Constitutive activation of PKA catalytic subunit in adrenal Cushing's syndrome

BACKGROUND

Corticotropin-independent Cushing's syndrome is caused by tumors or hyperplasia of the adrenal cortex. The molecular pathogenesis of cortisol-producing adrenal adenomas is not well understood.

METHODS

We performed exome sequencing of tumor-tissue specimens from 10 patients with cortisol-producing adrenal adenomas and evaluated recurrent mutations in candidate genes in an additional 171 patients with adrenocortical tumors. We also performed genomewide copy-number analysis in 35 patients with cortisol-secreting bilateral adrenal hyperplasias. We studied the effects of these genetic defects both clinically and in vitro.

RESULTS

Exome sequencing revealed somatic mutations in PRKACA, which encodes the catalytic subunit of cyclic AMP-dependent protein kinase (protein kinase A [PKA]), in 8 of 10 adenomas (c.617A→C in 7 and c.595_596insCAC in 1). Overall, PRKACA somatic mutations were identified in 22 of 59 unilateral adenomas (37%) from patients with overt Cushing's syndrome; these mutations were not detectable in 40 patients with subclinical hypercortisolism or in 82 patients with other adrenal tumors. Among 35 patients with cortisol-producing hyperplasias, 5 (including 2 first-degree relatives) carried a germline copy-number gain (duplication) of the genomic region on chromosome 19 that includes PRKACA. In vitro studies showed impaired inhibition of both PKA catalytic subunit mutants by the PKA regulatory subunit, whereas cells from patients with germline chromosomal gains showed increased protein levels of the PKA catalytic subunit; in both instances, basal PKA activity was increased.

CONCLUSIONS

Genetic alterations of the catalytic subunit of PKA were found to be associated with human disease. Germline duplications of this gene resulted in bilateral adrenal hyperplasias, whereas somatic PRKACA mutations resulted in unilateral cortisol-producing adrenal adenomas. (Funded by the European Commission Seventh Framework Program and others.).

Succinate dehydrogenase mutation underlies global epigenomic divergence in gastrointestinal stromal tumor

Gastrointestinal stromal tumors (GIST) harbor driver mutations of signal transduction kinases such as KIT, or, alternatively, manifest loss-of-function defects in the mitochondrial succinate dehydrogenase (SDH) complex, a component of the Krebs cycle and electron transport chain. We have uncovered a striking divergence between the DNA methylation profiles of SDH-deficient GIST (n = 24) versus KIT tyrosine kinase pathway-mutated GIST (n = 39). Infinium 450K methylation array analysis of formalin-fixed paraffin-embedded tissues disclosed an order of magnitude greater genomic hypermethylation relative to SDH-deficient GIST versus the KIT-mutant group (84.9 K vs. 8.4 K targets). Epigenomic divergence was further found among SDH-mutant paraganglioma/pheochromocytoma (n = 29), a developmentally distinct SDH-deficient tumor system. Comparison of SDH-mutant GIST with isocitrate dehydrogenase-mutant glioma, another Krebs cycle-defective tumor type, revealed comparable measures of global hypo- and hypermethylation. These data expose a vital connection between succinate metabolism and genomic DNA methylation during tumorigenesis, and generally implicate the mitochondrial Krebs cycle in nuclear epigenomic maintenance.

Gigantism and acromegaly due to Xq26 microduplications and GPR101 mutation

BACKGROUND

Increased secretion of growth hormone leads to gigantism in children and acromegaly in adults; the genetic causes of gigantism and acromegaly are poorly understood.

METHODS

We performed clinical and genetic studies of samples obtained from 43 patients with gigantism and then sequenced an implicated gene in samples from 248 patients with acromegaly.

RESULTS

We observed microduplication on chromosome Xq26.3 in samples from 13 patients with gigantism; of these samples, 4 were obtained from members of two unrelated kindreds, and 9 were from patients with sporadic cases. All the patients had disease onset during early childhood. Of the patients with gigantism who did not carry an Xq26.3 microduplication, none presented before the age of 5 years. Genomic characterization of the Xq26.3 region suggests that the microduplications are generated during chromosome replication and that they contain four protein-coding genes. Only one of these genes, GPR101, which encodes a G-protein-coupled receptor, was overexpressed in patients' pituitary lesions. We identified a recurrent GPR101 mutation (p.E308D) in 11 of 248 patients with acromegaly, with the mutation found mostly in tumors. When the mutation was transfected into rat GH3 cells, it led to increased release of growth hormone and proliferation of growth hormone-producing cells.

CONCLUSIONS

We describe a pediatric disorder (which we have termed X-linked acrogigantism [X-LAG]) that is caused by an Xq26.3 genomic duplication and is characterized by early-onset gigantism resulting from an excess of growth hormone. Duplication of GPR101 probably causes X-LAG. We also found a recurrent mutation in GPR101 in some adults with acromegaly. (Funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development and others.).

Macronodular adrenal hyperplasia due to mutations in an armadillo repeat containing 5 (ARMC5) gene: a clinical and genetic investigation

CONTEXT

Inactivating germline mutations of the probable tumor suppressor gene, armadillo repeat containing 5 (ARMC5), have recently been identified as a genetic cause of macronodular adrenal hyperplasia (MAH).

OBJECTIVE

We searched for ARMC5 mutations in a large cohort of patients with MAH. The clinical phenotype of patients with and without ARMC5 mutations was compared.

METHODS

Blood DNA from 34 MAH patients was genotyped using Sanger sequencing. Diurnal serum cortisol measurements, plasma ACTH levels, urinary steroids, 6-day Liddle's test, adrenal computed tomography, and weight of adrenal glands at adrenalectomy were assessed.

RESULTS

Germline ARMC5 mutations were found in 15 of 34 patients (44.1%). In silico analysis of the mutations indicated that seven (20.6%) predicted major implications for gene function. Late-night cortisol levels were higher in patients with ARMC5-damaging mutations compared with those without and/or with nonpathogenic mutations (14.5 ± 5.6 vs 6.7 ± 4.3, P < .001). All patients carrying a pathogenic ARMC5 mutation had clinical Cushing's syndrome (seven of seven, 100%) compared with 14 of 27 (52%) of those without or with mutations that were predicted to be benign (P = .029). Repeated-measures analysis showed overall higher urinary 17-hydroxycorticosteroids and free cortisol values in the patients with ARMC5-damaging mutations during the 6-day Liddle's test (P = .0002).

CONCLUSIONS

ARMC5 mutations are implicated in clinically severe Cushing's syndrome associated with MAH. Knowledge of a patient's ARMC5 status has important clinical implications for the diagnosis of Cushing's syndrome and genetic counseling of patients and their families.

Pituitary adenoma with paraganglioma/pheochromocytoma (3PAs) and succinate dehydrogenase defects in humans and mice

CONTEXT

Germline mutations in genes coding succinate dehydrogenase (SDH) subunits A, B, C, and D have been identified in familial paragangliomas (PGLs)/pheochromocytomas (PHEOs) and other tumors. We described a GH-secreting pituitary adenoma (PA) caused by SDHD mutation in a patient with familial PGLs. Additional patients with PAs and SDHx defects have since been reported.

DESIGN

We studied 168 patients with unselected sporadic PA and with the association of PAs, PGLs, and/or pheochromocytomas, a condition we named the 3P association (3PAs) for SDHx germline mutations. We also studied the pituitary gland and hormonal profile of Sdhb(+/-) mice and their wild-type littermates at different ages.

RESULTS

No SDHx mutations were detected among sporadic PA, whereas three of four familial cases were positive for a mutation (75%). Most of the SDHx-deficient PAs were either prolactinomas or somatotropinomas. Pituitaries of Sdhb(+/-) mice older than 12 months had an increased number mainly of prolactin-secreting cells and several ultrastructural abnormalities such as intranuclear inclusions, altered chromatin nuclear pattern, and abnormal mitochondria. Igf-1 levels of mutant mice tended to be higher across age groups, whereas Prl and Gh levels varied according to age and sex.

CONCLUSION

The present study confirms the existence of a new association that we termed 3PAs. It is due mostly to germline SDHx defects, although sporadic cases of 3PAs without SDHx defects also exist. Using Sdhb(+/-) mice, we provide evidence that pituitary hyperplasia in SDHx-deficient cells may be the initial abnormality in the cascade of events leading to PA formation.

Molecular genetics of the developing neuroendocrine hypothalamus

Formation of the mammalian endocrine system and neuroendocrine organs involves complex regulatory networks resulting in a highly specialized cell system able to secrete a diverse array of peptide hormones. The hypothalamus is located in the mediobasal region of the brain and acts as a gateway between the endocrine and nervous systems. From an endocrinology perspective, the parvicellular neurons of the hypothalamus are of particular interest as they function as a control centre for several critical physiological processes including growth, metabolism and reproduction by regulating hormonal signaling from target cognate cell types in the anterior pituitary. Delineating the genetic program that controls hypothalamic development is essential for complete understanding of parvicellular neuronal function and the etiology of congenital disorders that result from hypothalamic-pituitary axis dysfunction. In recent years, studies have shed light on the interactions between signaling molecules and activation of transcription factors that regulate hypothalamic cell fate commitment and terminal differentiation. The aim of this review is to summarize the recent molecular and genetic findings that have advanced our understanding of the emergence of the known important hypophysiotropic signaling molecules in the hypothalamus. We have focused on reviewing the literature that provides evidence of the dependence on expression of specific genes for the normal development and function of the cells that secrete these neuroendocrine factors, as well as studies of the elaboration of the spatial or temporal patterns of changes in gene expression that drive this development.

Germline PRKACA amplification causes variable phenotypes that may depend on the extent of the genomic defect: molecular mechanisms and clinical presentations

OBJECTIVE

We have recently reported five patients with bilateral adrenocortical hyperplasia (BAH) and Cushing's syndrome (CS) caused by constitutive activation of the catalytic subunit of protein kinase A (PRKACA). By doing new in-depth analysis of their cytogenetic abnormality, we attempted a better genotype-phenotype correlation of their PRKACA amplification.

DESIGN

This study is a case series.

METHODS

Molecular cytogenetic, genomic, clinical, and histopathological analyses were performed in five patients with CS.

RESULTS

Reinvestigation of the defects of previously described patients by state-of-the-art molecular cytogenetics showed complex genomic rearrangements in the chromosome 19p13.2p13.12 locus, resulting in copy number gains encompassing the entire PRKACA gene; three patients (one sporadic case and two related cases) were observed with gains consistent with duplications, while two sporadic patients were observed with gains consistent with triplications. Although all five patients presented with ACTH-independent CS, the three sporadic patients had micronodular BAH and underwent bilateral adrenalectomy in early childhood, whereas the two related patients, a mother and a son, presented with macronodular BAH as adults. In at least one patient, PRKACA triplication was associated with a more severe phenotype.

CONCLUSIONS

Constitutional chromosomal PRKACA gene amplification is a recently identified genetic defect associated with CS, a trait that may be inherited in an autosomal dominant manner or occur de novo. Genomic rearrangements can be complex and can result in different copy number states of dosage-sensitive genes, e.g., duplication and triplication. PRKACA amplification can lead to variable phenotypes clinically and pathologically, both micro- and macro-nodular BAH, the latter of which we speculate may depend on the extent of amplification.

PRKACA: the catalytic subunit of protein kinase A and adrenocortical tumors

Cyclic-AMP (cAMP)-dependent protein kinase (PKA) is the main effector of cAMP signaling in all tissues. Inactivating mutations of the PRKAR1A gene, coding for the type 1A regulatory subunit of PKA, are responsible for Carney complex and primary pigmented nodular adrenocortical disease (PPNAD). PRKAR1A inactivation and PKA dysregulation have been implicated in various types of adrenocortical pathologies associated with ACTH-independent Cushing syndrome (AICS) from PPNAD to adrenocortical adenomas and cancer, and other forms of bilateral adrenocortical hyperplasias (BAH). More recently, mutations of PRKACA, the gene coding for the catalytic subunit C alpha (Cα), were also identified in the pathogenesis of adrenocortical tumors. PRKACA copy number gain was found in the germline of several patients with cortisol-producing BAH, whereas the somatic Leu206Arg (c.617A>C) recurrent PRKACA mutation was found in as many as half of all adrenocortical adenomas associated with AICS. In vitro analysis demonstrated that this mutation led to constitutive Cα activity, unregulated by its main partners, the PKA regulatory subunits. In this review, we summarize the current understanding of the involvement of PRKACA in adrenocortical tumorigenesis, and our understanding of PKA's role in adrenocortical lesions. We also discuss potential therapeutic advances that can be made through targeting of PRKACA and the PKA pathway.

Expression of the murine transcription factor SOX3 during embryonic and adult neurogenesis

Previous studies have shown that Sox3 is expressed in nascent neuroprogenitor cells and is functionally required in mammals for development of the dorsal telencephalon and hypothalamus. However, Sox3 expression during embryonic and adult neurogenesis has not been examined in detail. Using a SOX3-specific antibody, we show that murine SOX3 expression is maintained throughout telencephalic neurogenesis and is restricted to progenitor cells with neuroepithelial and radial glial morphologies. We also demonstrate that SOX3 is expressed within the adult neurogenic regions and is coexpressed extensively with the neural stem cell marker SOX2 indicating that it is a lifelong marker of neuroprogenitor cells. In contrast to the telencephalon, Sox3 expression within the developing hypothalamus is upregulated in developing neurons and is maintained in a subset of differentiated hypothalamic cells through to adulthood. Together, these data show that Sox3 regulation is region-specific, consistent with it playing distinct biological roles in the dorsal telencephalon and hypothalamus.

Differentially regulated protein kinase A (PKA) activity in adipose tissue and liver is associated with resistance to diet-induced obesity and glucose intolerance in mice that lack PKA regulatory subunit type IIα

The cAMP-dependent protein kinase A (PKA) signaling system is widely expressed and has a central role in regulating cellular metabolism in all organ systems affected by obesity. PKA has four regulatory (RIα, RIIα, RIβ, RIIβ) and four catalytic (Cα, Cβ, Cγ, Prkx) subunit isoforms that have tissue-specific expression profiles. In mice, knockout (KO) of RIIβ, the primary PKA regulatory subunit in adipose tissue or knockout of the catalytic subunit Cβ resulted in a lean phenotype that resists diet-induced obesity and associated metabolic complications. Here we report that the disruption of the ubiquitously expressed PKA RIIα subunit in mice (RIIαKO) confers resistance to diet-induced obesity, glucose intolerance, and hepatic steatosis. After 2-week high-fat diet exposure, RIIαKO mice weighed less than wild-type littermates. Over time this effect was more pronounced in female mice that were also leaner than their wild-type counterparts, regardless of the diet. Decreased intake of a high-fat diet contributed to the attenuated weight gain in RIIαKO mice. Additionally, RIIα deficiency caused differential regulation of PKA in key metabolic organs: cAMP-stimulated PKA activity was decreased in liver and increased in gonadal adipose tissue. We conclude that RIIα represents a potential target for therapeutic interventions in obesity, glucose intolerance, and nonalcoholic fatty liver disease.

PKA regulatory subunit 1A inactivating mutation induces serotonin signaling in primary pigmented nodular adrenal disease

Primary pigmented nodular adrenocortical disease (PPNAD) is a rare cause of ACTH-independent hypercortisolism. The disease is primarily caused by germline mutations of the protein kinase A (PKA) regulatory subunit 1A (PRKAR1A) gene, which induces constitutive activation of PKA in adrenocortical cells. Hypercortisolism is thought to result from PKA hyperactivity, but PPNAD tissues exhibit features of neuroendocrine differentiation, which may lead to stimulation of steroidogenesis by abnormally expressed neurotransmitters. We hypothesized that serotonin (5-HT) may participate in the pathophysiology of PPNAD-associated hypercortisolism. We show that PPNAD tissues overexpress the 5-HT synthesizing enzyme tryptophan hydroxylase type 2 (Tph2) and the serotonin receptors types 4, 6, and 7, leading to formation of an illicit stimulatory serotonergic loop whose pharmacological inhibition in vitro decreases cortisol production. In the human PPNAD cell line CAR47, the PKA inhibitor H-89 decreases 5-HT₄ and 5-HT₇ receptor expression. Moreover, in the human adrenocortical cell line H295R, inhibition of PRKAR1A expression increases the expression of Tph2 and 5-HT_4/6/7 receptors, an effect that is blocked by H-89. These findings show that the serotonergic process observed in PPNAD tissues results from PKA activation by PRKAR1A mutations. They also suggest that Tph inhibitors may represent efficient treatments of hypercortisolism in patients with PPNAD.

Carney triad, SDH-deficient tumors, and Sdhb+/- mice share abnormal mitochondria

Carney triad (CTr) describes the association of paragangliomas (PGL), pulmonary chondromas, and gastrointestinal (GI) stromal tumors (GISTs) with a variety of other lesions, including pheochromocytomas and adrenocortical tumors. The gene(s) that cause CTr remain(s) unknown. PGL and GISTs may be caused by loss-of-function mutations in succinate dehydrogenase (SDH) (a condition known as Carney-Stratakis syndrome (CSS)). Mitochondrial structure and function are abnormal in tissues that carry SDH defects, but they have not been studied in CTr. For the present study, we examined mitochondrial structure in human tumors and GI tissue (GIT) of mice with SDH deficiency. Tissues from 16 CTr tumors (n=12), those with isolated GIST (n=1), and those with CSS caused by SDHC (n=1) and SDHD (n=2) mutations were studied by electron microscopy (EM). Samples of GIT from mice with a heterozygous deletion in Sdhb (Sdhb(+) (/-), n=4) were also studied by EM. CTr patients presented with mostly epithelioid GISTs that were characterized by plump cells containing a centrally located, round nucleus and prominent nucleoli; these changes were almost identical to those seen in the GISTs of patients with SDH. In tumor cells from patients, regardless of diagnosis or tumor type, cytoplasm contained an increased number of mitochondria with a 'hypoxic' phenotype: mitochondria were devoid of cristae, exhibited structural abnormalities, and were of variable size. Occasionally, mitochondria were small and round; rarely, they were thin and elongated with tubular cristae. Many mitochondria exhibited amorphous fluffy material with membranous whorls or cystic structures. A similar mitochondrial hypoxic phenotype was seen in Sdhb(+) (/-) mice. We concluded that tissues from SDH-deficient tumors, those from mouse GIT, and those from CTr tumors shared identical abnormalities in mitochondrial structure and other features. Thus, the still-elusive CTr defect(s) is(are) likely to affect mitochondrial function, just like germline SDH-deficiency does.

Prkar1a gene knockout in the pancreas leads to neuroendocrine tumorigenesis

Carney complex (CNC) is a rare disease associated with multiple neoplasias, including a predisposition to pancreatic tumors; it is caused most frequently by the inactivation of the PRKAR1A gene, a regulator of the cyclic AMP (cAMP)-dependent kinase (PKA). The method used was to create null alleles of prkar1a in mouse cells expressing pdx1 (Δ-Prkar1a). We found that these mice developed endocrine or mixed endocrine/acinar cell carcinomas with 100% penetrance by the age of 4-5 months. Malignant behavior of the tumors was seen as evidenced by stromal invasion and metastasis to locoregional lymph nodes. Histologically, most tumors exhibited an organoid pattern as seen in the islet-cell tumors. Biochemically, the lesions exhibited high PKA activity, as one would expect from deleting prkar1a The primary neuroendocrine nature of these tumor cells was confirmed by immunohistochemical staining and electron microscopy, the latter revealing the characteristic granules. Although the Δ-Prkar1a mice developed hypoglycemia after overnight fasting, insulin and glucagon levels in the plasma were normal. Negative immunohistochemical staining for the most commonly produced peptides (insulin, c-peptide, glucagon, gastrin and somatostatin) suggested that these tumors were non-functioning. We hypothesize that the recently identified multipotent pdx1+/insulin- cell in adult pancreas, gives rise to endocrine or mixed endocrine/acinar pancreatic malignancies with complete prkar1a deficiency. In conclusion, this mouse model supports the role of prkar1a as a tumor suppressor gene in the pancreas and points to the PKA pathway as a possible therapeutic target for these lesions.

Is IGSF1 involved in human pituitary tumor formation?

IGSF1 is a membrane glycoprotein highly expressed in the anterior pituitary. Pathogenic mutations in the IGSF1 gene (on Xq26.2) are associated with X-linked central hypothyroidism and testicular enlargement in males. In this study, we tested the hypothesis that IGSF1 is involved in the development of pituitary tumors, especially those that produce growth hormone (GH). IGSF1 was sequenced in 21 patients with gigantism or acromegaly and 92 healthy individuals. Expression studies with a candidate pathogenic IGSF1 variant were carried out in transfected cells and immunohistochemistry for IGSF1 was performed in the sections of GH-producing adenomas, familial somatomammotroph hyperplasia, and in normal pituitary. We identified the sequence variant p.N604T, which in silico analysis suggested could affect IGSF1 function, in two male patients and one female with somatomammotroph hyperplasia from the same family. Of 60 female controls, two carried the same variant and seven were heterozygous for other variants. Immunohistochemistry showed increased IGSF1 staining in the GH-producing tumor from the patient with the IGSF1 p.N604T variant compared with a GH-producing adenoma from a patient negative for any IGSF1 variants and with normal control pituitary tissue. The IGSF1 gene appears polymorphic in the general population. A potentially pathogenic variant identified in the germline of three patients with gigantism from the same family (segregating with the disease) was also detected in two healthy female controls. Variations in IGSF1 expression in pituitary tissue in patients with or without IGSF1 germline mutations point to the need for further studies of IGSF1 action in pituitary adenoma formation.

Ultra-structural identification of interstitial cells of Cajal in the zebrafish Danio rerio

The interstitial cells of Cajal (ICCs) are important mediators of gastrointestinal (GI) motility because of their role as pacemakers in the GI tract. In addition to their function, ICCs are also structurally distinct cells most easily identified by their ultra-structural features and expression of the tyrosine kinase receptor c-KIT. ICCs have been described in mammals, rodents, birds, reptiles, and amphibians, but there are no reports at the ultra-structural level of ICCs within the GI tract of an organism from the teleost lineage. We describe the presence of cells in the muscularis of the zebrafish intestine; these cells have similar features to ICCs in other vertebrates. The ICC-like cells are associated with the muscularis, are more electron-dense than surrounding smooth muscle cells, possess long cytoplasmic processes and mitochondria, and are situated opposing enteric nervous structures. In addition, immunofluorescent and immunoelectron-microscopic studies with antibodies targeting the zebrafish ortholog of a putative ICC marker, c-KIT (kita), showed c-kit immunoreactivity in zebrafish ICCs. Taken together, these data represent the first ultra-structural characterization of cells in the muscularis of the zebrafish Danio rerio and suggest that ICC differentiation in vertebrate evolution dates back to the teleost lineage.

Phosphodiesterases and adrenal Cushing in mice and humans

The majority of benign adrenal cortex lesions leading to Cushing syndrome are associated to one or another abnormality of the cAMP/cGMP-phosphodiesterase signaling pathway. Phosphodiesterases (PDEs) are key regulatory enzymes of intracellular cAMP/cGMP levels. These second messengers play important regulatory roles in controlling steroidogenesis in the adrenal. Disruption of PDEs has been associated with a number of adrenal diseases. Specifically, genetic mutations have been associated with benign adrenal lesions, leading to Cushing syndrome and/or related adrenal hyperplasias. A Genome Wide Association study, in 2006, led to the identification of mutations in 2 PDE genes: PDE8B and PDE11A; mutations in these 2 genes modulate steroidogenesis. Further human studies have identified PDE2 as also directly regulating steroidogenesis. PDE2 decreases aldosterone production. This review focuses on the most recent knowledge we have gained on PDEs and their association with adrenal steroidogenesis and altered function, through analysis of patient cohorts and what we have learned from mouse studies.

Hypothalamic input is required for development of normal numbers of thyrotrophs and gonadotrophs, but not other anterior pituitary cells in late gestation sheep

To evaluate the hypothalamic contribution to the development of anterior pituitary (AP) cells we surgically disconnected the hypothalamus from the pituitary (hypothalamo-pituitary disconnection, HPD) in fetal sheep and collected pituitaries 31 days later. Pituitaries (n = 6 per group) were obtained from fetal sheep (term = 147 +/- 3 days) at 110 days (unoperated group) of gestation and at 141 days from animals that had undergone HPD or sham surgery at 110 days. Cells were identified by labelling pituitary sections with antisera against the six AP hormones. Additionally, we investigated the colocalization of glycoprotein hormones. The proportions of somatotrophs and corticotrophs were unchanged by age or HPD. Lactotrophs increased 80% over time, but the proportion was unaffected by HPD. Thyrotrophs, which were unaffected by age, increased 70% following HPD. Gonadotrophs increased with gestational age (LH+ cells 55%; FSH+ cells 19-fold), but this was severely attenuated by HPD. We investigated the possible existence of a reciprocal effect of HPD on multipotential glycoprotein-expressing cells. Co-expression of LH and TSH was extremely rare (< 1%) and unchanged over the last month of gestation or HPD. The increase of gonadotrophs expressing FSH only or LH and FSH was attenuated by HPD. Therefore, the proportions of somatotrophs, lactotrophs and corticotrophs are regulated independently of hypothalamic input in the late gestation fetal pituitary. In marked contrast, the determination of the thyrotroph and gonadotroph lineages over the same time period is subject to complex mechanisms involving hypothalamic factors, which inhibit differentiation and/or proliferation of thyrotrophs, but stimulate gonadotrophs down the FSH lineage. Development of a distinct population of gonadotrophs, expressing only LH, appears to be subject to alternative mechanisms.

Phosphodiesterase sequence variants may predispose to prostate cancer

We hypothesized that mutations that inactivate phosphodiesterase (PDE) activity and lead to increased cAMP and cyclic guanosine monophosphate levels may be associated with prostate cancer (PCa). We sequenced the entire PDE coding sequences in the DNA of 16 biopsy samples from PCa patients. Novel mutations were confirmed in the somatic or germline state by Sanger sequencing. Data were then compared to the 1000 Genome Project. PDE, CREB and pCREB protein expression was also studied in all samples, in both normal and abnormal tissue, by immunofluorescence. We identified three previously described PDE sequence variants that were significantly more frequent in PCa. Four novel sequence variations, one each in the PDE4B,PDE6C, PDE7B and PDE10A genes, respectively, were also found in the PCa samples. Interestingly, PDE10A and PDE4B novel variants that were present in 19 and 6% of the patients were found in the tumor tissue only. In patients carrying PDE defects, there was pCREB accumulation (P<0.001), and an increase of the pCREB:CREB ratio (patients 0.97±0.03; controls 0.52±0.03; P-value <0.001) by immunohistochemical analysis. We conclude that PDE sequence variants may play a role in the predisposition and/or progression to PCa at the germline and/or somatic state respectively.

A phosphodiesterase 11 (Pde11a) knockout mouse expressed functional but reduced Pde11a: Phenotype and impact on adrenocortical function

Phosphodiesterases catalyze the hydrolysis of cyclic nucleotides and maintain physiologic levels of intracellular concentrations of cyclic adenosine and guanosine mono-phosphate (cAMP and cGMP, respectively). Increased cAMP signaling has been associated with adrenocortical tumors and Cushing syndrome. Genetic defects in phosphodiesterase 11A (PDE11A) may lead to increased cAMP signaling and have been found to predispose to the development of adrenocortical, prostate, and testicular tumors. A previously reported Pde11a knockout (Pde11a-/-) mouse line was studied and found to express PDE11A mRNA and protein still, albeit at reduced levels; functional studies in various tissues showed increased cAMP levels and reduced PDE11A activity. Since patients with PDE11A defects and Cushing syndrome have PDE11A haploinsufficiency, it was particularly pertinent to study this hypomorphic mouse line. Indeed, Pde11a-/- mice failed to suppress corticosterone secretion in response to low dose dexamethasone, and in addition exhibited adrenal subcapsular hyperplasia with predominant fetal-like features in the inner adrenal cortex, mimicking other mouse models of increased cAMP signaling in the adrenal cortex. We conclude that a previously reported Pde11a-/- mouse showed continuing expression and function of PDE11A in most tissues. Nevertheless, Pde11a partial inactivation in mice led to an adrenocortical phenotype that was consistent with what we see in patients with PDE11A haploinsufficiency.

Phosphodiesterase 8B and cyclic AMP signaling in the adrenal cortex

Bilateral adrenocortical hyperplasia (BAH) in humans and mice has been recently linked to phosphodiesterase (PDE) 8B (PDE8B) and 11 (PDE11A) defects. These findings have followed the discovery that defects of primary genes of the cyclic monophosphatase (cAMP) signaling pathway, such as guanine nucleotide binding alpha subunit and PRKAR1A, are involved in the pathogenesis of BAH in humans; complete absence of Prkar1a in the adrenal cortex of mice also led to pathology that mimicked the human disease. Here, we review the most recent findings in human and mouse studies on PDE8B, a cAMP-specific PDE that appears to be highly expressed in the adrenal cortex and whose deficiency may underlie predisposition to BAH and possibly other human diseases.

Lipofuscin Accumulation in Cortisol-Producing Adenomas With and Without PRKACA Mutations

The adrenal cortex accumulates lipofuscin granules with age. Lipofuscin accumulation is also seen in adrenocortical tumors associated with Cushing syndrome (CS), particularly those with PRKAR1A mutations, such as in primary pigmented nodular adrenocortical disease (PPNAD). We investigated the presence of lipofuscin in cortisol-producing adenomas (CPAs) responsible for CS with and without the PRKACA (pLeu206Arg) somatic mutation. Ten paraffin-embedded sections of CPAs from cases with overt CS with (n=4) and without (n=6) a PRKACA mutation were microscopically examined through three detection methods, the hematoxylin-Eosin (H & E) staining, the Fontana Masson (FM) staining using light microscopy, and lipofuscin autofluorescence, using confocal laser scanning microscopy (CLSM). Sections were examined quantitatively according to the intensity of the pigmentation, as well as qualitatively based on the total number of granular pigments at all visual fields per tissue slide. Tissues from CPAs were compared to peritumoral adjacent tissues (n=5), to Conn adenomas (n=4), and PPNAD (n=3). CPAs had significantly higher number of lipofuscin-pigment granules compared to peritumoral adrenal tissue and Conn adenomas (46.9±9.5 vs. 3.8±4.8, p=0.0001). The presence of the PRKACA mutation did not increase the chances of pigmentation in the form of lipofuscin granules within CPAs associated with CS. Thus, all CPAs leading to CS accumulate lipofuscin, which presents like pigmentation sometimes seen macroscopically but always detected microscopically. PPNAD caused by PRKAR1A mutations is the best known adrenal lesion leading to CS associated with intense lipofuscin pigmentation and this was confirmed here; CPAs harboring PRKACA mutations did not have statistically significantly more pigmentation than CPAs without mutation, but a larger study might have shown a difference.

Haploinsufficiency for either one of the type-II regulatory subunits of protein kinase A improves the bone phenotype of Prkar1a+/- mice

Carney Complex (CNC), a human genetic syndrome predisposing to multiple neoplasias, is associated with bone lesions such as osteochondromyxomas (OMX). The most frequent cause for CNC is PRKAR1A deficiency; PRKAR1A codes for type-I regulatory subunit of protein kinase A (PKA). Prkar1a(+/-) mice developed OMX, fibrous dysplasia-like lesions (FDL) and other tumors. Tumor tissues in these animals had increased PKA activity due to an unregulated PKA catalytic subunit and increased PKA type II (PKA-II) activity mediated by the PRKAR2A and PRKAR2B subunits. To better understand the effect of altered PKA activity on bone, we studied Prkar2a and Prkar2b knock out (KO) and heterozygous mice; none of these mice developed bone lesions. When Prkar2a(+/-) and Prkar2b(+/-) mice were used to generate Prkar1a(+/-)Prkar2a(+/-) and Prkar1a(+/-)Prkar2b(+/-) animals, bone lesions formed that looked like those of the Prkar1a(+/-) mice. However, better overall bone organization and mineralization and fewer FDL lesions were found in both double heterozygote groups, indicating a partial restoration of the immature bone structure observed in Prkar1a(+/-) mice. Further investigation indicated increased osteogenesis and higher new bone formation rates in both Prkar1a(+/-)Prkar2a(+/-) and Prkar1a(+/-)Prkar2b(+/-) mice with some minor differences between them. The observations were confirmed with a variety of markers and studies. PKA activity measurements showed the expected PKA-II decrease in both double heterozygote groups. Thus, haploinsufficiency for either of PKA-II regulatory subunits improved bone phenotype of mice haploinsufficient for Prkar1a, in support of the hypothesis that the PRKAR2A and PRKAR2B regulatory subunits were in part responsible for the bone phenotype of Prkar1a(+/-) mice.

Abstract 2736: Genetic deletion of the prkar1a in the endocrine pancreas promotes neuroendocrine carcinogenesis

Background: Carney complex (CNC) is a rare disease inherited as an autosomal dominant trait, associated with various tumors, and caused most frequently by inactivation of the PRKAR1A gene. Recently a possible association of pancreatic neoplasms with CNC was reported in 9 out of 354 patients (2.5%), suggesting the potential role of PRKAR1A as a tumor suppressor gene in the pancreas.

Methods: Prkar1afl/fl and pdx-1-CRE mice were previously reported (Kirschner et al, 2005; Lammert et al, 2001) and were kept in a mixed genetic background (C57Bl/6 x FVB). Pdx1 is a transcription factor expressed in beta-insulin producing cells and in some a-glucagon producing cells of the mouse adult pancreatic islet. Both prkar1a alleles were conditionally deleted during development by generating pdx1-Cre; prkar1af/f mice (Δ–prkar1a). Mice were phenotyped at the age of 2, 4 and 6 months and tissues were collected for histological and molecular analysis.

Results: Mice developed endocrine or mixed endocrine/acinar cell carcinomas with 100% penetration by the age of 4-5 months. Malignant behavior of the tumors was defined by stromal invasion and regional lymph node metastasis. Histologically most tumors exhibited an organoid pattern as seen in the islet-cell tumors. Some tumors exhibited in addition foci suggestive of acinar cell differentiation. The primary neuroendocrine nature of the tumor cells was confirmed by immunohistochemical (IHC) staining for chromogranin and by electron microscopy, which revealed the characteristic neuroendocrine granules. Focal acinar differentiation was further supported by the finding of scattered chymotrypsin-positive cells by immunofluorescence (IF). Although the Δ-prkar1a mice developed hypoglycemia after overnight fasting, insulin and glucagon levels in the plasma didn't differ. The negative IHC staining for the most common produced peptides (insulin, c-peptide, glucagon, gastrin, somatostatin) suggested that these tumors are non-functional. The recombination that was confirmed by the detection of the mutated allele for the prkar1a in the tumor DNA, but neither in the germline of the KO animals nor in the islets DNA of the WT mice, resulted in increased PKA activity and lack of protein expression in the tumor compared to the normal pancreatic tissue. The latter finding is suggestive of the oncogenic effect of PRKAR1A inactivation. IF staining showed that the tumor cells were composed of a pdx1+/insulin- cell-population. We hypothesized that the recently identified multipotent pdx1+/insulin- cell in the adult pancreas, gives rise to endocrine, or mixed endocrine/acinar pancreatic malignancies upon PKA manipulation.

Conclusions: Loss of prkar1a function predisposes the endocrine pancreas to invasive cancers. This supports the role of prkar1a as a tumor suppressor gene in the pancreas and provides valuable tools to evaluate novel therapeutics in endocrine pancreas malignancies.

Citation Format: Emmanouil Saloustros, Maria Tsokos, Paraskevi Salpea, Matthew Starost, Sisi Liu, Li Guang, Maria Nesterova, Eva Szarek, Mehboob A. Hussain, Constantine A. Stratakis. Genetic deletion of the prkar1a in the endocrine pancreas promotes neuroendocrine carcinogenesis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2736. doi:10.1158/1538-7445.AM2013-2736

Abstract LB-182: Constitutive activation of PRKACA in adrenal Cushing's syndrome

Corticotropin-independent Cushing's syndrome may be caused by tumors or hyperplasia of the adrenal cortex. Until now genetic alterations explain only a small fraction of cases. The observation that a subset of adrenal adenomas is characterized by abnormal PKA activity despite the absence of mutations in candidate genes suggested as yet unknown alterations in the cAMP/PKA signaling cascade in these tumors. The aim of this study was the analysis of the genetic basis of Cushing's syndrome in order to reveal the gene/s responsible for the disease. Exome sequencing was performed in ten cortisol-producing adenomas and recurrent mutations in candidate genes were evaluated in additional 171 patients with adrenocortical tumors. Genome-wide copy number analysis was performed in 35 patients with cortisol secreting bilateral hyperplasias. The effects of these genetic defects were studied both clinically and in vitro. Exome sequencing in 8/10 adenomas revealed somatic mutations in the PRKACA gene, which encodes the main catalytic subunit of cyclic AMP-dependent protein kinase (PKA) (c.617A&gt;C in seven and c.595_596insCAC in one). Overall, PRKACA somatic mutations were identified in a total of 22/59 (37%) adenomas from patients with overt Cushing's syndrome while these mutations were not detectable in patients with subclinical hypercortisolism (n=40) or in other adrenal tumors (n=82). Among 35 patients with cortisol producing hyperplasias, 5 (with two patients as first degree relatives) carried germline copy number gain of the chromosome 19 region including the PRKACA gene. In vitro studies demonstrated impaired inhibition of the mutant PRKACA by the PKA regulatory subunit, while cells from patients with germline chromosomal gains showed increased protein levels; in both cases, PKA activity was increased. The present study shows that more than one third of cortisol-producing adenomas associated with overt Cushing syndrome harbor unique somatic mutations of the main cAMP-dependent kinase catalytic subunit, PRKACA resulting in constitutive PKA activation. While in these patients the mutation is present only in tumor cells, germline duplication of the PRKACA gene was identified in a group of patients with bilateral adrenal hyperplasias. This is the first report of genetic alterations of the catalytic subunit of PKA linked to human disease: Germline PRKACA duplications with bilateral adrenal hyperplasias and somatic PRKACA mutations with unilateral cortisol producing adrenal adenomas.

Citation Format: Fabio R. Faucz, Felix Beuschlei, Martin Fassnacht, Guilaume Assie, Davide Calebiro, Constantine Stratakis, Andrea Osswald, Cristina L. Ronchi, Thomas Wieland, Silviu Sbiera, Katrin Schaak, Anett Schmittfull, Thomas Schwarzmayr, Olivia Barreau, Delphine Vezzosi, Marthe Rizk-Rabbin, Ulrike Zabel, Eva Szarek, Paraskevi Salpea, Antonella Forlino, Annalisa Vetro, Orsetta Zuffardi, Caroline Kisker, Susanne Diener, Thomas Meitinger, Martin J. Lohse, Martin Reincke, Jerome Bertherat, Tim M. Strom, Bruno Allolio. Constitutive activation of PRKACA in adrenal Cushing's syndrome. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-182. doi:10.1158/1538-7445.AM2014-LB-182