenal hyperplasia (PMAH), also known in the past as bilateral macronodular adrenalhyperplasia or adrenocorticotropin (ACTH)-independent macronodular adrenal hyperplasia, is a rare type of Cushing's syndrome (CS) and is associated with bilateralenlargement of the adrenal glands. It accounts for <1% of all endogenous cases of CS. In order toidentify the pathogenic mutations in the causative gene of (AIMAH pedigrees, Whole-genome sequencing of three patients in family I was used to retrieve candidate causative genes. Meanwhile, the causative gene was identified by Sanger sequencing from the two pedigrees. Sequencing of ARMC5 exons of three patients was carried out to identify somatic mutations. Moreover, haploid clone of one tumor DNA sample was conducted. ARMC5 was the causative gene of two pedigrees confirmed by whole-genome sequencing (WGA) and Sanger sequencing. The variant sites of the two families were c.C943T (p.R315W) and c.C1960T (p.R654X), respectively. Autosomal dominant inheritance of AIMAH was confirmed by genotypes of one family member. Several somatic mutations were discovered in tumor DNA samples. In addition, haploid clone of tumor DNA was confirmed by germline mutation and somaticmutation, which suggested the pathogenic mechanism of "two-hit-model." ARMC5 was the causative gene of AIMAH pedigrees. This AIMAH in this study presented autosomal dominant inheritance, fitting to Mendelian inheritance law. However, the pathogenic mode of this disease showed as compound heterozygote.

ARMC5 mutations in familial and sporadic primary bilateral macronodular adrenal hyperplasia

To investigate Armadillo repeat-containing 5 (ARMC5) mutations in Chinese patients with familial and sporadic primary bilateral macronodular adrenal hyperplasia (PBMAH), we performed clinical data collection and ARMC5 sequencing for three PBMAH families and 23 sporadic PBMAH patients. ARMC5 pathogenic germline mutations were identified in all 3 PBMAH families. Secondary ARMC5 somatic mutations were found in two adrenal nodules from two PBMAH family members with ARMC5 germline mutations. PBMAH family members with ARMC5 pathogenic germline mutations displayed various clinical manifestations. ARMC5 pathogenic germline mutations were identified in 5 sporadic PBMAH patients among whom one patient displayed both hypercortisolism and primary aldosteronism. We detected a total of 10 ARMC5 pathogenic mutations, of which 8 had not been previously reported. Our results suggest that ARMC5 pathogenic germline mutations are common in familial and sporadic Chinese PBMAH patients, and demonstrate the importance of ARMC5 screening in PBMAH family members to detect patients with insidious PBMAH.

The role of ARMC5 in human cell cultures from nodules of primary macronodular adrenocortical hyperplasia (PMAH)

The participation of aberrant receptors and intra-adrenal ACTH in hyperplastic tissue are considered mechanisms that regulate hypercortisolism in PMAH. Additionally, germline ARMC5 mutations have been described as the most frequent genetic abnormality found in patients diagnosed with PMAH. Previous functional studies analyzed ARMC5 role using H295R cells. Therefore, we investigated the role of ARMC5 in cell cultures obtained from PMAH nodules containing steroidogenic cells, aberrant receptors and intra-adrenal ACTH. ARMC5 silencing in non-mutated PMAH cell cultures decreased steroidogenesis-related genes and increased CCNE1 mRNA expression and proliferative capacity without affecting cell viability. Additionally, ARMC5 overexpression induced cell death in PMAH mutated cell cultures, thereby decreasing cell viability. We confirmed the role of ARMC5 as an important pro-apoptotic protein involved in PMAH-related steroidogenesis. We also report for the first time the involvement of ARMC5 in controlling proliferation and regulating cell cycle in PMAH cell cultures; these effects need to be explored further.

Genetics of Adrenocortical Development and Tumors

This article links the understanding of developmental physiology of the adrenal cortex to adrenocortical tumor formation. Many molecular mechanisms that lead to formation of adrenocortical tumors have been discovered via next-generation sequencing approaches. The most frequently mutated genes in adrenocortical tumors are also factors in normal adrenal development and homeostasis, including those that alter the p53 and Wnt/β-catenin pathways. In addition, dysregulated protein kinase A signaling and ARMC5 mutations have been identified as key mediators of adrenocortical tumorigenesis. The growing understanding of genetic changes that orchestrate adrenocortical development and disease pave the way for potential targeted treatment strategies.

A multicenter experience on the prevalence of ARMC5 mutations in patients with primary bilateral macronodular adrenal hyperplasia: from genetic characterization to clinical phenotype

ARMC5 mutations have recently been identified as a common genetic cause of primary bilateral macronodular adrenal hyperplasia (PBMAH). We aimed to assess the prevalence of ARMC5 germline mutations and correlate genotype with phenotype in a large cohort of PBMAH patients. A multicenter study was performed, collecting patients from different endocrinology units in Italy. Seventy-one PBMAH patients were screened for small mutations and large rearrangements in the ARMC5 gene: 53 were cortisol-secreting (two with a family history of adrenal hyperplasia) and 18 were non-secreting cases of PBMAH. Non-mutated and mutated patients' clinical phenotypes were compared and related to the type of mutation. A likely causative germline ARMC5 mutation was only identified in cortisol-secreting PBMAH patients (one with a family history of adrenal hyperplasia and ten apparently sporadic cases). Screening in eight first-degree relatives of three index cases revealed four carriers of an ARMC5 mutation. Evidence of a second hit at somatic level was identified in five nodules. Mutated patients had higher cortisol levels (p = 0.062), and more severe hypertension and diabetes (p < 0.05). Adrenal glands were significantly larger, with a multinodular phenotype, in the mutant group (p < 0.01). No correlation emerged between type of mutation and clinical parameters. ARMC5 mutations are frequent in cortisol-secreting PBMAH and seem to be associated with a particular pattern of the adrenal masses. Their identification may have implications for the clinical care of PBMAH cases and their relatives.

Analysis of ARMC5 expression in human tissues

Mutations in ARMC5 gene have been recently identified as the main cause of Primary Macronodular Adrenocortical Hyperplasia (PMAH). PMAH patients have an ARMC5 germline mutation and, in addition, somatic tissue-specific mutations. This is consistent with the two-hit hypothesis of tumorigenesis and suggests that ARMC5 may be a tumor suppressor gene. As its function is still unclear, we analyzed the expression of the four ARMC5 isoforms in 46 normal human tissues. This showed that at least one ARMC5 isoform is ubiquitously expressed throughout the body; however, only 7 tissues expressed all isoforms, including the adrenal gland and the brain. Interestingly, the highest expression for ARMC5 in the brain is in the pituitary gland. The isoform ARMC5-003 was present in most endocrine tissues including the pituitary, adrenal glands and the pancreas. In this report, we present new data about the ARMC5 expression pattern in human tissues; its wide expression in brain, pituitary gland and other tissues suggest that mutations may be responsible for additional pathologies, beyond what is already known in PMAH and meningiomas.

Do patients with incidentally discovered bilateral adrenal nodules represent an early form of ARMC5-mediated bilateral macronodular hyperplasia?

Bilateral adrenal macronodular hyperplasia (BMAH) is a rare form of Cushing's syndrome characterised by the presence of bilateral secretory adrenal nodules and hypercortisolism. Familial studies support a genetic basis for BMAH, and the disease has been linked to mutations in ARMC5, a gene shown to have a tumour suppressor-like action in the development of adrenal nodules. This study aimed to investigate whether ARMC5 mutations play a role in the development of incidentally discovered bilateral adrenal nodules. We investigated 39 patients with incidentally discovered bilateral adrenal nodules >0.8 cm in diameter who underwent extensive biochemical testing to look for signs of subclinical hypercortisolism. Genomic DNA was analysed by Sanger sequencing, using primers targeted to ARMC5 transcripts. Of the 39 patients included in our study, three were identified as having variants in ARMC5. Two of these are unlikely to be clinically significant, but there is evidence that the third mutation, Chr16:g.31476122;c.1778G>C (p.Arg593Pro), may be pathogenic. Another variant, affecting the same amino-acid residue c.1777C>T (p.Arg593Trp), has been identified previously in two studies of BMAH patients, where it has been shown to segregate with disease in one BMAH family. This patient had biochemical evidence of hypercortisolism in the absence of overt Cushing's syndrome, and underwent bilateral adrenalectomy separated in time. The presence of a probably clinically significant mutation in ARMC5 in one patient with bilateral adrenal incidentalomas adds to the growing body of evidence in support of ARMC5 as a critical mediator of adrenal nodule development. In addition, the absence of significant ARMC5 mutations in 38 of our patients represents an important negative finding, demonstrating the degree of variability within the pathogenesis of adrenal nodule development.

ARMC5 mutations in a large French-Canadian family with cortisol-secreting β-adrenergic/vasopressin responsive bilateral macronodular adrenal hyperplasia

BACKGROUND

Bilateral macronodular adrenal hyperplasia (BMAH) is a rare cause of Cushing's syndrome (CS) and its familial clustering has been described previously. Recent studies identified that ARMC5 mutations occur frequently in BMAH, but the relation between ARMC5 mutation and the expression of aberrant G-protein-coupled receptor has not been examined in detail yet.

METHODS

We studied a large French-Canadian family with BMAH and sub-clinical or overt CS. Screening was performed using the 1-mg dexamethasone suppression test (DST) in 28 family members. Screening for aberrant regulation of cortisol by various hormone receptors were examined in vivo in nine individuals. Sequencing of the coding regions of ARMC5 gene was carried out.

RESULTS

Morning ambulating cortisol post 1 mg DST were >50 nmol/l in 5/8 members in generation II (57-68 years old), 9/22 in generation III (26-46 years old). Adrenal size was enlarged at different degrees. All affected patients increased cortisol following upright posture, insulin-induced hypoglycemia and/or isoproterenol infusion. β-blockers led to the reduction of cortisol secretion in all patients with the exception of two who had adrenalectomies because of β-blockers intolerance. We identified a heterozygous germline variant in the ARMC5 gene c.327_328insC, (p.Ala110Argfs*9) in nine individuals with clinical or subclinical CS, in four out of six individuals with abnormal suppression to dexamethasone at initial investigation and one out of six individuals with current normal clinical screening tests.

CONCLUSIONS

Systematic screening of members of the same family with hereditary BMAH allows the diagnosis of unsuspected subclinical CS associated with early BMAH. The relation between the causative ARMC5 mutation and the reproducible pattern of aberrant β-adrenergic and V1-vasopressin receptors identified in this family remains to be elucidated.

5th International ACC Symposium: The New Genetics of Benign Adrenocortical Neoplasia: Hyperplasias, Adenomas, and Their Implications for Progression into Cancer

Genetic tools for the analysis of human tumors have developed rapidly over the past 20 years. Adrenocortical neoplasms have been subject to multiple analyses using these new genetic tools. Analysis of adrenocortical carcinomas (ACCs) has been complicated by the fact that these tumors tend to exhibit multiple somatic abnormalities, so that identifying driver mutations is complex task. In contrast, benign adrenocortical neoplasms have proven to be a fertile ground for the identification of the genetic causes of adrenocortical adenomas, as well as a variety of adrenocortical hyperplasia. Analysis of cortisol-producing adrenocortical adenomas has revealed alterations leading to enhanced signaling through the cAMP-dependent protein kinase (PKA) pathway. In contrast, macronodular cortisol-producing neoplasias have been shown to result from mutations in the ARMC5 gene, whose function is not yet quite so clear. In contrast, adrenal tumors resulting in excess production of the blood pressure hormone aldosterone almost always result from abnormalities of calcium handling, both in single adenomas and in bilateral hyperplasias. In both cases, there is elevation of a signaling pathway responsible both for hormone secretion and for gland growth and maintenance, thus confirming the linkage of these two output of cellular physiology. The connection between the benign hyperplasia observed in these states and adrenocortical carcinogenesis is not nearly as clear, although genetic studies are beginning to elucidate the relationship between benign and malignant tumors of this gland.

Genetics of primary bilateral macronodular adrenal hyperplasia: a model for early diagnosis of Cushing's syndrome?

Long-term consequences of cortisol excess are frequent despite appropriate treatment after cure of Cushing's syndrome. This might be due to diagnostic delay, often difficult to reduce in rare diseases. The identification of a genetic predisposing factor might help to improve early diagnosis by familial screening. Primary bilateral macronodular adrenal hyperplasia (PBMAH) is a rare cause of Cushing's syndrome. Hypercortisolism in PBMAH is most often diagnosed between the fifth and sixth decades of life. The bilateral nature of the adrenocortical tumors and the occurrence of rare clear familial forms suggest a genetic origin. Indeed, a limited subset of PBMAH can be observed as part of multiple tumors syndromes due to alterations of the APC, Menin or Fumarate Hydratase genes. Rare variants of the phosphodiesterases PDE11A have been associated with PBMAH. The recent identification of ARMC5 germline alterations in 25-50% of PBMAH patients without obvious familial history or associated tumors opens new perspectives. ARMC5 alterations follow the model of a tumor suppressor gene: a first germline inactivating mutation of this 16p located gene is followed by a somatic secondary hit on the other allele (inactivating mutation or allelic loss). Functional studies demonstrate that ARMC5 controls apoptosis and steroid synthesis. The phenotype of index cases patients with the mutation seems more severe than the one of WT index cases. However, phenotype variability within a family is often observed. This review summarizes the genetics of PBMAH, focusing on ARMC5, which offer new perspectives for early diagnosis of Cushing's syndrome.

Primary Aldosteronism and ARMC5 Variants

CONTEXT

Primary aldosteronism is one of the leading causes of secondary hypertension, causing significant morbidity and mortality. A number of genetic defects have recently been identified in primary aldosteronism, whereas we identified mutations in ARMC5, a tumor-suppressor gene, in cortisol-producing primary macronodular adrenal hyperplasia.

OBJECTIVE

We investigated a cohort of 56 patients who were referred to the National Institutes of Health for evaluation of primary aldosteronism for ARMC5 defects.

METHODS

Patients underwent step-wise diagnosis, with measurement of serum aldosterone and plasma renin activity followed by imaging, saline suppression and/or oral salt loading tests, plus adrenal venous sampling. Cortisol secretion was also evaluated; unilateral or bilateral adrenalectomy was performed, if indicated. DNA, protein, and transfection studies in H295R cells were conducted by standard methods.

RESULTS

We identified 12 germline ARMC5 genetic alterations in 20 unrelated and two related individuals in our cohort (39.3%). ARMC5 sequence changes in 6 patients (10.7%) were predicted to be damaging by in silico analysis. All affected patients carrying a variant predicted to be damaging were African Americans (P = .0023).

CONCLUSIONS

Germline ARMC5 variants may be associated with primary aldosteronism. Additional cohorts of patients with primary aldosteronism and metabolic syndrome, particularly African Americans, should be screened for ARMC5 sequence variants because these may underlie part of the known increased predisposition of African Americans to low renin hypertension.

ARMC5 Mutations in a Large Cohort of Primary Macronodular Adrenal Hyperplasia: Clinical and Functional Consequences

CONTEXT

Primary bilateral macronodular adrenal hyperplasia (PBMAH) is a rare cause of primary adrenal Cushing's syndrome (CS). ARMC5 germline mutations have been identified recently in PBMAH.

OBJECTIVE

To determine the prevalence of ARMC5 mutations and analyze genotype-phenotype correlation in a large cohort of unrelated PBMAH patients with subclinical or clinical CS.

PATIENTS AND METHODS

ARMC5 was sequenced in 98 unrelated PBMAH index cases. PBMAH was identified by bilateral adrenal nodular enlargement on computed tomography scan. The effect on apoptosis of ARMC5 missense mutants was tested in H295R and HeLa cells. Clinical and hormonal data were collected including midnight and urinary free cortisol levels, ACTH, androgens, renin/aldosterone ratio, cortisol after overnight dexamethasone suppression test, cortisol and 17-hydroxyprogesterone after ACTH 1-24 stimulation and illegitimate receptor responses. Computed tomography and histological reports were analyzed.

RESULTS

ARMC5-damaging mutations were identified in 24 patients (26%). The missense mutants and the p.F700del deletion were unable to induce apoptosis in both H295R and HeLa cell lines, unlike the wild-type gene. ARMC5-mutated patients showed an overt CS more frequently, compared to wild-type patients: lower ACTH, higher midnight plasma cortisol, urinary free cortisol, and cortisol after dexamethasone suppression test (P = .003, .019, .006, and <.001, respectively). Adrenals of patients with mutations were bigger and had a higher number of nodules (P = .001 and <.001, respectively).

CONCLUSIONS

ARMC5 germline mutations are common in PBMAH. Index cases of mutation carriers show a more severe hypercortisolism and larger adrenals. ARMC5 genotyping may help to identify clinical forms of PBMAH better and may also allow earlier diagnosis of this disease.

The genetics of adrenocortical tumors

Advances in genomics accelerated greatly progress in the study of the genetics adrenocortical tumors. Bilateral nodular hyperplasias causing Cushing's syndrome are frequently caused by germline alterations leading to cAMP/PKA pathway activation (micronodular) and ARMC5 inactivation (macronodular). Somatic mutations of β-catenin and PRKACA are observed in non secreting or cortisol producing adenomas, respectively. Alterations of the β-catenin (CTNN1B, ZNFR3) or TP53 pathways are found in carcinomas. Mutations in cancers are more common in aggressive tumors and correlate with transcriptome or methylation profiles. Identification of these alterations helps to refine the molecular classification of these tumors and to develop molecular diagnostic tools.

Molecular and clinical evidence for an ARMC5 tumor syndrome: concurrent inactivating germline and somatic mutations are associated with both primary macronodular adrenal hyperplasia and meningioma

CONTEXT

Primary macronodular adrenal hyperplasia (PMAH) is a rare cause of Cushing's syndrome, which may present in the context of different familial multitumor syndromes. Heterozygous inactivating germline mutations of armadillo repeat containing 5 (ARMC5) have very recently been described as cause for sporadic PMAH. Whether this genetic condition also causes familial PMAH in association with other neoplasias is unclear.

OBJECTIVE

The aim of the present study was to delineate the molecular cause in a large family with PMAH and other neoplasias.

PATIENTS AND METHODS

Whole-genome sequencing and comprehensive clinical and biochemical phenotyping was performed in members of a PMAH affected family. Nodules derived from adrenal surgery and pancreatic and meningeal tumor tissue were analyzed for accompanying somatic mutations in the identified target genes.

RESULTS

PMAH presenting either as overt or subclinical Cushing's syndrome was accompanied by a heterozygous germline mutation in ARMC5 (p.A110fs*9) located on chromosome 16. Analysis of tumor tissue showed different somatic ARMC5 mutations in adrenal nodules supporting a second hit hypothesis with inactivation of a tumor suppressor gene. A damaging somatic ARMC5 mutation was also found in a concomitant meningioma (p.R502fs) but not in a pancreatic tumor, suggesting biallelic inactivation of ARMC5 as causal also for the intracranial meningioma.

CONCLUSIONS

Our analysis further confirms inherited inactivating ARMC5 mutations as a cause of familial PMAH and suggests an additional role for the development of concomitant intracranial meningiomas.

Genetic basis of bilateral macronodular hyperplasia

OBJECTIVE

To review the genetic basis of bilateral macronodular hyperplasia (BMAH).

METHODS

Case presentation, review of literature, table, and bullet point conclusions.

RESULTS

BMAH, also known as adrenocorticotropic hormone (ACTH)-independent macronodular hyperplasia (AIMH), can cause Cushing syndrome or mild hypercortisolism. Recent studies have demonstrated that hyperplastic tissue reproduces ectopic ACTH, implying that BMAH is the more proper term, as the syndrome is not ACTH-independent. BMAH was thought to be sporadic, but recent data have shown that there is likely a genetic component in the majority of cases. Mutations in ARMC5, a putative suppressor gene, have been found in many familial cases of BMAH and are thought to be responsible for the disorder. As these nodules inefficiently produce cortisol, large nodules are required to produce a clinical syndrome. ARMC5 likely requires a second somatic mutation to become clinically apparent. Clinical manifestations are not generally noted until the fifth to sixth decades of life.

CONCLUSION

BMAH is an underrecognized genetic condition that can lead to Cushing syndrome and should be screened for in patients and susceptible family members.

ARMC5 mutations are common in familial bilateral macronodular adrenal hyperplasia

CONTEXT

Bilateral macronodular adrenal hyperplasia (BMAH) is a rare form of adrenal Cushing's syndrome. Familial cases have been reported, but at the time we conducted this study, the genetic basis of BMAH was unknown. Recently, germline variants of armadillo repeat containing 5 (ARMC5) in patients with isolated BMAH and somatic, second-hit mutations in tumor nodules, were identified.

OBJECTIVE

Our objective was to identify the genetic basis of familial BMAH.

DESIGN

We performed whole exome capture and sequencing of 2 affected individuals from each of 4 BMAH families (BMAH-01, BMAH-02, BMAH-03, and BMAH-05). Based on clinical evaluation, there were 7, 3, 3, and 4 affected individuals in these families, respectively. Sanger sequencing of ARMC5 was performed in 1 other BMAH kindred, BMAH-06.

RESULTS

Exome sequencing identified novel variants Chr16:g.31477540, c.2139delT, p.(Thr715Leufs*1) (BMAH-02) and Chr16:g.31473811, c.943C→T, p.(Arg315Trp) (BMAH-03) in ARMC5 (GRch37/hg19), validated by Sanger sequencing. BMAH-01 had a recently reported mutation Chr16:g.31476121, c.1777C→T, p.(Arg593Trp). Sanger sequencing of ARMC5 in BMAH-06 identified a previously reported mutation, Chr16:g. 31473688; c.799C→T, p.(Arg267*). The genetic basis of BMAH in BMAH-05 was not identified.

CONCLUSIONS

Our studies have detected ARMC5 mutations in 4 of 5 BMAH families tested, confirming that these mutations are a frequent cause of BMAH. Two of the 4 families had novel mutations, indicating allelic heterogeneity. Preclinical evaluation did not predict mutation status. The ARMC5-negative family had unusual prominent hyperaldosteronism. Further studies are needed to determine the penetrance of BMAH in ARMC5 mutation-positive relatives of affected patients, the practical utility of genetic screening and genotype-phenotype correlations.

ARMC5 mutations are a frequent cause of primary macronodular adrenal Hyperplasia

CONTEXT

Primary macronodular adrenal hyperplasia (PMAH) is a rare cause of Cushing's syndrome, usually characterized by functioning adrenal macronodules and increased cortisol production. Familial clustering of PMAH has been described, suggesting an inherited genetic cause for this condition.

OBJECTIVE

The aim of the present study was to identify the gene responsible for familial PMAH.

PATIENTS AND METHODS

Forty-seven individuals of a Brazilian family with PMAH were evaluated. A single-nucleotide polymorphism-based genome-wide linkage analysis followed by whole-exome sequencing were then performed in selected family members. Additionally, 29 other patients with PMAH and 125 randomly selected healthy individuals were studied to validate the genetic findings. Moreover, PMAH tissue was also analyzed through whole-exome sequencing, conventional sequencing, and microsatellite analysis.

RESULTS

A heterozygous germline variant in the ARMC5 gene (p.Leu365Pro) was identified by whole-exome sequencing in a candidate genomic region (16p11.2). Subsequently, the same variant was confirmed by conventional sequencing in all 16 affected family members. The variant was predicted to be damaging by in silico methods and was not found in available online databases or in the 125 selected healthy individuals. Seven additional ARMC5 variants were subsequently identified in 5 of 21 patients with apparently sporadic PMAH and in 2 of 3 families with the disease. Further molecular analysis identified a somatic mutational event in 4 patients whose adrenal tissue was available.

CONCLUSIONS

Inherited autosomal dominant mutations in the ARMC5 gene are a frequent cause of PMAH. Biallelic inactivation of ARMC5 is consistent with its role as a potential tumor suppressor gene.

Primary bilateral macronodular adrenal hyperplasia

PURPOSE OF REVIEW

Primary bilateral macronodular adrenal hyperplasia is a rare cause of Cushing's syndrome and is more often diagnosed as bilateral adrenal incidentalomas with subclinical cortisol production. We summarize the recent insights concerning its epidemiology, diagnosis, genetics, pathophysiology, and therapeutic options.

RECENT FINDINGS

Recent publications have modified our notions on the genetics and pathophysiology of bilateral macronodular adrenal hyperplasia. Combined germline and somatic mutations of armadillo repeat containing 5 gene were identified in familial cases, in approximately 50% of apparently sporadic cases and in the relatives of index cases; genetic testing should allow early diagnosis in the near future. The recent finding of ectopic adrenocortical production of adrenocorticotropic hormone in clusters of bilateral macronodular adrenal hyperplasia tissues and its regulation by aberrant hormone receptors opens new horizons for eventual medical therapy using melanocortin-2 receptor and G-protein-coupled receptor antagonists. Finally, some medical and surgical treatments have been updated.

SUMMARY

Recent findings indicate that bilateral macronodular adrenal hyperplasia is more frequently genetically determined than previously believed. Considering the role of paracrine adrenocorticotropic hormone production on cortisol secretion, the previous nomenclature of adrenocorticotropic hormone-independent macronodular adrenal hyperplasia appears inappropriate, and this disease should now be named primary bilateral macronodular adrenal hyperplasia.

ARMC5 mutations in macronodular adrenal hyperplasia with Cushing's syndrome

BACKGROUND

Corticotropin-independent macronodular adrenal hyperplasia may be an incidental finding or it may be identified during evaluation for Cushing's syndrome. Reports of familial cases and the involvement of both adrenal glands suggest a genetic origin of this condition.

METHODS

We genotyped blood and tumor DNA obtained from 33 patients with corticotropin-independent macronodular adrenal hyperplasia (12 men and 21 women who were 30 to 73 years of age), using single-nucleotide polymorphism arrays, microsatellite markers, and whole-genome and Sanger sequencing. The effects of armadillo repeat containing 5 (ARMC5) inactivation and overexpression were tested in cell-culture models.

RESULTS

The most frequent somatic chromosome alteration was loss of heterozygosity at 16p (in 8 of 33 patients for whom data were available [24%]). The most frequent mutation identified by means of whole-genome sequencing was in ARMC5, located at 16p11.2. ARMC5 mutations were detected in tumors obtained from 18 of 33 patients (55%). In all cases, both alleles of ARMC5 carried mutations: one germline and the other somatic. In 4 patients with a germline ARMC5 mutation, different nodules from the affected adrenals harbored different secondary ARMC5 alterations. Transcriptome-based classification of corticotropin-independent macronodular adrenal hyperplasia indicated that ARMC5 mutations influenced gene expression, since all cases with mutations clustered together. ARMC5 inactivation decreased steroidogenesis in vitro, and its overexpression altered cell survival.

CONCLUSIONS

Some cases of corticotropin-independent macronodular adrenal hyperplasia appear to be genetic, most often with inactivating mutations of ARMC5, a putative tumor-suppressor gene. Genetic testing for this condition, which often has a long and insidious prediagnostic course, might result in earlier identification and better management. (Funded by Agence Nationale de la Recherche and others.).

The Armadillo repeat protein PF16 is essential for flagellar structure and function in Plasmodium male gametes

Malaria, caused by the apicomplexan parasite Plasmodium, threatens 40% of the world's population. Transmission between vertebrate and insect hosts depends on the sexual stages of the life-cycle. The male gamete of Plasmodium parasite is the only developmental stage that possesses a flagellum. Very little is known about the identity or function of proteins in the parasite's flagellar biology. Here, we characterise a Plasmodium PF16 homologue using reverse genetics in the mouse malaria parasite Plasmodium berghei. PF16 is a conserved Armadillo-repeat protein that regulates flagellar structure and motility in organisms as diverse as green algae and mice. We show that P. berghei PF16 is expressed in the male gamete flagellum, where it plays a crucial role maintaining the correct microtubule structure in the central apparatus of the axoneme as studied by electron microscopy. Disruption of the PF16 gene results in abnormal flagellar movement and reduced fertility, but does not lead to complete sterility, unlike pf16 mutations in other organisms. Using homology modelling, bioinformatics analysis and complementation studies in Chlamydomonas, we show that some regions of the PF16 protein are highly conserved across all eukaryotes, whereas other regions may have species-specific functions. PF16 is the first ARM-repeat protein characterised in the malaria parasite genus Plasmodium and this study opens up a novel model for analysis of Plasmodium flagellar biology that may provide unique insights into an ancient organelle and suggest novel intervention strategies to control the malaria parasite.

Regulatory mechanisms required for DE-cadherin function in cell migration and other types of adhesion

Cadherin-mediated adhesion can be regulated at many levels, as demonstrated by detailed analysis in cell lines. We have investigated the requirements for Drosophila melanogaster epithelial (DE) cadherin regulation in vivo. Investigating D. melanogaster oogenesis as a model system allowed the dissection of DE-cadherin function in several types of adhesion: cell sorting, cell positioning, epithelial integrity, and the cadherin-dependent process of border cell migration. We generated multiple fusions between DE-cadherin and α-catenin as well as point-mutated β-catenin and analyzed their ability to support these types of adhesion. We found that (1) although linking DE-cadherin to α-catenin is essential, regulation of the link is not required in any of these types of adhesion; (2) β-catenin is required only to link DE-cadherin to α-catenin; and (3) the cytoplasmic domain of DE-cadherin has an additional specific function for the invasive migration of border cells, which is conserved to other cadherins. The nature of this additional function is discussed.

Novel brain 14-3-3 interacting proteins involved in neurodegenerative disease

We isolated two novel 14-3-3 binding proteins using 14-3-3 zeta as bait in a yeast two-hybrid screen of a human brain cDNA library. One of these encoded the C-terminus of a neural specific armadillo-repeat protein, delta-catenin (neural plakophilin-related arm-repeat protein or neurojungin). delta-Catenin from brain lysates was retained on a 14-3-3 affinity column. Mutation of serine 1072 in the human protein and serine 1094 in the equivalent site in the mouse homologue (in a consensus binding motif for 14-3-3) abolished 14-3-3 binding to delta-catenin in vitro and in transfected cells. delta-catenin binds to presenilin-1, encoded by the gene most commonly mutated in familial Alzheimer's disease. The other clone was identified as the insulin receptor tyrosine kinase substrate protein of 53 kDa (IRSp53). Human IRSp53 interacts with the gene product implicated in dentatorubral-pallidoluysian atrophy, an autosomal recessive disorder associated with glutamine repeat expansion of atrophin-1.

Drosophila Exocyst Components Sec5, Sec6, and Sec15 Regulate DE-Cadherin Trafficking from Recycling Endosomes to the Plasma Membrane

The E-Cadherin-catenin complex plays a critical role in epithelial cell-cell adhesion, polarization, and morphogenesis. Here, we have analyzed the mechanism of Drosophila E-Cadherin (DE-Cad) localization. Loss of function of the Drosophila exocyst components sec5, sec6, and sec15 in epithelial cells results in DE-Cad accumulation in an enlarged Rab11 recycling endosomal compartment and inhibits DE-Cad delivery to the membrane. Furthermore, Rab11 and Armadillo interact with the exocyst components Sec15 and Sec10, respectively. Our results support a model whereby the exocyst regulates DE-Cadherin trafficking, from recycling endosomes to sites on the epithelial cell membrane where Armadillo is located.

The p120 family of cell adhesion molecules

p120 is the prototypic member of the p120 subfamily of armadillo-related proteins that includes p0071, delta-catenin/NPRAP, ARVCF and the more distantly related plakophilins 1-3. Like armadillo, beta-catenin and plakoglobin these proteins are involved in mediating cell-cell adhesion. Besides their junctional localization they also reveal a cytoplasmic and nuclear localization. Non-cadherin-associated, cytoplasmic p120 functions in Rho signaling and regulation of cytoskeletal organization and actin dynamics. The nuclear function remains largely unsolved. Some characteristics seem to be shared by the various members of the family but it seems unlikely that p120-related proteins have solely redundant functions and compete for interactions with identical binding partners. Stabilization of cadherins at the membrane seems a common function of p120, p0071, delta-catenin and ARVCF but it is not yet known if and how these proteins confer distinct properties to cellular junctions. Moreover, p0071, NPRAP and ARVCF have a C-terminal PDZ-binding motif that is lacking in p120 pointing to distinct roles of these proteins. PDZ domains are found in a series of proteins involved in establishing cell polarity in epithelial cells. Thus, p120 proteins may not only be master regulators of cadherin abundance and activity but play additional roles in regulating cell polarity. This review focuses on the putative roles of p120 proteins in cell polarity.

Synaptic contact dynamics controlled by cadherin and catenins

A synapse is the connection between neurons that joins an axon of one neuron to the dendrite of another. One class of synapses is formed at the contact point between an axon and a small protrusion from a dendrite, called a dendritic spine. These spines are motile and deformable, which indicates that synaptic functions are controlled, at least in part, by their morphological changes. Recent studies show that the cadherin cell-adhesion molecules and their cytoplasmic partners, catenins, can modulate axon-spine contacts in a manner that responds to neural activity. These observations indicate that cadherins, which are essential for general cell-cell adhesion, also play a role in the control of synaptic dynamics.

Delta-catenin at the synaptic-adherens junction

Delta-catenin belongs to the p120-catenin (p120(ctn)) protein family, which is characterized by ten, characteristically spaced Armadillo repeats that bind to the juxtamembrane segment of the classical cadherins. Delta-catenin is the only member of this family that is expressed specifically in neurons, where it binds to PDZ domain proteins in the post-synaptic compartment. As a component of both adherens and synaptic junctions, delta-catenin can link the adherens junction to the synapse and, thereby, coordinate synaptic input with changes in the adherens junction. By virtue of its restriction to the post-synaptic area, delta-catenin creates an asymmetric adherens junction in the region of the synapse. The crucial nature of the specialized function of delta-catenin in neurons is demonstrated by a targeted gene mutation, which causes deficits in learning and in synaptic plasticity. Taken together, recent evidence indicates that delta-catenin is a sensor of synaptic activity and implements activity-related morphological changes at the synapse.

Functional analyses in the milkweed bug Oncopeltus fasciatus (Hemiptera) support a role for Wnt signaling in body segmentation but not appendage development

Specification of the proximal-distal (PD) axis of insect appendages is best understood in Drosophila melanogaster, where conserved signaling molecules encoded by the genes decapentaplegic (dpp) and wingless (wg) play key roles. However, the development of appendages from imaginal discs as in Drosophila is a derived state, while more basal insects produce appendages from embryonic limb buds. Therefore, the universality of the Drosophila limb PD axis specification mechanism has been debated since dpp expression in more basal insect species differs dramatically from Drosophila. Here, we test the function of Wnt signaling in the development of the milkweed bug Oncopeltus fasciatus, a species with the basal state of appendage development from limb buds. RNA interference of wg and pangolin (pan) produce defects in the germband and eyes, but not in the appendages. Distal-less and dachshund, two genes regulated by Wg signaling in Drosophila and expressed in specific PD domains along the limbs of both species, are expressed normally in the limbs of pan-depleted Oncopeltus embryos. Despite these apparently paradoxical results, Armadillo protein, the transducer of Wnt signaling, does not accumulate properly in the nuclei of cells in the legs of pan-depleted embryos. In contrast, engrailed RNAi in Oncopeltus produces cuticular and appendage defects similar to Drosophila. Therefore, our data suggest that Wg signaling is functionally conserved in the development of the germband, while it is not essential in the specification of the limb PD axis in Oncopeltus and perhaps basal insects.

Pygopus and Legless Provide Essential Transcriptional Coactivator Functions to Armadillo/β-Catenin

Wnt signaling controls important aspects of animal development, and its deregulation has been causally linked to cancer. Transduction of Wnt signals entails the association of beta-catenin with nuclear TCF DNA binding proteins and the subsequent activation of target genes. The transcriptional activity of Armadillo (Arm, the Drosophila beta-catenin homolog) largely depends on two recently discovered components, Legless (Lgs) and Pygopus (Pygo). Lgs functions as an adaptor between Arm/beta-catenin and Pygo, but different mechanisms have been proposed as to how Arm/beta-catenin is controlled by Lgs and Pygo. Although Lgs and Pygo were originally thought to serve as nuclear cofactors for Arm/beta-catenin to enhance its transactivation capacity, a recent analysis argued that they function instead to target Arm/beta-catenin to the nucleus. Here, we used genetic assays in cultured cells and in vivo to discriminate between the two paradigms. Regardless of the measures taken to maintain the nuclear presence of Arm/beta-catenin, a transcriptional-activation function of Pygo could not be bypassed. Our findings therefore indicate that Arm/beta-catenin depends on Lgs and Pygo primarily for its transcriptional output rather than for its nuclear import.

Regulation of desmosome assembly and adhesion

Desmosomes are highly organized intercellular junctions that provide mechanical integrity to tissues by anchoring intermediate filaments to sites of strong adhesion. Transcriptional regulation of desmosomal cadherins specifies their expression pattern and assembly into junctions of distinct composition, thus tailoring desmosome functions in adhesion and morphogenesis within different cells and complex tissues. Desmosome assembly and disassembly are regulated post-translationally by calcium, kinase/phosphatase activity, proteolytic processing, and cross talk with adherens junctions. Post-translational events also govern the level of non-junctional forms of plakoglobin and plakophilins. These armadillo proteins participate in various nuclear functions, in some cases transducing signals regulating cell growth and differentiation.

Requirements of genetic interactions between Src42A, armadillo and shotgun, a gene encoding E-cadherin, for normal development in Drosophila

Src42A is one of the two Src homologs in Drosophila. Src42A protein accumulates at sites of cell-cell or cell-matrix adhesion. Anti-Engrailed antibody staining of Src42A protein-null mutant embryos indicated that Src42A is essential for proper cell-cell matching during dorsal closure. Src42A, which is functionally redundant to Src64, was found to interact genetically with shotgun, a gene encoding E-cadherin, and armadillo, a Drosophila beta-catenin. Immunoprecipitation and a pull-down assay indicated that Src42A forms a ternary complex with E-cadherin and Armadillo, and that Src42A binds to Armadillo repeats via a 14 amino acid region, which contains the major autophosphorylation site. The leading edge of Src mutant embryos exhibiting the dorsal open phenotype was frequently kinked and associated with significant reduction in E-cadherin, Armadillo and F-actin accumulation, suggesting that not only Src signaling but also Src-dependent adherens-junction stabilization would appear likely to be essential for normal dorsal closure. Src42A and Src64 were required for Armadillo tyrosine residue phosphorylation but Src activity may not be directly involved in Armadillo tyrosine residue phosphorylation at the adherens junction.

Identification of Human Aminopeptidase O, a Novel Metalloprotease with Structural Similarity to Aminopeptidase B and Leukotriene A4 Hydrolase

We have cloned and characterized a human brain cDNA encoding a new metalloprotease that has been called aminopeptidase O (AP-O). AP-O exhibits a series of structural features characteristic of aminopeptidases, including a conserved catalytic domain with a zinc-binding site (HEXXHX18E) that allows its classification in the M1 family of metallopeptidases or gluzincins. The structural complexity of AP-O is further increased by the presence of an additional C-terminal domain 170 residues long, which is predicted to have an ARM repeat fold originally identified in the Drosophila segment polarity gene product Armadillo. This ARM repeat domain is also present in aminopeptidase B, aminopeptidase B-like, and leukotriene A4 hydrolase and defines a novel subfamily of aminopeptidases that we have called ARM aminopeptidases. Northern blot analysis revealed that AP-O is mainly expressed in the pancreas, placenta, liver, testis, and heart. Human AP-O was produced in Escherichia coli, and the purified recombinant protein hydrolyzed synthetic substrates used for assaying aminopeptidase activity. This activity was abolished by general inhibitors of metalloproteases and specific inhibitors of aminopeptidases. Recombinant AP-O also cleaved angiotensin III to generate angiotensin IV, a bioactive peptide of the renin-angiotensin pathway with multiple actions on diverse tissues, including brain, testis, and heart. On the basis of these results we suggest that AP-O could play a role in the proteolytic processing of bioactive peptides in those tissues where it is expressed.

Haplotypic association spanning the 22q11.21 genes COMT and ARVCF with schizophrenia

Catechol-O-methyltransferase (COMT) has been implicated in schizophrenia by its function through its roles in monoamine neurotransmitter metabolism and its impact on prefrontal cognition, and also by its position through linkage scans and a strong cytogenetic association. Further support comes from association studies, especially family-based ones examining the COMT variant, Val(108/158)Met. We have studied eight markers spanning COMT and including portions of the two immediately adjacent genes, thioredoxin reductase 2 and armadillo repeat deleted in velocardiofacial syndrome (ARVCF), using association testing in 136 schizophrenia families. We found nominal evidence for association of illness to rs165849 (P=0.051) in ARVCF, and a stronger signal (global P=0.0019-0.0036) from three-marker haplotypes spanning the 3' portions of COMT and ARVCF, including Val(108/158)Met with Val(108/158) being the overtransmitted allele, consistent with previous studies. We also find Val(108/158)Met to be in linkage disequilibrium with the markers in ARVCF. These findings support previous association signals of schizophrenia to COMT markers, and suggest that ARVCF might contribute to this signal. ARVCF, a member of the catenin family, besides being a positional candidate, is also one due to its function, that is, its potential role in neurodevelopment, which is implicated in schizophrenia pathogenesis by several lines of evidence.

Notch modulates Wnt signalling by associating with Armadillo/beta-catenin and regulating its transcriptional activity

The establishment and stability of cell fates during development depend on the integration of multiple signals, which ultimately modulate specific patterns of gene expression. While there is ample evidence for this integration at the level of gene regulatory sequences, little is known about its operation at other levels of cellular activity. Wnt and Notch signalling are important elements of the circuitry that regulates gene expression in development and disease. Genetic analysis has suggested that in addition to convergence on the transcription of specific genes, there are modulatory cross-regulatory interactions between these signalling pathways. We report that the nodal point of these interactions is an activity of Notch that regulates the activity and the amount of the active/oncogenic form of Armadillo/beta-catenin. This activity of Notch is independent of that induced upon cleavage of its intracellular domain and which mediates transcription through Su(H)/CBF1. The modulatory function of Notch described here, contributes to the establishment of a robust threshold for Wnt signalling which is likely to play important roles in both normal and pathological situations.

Rho1 regulates signaling events required for proper Drosophila embryonic development

The Rho small GTPase has been implicated in many cellular processes, including actin cytoskeletal regulation and transcriptional activation. The molecular mechanisms underlying Rho function in many of these processes are not yet clear. Here we report that in Drosophila, reduction of maternal Rho1 compromises signaling pathways consistent with defects in membrane trafficking events. These mutants fail to maintain expression of the segment polarity genes engrailed (en), wingless (wg), and hedgehog (hh), contributing to a segmentation phenotype. Formation of the Wg protein gradient involves the internalization of Wg into vesicles. The number of these Wg-containing vesicles is reduced in maternal Rho1 mutants, suggesting a defect in endocytosis. Consistent with this, stripes of cytoplasmic beta-catenin that accumulate in response to Wg signaling are narrower in these mutants relative to wild type. Additionally, the amount of extracellular Wg protein is reduced in maternal Rho1 mutants, indicating a defect in secretion. Signaling pathways downregulated by endocytosis, such as the epidermal growth factor receptor (EGFR) and Torso pathways, are hyperactivated in maternal Rho1 mutants, consistent with a general role for Rho1 in regulating signaling events governing proper patterning during Drosophila development.

Delta-catenin/NPRAP (neural plakophilin-related armadillo repeat protein) interacts with and activates sphingosine kinase 1

Sphingosine kinase (SPHK) is a key enzyme catalysing the formation of sphingosine 1-phosphate (SPP), a lipid messenger that is implicated in the regulation of a wide variety of important cellular events acting through intracellular, as well as extracellular, mechanisms. However, the molecular mechanism of intracellular actions of SPP remains unclear. Here, we have identified delta-catenin/NPRAP (neural plakophilin-related armadillo repeat protein) as a potential binding partner for SPHK1 by yeast two-hybrid screening. From co-immunoprecipitation analyses, the C-terminal portion of delta-catenin/NPRAP containing the seventh to tenth armadillo repeats was found to be required for interaction with SPHK1. Endogenous delta-catenin/NPRAP was co-localized with endogenous SPHK1 and transfected delta-catenin/NPRAP was co-localized with transfected SPHK1 in dissociated rat hippocampal neurons. MDCK (Madin-Darby canine kidney) cells stably expressing delta-catenin/NPRAP contained elevated levels of intracellular SPP. In a purified system delta-catenin/NPRAP stimulated SPHK1 in a dose-dependent manner. Furthermore, delta-catenin/NPRAP-induced increased cell motility in MDCK cells was completely inhibited by dimethylsphingosine, a specific inhibitor of SPHK1. These results strongly suggest that at least some of delta-catenin/NPRAP functions, including increased cell motility, are mediated by an SPHK-SPP signalling pathway.

Deletion of the neuron-specific protein delta-catenin leads to severe cognitive and synaptic dysfunction

Delta-catenin (delta-catenin) is a neuron-specific catenin, which has been implicated in adhesion and dendritic branching. Moreover, deletions of delta-catenin correlate with the severity of mental retardation in Cri-du-Chat syndrome (CDCS), which may account for 1% of all mentally retarded individuals. Interestingly, delta-catenin was first identified through its interaction with Presenilin-1 (PS1), the molecule most frequently mutated in familial Alzheimer's Disease (FAD). We investigated whether deletion of delta-catenin would be sufficient to cause cognitive dysfunction by generating mice with a targeted mutation of the delta-catenin gene (delta-cat(-/-)). We observed that delta-cat(-/-) animals are viable and have severe impairments in cognitive function. Furthermore, mutant mice display a range of abnormalities in hippocampal short-term and long-term synaptic plasticity. Also, N-cadherin and PSD-95, two proteins that interact with delta-catenin, are significantly reduced in mutant mice. These deficits are severe but specific because delta-cat(-/-) mice display a variety of normal behaviors, exhibit normal baseline synaptic transmission, and have normal levels of the synaptic adherens proteins E-cadherin and beta-catenin. These data reveal a critical role for delta-catenin in brain function and may have important implications for understanding mental retardation syndromes such as Cri-du-Chat and neurodegenerative disorders, such as Alzheimer's disease, that are characterized by cognitive decline.

RacGap50C negatively regulates wingless pathway activity during Drosophila embryonic development

The Wingless (Wg)/Wnt signal transduction pathway directs a variety of cell fate decisions in developing animal embryos. Despite the identification of many Wg pathway components to date, it is still not clear how these elements work together to generate cellular identities. In the ventral epidermis of Drosophila embryos, Wg specifies cells to secrete a characteristic pattern of denticles and naked cuticle that decorate the larval cuticle at the end of embryonic development. We have used the Drosophila ventral epidermis as our assay system in a series of genetic screens to identify new components involved in Wg signaling. Two mutant lines that modify wg-mediated epidermal patterning represent the first loss-of-function mutations in the RacGap50C gene. These mutations on their own cause increased stabilization of Armadillo and cuticle pattern disruptions that include replacement of ventral denticles with naked cuticle, which suggests that the mutant embryos suffer from ectopic Wg pathway activation. In addition, RacGap50C mutations interact genetically with naked cuticle and Axin, known negative regulators of the Wg pathway. These phenotypes suggest that the RacGap50C gene product participates in the negative regulation of Wg pathway activity.