We recently identified a high prevalence of mutations affecting the catalytic (Cα) subunit of protein kinase A (PKA) in cortisol-secreting adrenocortical adenomas. The two identified mutations (Leu206Arg and Leu199_Cys200insTrp) are associated with increased PKA catalytic activity, but the underlying mechanisms are highly controversial. Here we utilize a combination of biochemical and optical assays, including fluorescence resonance energy transfer in living cells, to analyze the consequences of the two mutations with respect to the formation of the PKA holoenzyme and its regulation by cAMP. Our results indicate that neither mutant can form a stable PKA complex, due to the location of the mutations at the interface between the catalytic and the regulatory subunits. We conclude that the two mutations cause high basal catalytic activity and lack of regulation by cAMP through interference of complex formation between the regulatory and the catalytic subunits of PKA.

Aldosterone and cortisol, the main mineralocorticoid and glucocorticoid hormones in humans, are produced in the adrenal cortex, which is composed of three concentric zones with specific functional characteristics. Adrenocortical adenomas (ACAs) can lead to the autonomous secretion of aldosterone responsible for primary aldosteronism, the most frequent form of secondary arterial hypertension. In the case of cortisol production, ACAs lead to overt or subclinical Cushing syndrome. Genetic analysis driven by next-generation sequencing technology has enabled the discovery, during the past 7 years, of the genetic causes of a large subset of ACAs. In particular, somatic mutations in genes regulating intracellular ionic homeostasis and membrane potential have been identified in aldosterone-producing adenomas. These mutations all promote increased intracellular calcium concentrations, with activation of calcium signaling, the main trigger for aldosterone production. In cortisol-producing adenomas, recurrent somatic mutations in PRKACA (coding for the cyclic adenosine monophosphate-dependent protein kinase catalytic subunit α) affect cyclic adenosine monophosphate-dependent protein kinase A signaling, leading to activation of cortisol biosynthesis. In addition to these specific pathways, the Wnt/β-catenin pathway appears to play an important role in adrenal tumorigenesis, because β-catenin mutations have been identified in both aldosterone- and cortisol-producing adenomas. This, together with different intermediate states of aldosterone and cortisol cosecretion, raises the possibility that the two conditions share a certain degree of genetic susceptibility. Alternatively, different hits might be responsible for the diseases, with one hit leading to adrenocortical cell proliferation and nodule formation and the second specifying the hormonal secretory pattern.

The cyclic AMP (cAMP) pathway plays a major role in the development of endocrine tissues and various molecular defects of key components of this pathway (G protein, receptors, PKA, ...) have been observed in endocrine tumors. Hypersecretion of adrenocorticotropin hormone (ACTH), the key activator of the cAMP pathway in adrenal cortex, is associated with adrenocortical hyperplasia and cortisol oversecretion (Cushing's syndrome). The best example of "illegitimate" membrane receptors expression reported is the abnormal expression of the adenylyl cyclase activating gastric inhibitory peptide receptor (GIP-R) in ACTH-independent Cushing's syndrome (ACS). We have observed that ectopic expression of the GIP-R is frequent in ACTH-Independent Macronodular Adrenal Hyperplasia (AIMAH), rare in benign adrenal adenoma (AA), but seems absent in Adrenal Cancer (AC). In vivo systematic screening of AIMAH shows at least one abnormal response of cortisol (suggesting "illegitimate" membrane receptor expression) in almost all patients. Somatic and germ line inactivating mutations of PRKAR1 (regulatory subunit R1A of PKA) can be observed in patient with isolated primary pigmented nodular adrenocortical disease (PPNAD) and AA responsible for ACS. At the nuclear level, the cAMP pathway regulates transcription mainly by PKA-dependent phosphorylation of the cyclic AMP response element binding (CREB) family of transcription factors (CREB, CREM, and ATF-1). Cyclic AMP response element binding protein (CREB) is expressed in normal adrenal cortex. Alterations of CRE binding proteins with loss of CREB expression and compensatory overexpression of CREMtau is observed in the human adrenocortical cancer cell line H295R. Similar alterations are found at the protein level in human malignant adrenocortical tumors. In conclusion, various alterations leading to activation or inactivation of key components of the cAMP signaling pathway can be observed in adrenocortical tumorigenesis.

INTRODUCTION:Endogenous Cushing's syndrome is a clinical state resulting from prolonged, inappropriate exposure to excessive endogenous secretion of cortisol and hence excess circulating free cortisol, characterized by loss of the normal feedback mechanisms of the hypothalamo-pituitary-adrenal axis and the normal circadian rhythm of cortisol secretion [2]. The etiology of Cushing's syndrome may be excessive ACTH secretion from the pituitary gland, ectopic ACTH secretion by nonpituitary tumor, or excessive autonomous secretion of cortisol from a hyperfunctioning adrenal adenoma or carcinoma. Other than this broad ACTH-dependent and ACTH-independent categories, the syndrome may be caused by ectopic CRH secretion, PPNAD, MAH, ectopic action of GIP or catecholamines, and other adrenel-dependent processes associated with adrenocortical hyperfunction. CASE REPORT:A 31 year-old men with 6-month history of hyperpigmentation, weight gain and proximal myopathy was refereed to Institute of Endocrinology for evaluation of hypercortisolism. At admission, patient had classic cushingold habit with plethoric face, dermal and muscle atrophy, abdominal strie rubrae and centripetal obesity. The standard laboratory data showed hyperglycaemia and hypokaliemia with high potassium excretion level. The circadian rhythm of cortisol secretion was blunted, with moderately elevated ACTH level, and without cortisol suppression after low-dose and high-dose dexamethason suppression test. Urinary SHIAA was elevated. Abdominal and sellar region magnetic resonance imaging was negative. CRH stimulation resulted in ACTH increase of 87% of basal, but without significant increase of cortisol level, only 7%. Thoracal CT scan revealed 14 mm mass in right apical pulmonary segment. A wedge resection of anterior segment of right upper lobe was performed. Microscopic evaluation showed tumor tissue consisting of solid areas of uniform, oval cells with eosinophilic cytoplasm and centrally located nuclei. Stromal tissue was scanty, and mitotic figures were infrequent. Tumor cells were immunoreactive for synaptophysin, neuron-specific enolase, and ACTH. The postoperative course was uneventful and the patient was discharged on glucocorticoid supplementation. Signs of Cushing's syndrome were in regression, and patient remained normotensive and normoglycaemic without therapy. DISCUSSION:A multitude of normal nonpituitary cells from different organs and tissues have been shown to express the POMC gene from which ACTH is derived. The tumors most commonly associated the ectopic ACTH syndrome arise from neuroendocrine tissues, APUD cells. POMC gene expression in non-pituitary cells differs from that in pituitary cells both qualitatively and quantitatively [8]. Aggressive tumors, like small cell cancer of the lung (SCCL) preferentially release intact POMC, whereas carcinoids rather overprocess the precursor, releasing ACTH and smaller peptides like CLIP. Some tumors associated with ectopic ACTH syndrome express other markers of neuroendocrine differentiation like two specific prohormone convertases (PCs). Assessment of vasopressin (V3) receptor gene expression in ACTH-producing nonpitultary tumors revealed bronchial carcinoid as a particular subset of tumors where both V3 receptor and POMC gene may be expressed in pattern indistinguishable from that in corticotroph adenoma [9]. In most, but not all, patients with ectopic ACTH syndrome, cortisol is unresponsive to high-dose dexamethason suppression test, what is used as diagnostic tool. It is not clear if the primary resistance resulted from structural abnormality of the native glucocorticoid receptor (GR), a low level of expression, or some intrinsic property of the cell line [9]. It appears that ectopic ACTH syndrome is made of two different entities. When it is because of highly differentiated tumors, with highest level of pituitary-like POMC mRNA, expressing PCs, high level of V3 receptors and GR, like bronchial carcinoids, it might be called ectopic corticotroph syndrome. In contrast, when it is caused by aggressive, poorly differentiated tumors, with much lower expression of V3 receptor, like SCCL, it might be called aberrant ACTH secretion syndrome. Carcinoid tumors have been reported in a wide range of organs but most commonly involve the lungs, bronchi, and gastrointestinal tract. They arise from neuroendocrine cells and are characterized by positive reactions to markers of neuroendocrine tissue, including neuron specific enolase, synaptophysin, and chromogranina [11]. Carcinoid tumors are typically found to contain numerous membrane-bound neurosecretory granules composed of variety of hormones and biogenic amines. One of the best characterized is serotonin, subsequently metabolized to 5-hydrohy-indolacetic acid (5-HIAA), which is excreted in the urine. In addition to serotonin, carcinoid tumors have been found to secrete ACTH, histamine, dopamine, substance P, neurotensin, prostaglandins and kallikrein. The release of serotonin and other vasoactive substances is thought to cause carcinoid syndrome, which manifestations are episodic flushing, weezing, diarrhea, and eventual right-sided valvular heart disease. These tumors have been classified as either well-differentiated or poorly differentiated neuroendocrine carcinomas. The term "pulmonary tumorlets" describes multiple microscopic nests of neuroendocrine cells in the lungs [12]. Pulmonary carcinoids make up approximately 2 percents of primary lung tumors. The majority of these tumors are perihilar in location, and patients often presents with recurrent pneumonia, cough, hemoptisis, or chest pain. The carcinoid syndrome occurs in less than 5 percent of cases. Ectopic secretion of ACTH from pulmonary carcinoid accounts for 1 percent of all cases of Cushing's syndrome. They are distinct clinical and pathologic entity, generally peripheral in location. Although they are usually typical by standard histologic criteria, they have mush greater metastatic potential than hormonally quiescent typical carcinoids [13]. Surgical treatment therefore should be one proposed for more aggressive malignant tumors. In all cases of ACTH-dependent Cushing's syndrome with regular pituitary MRI and bilateral inferior petrosal sinus sampling, thin-section and spiral CT scanning of the chest should be routine diagnostic procedure [14]. We present thirty-one year old patient with typical pulmonary carcinod with ACTH ectopic secretion consequently confirmed by histology.

In the normal human adrenal gland, steroid secretion is regulated by a complex network of autocrine/paracrine interactions involving bioactive signals released by endothelial cells, nerve terminals, chromaffin cells, immunocompetent cells, and adrenocortical cells themselves. ACTH can be locally produced by medullary chromaffin cells and is, therefore, a major mediator of the corticomedullary functional interplay. Plasma ACTH also triggers the release of angiogenic and vasoactive agents from adrenocortical cells and adrenal mast cells and, thus, indirectly regulates steroid production through modulation of the adrenal blood flow. Adrenocortical neoplasms associated with steroid hypersecretion exhibit molecular and cellular defects that tend to reinforce the influence of paracrine regulatory loops on corticosteroidogenesis. Especially, ACTH has been found to be abnormally synthesized in bilateral macronodular adrenal hyperplasia responsible for hypercortisolism. In these tissues, ACTH is detected in a subpopulation of adrenocortical cells that express gonadal markers. This observation suggests that ectopic production of ACTH may result from impaired embryogenesis leading to abnormal maturation of the adrenogonadal primordium. Globally, the current literature indicates that ACTH is a major player in the autocrine/paracrine processes occurring in the adrenal gland in both physiological and pathological conditions.