Alternate protein kinase A activity identifies a unique population of stromal cells in adult bone

Levofloxacin induces differential effects in the transcriptome between the gut, peripheral and axial joints in the Spondyloarthritis DBA/1 mice: Improvement of intestinal dysbiosis and the overall inflammatory process

To analyze the effect of levofloxacin-induced intestinal microbiota modifications on intestinal, joint, and systemic inflammation in the DBA/1 mice with spontaneous arthritis. The study included two groups of mice, one of which received levofloxacin. The composition and structure of the microbiota were determined in the mice's stool using 16S rRNA sequencing; the differential taxa and metabolic pathway between mice treated with levofloxacin and control mice were also defied. The effect of levofloxacin was evaluated in the intestines, hind paws, and spines of mice through DNA microarray transcriptome and histopathological analyses; systemic inflammation was measured by flow cytometry. Levofloxacin decreased the pro-inflammatory bacteria, including Prevotellaceae, Odoribacter, and Blautia, and increased the anti-inflammatory Muribaculaceae in mice's stool. Histological analysis confirmed the intestinal inflammation in control mice, while in levofloxacin-treated mice, inflammation was reduced; in the hind paws and spines, levofloxacin also decreased the inflammation. Microarray showed the downregulation of genes and signaling pathways relevant in spondyloarthritis, including several cytokines and chemokines. Levofloxacin-treated mice showed differential transcriptomic profiles between peripheral and axial joints and intestines. Levofloxacin decreased the expression of TNF-α, IL-23a, and JAK3 in the three tissues, but IL-17 behaved differently in the intestine and the joints. Serum TNF-α was also reduced in levofloxacin-treated mice. Our results suggest that the microbiota modification aimed at reducing pro-inflammatory and increasing anti-inflammatory bacteria could potentially be a coadjuvant in treating inflammatory arthropathies.

Fourier Transform Infrared Spectroscopy (FT-IR) of Pseudomonas aeruginosa post photodynamic therapy with Curcumin in vitro

Alternative therapies against pathogens are under intense investigation because of their increasing resistance to antibiotics. Photodynamic therapy (PDT) is one such alternative that has shown promising results. However, for the widespread use of PDT, it is essential to decipher underlying mechanisms, so as to improve PDT's therapeutic applications. Because of this, we have studied biochemical changes in pathogen Pseudomonas aeruginosa, a medically important bacteria that has developed antibiotic resistance, after PDT with curcumin photosensitizer. Results show a drastic decrease in α-helix protein and increased disordered and β-sheet secondary structure proteins in P. Aeruginosa post-PDT compared to control. Interestingly, these biochemical changes differ from PDT of pathogens Leishmania braziliensis and Leishmania major with photosensitizer methylene blue. This observation underlines the need for extensive studies on PDT of different pathogens to understand mechanisms of action and develop better PDT strategies.

Fibrous dysplasia animal models: A systematic review

BACKGROUND

Fibrous dysplasia (FD) is a rare genetic bone disorder resulting in an overproduction of cAMP leading to a structurally unsound tissue, caused by a genetic mutation in the guanine nucleotide-binding protein gene (GNAS). In order to better understand this disease, several animal models have been developed with different strategies and features.

OBJECTIVE

Conduct a systematic review to analyze and compare animal models with the causative mutation and features of FD.

METHODS

A PRISMA search was conducted in Scopus, PubMed, and Web of Science. Studies reporting an in vivo model of FD that expressed the causative mutation were included for analysis. Models without the causative mutation, but developed an FD phenotype and models of FD cell implantation were included for subanalysis.

RESULTS

Seven unique models were identified. The models were assessed and compared for their face validity, construct validity, mosaicism, and induction methods. This was based on the features of clinical FD that were reported within the categories of: macroscopic features, imaging, histology and histomorphometry, histochemical and cellular markers, and blood/urine markers.

LIMITATIONS

None of the models reported all features of FD and some features were only reported in one model. This made comparing models a challenge, but indicates areas where further research is necessary.

CONCLUSION

The benefits and disadvantages of every model were assessed from a practical and scientific standpoint. While all published reports lacked complete data, the models have nonetheless informed our understanding of FD and provided meaningful information to guide researchers in bench and clinical research.

Prkar1a haploinsufficiency ameliorates the growth hormone excess phenotype in Aip-deficient mice

Mutations of the regulatory subunit (PRKAR1A) of the cyclic adenosine monophosphate (cAMP)-dependent protein kinase (PKA), leading to activation of the PKA pathway, are the genetic cause of Carney complex which is frequently accompanied by somatotroph tumors. Aryl hydrocarbon receptor-interacting protein (AIP) mutations lead to somatotroph tumorigenesis in mice and humans. The mechanisms of AIP-dependent pituitary tumorigenesis are still under investigation and evidence points to a connection between the AIP and PKA pathways. In this study, we explore the combined effects of Aip and Prkar1a deficiency on mouse phenotype and, specifically, pituitary histopathology. Aip+/- mice were compared with double heterozygous Aip+/-, Prkar1a+/- mice. The phenotype (including histopathology and serological studies) was recorded at 3, 6, 9 and 12 months of age. Detailed pituitary histological and immunohistochemical studies were performed at 12 months. Twelve-month old Aip+/- mice demonstrated phenotypic and biochemical evidence of GH excess including significantly elevated insulin-like growth factor 1 levels, larger weight and body length, higher hemoglobin and cholesterol levels and a higher frequency of growth plate thickening in comparison to Aip+/, Prkar1a+/- mice. Pituitary histopathology did not uncover any pituitary adenomas or somatotroph hyperplasia in either group. These results demonstrate a slow progression from elevated GH release to the formation of overt somatotropinomas in Aip+/- mice; the acromegalic phenotype of these mice is surprisingly ameliorated in Aip+/-, Prkar1a+/- mice. This highlights the complexities of interaction between the AIP and PKA pathway. Specifically targeting GH secretion rather than somatotroph proliferation may be an advantage in the medical treatment of AIP-dependent human acromegaly.

Germline and Mosaic Variants in PRKACA and PRKACB Cause a Multiple Congenital Malformation Syndrome

PRKACA and PRKACB code for two catalytic subunits (Cα and Cβ) of cAMP-dependent protein kinase (PKA), a pleiotropic holoenzyme that regulates numerous fundamental biological processes such as metabolism, development, memory, and immune response. We report seven unrelated individuals presenting with a multiple congenital malformation syndrome in whom we identified heterozygous germline or mosaic missense variants in PRKACA or PRKACB. Three affected individuals were found with the same PRKACA variant, and the other four had different PRKACB mutations. In most cases, the mutations arose de novo, and two individuals had offspring with the same condition. Nearly all affected individuals and their affected offspring shared an atrioventricular septal defect or a common atrium along with postaxial polydactyly. Additional features included skeletal abnormalities and ectodermal defects of variable severity in five individuals, cognitive deficit in two individuals, and various unusual tumors in one individual. We investigated the structural and functional consequences of the variants identified in PRKACA and PRKACB through the use of several computational and experimental approaches, and we found that they lead to PKA holoenzymes which are more sensitive to activation by cAMP than are the wild-type proteins. Furthermore, expression of PRKACA or PRKACB variants detected in the affected individuals inhibited hedgehog signaling in NIH 3T3 fibroblasts, thereby providing an underlying mechanism for the developmental defects observed in these cases. Our findings highlight the importance of both Cα and Cβ subunits of PKA during human development.

PRKACB variants in skeletal disease or adrenocortical hyperplasia: effects on protein kinase A

Genetic variants in components of the protein kinase A (PKA) enzyme have been associated with various defects and neoplasms in the context of Carney complex (CNC) and in isolated cases, such as in primary pigmented nodular adrenocortical disease (PPNAD), cortisol-producing adrenal adenomas (CPAs), and various cancers. PRKAR1A mutations have been found in subjects with impaired cAMP-dependent signaling and skeletal defects; bone tumors also develop in both humans and mice with PKA abnormalities. We studied the PRKACB gene in 148 subjects with PPNAD and related disorders, who did not have other PKA-related defects and identified two subjects with possibly pathogenic PRKACB gene variants and unusual bone and endocrine phenotypes. The first presented with bone and other abnormalities and carried a de novo c.858_860GAA (p.K286del) variant. The second subject carried the c.899C>T (p.T300M or p.T347M in another isoform) variant and had a PPNAD-like phenotype. Both variants are highly conserved in the PRKACB gene. In functional studies, the p.K286del variant affected PRKACB protein stability and led to increased PKA signaling. The p.T300M variant did not affect protein stability or response to cAMP and its pathogenicity remains uncertain. We conclude that PRKACB germline variants are uncommon but may be associated with phenotypes that resemble those of other PKA-related defects. However, detailed investigation of each variant is needed as PRKACB appears to be only rarely affected in these conditions, and variants such as p.T300M maybe proven to be clinically insignificant, whereas others (such as p.K286del) are clearly pathogenic and may be responsible for a novel syndrome, associated with endocrine and skeletal abnormalities.

Knock-In of the Recurrent R368X Mutation of PRKAR1A that Represses cAMP-Dependent Protein Kinase A Activation: A Model of Type 1 Acrodysostosis

In humans, activating mutations in the PRKAR1A gene cause acrodysostosis 1 (ACRDYS1). These mutations result in a reduction in PKA activation caused by an impaired ability of cAMP to dissociate mutant PRKAR1A from catalytic PKA subunits. Two striking features of this rare developmental disease are renal resistance to PTH and chondrodysplasia resulting from the constitutive inhibition of PTHR1/Gsa/AC/cAMP/PKA signaling. We developed a knock-in of the recurrent ACRDYS1 R368X PRKAR1A mutation in the mouse. No litters were obtained from [R368X]/[+] females (thus no homozygous [R368X]/[R368X] mice). In [R368X]/[+] mice, Western blot analysis confirmed mutant allele heterozygous expression. Growth retardation, peripheral acrodysostosis (including brachydactyly affecting all digits), and facial dysostosis were shown in [R368X]/[+] mice by weight curves and skeletal measurements (μCT scan) as a function of time. [R368X]/[+] male and female mice were similarly affected. Unexpected, however, whole-mount skeletal preparations revealed a striking delay in mineralization in newborn mutant mice, accompanied by a decrease in the height of terminal hypertrophic chondrocyte layer, an increase in the height of columnar proliferative prehypertrophic chondrocyte layer, and changes in the number and spatial arrangement of proliferating cell nuclear antigen (PCNA)-positive chondrocytes. Plasma PTH and basal urinary cAMP were significantly higher in [R368X]/[+] compared to WT mice. PTH injection increased urinary cAMP similarly in [R368X]/[+] and WT mice. PRKACA expression was regulated in a tissue (kidney not bone and liver) manner. This model, the first describing the germline expression of a PRKAR1A mutation causing dominant repression of cAMP-dependent PKA, reproduced the main features of ACRDYS1 in humans. It should help decipher the specificity of the cAMP/PKA signaling pathway, crucial for numerous stimuli. In addition, our results indicate that PRKAR1A, by tempering intracellular cAMP levels, is a molecular switch at the crossroads of signaling pathways regulating chondrocyte proliferation and differentiation. © 2016 American Society for Bone and Mineral Research.

Celecoxib treatment of fibrous dysplasia (FD) in a human FD cell line and FD-like lesions in mice with protein kinase A (PKA) defects

Osteochondromyxomas (OMX) in the context of Carney complex (CNC) and fibrous dysplasia (FD)-like lesions (FDLL) in mice, as well as isolated myxomas in humans may be caused by inactivation of PRKAR1A, the gene coding for the type 1a regulatory subunit (R1α) of cAMP-dependent protein kinase (PKA). OMXs and FDLL in mice lacking Prkar1a grow from abnormal proliferation of adult bone stromal cells (aBSCs). Prkar1a and Prkaca (coding for Cα) haploinsufficiency leads to COX2 activation and prostaglandin E2 (PGE2) production that, in turn, activates proliferation of aBSCs. Celecoxib is a cyclooxygenase-2 (COX2) inhibitor. We hypothesized that COX-2 inhibition may have an effect in FD and FDLL. In vitro treatment of a human cell line prepared from a FD patient with Celecoxib resulted in decreased PGE2 and cell proliferation. Treatment of mice haploinsufficient for R1α and Cα with 1500 mg/kg Celecoxib led to decreased PGE2 and proliferation and increased apoptosis, with a corresponding gene expression profile, resulting in dramatic reduction of tumor growth. Furthermore, the treatment improved the organization of cortical bone that was adjacent to the tumor. We conclude that, in vitro and in vivo, Celecoxib had an inhibitory effect on FD cell proliferation and in mouse FDLL structure, respectively. We speculate that COX-2 inhibitors offer an attractive alternative to current treatments for benign tumors such as OMX and FD that, apart from tumor suppression, may mechanically stabilize affected bones.

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.

MEN1, MEN4, and Carney Complex: Pathology and Molecular Genetics

Pituitary adenomas are a common feature of a subset of endocrine neoplasia syndromes, which have otherwise highly variable disease manifestations. We provide here a review of the clinical features and human molecular genetics of multiple endocrine neoplasia (MEN) type 1 and 4 (MEN1 and MEN4, respectively) and Carney complex (CNC). MEN1, MEN4, and CNC are hereditary autosomal dominant syndromes that can present with pituitary adenomas. MEN1 is caused by inactivating mutations in the MEN1 gene, whose product menin is involved in multiple intracellular pathways contributing to transcriptional control and cell proliferation. MEN1 clinical features include primary hyperparathyroidism, pancreatic neuroendocrine tumours and prolactinomas as well as other pituitary adenomas. A subset of patients with pituitary adenomas and other MEN1 features have mutations in the CDKN1B gene; their disease has been called MEN4. Inactivating mutations in the type 1α regulatory subunit of protein kinase A (PKA; the PRKAR1A gene), that lead to dysregulation and activation of the PKA pathway, are the main genetic cause of CNC, which is clinically characterised by primary pigmented nodular adrenocortical disease, spotty skin pigmentation (lentigines), cardiac and other myxomas and acromegaly due to somatotropinomas or somatotrope hyperplasia.

Activation of Protein Kinase A in Mature Osteoblasts Promotes a Major Bone Anabolic Response

Protein kinase A (PKA) regulates osteoblast cell function in vitro and is activated by important bone mass modulating agents. We determined whether PKA activation in osteoblasts is sufficient to mediate a bone anabolic response. Thus, a mouse model conditionally expressing a constitutively active PKA (CA-PKA) in osteoblasts (CA-PKA-OB mouse) was developed by crossing a 2.3-kb α1 (I)-collagen promoter-Cre mouse with a floxed-CA-PKA mouse. Primary osteoblasts from the CA-PKA-OB mice exhibited higher basal PKA activity than those from control mice. Microcomputed tomographic analysis revealed that CA-PKA-OB female mice had an 8.6-fold increase in femoral but only 1.16-fold increase in lumbar 5 vertebral bone volume/total volume. Femur cortical thickness and volume were also higher in the CA-PKA-OB mice. In contrast, alterations in many femoral microcomputed tomographic parameters in male CA-PKA-OB mice were modest. Interestingly, the 3-dimensional structure model index was substantially lower both in femur and lumbar 5 of male and female CA-PKA-OB mice, reflecting an increase in the plate to rod-like structure ratio. In agreement, femurs from female CA-PKA-OB mice had greater load to failure and were stiffer compared with those of control mice. Furthermore, the CA-PKA-OB mice had higher levels of serum bone turnover markers and increased osteoblast and osteoclast numbers per total tissue area compared with control animals. In summary, constitutive activation of PKA in osteoblasts is sufficient to increase bone mass and favorably modify bone architecture and improve mechanical properties. PKA activation in mature osteoblasts is, therefore, an important target for designing anabolic drugs for treating diseases with bone loss.

Celecoxib reduces glucocorticoids in vitro and in a mouse model with adrenocortical hyperplasia

Primary pigmented nodular adrenocortical disease (PPNAD), whether in the context of Carney complex (CNC) or isolated, leads to ACTH-independent Cushing's syndrome (CS). CNC and PPNAD are caused typically by inactivating mutations of PRKAR1A, a gene coding for the type 1a regulatory subunit (R1α) of cAMP-dependent protein kinase (PKA). Mice lacking Prkar1a, specifically in the adrenal cortex (AdKO) developed CS caused by bilateral adrenal hyperplasia (BAH), which is formed from the abnormal proliferation of fetal-like adrenocortical cells. Celecoxib is a cyclooxygenase 2 (COX2) inhibitor. In bone, Prkar1a inhibition is associated with COX2 activation and prostaglandin E2 (PGE2) production that, in turn, activates proliferation of bone stromal cells. We hypothesized that COX2 inhibition may have an effect in PPNAD. In vitro treatment of human cell lines, including one from a patient with PPNAD, with celecoxib resulted in decreased cell viability. We then treated AdKO and control mice with 1500 mg/kg celecoxib or vehicle. Celecoxib treatment led to decreased PGE2 and corticosterone levels, reduced proliferation and increased apoptosis of adrenocortical cells, and decreased steroidogenic gene expression. We conclude that, in vitro and in vivo, celecoxib led to decreased steroidogenesis. In a mouse model of PPNAD, celecoxib caused histological changes that, at least in part, reversed BAH and this was associated with a reduction of corticosterone levels.

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.

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.

DNAJB1-PRKACA is specific for fibrolamellar carcinoma

Fibrolamellar carcinoma is a distinct subtype of hepatocellular carcinoma that predominantly affects young patients without underlying cirrhosis. A recurrent DNAJB1-PRKACA fusion has recently been reported in fibrolamellar carcinomas. To determine the specificity of this fusion and to develop routinely available clinical methods of detection, we developed an RT-PCR assay for paraffin-embedded tissues and a FISH probe for detection of the rearrangements of the PRKACA locus. We also developed an RNA in situ hybridization assay to assess expression levels of the total chimeric transcript and wild-type transcripts. A total of 106 primary liver tumors were studied by RT-PCR, including 26 fibrolamellar carcinomas (4 of which were metastases to the abdominal wall or lymph nodes), 25 conventional hepatocellular carcinomas, 25 cholangiocarcinomas, 25 hepatic adenomas, and 5 hepatoblastomas. RT-PCR was successful in 92% of tested fibrolamellar carcinoma cases (24/26) and the DNAJB1-PRKACA fusion transcript was found in all fibrolamellar carcinomas but not in other tumor types. FISH was tested in 19 fibrolamellar carcinomas and in 6 scirrhous hepatocellular carcinomas, which can closely mimic fibrolamellar carcinoma. Rearrangements of the PRKACA locus was seen in all 19 fibrolamellar carcinoma specimens, but in none of the scirrhous hepatocellular carcinomas. Finally, a RNA in situ hybridization strategy was positive in 7/7 successfully hybridized cases, and showed mRNA over-expression in all of the fibrolamellar carcinomas. In addition, the stromal cells embedded in the characteristic intratumoral fibrosis of fibrolamellar carcinomas and the background liver tissues were negative for the DNAJB1-PRKACA fusion by all tested methods. In conclusion, detection of DNAJB1-PRKACA is a very sensitive and specific finding in support of the diagnosis of fibrolamellar carcinoma.

Osteoblast-specific expression of the fibrous dysplasia (FD)-causing mutation Gsα(R201C) produces a high bone mass phenotype but does not reproduce FD in the mouse

We recently reported the generation and initial characterization of the first direct model of human fibrous dysplasia (FD; OMIM #174800), obtained through the constitutive systemic expression of one of the disease-causing mutations, Gsα(R201C) , in the mouse. To define the specific pathogenetic role(s) of individual cell types within the stromal/osteogenic system in FD, we generated mice expressing Gsα(R201C) selectively in mature osteoblasts using the 2.3kb Col1a1 promoter. We show here that this results in a striking high bone mass phenotype but not in a mimicry of human FD. The high bone mass phenotype involves specifically a deforming excess of cortical bone and prolonged and ectopic cortical bone remodeling. Expression of genes characteristic of late stages of bone cell differentiation/maturation is profoundly altered as a result of expression of Gsα(R201C) in osteoblasts, and expression of the Wnt inhibitor Sost is reduced. Although high bone mass is, in fact, a feature of some types/stages of FD lesions in humans, it is marrow fibrosis, localized loss of adipocytes and hematopoietic tissue, osteomalacia, and osteolytic changes that together represent the characteristic pathological profile of FD, as well as the sources of specific morbidity. None of these features are reproduced in mice with osteoblast-specific expression of Gsα(R201C) . We further show that hematopoietic progenitor/stem cells, as well as more mature cell compartments, and adipocyte development are normal in these mice. These data demonstrate that effects of Gsα mutations underpinning FD-defining tissue changes and morbidity do not reflect the effects of the mutations on osteoblasts proper.

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.

Constitutive expression of Gsα(R201C) in mice produces a heritable, direct replica of human fibrous dysplasia bone pathology and demonstrates its natural history

Fibrous dysplasia of bone (FD) is a crippling skeletal disease associated with postzygotic mutations (R201C, R201H) of the gene encoding the α subunit of the stimulatory G protein, Gs. By causing a characteristic structural subversion of bone and bone marrow, the disease results in deformity, hypomineralization, and fracture of the affected bones, with severe morbidity arising in childhood or adolescence. Lack of inheritance of the disease in humans is thought to reflect embryonic lethality of germline-transmitted activating Gsα mutations, which would only survive through somatic mosaicism. We have generated multiple lines of mice that express Gsα(R201C) constitutively and develop an inherited, histopathologically exact replica of human FD. Robust transgene expression in neonatal and embryonic tissues and embryonic stem (ES) cells were associated with normal development of skeletal tissues and differentiation of skeletal cells. As in humans, FD lesions in mice developed only in the postnatal life; a defined spatial and temporal pattern characterized the onset and progression of lesions across the skeleton. In individual bones, lesions developed through a sequence of three distinct histopathological stages: a primary modeling phase defined by endosteal/medullary excess bone formation and normal resorption; a secondary phase, with excess, inappropriate remodeling; and a tertiary fibrous dysplastic phase, which reproduced a full-blown replica of the human bone pathology in mice of age ≥1 year. Gsα mutations are sufficient to cause FD, and are per se compatible with germline transmission and normal embryonic development in mice. Our novel murine lines constitute the first model of FD.

Clinical and molecular genetics of the phosphodiesterases (PDEs)

Cyclic nucleotide phosphodiesterases (PDEs) are enzymes that have the unique function of terminating cyclic nucleotide signaling by catalyzing the hydrolysis of cAMP and GMP. They are critical regulators of the intracellular concentrations of cAMP and cGMP as well as of their signaling pathways and downstream biological effects. PDEs have been exploited pharmacologically for more than half a century, and some of the most successful drugs worldwide today affect PDE function. Recently, mutations in PDE genes have been identified as causative of certain human genetic diseases; even more recently, functional variants of PDE genes have been suggested to play a potential role in predisposition to tumors and/or cancer, especially in cAMP-sensitive tissues. Mouse models have been developed that point to wide developmental effects of PDEs from heart function to reproduction, to tumors, and beyond. This review brings together knowledge from a variety of disciplines (biochemistry and pharmacology, oncology, endocrinology, and reproductive sciences) with emphasis on recent research on PDEs, how PDEs affect cAMP and cGMP signaling in health and disease, and what pharmacological exploitations of PDEs may be useful in modulating cyclic nucleotide signaling in a way that prevents or treats certain human diseases.

Knockdown of PRKAR1A, the gene responsible for Carney complex, interferes with differentiation in osteoblastic cells

PRKAR1A is the gene encoding the type 1A regulatory subunit of protein kinase A, and it is the cause of the inherited human tumor syndrome Carney complex. Data from our laboratory has demonstrated that Prkar1a loss causes tumors in multiple cell lineages, including neural crest cells and osteoblasts. We have proposed that one mechanism by which tumorigenesis occurs is through the failure of terminal differentiation. In the present study, we directly test the effects of Prkar1a reduction on osteogenic differentiation in mouse and human cells in vitro. We found that Prkar1a levels noticeably increased during osteoblastic differentiation, indicating a positive correlation between the expression of Prkar1a and osteogenic potential. To validate this hypothesis, we generated stable Prkar1a knockdown in both mouse and human cells. These cells displayed significantly suppressed bone nodule formation and decreased expression of osteoblast markers such as osteocalcin and osteopontin. These observations imply that the antiosteogenic effect of Prkar1a ablation is not species or cell line specific. Furthermore, because Runt-related transcription factor-2 (Runx2) is a key mediator of osteoblast differentiation, we reasoned that the function of this transcription factor may be inhibited by Prkar1a knockdown. Chromatin immunoprecipitation and luciferase assays demonstrated that Prkar1a ablation repressed DNA binding and function of Runx2 at its target genes. Additionally, we determined that this effect is likely due to reductions in the Runx2-cooperating transcription factors forkhead box O1 and activating transcription factor 4. Taken together, this study provides direct evidence that ablation of Prkar1a interferes with signaling pathways necessary for osteoblast differentiation.

Inactivation of the Carney complex gene 1 (PRKAR1A) alters spatiotemporal regulation of cAMP and cAMP-dependent protein kinase: a study using genetically encoded FRET-based reporters

Carney complex (CNC) is a hereditary disease associating cardiac myxoma, spotty skin pigmentation and endocrine overactivity. CNC is caused by inactivating mutations in the PRKAR1A gene encoding PKA type I alpha regulatory subunit (RIα). Although PKA activity is enhanced in CNC, the mechanisms linking PKA dysregulation to endocrine tumorigenesis are poorly understood. In this study, we used Förster resonance energy transfer (FRET)-based sensors for cAMP and PKA activity to define the role of RIα in the spatiotemporal organization of the cAMP/PKA pathway. RIα knockdown in HEK293 cells increased basal as well as forskolin or prostaglandin E1 (PGE1)-stimulated total cellular PKA activity as reported by western blots of endogenous PKA targets and the FRET-based global PKA activity reporter, AKAR3. Using variants of AKAR3 targeted to subcellular compartments, we identified similar increases in the response to PGE1 in the cytoplasm and at the outer mitochondrial membrane. In contrast, at the plasma membrane, the response to PGE1 was decreased along with an increase in basal FRET ratio. These results were confirmed by western blot analysis of basal and PGE1-induced phosphorylation of membrane-associated vasodilator-stimulated phosphoprotein. Similar differences were observed between the cytoplasm and the plasma membrane in human adrenal cells carrying a RIα inactivating mutation. RIα inactivation also increased cAMP in the cytoplasm, at the outer mitochondrial membrane and at the plasma membrane, as reported by targeted versions of the cAMP indicator Epac1-camps. These results show that RIα inactivation leads to multiple, compartment-specific alterations of the cAMP/PKA pathway revealing new aspects of signaling dysregulation in tumorigenesis.

cAMP/PKA signaling defects in tumors: genetics and tissue-specific pluripotential cell-derived lesions in human and mouse

In the last few years, bench and clinical studies led to significant new insight into how cyclic adenosine monophosphate (cAMP) signaling, the molecular pathway that had been identified in the early 2000s as the one involved in most benign cortisol-producing adrenal hyperplasias, affects adrenocortical growth and development, as well as tumor formation. A major discovery was the identification of tissue-specific pluripotential cells (TSPCs) as the culprit behind tumor formation not only in the adrenal, but also in bone. Discoveries in animal studies complemented a number of clinical observations in patients. Gene identification continued in parallel with mouse and other studies on the cAMP signaling and other pathways.

Downregulation of PKD1 by shRNA results in defective osteogenic differentiation via cAMP/PKA pathway in human MG-63 cells

Mutations and/or deletions of Pkd1 in mouse models resulted in attenuation of osteoblast function and defective bone formation; however, the function of PKD1 in human osteoblast and bone remains uncertain. In the current study, we used lentivirus-mediated shRNA technology to stably knock down PKD1 in the human osteoblastic MG-63 cell line and to investigate the role of PKD1 on human osteoblast function and molecular mechanisms. We found that a 53% reduction of PKD1 by PKD1 shRNA in stable, transfected MG-63 cells resulted in increased cell proliferation and impaired osteoblastic differentiation as reflected by increased BrdU incorporation, decreased alkaline phosphatase activity, and calcium deposition and by decreased expression of RUNX2 and OSTERIX compared to control shRNA MG-63 cells. In addition, knockdown of PKD1 mRNA caused enhanced adipogenesis in stable PKD1 shRNA MG-63 cells as evidenced by elevated lipid accumulation and increased expression of adipocyte-related markers such as PPARγ and aP2. The stable PKD1 shRNA MG-63 cells exhibited lower basal intracellular calcium, which led to attenuated cytosolic calcium signaling in response to fluid flow shear stress, as well as increased intracellular cAMP messages in response to forskolin (10 µM) stimulation. Moreover, increased cell proliferation, inhibited osteoblastic differentiation, and osteogenic and adipogenic gene markers were significantly reversed in stable PKD1 shRNA MG-63 cells when treated with H89 (1 µM), an inhibitor of PKA. These findings suggest that downregulation of PKD1 in human MG-63 cells resulted in defective osteoblast function via intracellular calcium-cAMP/PKA signaling pathway.

Anxiety phenotype in mice that overexpress protein kinase A

The role of cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) signaling in the molecular pathways involved in fear and memory is well established. Prior studies in our lab reported that transgenic mice with an inactivating mutation in Prkar1a gene (codes for the 1-alpha regulatory subunit (R1α) of PKA) exhibited behavioral abnormalities including anxiety and depression. In the present study, we examined the role of altered PKA signaling on anxiety-like behaviors in Prkar1a(+/-) mice compared to wild-type (WT) littermates. The elevated plus maze (EPM) and marble bury (MB) tests were used to assess anxiety-like behavior. The hotplate test was performed to evaluate analgesia. We further examined the impact of the Prkar1a inactivating mutation on PKA activity in specific nuclei of the brain associated with anxiety-like behavior. Results for the MB test showed a genotype effect, with increased anxiety-like behavior in Prkar1a(+/-) mice, compared to WT littermates (p<0.05). MANOVA analysis showed a significant genotype difference in anxiety-like behavior in the EPM between WT and Prkar1a(+/-) mice on combined dependent variables (open arm time and open to total time ratio; p<0.05). Results of hotplate testing showed no genotype effect however; the expected sex difference was noted. Analysis of PKA activity showed the loss of one Prkar1a allele led to an increase in basal and cAMP-stimulated kinase activity in both the basolateral and central amygdala. These results suggest that the alteration in PKA signaling in Prkar1a(+/-) mice is not a ubiquitous effect; and supports the importance of cAMP/PKA pathway in neurobiological processes involved in anxiety and fear sensitization.

The transcriptome that mediates increased cyclic adenosine monophosphate signaling in PRKAR1A defects and other settings

OBJECTIVE

To review current knowledge on the involvement of cyclic adenosine monophosphate (cAMP) and interacting signaling pathways in predisposition to tumor formation in primary pigmented nodular adrenocortical disease (PPNAD), a type of bilateral adrenal hyperplasia (BAH) related to the multiple endocrine neoplasia Carney complex, and also in isolated PPNAD and other BAHs.

METHODS

We review the pertinent literature and discuss genetic defects associated with various endocrine and nonendocrine tumors.

RESULTS

A decade ago, we discovered that PPNAD and the Carney complex are caused by PRKAR1A mutations. PRKAR1A encodes the protein kinase A (PKA) regulatory subunit type IA, an important regulator of cAMP signaling in most cells. Recently, we described PKA or PRKAR1A abnormalities in a variety of other BAHs; in some of these cases, mutations in additional genes of the cAMP signaling pathway, the phosphodiesterases, were identified. Transcriptomic analyses of human lesions or animal models showed that abnormal cAMP/PKA signaling in the adrenal glands, and also in other tissues such as bone, leads to proliferation of tissue-specific pluripotential cells through activation of Wnt signaling.

CONCLUSION

Recent findings indicate the relevance of cAMP signaling in the pathogenesis of adrenocortical disease and point to the Wnt signaling pathway as a potential important mediator of tumorigenesis related to increased cAMP or PKA signaling (or both).

Differential role of PKA catalytic subunits in mediating phenotypes caused by knockout of the Carney complex gene Prkar1a

The Carney complex is an inherited tumor predisposition caused by activation of the cAMP-dependent protein kinase [protein kinase A (PKA)] resulting from mutation of the PKA-regulatory subunit gene PRKAR1A. Myxomas and tumors in cAMP-responsive tissues are cardinal features of this syndrome, which is unsurprising given the important role played by PKA in modulating cell growth and function. Previous studies demonstrated that cardiac-specific knockout of Prkar1a causes embryonic heart failure and myxomatous degeneration in the heart, whereas limited Schwann cell-specific knockout of the gene causes schwannoma formation. In this study, we sought to determine the role of PKA activation in this phenotype by using genetic means to reduce PKA enzymatic activity. To accomplish this goal, we introduced null alleles of the PKA catalytic subunits Prkaca (Ca) or Prkacb (Cb) into the Prkar1a-cardiac knockout (R1a-CKO) or limited Schwann cell knockout (R1a-TEC3KO) line. Heterozygosity for Prkaca rescued the embryonic lethality of the R1a-CKO, although mice had a shorter than normal lifespan and died from cardiac failure with atrial thrombosis. In contrast, heterozygosity for Prkacb only enabled the mice to survive 1 extra day during embryogenesis. Biochemical analysis indicated that reduction of Ca markedly reduced PKA activity in embryonic hearts, whereas reduction of Cb had minimal effects. In R1a-TEC3KO mice, tumorigenesis was completely suppressed by a heterozygosity for Prkaca, and by more than 80% by heterozygosity for Prkacb. These data suggest that both developmental and tumor phenotypes caused by Prkar1a mutation result from excess PKA activity due to PKA-Ca.

Role of nonselective cation channels in spontaneous and protein kinase A-stimulated calcium signaling in pituitary cells

Several receptors linked to the adenylyl cyclase signaling pathway stimulate electrical activity and calcium influx in endocrine pituitary cells, and a role for an unidentified sodium-conducting channel in this process has been proposed. Here we show that forskolin dose-dependently increases cAMP production and facilitates calcium influx in about 30% of rat and mouse pituitary cells at its maximal concentration. The stimulatory effect of forskolin on calcium influx was lost in cells with inhibited PKA (cAMP-dependent protein kinase) and in cells that were haploinsufficient for the main PKA regulatory subunit but was preserved in cells that were also haploinsufficient for the main PKA catalytic subunit. Spontaneous and forskolin-stimulated calcium influx was present in cells with inhibited voltage-gated sodium and hyperpolarization-activated cation channels but not in cells bathed in medium, in which sodium was replaced with organic cations. Consistent with the role of sodium-conducting nonselective cation channels in PKA-stimulated Ca(2+) influx, cAMP induced a slowly developing current with a reversal potential of about 0 mV. Two TRP (transient receptor potential) channel blockers, SKF96365 and 2-APB, as well as flufenamic acid, an inhibitor of nonselective cation channels, also inhibited spontaneous and forskolin-stimulated electrical activity and calcium influx. Quantitative RT-PCR analysis indicated the expression of mRNA transcripts for TRPC1 >> TRPC6 > TRPC4 > TRPC5 > TRPC3 in rat pituitary cells. These experiments suggest that in pituitary cells constitutively active cation channels are stimulated further by PKA and contribute to calcium signaling indirectly by controlling the pacemaking depolarization in a sodium-dependent manner and directly by conducting calcium.

Recurrent PRKAR1A mutation in acrodysostosis with hormone resistance

The skeletal dysplasia characteristic of acrodysostosis resembles the Albright's hereditary osteodystrophy seen in patients with pseudohypoparathyroidism type 1a, but defects in the α-stimulatory subunit of the G-protein (GNAS), the cause of pseudohypoparathyroidism type 1a, are not present in patients with acrodysostosis. We report a germ-line mutation in the gene encoding PRKAR1A, the cyclic AMP (cAMP)-dependent regulatory subunit of protein kinase A, in three unrelated patients with acrodysostosis and resistance to multiple hormones. The mutated subunit impairs the protein kinase A response to stimulation by cAMP; this explains our patients' hormone resistance and the similarities of their skeletal abnormalities with those observed in patients with pseudohypoparathyroidism type 1a.

How does cAMP/protein kinase A signaling lead to tumors in the adrenal cortex and other tissues?

The overwhelming majority of benign lesions of the adrenal cortex leading to Cushing syndrome are linked to one or another abnormality of the cAMP signaling pathway. A small number of both massive macronodular adrenocortical disease and cortisol-producing adenomas harbor somatic GNAS mutations. Micronodular adrenocortical hyperplasias are either pigmented (the classic form being that of primary pigmented nodular adrenocortical disease) or non-pigmented; micronodular adrenocortical hyperplasias can be seen in the context of other conditions or isolated; for example, primary pigmented nodular adrenocortical disease usually occurs in the context of Carney complex, but isolated primary pigmented nodular adrenocortical disease has also been described. Both Carney complex and isolated primary pigmented nodular adrenocortical disease are caused by germline PRKAR1A mutations; somatic mutations of this gene that regulates cAMP-dependent protein kinase are also found in cortisol-producing adenomas, and abnormalities of PKA are present in most cases of massive macronodular adrenocortical disease. Micronodular adrenocortical hyperplasias and some cortisol-producing adenomas are associated with phosphodiesterase 11A and 8B defects, coded, respectively, by the PDE11A and PDE8B genes. Mouse models of Prkar1a deficiency also show that increased cAMP signaling leads to tumors in adrenal cortex and other tissues. In this review, we summarize all recent data from ours and other laboratories, supporting the view that Wnt-signaling acts as an important mediator of tumorigenicity induced by abnormal PRKAR1A function and aberrant cAMP signaling.

Protein kinase A regulates caspase-1 via Ets-1 in bone stromal cell-derived lesions: a link between cyclic AMP and pro-inflammatory pathways in osteoblast progenitors

Patients with genetic defects of the cyclic (c) adenosine-monophosphate (AMP)-signaling pathway and those with neonatal-onset multisystem inflammatory disease (NOMID) develop tumor-like lesions of the long bones. The molecular basis of this similarity is unknown. NOMID is caused by inappropriate caspase-1 activity, which in turn activates the inflammasome. The present study demonstrates that NOMID bone lesions are derived from the same osteoblast progenitor cells that form fibroblastoid tumors in mice and humans with defects that lead to increased cAMP-dependent protein kinase A (PKA) signaling. NOMID tumor cells showed high PKA activity, and an increase in their cAMP signaling led to PKA-specific activation of caspase-1. Increased PKA led to inflammation-independent activation of caspase-1 via over-expression of the proto-oncogene (and early osteoblast factor) Ets-1. In NOMID tumor cells, as in cells with defective PKA regulation, increased prostaglandin E2 (PGE2) led to increased cAMP levels and activation of Wnt signaling, like in other states of inappropriate PKA activity. Caspase-1 and PGE2 inhibition led to a decrease in cell proliferation of both NOMID and cells with abnormal PKA. These data reveal a previously unsuspected link between abnormal cAMP signaling and defective regulation of the inflammasome and suggest that caspase-1 and PGE2 inhibition may be therapeutic targets in bone lesions associated with defects of these two pathways.

Prkar1a is an osteosarcoma tumor suppressor that defines a molecular subclass in mice

Some cancers have been stratified into subclasses based on their unique involvement of specific signaling pathways. The mapping of human cancer genomes is revealing a vast number of somatic alterations; however, the identification of clinically relevant molecular tumor subclasses and their respective driver genes presents challenges. This information is key to developing more targeted and personalized cancer therapies. Here, we generate a new mouse model of genomically unstable osteosarcoma (OSA) that phenocopies the human disease. Integrative oncogenomics pinpointed cAMP-dependent protein kinase type I, alpha regulatory subunit (Prkar1a) gene deletions at 11qE1 as a recurrent genetic trait for a molecularly distinct subclass of mouse OSA featuring RANKL overexpression. Using mouse genetics, we established that Prkar1a is a bone tumor suppressor gene capable of directing subclass development and driving RANKL overexpression during OSA tumorigenesis. Finally, we uncovered evidence for a PRKAR1A-low subset of human OSA with distinct clinical behavior. Thus, tumor subclasses develop in mice and can potentially provide information toward the molecular stratification of human cancers.