Ret oncogene signal transduction via a IRS-2/PI 3-kinase/PKB and a SHC/Grb-2 dependent pathway: possible implication for transforming activity in NIH3T3 cells

Multiple endocrine neoplasia 2A (MEN 2A) is an inherited disease caused by mutations of the Ret proto-oncogene. Although many different Ret mutations have been described, little is known about the signaling pathways triggered by the Ret oncogene. In this study, we have determined the signaling properties of a Ret-9bp duplication encoding amino acids 634-636, which was recently identified in a patient with all clinical features of the MEN 2A syndrome. The Ret-9bp duplication leads to constitutive activation of the Ret tyrosine kinase. Furthermore, Ret-9bp increased mitogenic and transforming activity demonstrated by thymidine incorporation as well as colony formation in soft agar. Studying intracellular signaling pathways, which may be involved in malignant transformation of Ret-9bp expressing NIH3T3 cells, we could demonstrate Ret-9bp dependent phosphorylation of insulin receptor substrate-2 (IRS-2) with consecutive activation of phosphatidylinositol 3-kinase (PI 3-kinase) and protein kinase B (PKB/AKT). Moreover, Ret-9bp induces phosphorylation of SHC resulting in growth factor receptor binding protein-2 (Grb-2) binding and activation of the mitogen activating protein (MAP) kinase pathway. In addition to these postreceptor cytoplasmic signaling events, we have studied nuclear signal by Ret-9bp and found activation of c-jun and jun-D, two members of the jun/AP-1 family of transcription factors. In summary, an oncogenic 9bp duplication of Ret causes Ret dimer formation and ligand independent activation of the tyrosine kinase. Besides the signaling steps leading to MAPK activation, we could demonstrate that Ret-9bp induced constitutive activation of a signaling pathway involving IRS-2, PI 3-kinase and PKB/AKT which could transduce the oncogenic Ret signal to increased gene transcription via activation of the jun/AP-1 transcription factor family.

[The unmasking of secondary adrenal insufficiency and central diabetes insipidus by a highly febrile acute Hantaan virus infection]

CASE REPORT

A 32-year-old obese patient was admitted to our hospital as an emergency with very severe abdominal pain. Routine examinations initially failed to establish a diagnosis. The patient then went on to develop a high fever that was associated with polydipsia and polyuria. Serological studies revealed an acute infection with the Hantaan virus. Laboratory investigations showed hypofunction of the anterior and posterior lobes of the pituitary, with complete absence of ACTH, which was caused by two germinomas located intracranially.

CONCLUSION

The clinical symptoms had thus been the result of acute secondary insufficiency of the adrenal cortex, which was unmasked by the acute, highly febrile Hantaan viral infection.

Upregulation of cholesterol synthesis after acute reduction of low density lipoprotein by apheresis in normocholesterolaemic subjects: evidence for a threshold effect

The influence of low density lipoproteins (LDL) in the plasma on the regulation of cholesterol biosynthesis is not clear. We studied the changes in plasma mevalonic acid (MVA) concentration and the lathosterol/cholesterol (L/C) ratio, which are well established indices of whole body cholesterol synthesis, in four normocholesterolaemic subjects after each had undergone LDL apheresis on two occasions. LDL apheresis of 75% of the calculated plasma volume reduced LDL-cholesterol by 44% to 1.5 +/- 0.2 mmol/l without changing plasma MVA levels or L/C ratios. Apheresis of 125% of the calculated plasma volume decreased plasma LDL-cholesterol by 69% to 0.9 +/- 0.2 mmol/l, with significant increases in plasma MVA and L/C ratio on the day after the procedure. These results imply that LDL-cholesterol is an integral part of the sterol regulatory pool and suggest that plasma levels cannot be lowered below 1-1.4 mmol/l in normal subjects without upregulating cholesterol biosynthesis.

Detection of the apolipoprotein B-100 arg(3500) > gl mutation in familial defective apoB-100 by temperature-gradient gel electrophoresis

Familial defective apolipoprotein B-100 (FDB) is caused by a point mutation in exon 26 of the apolipoprotein B gene leading to a decreased binding to the LDL-receptor. Patients with FDB have hypercholesterolemia and atherosclerotic disease. Since other mutations of apoB-100 could also cause binding abnormalities we established a temperature-gradient gel electrophoresis (TGGE) method and started to screen hypercholesterolemic patients for the presence of point mutations in this region. 4 of 43 patients were positive according to TGGE and subsequent sequencing showed the familiar guanine to adenine transition in codon 3500 in all cases.

Analysis of thyroid stimulating hormone-receptor mutations by temperature-gradient gel electrophoresis

Somatic mutations in the genes for G-protein-coupled receptors which regulate intracellular levels of cyclic AMP have been found in several regions coding for the receptors of melanocyte-stimulating hormone, adrenaline, luteinizing hormone, rhodopsin and thyrotropin. The mutations found in the thyroid-stimulating hormone (TSH) receptor are restricted to cells of hyperfunctioning thyroid adenomas and other thyroid tumors. They are thought to lead to a constitutive activation of the receptor independent of TSH. We have developed a temperature-gradient gel electrophoresis (TGGE) assay starting with the amplification of a part of exon 10 of the TSH-receptor gene to screen tissue of thyroid tumours. TGGE allows the detection of point mutations even if there are only a few cells with somatic mutations in tissue sections.

Spontaneous transient remission of disseminated histiocytosis X during pregnancy

Disseminated histiocytosis X with cutaneous and lymph node involvement was diagnosed in a 25-year-old women. The diagnosis was established on the basis of a positive cell-surface staining with OKT 6 and typical signs on electron microscopy. Both the specific skin rash and lymph node swelling completely disappeared during pregnancy, but recurred 2 weeks before delivery. Therapeutic trials with 0.25 mg ethinylestradiol/day and a later application of human chorionic gonadotropin up to 5000 IU i.m. twice weekly as well as prednisolone 25 mg three times per day were unsuccessful. A second pregnancy was not desired. Polychemotherapy with initial high-dose prednisolone plus vincristine and a consolidation therapy with 5-mercaptopurine 300 mg/day led to full recovery. The observation of transient remission of histiocytosis X during pregnancy suggests that at least some forms of this disease may have prevailing immunological features where an immunosuppressive effect of pregnancy could be beneficial.

Ectopic ACTH secretion due to a bronchopulmonary carcinoid localized by somatostatin receptor scintigraphy

We present the case of a 65-year-old woman with an adrenocorticotropic hormone (ACTH) secreting bronchopulmonary carcinoid. This patient showed the typical long history of Cushing's syndrome, including hypokaliemia, impaired glucose tolerance, high levels of ACTH and beta-endorphin, and coproduction of other peptides. At the onset of clinical symptoms in 1979 an adrenal adenoma was suspected, and left-sided adrenalectomy was performed. The symptoms soon recurred, and the diagnosis of ACTH-dependent Cushing's syndrome was made. As no ACTH-secreting tumor was found, the right adrenal was resected, and the patient was followed up regularly. Fourteen years later chest roentgenography and computed tomography revealed a para-aortic pulmonary lesion, which was suspicious for a bronchopulmonary carcinoid. ACTH and beta-endorphin were excessively, pancreatic polypeptide slightly elevated at that time. The final diagnosis was made using somatostatin receptor scintigraphy which confirmed the hormonal activity of the suspicious lesion; no additional focus was found. This method turned out to be not only a useful additional localization technique but also a promising tool for characterization and staging of a suspected ACTH-producing carcinoid. The tumor was resected curatively, and the diagnosis was confirmed histologically.

[Diagnosis, therapy and screening of multiple endocrine neoplasia type I (MEN I) in four endocrinologic centers]

BACKGROUND

Multiple endocrine neoplasia type I (MEN I) is a hereditary disease characterised by involvement of several endocrine organs (parathyroid, anterior pituitary, pancreatic islet cells and other). In order to build up a German MEN I-register a questionnaire was developed.

PATIENTS

In four centres we diagnosed 29 cases of MEN I (average age 53 years, range 27 to 72 years, 21 women, eight men).

RESULTS

In 25 patients (86%) we found a primary hyperparathyroidism, in 15 patients (52%) an adenoma of the anterior pituitary (seven patients with growth hormone-secreting adenomas, five patients with prolactinomas, two patients with hormone-inactive and one patient with an ACTH-secreting adenoma), in ten patients (34%) a neoplasm of the pancreatic islet cells (six patients with gastrinomas, four patients with insulinomas and two patients with multihormone tumors) and in ten patients (34%) other endocrine tumors (five carcinoid tumors, three adenomas of the adrenal cortex, one papillary thyroid carcinoma and one thymic tumor). In nine cases nephrolithiasis was the leading symptom of primary hyperparathyroidism. All female patients with prolactinomas developed secondary amenorrhea. In three cases gastrinomas caused duodenal ulcers and three insulinomas were detected by fasting hypoglycemia. A primary hyperparathyroidism was most frequently combined with an adenoma of the anterior pituitary (21%). Detailed screening of 13 families early revealed MEN I in eleven cases.

CONCLUSIONS

The manifestation of an endocrine disease in MEN I should initiate further diagnostics. Having established the diagnosis of MEN I, a meticulous work-up of all family members is warranted. The set-up of a register by the successfully tested questionnaire will support these activities and facilitate further research of new genetic markers, follow-up and treatment.

The importance of multiple endocrine neoplasia syndromes in differential diagnosis

In the differential diagnosis of endocrine symptoms, the autosomal dominant multiple endocrine neoplasia (MEN) syndromes are rare but important. We found seven index cases of MEN-I in 176 patients with adenomas of the anterior pituitary and 26 patients with primary hyperparathyroidism. Of 23 cases of medullary thyroid carcinoma and eight cases of pheochromocytoma, 14 patients are classified as MEN-IIa and one as MEN-IIb. Family screening identified six MEN-I and seven MEN-II cases among 32 individuals examined. Because of autosomal dominant inheritance and sometimes-delayed manifestation of the complete syndrome, screening of healthy and affected family members should be repeated at least every other year.

[Thyrotropin-displacing antibodies in thyroid gland diseases]

Thyroid-stimulating antibodies were assayed in 798 patients with thyroid diseases and 122 controls by means of a heterologous radioreceptor assay as thyrotropin displacement activity (TDA). With an intraassay variance of 5-6% and an interassay variance of 8-13% in higher TDA values, test results were well reproducible. Thus, TDA assay is suitable for routine testing and follow-up of titers in the upper range. With only few exceptions TDA values of F greater than or equal to 11% are found exclusively in Graves' disease (sensitivity 39.2%; specificity vs other thyroid diseases 99.7%). In patients with functional autonomy in nodular goitre (Plummer's disease) TDA is consistently negative. TDA measurement is a valuable means for the detection of Graves' disease and for differential diagnosis of hyperthyroidism of undetermined pathogenesis.

[Partial lipodystrophy syndrome (Dunnigan type)]

Special forms of partial lipodystrophy, which in contrast to the progressive lipodystrophy of Barraquer-Simons spare the face, have been reported by Dunnigan and Köbberling. Lipodystrophy of the Dunnigan type affects the trunk and limbs; in lipodystrophy of the Köbberling type the loss of subcutaneous fat is restricted to the extremities. The following case report deals with the main clinical and laboratory findings in lipodystrophy of the Dunnigan type.

Myasthenia gravis: overlap with 'polyendocrine' autoimmunity

81 patients with spontaneously acquired myasthenia gravis (MG) were investigated for the presence of autoimmune (AI) diseases and their sera were tested for a range of organ-specific autoantibodies. 77 of the patients were HLA-phenotyped. Antibody titres to acetylcholine receptors (AChR) were higher in non-thymomatous patients who possessed HLA-B8 (p less than 0.05) and/or -DR3 (p less than 0.05) as compared to patients lacking these HLA antigens. 3 out of 20 (15%) patients with ocular MG, 7/23 (30%) with generalized MG of early onset, 11/23 (48%) generalized MG of late onset and 5/14 (35%) patients with thymoma had either overt AI diseases or significant titres of organ-specific autoantibodies suggesting subclinical AI disease. In ocular MG, low titres and an infrequent finding of antibodies to AChR (32%) as well as the low prevalence of associated autoantibodies and AI diseases indicate that this subgroup of MG consists of patients with restricted AI reactivity. HLA-B8 and -DR3 were present in all the patients with associated AI disorders in the young onset group but in none of the patients with old age of onset. In the young group, 6 out of 7 patients with associated AI conditions were women whereas the sex ratio was about equal in the older cases in both, patients with and without associated AI diseases or autoantibodies. We conclude from these observations that ageing provides conditions that allow the breakdown of self tolerance. The simultaneous presence of HLA B8, DR3 and female sex provide important additional factors for early expression of MG.

[Changes in thyroid function following iodine-containing contrast administration in patients in an endemic goitre area (author's transl)]

A prospective study of thyroid function after the administration of iodine-containing radiographic contrast media was carried out on 119 patients from an area where goitres are endemic. Eighteen patients had a negative TRH test after 28 days. 27.9% of patients after oral cholecystography, 15.1% of patients after intravenous cholangiography and 5.3% of patients after infusion urography, showed hyperthyroid function. In these patients, thyroxin and triiodothyronine levels were higher than in euthyroid patients. Thyroid stimulating antibodies could not be demonstrated. Induction of hyperthyroidism by iodine is considered to be due to autonomy of the thyroid gland parenchyma. For this reason the risk of iodine-induced hyperthyroidism is greater in patients from a goitre endemic region (by a factor of 1.3 to 17.1).

Micromethod of human thyrocyte cultures for detection of thyroid-stimulating antibodies and thyrotrophin

The activation of adenylate cyclase of human thyrocytes in primary cell cultures and the release of cAMP into the medium are used to detect thyrotropin (TSH) and thyroid-stimulating antibodies (TSAb) in sera of patients with Graves' disease. Tissue digestion and cell dispersion are performed using a neutral protease of Bacillus polymyxa (Dipase II), which harvests more vital thyrocytes than does trypsin. The cells show an enhanced response to stimulation. The efficiency of the cell preparation and cultivation is increased by using microtest plates instead of culture flasks. By this minimization only 0.6-1.8 X 10(6) cells are needed to evaluate a single sample. Cyclic AMP concentrations are measured directly in the supernatant culture medium by a competitive protein binding assay with charcoal separation. The minimal detectable dose of bTSH is about 10 microU/ml. With increasing doses of bTSH cAMP concentrations rise to a peak at about 50 to 100 mU/ml, beyond which there is a gradual decrease of cAMP indicating negative cooperativity in the activating mechanisms. The 'long-acting thyroid stimulator' effect of TSAb is reflected by a protracted increase of cAMP to its maximal value. All 41 sera of hyperthyroid patients with Graves' disease were TSAb-positive, whereas sera of patients with toxic nodular goitre and euthyroid controls were TSAb-negative.

[Iodine-induced hyperthyroidism due to contrast media (author's transl)]

A prospective study in an area with endemic goitre showed 18 patients (15.1%) out of 119 investigated with iodine containing contrast media to be hyperthyroid after 28 days. Oral cholecystography led to the highest (27.9%) and infusion urography to the lowest (5.3%) rate of hyperthyroidism. Determination of the serum concentration of thyroxine, triiodothyronine, basal and stimulated thyrotropine is not a suitable method to detect the risk for hormonally euthyroid patients before a contrast media investigation.

[Rheumatoid factors in Basedow's disease]

In patients with untreated Basedow's disease rheumatoid factors were determined by Waaler-Rose and Latex tests. The Waaler-Rose test was positive in 61.5% of 143 cases. After the acute disease stage settled the titers fell in more than 90% of the re-tested cases. In 50% the decrease in titre was of two dilutions or more. The Latex test was carried out in 152 patients. It was positive in 9.2% of the cases and became negative in 50% of the cases after the acute disease stage settled. In 5 out of 6 patients in whom the test remained positive there was in addition a rheumatic disease. The detectable rheumatoid factors are regarded as auto-antibodies against immuno-globulins. This suggests that polyarthritis in Basedow's disease is based on the same pathogenetic mechanisms as rheumatoid arthritis.

[Ectopic production of chorionic gonadotropin in apudomas (author's transl)]

Two pheochromocytomas, two carcinoid tumours of the ileum and one pancreatic vipoma showed APUD-system properties and formed electron-dense secretory granules indicating synthesis and storage of proteohormones. Besides catecholamines, 5-hydroxytryptamine and vasoactive intestinal polypeptide, all five tumours contained immunoreactive chorionic gonadotropin and also its free, protomeric beta chain as a sign of de-differentiation. Plasma of the tumour patients also contained immunoreactive chorionic gonadotropin and the free protomeric beta chain, both of which are useful tumour markers.

Mathematical model of pituitary thyrotropic function

A nonlinear differential equation is used to develop a mathematical model describing the time course of thyrotropin (TSH) concentral to real data shows that pituitary responsiveness to TRH is highest in euthyroidism, reduced in primary hypothyroidism, and lowest in hyperthyroidism.

[The vaso-active intestinal polypeptide in Verner-Morrison syndrome]

A 40-year-old man with the Verner-Morrison syndrome (refractory watery diarrhoea and hypokalaemia in islet-cell tumour of the pancreas) had an islet-cell carcinoma of the non-B-cell type with metastases to liver and mesenteric lymph nodes. High concentrations of a vasoactive intestinal polypeptide (VIP) were demonstrated in tumour tissue and plasma by radioimmunological tests. After surgical removal of the tumour the plasma VIP concentration fell to normal. Immunohistochemical tests of the tumour for gastrointestinal hormones demonstrated marked fluorescence only for vaso-active intestinal polypeptide. It is assumed that this polypeptide is largely responsible for the clinical signs. In the described case the severe watery diarrhoea ceased after glucocorticoid administration.