Secretory mechanisms of growth hormone (GH)-releasing peptide-, GH-releasing hormone-, and thyrotropin-releasing hormone-induced GH release in patients with acromegaly.

The GH secretory mechanism of GH-releasing hexapeptide (GHRP-6), GHRH, and TRH were studied in vivo and in vitro in seven patients with acromegaly. In an in vivo study, these patients showed clear GH responses to single administration of GHRP (four of four patients), GHRH (seven of seven patients), and TRH (seven of seven patients) and enhanced responses to GHRP plus GHRH (two of four patients) or TRH plus GHRH (six of six patients). In an in vitro dispersed cell study, the majority of patients examined also showed clear GH responses to GHRP (four of four patients), GHRH (six of six patients), and TRH (four of four patients) and an enhanced response to GHRP plus GHRH (three of three patients) or TRH plus GHRH (three of four patients). In one patient (no. 3), GHRP plus forskolin (adenylate cyclase activator), but not GHRP plus phorbol 12-myristate 13-acetate (protein kinase C activator), additively enhanced the GH response. Nordihydroguaiaretic acid (NDGA; inhibitor of arachidonic cascade) inhibited GH release induced by GHRP, TRH, GHRH, TRH plus GHRH, or GHRP plus GHRH, but did not inhibit basal GH secretion. In contrast, NDGA distinctly elevated intracellular cAMP levels in another patient (no. 7) when coadministered with GHRP, GHRH, or GHRP plus GHRH, whereas cAMP levels were not modified by single administration of GHRP and NDGA. The GH response to the combined administration of GHRP and GHRH was synergistic in this patient, but was additive in the other two patients. It is concluded that GHRP, TRH, and GHRH directly stimulate in vivo and in vitro GH release from human somatotropinomas, and GHRP and TRH mainly exert their action through activation of the phosphatidylinositol-protein kinase C pathway, whereas GHRH exerts its action through the adenylate cyclase-protein kinase A pathway. These three agents seem to release GH via the arachidonic cascade.

Identification of a single cytosine base insertion mutation at Arg-597 of the beta subunit of the human epithelial sodium channel in a family with Liddle's disease.

We describe a family with Liddle's disease caused by a novel mutation of the beta subunit of the human epithelial sodium channel (ENaC). A 15-year-old Japanese female was referred to our outclinic because of hypertension. The physical examination showed no abnormal findings except mild hypertension, but the laboratory data revealed low levels of plasma renin activity, plasma aldosterone and serum potassium. A comprehensive analysis of steroid hormones showed only high levels of urinary free cortisol and 17-hydroxycorticosteroids. During loading tests, blood pressure and serum potassium responded well to triamterene and slightly to spironolactone, but did not respond to dexamethasone. In addition, the normal ratio of tetrahydrocortisol plus 5alpha-tetrahydrocortisol to tetrahydrocortisone in a 24 h urinary excretion test strongly suggested a diagnosis of Liddle's disease rather than apparent mineralocorticoid excess syndrome. DNA sequence analysis of members of this family revealed a single cytosine base insertion at Arg-597 of the beta human ENaC in the proband and her mother, leading to a loss of the last 34 amino acids from the normally encoded protein as the result of a frameshift. We conclude that a de novo cytosine insertion into the final exon of the C-terminus of the beta human ENaC is responsible for Liddle's disease in this Japanese family.

[Abnormal serum uric acid level in endocrine disorders].

Among the factors, which may influence on the uric acid metabolism, the excess or deficiency of some hormones apparently induces the abnormal serum uric acid level. We described hyperuricemia and hypouricemia associated with endocrine disorders. Hyperuricemia due to the increased production of uric acid is observed in myopathy associated with hypothyroidism, hyperthyroidism or hypoparathyroidism. Hyperuricemia due to the decreased renal uric acid clearance is associated with hypopituitarism, hypothyroidism, hyperparathyroidism, central diabetes insipidus, nephrogenic diabetes insipidus, Bartter syndrome, and diabetic ketoacidosis. Hypouricemia due to the increased renal uric acid clearance is associated with hypoparathyroidism, primary aldosteronism and inappropriate secretion of antidiuretic hormone (SIADH).

Tissue-specific molecular heterogeneity of human growth hormone-releasing hormone receptor protein.

A site-directed anti-peptide antibody (anti-hGHRHRc18) was generated against the cytoplasmic tail of human GHRH receptor. The dissociation constant (Kd) and the antibody binding site (AbT) of anti-hGHRHRc18 were 2.5 nmol/l and 0.54 nmol/l, respectively. In an immunoblotting experiment, affinity-purified anti-hGHRHRc18 specifically recognized a single 50-kDa protein in human pituitary. In a screening of the expression of GHRH receptor protein in extra-pituitary tissues, only human kidney showed a single 52-kDa protein. Our results suggest that the GHRH receptor protein exhibits tissue-specific molecular heterogeneity.

Point mutations of ras and Gs alpha subunit genes in thyroid tumors.

We studied 43 thyroid tumors including 5 adenomatous goiters, 7 follicular adenomas, 22 papillary carcinomas, and 9 medullary carcinomas with regard to the presence of point mutations in the genes of Gs alpha subunit (Gs alpha), Gi2 alpha subunit (Gi2 alpha), H-ras, K-ras, and N-ras by a polymerase chain reaction-direct sequencing method. An adenomatous goiter and a follicular adenoma showed double mutations at codon 227 and 231, and 4 papillary carcinomas showed mutation at codon 231 of the Gs alpha gene. An adenomatous goiter, a follicular adenoma, and a papillary carcinoma showed a missense mutation in codon 13 of the K-ras gene. There were no such missense mutations of these G-protein or ras genes in medullary carcinomas. These data indicate that the genetic events involved in the oncogenesis of parafollicular C-cells are different from those of thyroid follicular cells, in which missense mutations of Gs alpha and ras genes seem to play important roles in tumorigenesis.

Mutations in the cysteine-rich region of the RET proto-oncogene in patients diagnosed as having sporadic medullary thyroid carcinoma.

Medullary thyroid carcinoma (MTC) and pheochromocytoma appear in either a sporadic or a hereditary form as components of multiple endocrine neoplasia (MEN). Many germline mutations of the RET proto-oncogene have been reported in patients with MEN 2A and 2B, and familial MTC (FMTC). To elucidate the etiological roles in tumorigenesis of sporadic MTCs and pheochromocytomas, mutations in the cysteine-rich region of the RET proto-oncogene were analyzed by using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis. Exons 10 and 11 were studied in genomic DNAs from 3 clinically apparent sporadic MTCs, MTCs and pheochromocytomas from 2 patients with MEN 2A, 1 with FMTC, 4 with MEN 2B, 3 with neurofibromatosis type 1 (NF1), 12 sporadic pheochromocytomas and an MTC cell line, TT. All tumors from two patients with MEN 2A and one patient with FMTC had mutations at codon 618 and 634 as well as their leukocytes, reflecting their germline mutations. In this region, no mutations were detected in any tumors from patients with MEN 2B and NF1, and sporadic pheochromocytomas. But mutations were detected and identified in 3 clinically apparent sporadic MTCs and TT cells. A 6 base pair (bp) deletion causing the loss of a cysteine residue at codon 634 and a mutation causing substitution from cysteine to tyrosine at codon 634 were detected in 2 sporadic MTCs as somatic events. In a female patient diagnosed as having sporadic MTC, a mutation at codon 618 was detected not only in tumor tissues, but also in her leukocytes, suggesting a germline mutation of the RET proto-oncogene.(ABSTRACT TRUNCATED AT 250 WORDS)

Two different pituitary adenomas in a patient with multiple endocrine neoplasia type 1 associated with growth hormone-releasing hormone-producing pancreatic tumor: clinical and genetic features.

The clinical and genetic features of a 43-year-old male patient with multiple endocrine neoplasia type 1 were reported. He developed hyperparathyroidism, a GHRH-producing pancreatic tumor, and acromegaly between 1980 and 1983. Because his pituitary gland increased in size even after resecting the GHRH-producing pancreatic tumor, transsphenoidal hypophysectomy was performed six years later. The pituitary contained two histologically-different adenomas composed of somatotroph cells and null cells. Genetic analyses revealed loss of heterozygosity on chromosome 11 in common in the pituitary adenomas, the pancreatic endocrine tumors, and a parathyroid hyperplasia. On the other hand, mutations of ras, p53, Gs alpha, and Gi2 alpha genes were not found in these tumors. The loss of the tumor suppressor gene on chromosome 11q12-13 was involved in the formation of two pituitary adenomas, two pancreatic endocrine functioning tumors, and a parathyroid hyperplasia in this patient, but the tumorigenic factors in the specific endocrine organs remain to be studied.

Point mutation of the somatostatin receptor 2 gene in the human small cell lung cancer cell line COR-L103.

The effect of somatostatin (SS) on adrenocorticotrophic hormone (ACTH) secretion from COR-L103 cells derived from a human small cell lung carcinoma was examined. SS at 1 microM had no effect on ACTH secretion from the cells on either short-term or long-term incubation. Studies by the reverse transcription-polymerase chain reaction (RT-PCR) showed that mRNA transcripts of the somatostatin receptor (SSTR) 2, SSTR3 and SSTR4 genes were present in COR-L103 cells. Extra bands were obtained by PCR-single strand conformation polymorphism (SSCP) analysis of the SSTR2 gene Sequence analysis of the SSTR2 gene demonstrated one point mutation in codon 188 of TGG for tryptophan to TGA for a stop codon causing loss of 182 C-terminal amino acid residues of SSTR2. The nucleotide sequences of the SSTR3 and SSTR4 genes in COR-L103 cells were normal. Binding studies using 125I-Tyr11-SS-14 showed specific affinity binding sites on COR-L103 cells and mouse pituitary tumor AtT-20 cells. Octreotide acetate suppressed the binding of 125I-Tyr11-SS-14 to these two cell lines, but the Kd of COR-L103 cells (160 nM) was 60-fold higher than that of AtT-20 cells (2.6 nM). Affinity cross-linking studies using 125I-Tyr11-SS-14 gave three bands of 72 KDa, 55 KDa and 32 KDa from AtT-20 cells, but only two bands of 55KDa and 32kDa from COR-L103 cells. These findings suggest that SSTR2 is not expressed in the plasma membranes of COR-L103 cells due to a point mutation, but that this may have no influence on the effect of SS on ACTH secretion.

Calcium ionophore A23187 inhibits ACTH secretion from a human small cell lung cancer cell line, COR-L103.

The mechanism of ectopic adrenocorticotrophic hormone (ACTH) secretion was examined by studies on the effects of corticotropin-releasing hormone (CRH), dexamethasone, interleukin (IL)-1 beta and 2, somatostatin, calcium ionophore A23187, 12-O-tetradecanoylphorbol-13-acetate (TPA) and 8-bromo-cAMP on pro-opiomelanocortin (POMC) expression and ACTH secretion from a human small cell lung cancer cell line COR-L103. None of these agents except TPA and A23187 had any effect on ACTH secretion from the cell line in short (0-8 hrs) or long term (1-4 days) cultures. In long term cultures, 1-100 nM TPA stimulated ACTH secretion dose-dependently, whereas 500nM A23187 inhibited ACTH secretion completely. When the cells were incubated with 10nM TPA plus 500 nM A23187, the inhibitory action of A23187 on ACTH secretion was suppressed by TPA. These results suggest that the mechanisms of ACTH secretion by COR-L103 cells and normal pituitary cells are different.

Molecular cloning and sequencing of porcine somatostatin receptor 2.

The porcine somatostatin receptor gene was isolated from a porcine genomic library. Based on the deduced amino acid sequence, this gene encodes a 369 amino acid protein with seven hydrophobic segments, a characteristic of G-protein coupled receptors, and shows only 13 amino acid difference (identity 96.5%, similarity 99.2%) in amino acid sequence from human somatostatin receptor 2. The data indicate that the amino acid sequence is highly conserved in pig, human, rat and mouse somatostatin receptor 2.

Analysis of the Gs alpha gene in growth hormone-secreting pituitary adenomas by the polymerase chain reaction-direct sequencing method using paraffin-embedded tissues.

We investigated the prevalence of Gs alpha gene mutations in growth hormone (GH) secreting pituitary adenomas from Japanese patients with acromegaly. Forty-five GH-secreting adenomas were examined for the presence of point mutations in codons 201 or 227 of the Gs alpha gene using the polymerase chain reaction-direct sequencing method and deoxyribonucleic acid extracted from paraffin-embedded tumor specimens. Mutation of codon 227 of the Gs alpha gene was not observed in any of the tumors, but a mis-sense mutation of codon 201 was identified in two tumors (4.4%). One lesion was a densely granulated GH cell adenoma in a patient with adenomatous goiter and breast cancer. The other was a mixed GH cell-prolactin cell adenoma in a patient with multiple endocrine neoplasia type 1 associated with parathyroid hyperplasia and a pancreatic islet cell tumor. The Gs alpha gene detected in parathyroid tissue and pancreatic tumor tissue was of the wild type in this second patient, and the mutation was specific to the pituitary tumor. These results suggest that point mutations of codons 201 or 227 of the Gs alpha gene may not be important mediators of oncogenesis for GH-secreting pituitary adenomas in Japan.

[Pathogenesis of pituitary tumor].

Pituitary adenoma originates from adenohypophysial cells producing various pituitary hormones. Some of pituitary adenomas are associated with pathological states including primary hypothyroidism, Nelson's syndrome, hypothalamic hormone-producing tumors, multiple endocrine neoplasia type 1, McCune-Albright syndrome and transgenic animals transfected with hypothalamic hormones (HP). These facts suggest that excessive secretion of HP induces hyperplasia of the adenohypophysial cells, leading to adenoma by additive effects of other unknown factors. The majority of the pituitary adenomas are associated with de novo genetic changes in the adenohypophysial cells, which induce growth factor independent proliferation and clonal expansion of the tumor cells, due to mutation of Gsa gene, activation of hst gene, expression of growth factors (HP, AT II, bFGF), loss of heterozygosity or loss of imprinting.

Tryptase Clara, an activating protease for Sendai virus in rat lungs, is involved in pneumopathogenicity.

Tryptase Clara is an arginine-specific serine protease localized exclusively in and secreted from Clara cells of the bronchial epithelium of rats (H. Kido, Y. Yokogoshi, K. Sakai, M. Tashiro, Y. Kishino, A. Fukutomi, and N. Katunuma, J. Biol. Chem. 267:13573-13579, 1992). The purified protease was shown in vitro to behave similarly to trypsin, cleaving the precursor glycoprotein F of Sendai virus at residue Arg-116 and activating viral infectivity in a dose-dependent manner. Anti-tryptase Clara antibody inhibited viral activation by the protease in vitro in lung block cultures and in vivo in infected rats. When the enzyme-specific antibody was administered intranasally to rats that were also infected intranasally with Sendai virus, activation of progeny virus in the lungs was significantly inhibited. Thus, multiple cycles of viral replication were suppressed, resulting in a reduction in lung lesions and in the mortality rate. These findings indicate that tryptase Clara is an activating protease for Sendai virus in rat lungs and is therefore involved in pulmonary pathogenicity of the virus in rats.

Serum parathyroid hormone-related protein concentrations in patients with hematologic malignancies or solid tumors.

The clinical significance of parathyroid hormone-related protein in humoral hypercalcemia of malignancy was investigated by determining the serum parathyroid hormone-related protein concentrations in 167 normal subjects, 56 patients with hematologic malignancy and 144 patients with solid tumor. Serum parathyroid hormone-related protein was measured with a radioimmunoassay kit that recognizes the C-terminal portion of the molecule. The serum parathyroid hormone-related protein concentrations were 20.2-50.8 pmol/l (mean +/- 2 SD) in normal subjects, and were elevated in 80% of the patients with malignancies with hypercalcemia, including squamous cell carcinoma and adult T cell leukemia. Moreover, two cases of B cell non-Hodgkin's lymphoma with hypercalcemia had high serum parathyroid hormone-related protein concentrations, which varied in parallel with the tumor size during the clinical course. Of 136 patients with solid tumors with normocalcemia, the serum parathyroid hormone-related protein concentration was slightly elevated in only 5.1%, all of whom were at an advanced stage. These data indicate that determination of the serum parathyroid hormone-related protein concentration is useful for differential diagnosis of humoral hypercalcemia of malignancy and prediction of its development.

Isolation and characterization of a novel trypsin-like protease found in rat bronchiolar epithelial Clara cells. A possible activator of the viral fusion glycoprotein.

A novel trypsin-like protease associated with rat bronchiolar epithelial Clara cells, named Tryptase Clara, was purified to homogeneity from rat lung by a series of standard chromatographic procedures. The enzyme has apparent molecular masses of 180 +/- 16 kDa on gel filtration and 30 +/- 1.5 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. Its isoelectric point is pH 4.75. Studies with model peptide substrates showed that the enzyme preferentially recognizes a single arginine cleavage site, cleaving Boc-Gln-Ala-Arg-4-methylcoumaryl-7-amide most efficiently and having a pH optimum of 7.5 with this substrate. The enzyme is strongly inhibited by aprotinin, diisopropylfluorophosphate, antipain, leupeptin, and Kunitz-type soybean trypsin inhibitor, but inhibited only slightly by Bowman-Birk soybean trypsin inhibitor, benzamidine, and alpha 1-antitrypsin. Immunohistochemical studies indicated that the enzyme is located exclusively in the bronchiolar epithelial Clara cells and colocalized with surfactant. An immunoreactive protein with a molecular mass of 28.5 kDa was also detected in airway secretions by Western blotting analyses, suggesting that the 30-kDa protease in Clara cells is processed before or after its secretion. Proteolytic cleavage of the hemagglutinin of influenza virus is a prerequisite for the virus to become infectious. Tryptase Clara was shown to cleave the hemagglutinin and activate infectivity of influenza A virus in a dose-dependent way. These results suggest that the enzyme is a possible activator of inactive viral fusion glycoprotein in the respiratory tract and thus responsible for pneumopathogenicity of the virus.

A pituitary specific point mutation of codon 201 of the Gs alpha gene in a pituitary adenoma of a patient with multiple endocrine neoplasia (MEN) type 1.

The DNA from a pituitary adenoma of a patient with multiple endocrine neoplasia (MEN) type 1 was analyzed to detect a point mutation of the Gs alpha gene (gsp) by the PCR direct-sequencing method. The patient had galactorrhea, amenorrhea and acromegalic features. Hormonal examination revealed high serum levels of PRL and GH. The tumor was histologically diagnosed as a mixed GH cell-PRL cell adenoma in which GH and PRL were produced by different cells. Sequence analysis of the DNAs extracted from paraffin sections of pituitary, parathyroid, and pancreas tumors demonstrated the substitution of thymidine for cytidine in codon 201 of the Gs alpha gene that resulted in replacement of arginine (CGT) with cysteine (TGT) only in the pituitary adenoma, but not in the parathyroid and pancreas tumors. These results suggest that a pituitary specific point mutational activation of the Gs alpha gene may be involved in the development of the pituitary adenoma in this patient.

Loss of heterozygosity on chromosome 1p in thyroid adenoma and medullary carcinoma, but not in papillary carcinoma.

We analyzed 53 loci on 21 chromosomes other than chromosome 4 to detect possible loss of heterozygosity in 31 thyroid tumors using polymorphic DNA markers that detect allelic deletions at specific chromosomal loci. Loss of heterozygosity on chromosomes 1, 7 and 12 was detected in one follicular thyroid adenoma, and on chromosome 1 in two medullary thyroid carcinomas. However, no loss of heterozygosity was detected at any of the loci examined in papillary thyroid carcinomas. These results suggest that chromosomal loss detected in thyroid adenoma is one of the signals for risk of premalignant transformation, and that inactivation of unknown genes on chromosome 1p contributes to tumorigenesis of medullary thyroid carcinoma. Some genetic changes other than chromosomal losses may participate in the tumorigenesis of papillary thyroid carcinoma.

Loss of heterozygosity on chromosomes 1 and 11 in sporadic pheochromocytomas.

Molecular genetic analysis was performed with 20 oncogene probes and 32 polymorphic DNA probes on tumor DNA samples from seven pheochromocytomas; namely, one multiple endocrine neoplasia type 2B, and two familial and four sporadic pheochromocytomas. No amplification or rearrangement of the oncogenes was detected in any of the tumors. However, loss of heterozygosity on chromosome 1p, 11p or 11q was detected in these cases. In addition, a locus related to ETS1 was deleted in two of the sporadic tumors. These results suggest that pheochromocytomas may be genetically heterogeneous, and that inactivation of unknown genes on chromosome 1p, 11p or 11q may contribute to their development.

A low-molecular-mass Kazal-type protease inhibitor isolated from rat hepatocytes is identical to rat pancreatic secretory trypsin inhibitor II. Purification and amino acid sequence.

A low-molecular-mass serine protease inhibitor was purified from hepatocytes and liver of rats. It was found to be a single polypeptide of 56 amino acid residues corresponding to Mr = 6224, a value that is in agreement with the molecular mass determined by gel chromatography. The inhibitor formed a complex in a molar ratio of 1:1 with trypsin. Its complete amino acid sequence was identical with that of pancreatic secretory trypsin inhibitor II (PSTI-II) in pancreatic juice, but not with that of PSTI-I [Uda, K., Ogawa, M., Shibata, T., Murata, A., Mori, T., Kikuchi, N., Yoshida, N., Tsunasawa, S. & Sakiyama, F. (1988) Biol. Chem. Hoppe-Seyler 369, 55-61]. PSTIs have been reported to be primarily pancreatic secretory products, but in have been reported to be primarily pancreatic secretory products, but in patients immunoreactive PSTI was found in the plasma and urine during acute inflammatory disease and shown to be produced ectopically in cancer tissues. Here we report for the first time that PSTI-II is present in other normal tissues besides the pancreas.