1,721,019 research outputs found
Mechanisms of disease : mutations of G proteins and G-protein-coupled receptors in endocrine diseases
No full textG proteins and G-protein-coupled receptors (GPCRs) mediate the effects of a number of hormones. Genes that encode these molecules are subject to loss-of function or gain-of-function mutations that result in endocrine disorders. Loss-of-function mutations prevent signaling in response to the corresponding agonist and cause resistance to hormone actions, which mimics hormone deficiency. Gain-of-function mutations lead to constitutive, agonist-independent activation of signaling, which mimics hormone excess. Disease-causing mutations of GPCRs have been identified in patients with various disorders of the pituitary-thyroid, pituitary-gonadal and pituitary-adrenal axes, and in those with abnormalities in food intake, growth, water balance and mineral-ion turnover. The only mutational changes in G proteins unequivocally associated with endocrine disorders occur in GNAS (guanine nucleotide-binding protein G-stimulatory subunit α, or Gsα). Heterozygous loss-of-function mutations of GNAS in the active, maternal allele cause resistance to hormones that act through Gsα-coupled GPCRs, whereas somatic gain-of-function mutations cause proliferation of endocrine cells that recognize cyclic AMP as a mitogen. The study of mutations in G proteins and GPCRs has already had major implications for understanding the molecular basis of rare endocrine diseases, as well as susceptibility to multifactorial disorders that are associated with polymorphisms in these genes
An unusual case of recurrent autoimmune hypophysitis
No full textAutoimmune hypophysitis (AH) is an inflammatory disease that can present either as empty sella or as pituitary mass. A 16-years-old girl was admitted at our Unit for primary amenorrhea. A pituitary MRI performed 2 years before for severe headache demonstrated a large sellar and suprasellar lesion. As a craniopharyngioma was suspected, the consultant neurosurgeon suggested the removal of the lesion. Two months later, a preoperative MRI showed the disappearance of the lesion and a residual empty sella, figure consistent with AH. When the patient came at our observation, basal and dynamic testing documented a state of hypopituitarism, high titers of antipituitary antibodies and a partial empty sella at MRI. Hormonal replacement therapy was started, obtaining a good clinical and biochemical control. Four years later, severe headache and a MRI suggestive of pituitary adenoma recurred. A relapse of the autoimmune phenomenon seemed the most feasible hypothesis. A MRI performed 3 months later did not show any pituitary lesion and empty sella was again described. This patient represents one of the few reported cases of recurrent hypophysitis and demonstrates that both pituitary enlargement and empty-sella can be seen in the same patient at different times of his history
Adequacy of current postglucose GH nadir limit (< 1 microg/l) to define long-lasting remission of acromegalic disease
No full textObjective: Some authors proposed to lower the present postglucose GH nadir cut-off (i.e. 0.26 μg/l in 24 patients (Group B). Group B had only slightly higher IGF-1 SDS (0.4 ± 1.0 vs. - 0.1 ± 1.0, P = ns) and lower body mass index (BMI) than Group A (26.2 ± 2.4 vs. 30.6 ± 4.5 kg/m2, P < 0.005). GH nadir positively correlated with IGF-1 (P < 0.05, r = 0.32) and negatively with BMI (P < 0.05, r = 0.42). In Phase 2, all patients had IGF-1 levels in the normal range and GH nadir < 1 μg/l, both parameters being even lower than those found at the time of remission. No patient had either clinical or neuroradiological evidence of disease recurrence. Conclusions: The current GH nadir limit is still adequate to define both short- and long-lasting remission of acromegaly, independently of the type of definitive treatment. Patients with the lowest GH nadir should probably be monitored long-term for adequacy of their GH secretion
Patients with macroprolactinaemia : clinical and radiological features
No full textBackground: Macroprolactinaemia may represent a relevant cause of misdiagnosis, unnecessary investigation and inappropriate treatment. The aim of this study was to investigate the clinical and neuroradiological characteristics of patients with and without macroprolactinaemia and to evaluate the impact of macroprolactin determination on the diagnostic work-up of hyperprolactinaemic patients. Materials and methods: Retrospective analysis in 135 consecutive hyperprolactinaemic patients (111 women and 24 men; mean age 37 ± 11.6 years) whose archived sera were subsequently tested for macroprolactin. Recoveries ≤ 40% after polyethylene glycol precipitation were indicative of macroprolactinaemia. Results: Macroprolactin, entirely explaining biochemical hyperprolactinaemia, was found in 42.2% of patients, a third of whom presented with signs and symptoms of hyperprolactinaemia. Determination of macroprolactin changed the initial diagnosis in a consistent proportion of patients. In particular, idiopathic hyperprolactinaemia, initially diagnosed in 41 patients, was then excluded in 28 of them. Diagnosis of prolactin-secreting pituitary microadenoma shifted to non-secreting pituitary microadenoma in 10 of 49 patients, while in all patients with prolactin-secreting pituitary macroadenoma or hyperprolactinaemia due to stalk deafferentation the presence of macroprolactin was excluded and the initial diagnosis confirmed. Finally, macroprolactin was present in the majority of patients with magnetic resonance imaging (MRI) scans suggestive for primary empty sella (4 of 5 women) or pituitary hyperplasia (12 of 17 women, 3 of 3 men). Collectively, about half of subjects with macroprolactinaemia showed variable MRI abnormalities. Conclusions: The presence of macroprolactin was a relevant cause of misdiagnosis in patients with hyperprolactinaemia. However, due to the unexpected high frequency of pituitary abnormalities observed in the present series, we suggest that the diagnostic algorithm of hyperprolactinaemic states should include both polyethylene glycol precipitation test and MRI imaging
Filamin A in somatostatin and dopamine receptor regulation in pituitary and the role of cAMP/PKA dependent phosphorylation
No full textMolecular mechanisms underlying resistance of pituitary tumors to somatostatin (SS) and dopamine (DA) analogues treatment are not completely understood. Resistance has been associated with defective expression of functional somatostatin and dopamine receptors SSTR2, SSTR5, and DRD2, respectively. Recently, a role of cytoskeleton protein filamin A (FLNA) in DRD2 and SSTR receptors expression and signaling in PRL- and GH-secreting tumors, respectively, has been demonstrated, first revealing a link between FLNA expression and responsiveness of pituitary tumors to pharmacological therapy. No molecular events underlying the reduction of FLNA levels in resistant tumors have been so far identified. FLNA can be phosphorylated by PKA on Ser2152, with increased FLNA resistance to cleavage by calpain and conformational changes affecting FLNA regions involved in SSTR2 and DRD2 binding and signal transduction. In this respect, the effect of cAMP/PKA pathway in the regulation of FLNA stability and/or function by modulating its phosphorylation status could assume particular importance in pituitary, where cAMP cascade plays a crucial role in pituitary cell functions and tumorigenesis. This review will discuss the role of FLNA in the regulation of the main GPCRs target of pharmacological treatment of pituitary tumors, that is, SSTR2 and DRD2, focusing on the effects of cAMP/PKA-mediated FLNA phosphorylation on FLNA biological functions
Mutational analysis of PRKAR1A and Gs(alpha) in sporadic adrenocortical tumors
No full textLittle is known about the pathogenesis of adrenocortical tumors. The cAMP-dependent pathway is physiologically activated by ACTH in adrenocortical cells and different components of this cascade may be altered in some functioning adrenocortical tumors. Recently, mutations of the gene encoding the PKA type 1 A regulatory subunit (R1 A), PRKAR1A, associated with loss of heterozygosity (LOH) at PRKAR1A locus, have been demonstrated in primary pigmented nodular adrenocortical disease (PPNAD), either isolated or associated with Carney complex. Moreover, activating mutations of the Gsα gene (the gsp oncogene) have also been found in a small number of adrenocortical cortisol-secreting adenomas. Aim of this study was to investigate the presence of such genetic alterations on a series of 10 ACTH-independent Cushing syndrome due to non-PPNAD adrenocortical adenomas. The coding sequence of PRKAR1A, evaluated by PCR and direct sequencing analysis, revealed the absence of mutations while heterozygosity for at least 1 polymorphism excluded LOH in most tumors. In one single adenoma gsp mutation was detected. In conclusion, we provide additional evidence that the only mutational changes able to activate the cAMP pathway so far identified, i.e. PRKAR1A mutations and gsp oncogene, are a rare event in adrenocortical tumors
Expression of the two alternatively spliced PRKAR1A RNAs in human endocrine glands
No full textHeterozygous loss of function mutations in human PKARlA gene (PRKARlA) have been identified in patients with Carney complex (CNC), an autosomal dominant familial multiple neoplasia syndrome displaying different endocrine tumors, including adrenocortical tumors, GH-secreting pituitary tumors and thyroid adenomas. Although PRKARlA is encoded by a single gene, it is transcribed from at least two different promoters, adjacent to different first non-coding exons (1 a and 1 b), giving rise to alternately spliced transcripts coding for identical proteins. The separate regulation of the two distinct promoters and the presence of multiple alternatively spliced first exons suggest a complex mechanism of PRKARlA expression regulation. In order to investigate the relative expression of the two mRNA transcripts (1a and 1b) in human adult endocrine tissues involved in the determination of CNC phenotype, we selected 17 pituitary, 20 adrenal and seven thyroid tissues from tumoral and peri-tumoral lesion samples. Expression of the two transcripts was evaluated by semi-quantitative RT-PCR and real-time RT-PCR. This study first reports that human pituitary and thyroid tissues show a similar expression of the two transcripts, whereas in adrenal tissues transcript I b is the most abundant one
Effect of growth hormone deficiency and recombinant hGH (rhGH) replacement on the hypothalamic-pituitary-adrenal axis in children with idiopathic isolated GH deficiency
No full textObjective: Recombinant hGH (rhGH) therapy may unmask central hypoadrenalism in adults with organic GH deficiency (GHD), likely by normalizing 11β-hydroxysteroid dehydrogenase type 1 isoenzyme (11βHSD1) activity and reducing cortisone to cortisol conversion. The aim of the present study was to evaluate the hypothalamic-pituitary-adrenal (HPA) axis in children with idiopathic isolated GHD and normal pituitary magnetic resonance imaging (MRI) both before and during rhGH therapy. Design and patients: This was a single-centre study of 10 consecutive children [five males and five females, mean age: 12.2 ± 1.0 year]. Evaluation was performed at baseline and on rhGH (mean duration: 10.9 ± 2.9 months, mean dose: 0.030 ± 0.002 mg/kg bw/day). Measurements: HPA function was assessed by serum cortisol levels before and after appropriate provocative stimuli, that is, 1 μg ACTH test (N = 5 patients) or insulin tolerance test (ITT, N = 5 patients), evaluating all children with the same stimulation test both before and during rhGH therapy. Central hypoadrenalism was excluded by the presence of either a peak of > 500 nmol/l or a rise in cortisol levels of > 200 nmol/l, after both tests. Results: On rhGH therapy, serum IGF-I levels normalized, while serum cortisol and ACTH levels did not significantly differ from those recorded at baseline. The mean serum cortisol peak after both provocative tests was not significantly different on rhGH therapy and at baseline (498 ± 41 vs. 580 ± 35 nmol/l, respectively, P = 0.06), the mean cortisol rise being 280 ± 45 and 270 ± 36 nmol/l on rhGH and at baseline, respectively. Conclusions: According to the diagnostic criteria, no child became hypoadrenal on rhGH, contrary to what observed in patients with organic GHD, further supporting the view that only in patients with organic multiple pituitary hormone deficiency GHD masks the presence of a hidden central hypoadrenalism
Cyclic adenosine 3'-5'-monophosphate (cAMP) exerts proliferative and anti-proliferative effects in pituitary cells of different types by activating both cAMP-dependent protein kinase A (PKA) and exchange proteins directly activated by cAMP (Epac)
No full textIn the pituitary the activation of cyclic adenosine 3'-5'-monophosphate (cAMP) dependent pathways generates proliferative signals in somatotrophs, whereas in pituitary cells of other lineages its effect remains uncertain. Moreover, the specific role of the two main cAMP effectors, protein kinase A (PKA) and exchange proteins directly activated by cAMP (Epac), has not been defined. Aim of this study was to investigate the effect of cAMP on pituitary adenomatous cells proliferation and to identify PKA and Epac differential involvement. We found that cAMP increased DNA synthesis and cyclin D1 expression in somatotropinomas, whereas it reduced both parameters in prolactinomas and nonfunctioning adenomas, these effects being replicated in corresponding cell lines. Moreover, the divergent cAMP effects were mimicked by Epac and PKA analogs, which activated Rap1 and CREB, respectively. In conclusion, we demonstrated that cAMP exerted opposite effects on different pituitary cell types proliferation, these effects being mediated by both Epac and PKA
Dopamine receptor type 2 (DRD2) inhibits migration and invasion of human tumorous pituitary cells through ROCK-mediated cofilin inactivation
No full textNon-functioning pituitary tumors (NFPTs) frequently present local invasiveness. Dopamine receptor 2 (DRD2) agonists are the only medical therapy that induces tumor shrinkage in some patients. Invasion requires cytoskeleton rearrangements that are tightly regulated by cofilin pathway, whose alterations correlate with invasion in different tumors. We investigated the effect of DR2D agonist on NFPT cells migration/invasion and the molecular mechanisms involved. We demonstrated that DRD2 agonist reduced migration (−44 ± 25%, p < 0.01) and invasion (−34 ± 6%, p < 0.001) and increased about 4-fold Ser3-phosphorylated inactive cofilin (P-cofilin) in NFPT cells. These effects were abolished by inhibiting ROCK, a kinase that phosphorylates cofilin. The overexpression of wild-type or phosphodeficient S3A-cofilin increased HP75 cells migration (+49 ± 6% and +57 ± 9% vs empty vector, respectively, p < 0.05), while phosphomimetic mutant had no effect. Interestingly, P-cofilin levels were lower in invasive vs non-invasive tumors by both western blot (mean P-cofilin/total cofilin ratio 0.77 and 1.93, respectively, p < 0.05) and immunohistochemistry (mean percentage of P-cofilin positive cells 17.6 and 45.7, respectively, p < 0.05). In conclusion, we showed that the invasiveness of pituitary tumors is promoted by the activation of cofilin, which can be regulated by DRD2 and might represent a novel biomarker for pituitary tumors' invasive behavior
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