Inactivation of menin, a Smad3-interacting protein, blocks transforming growth factor type beta signaling

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterized by endocrine tumors of parathyroids, pancreatic islets, and anterior pituitary. The MEN1 gene encodes a nuclear protein called menin. In MEN1 carriers inactivating mutations give rise to a truncated product consistent with menin acting as a tumor suppressor gene. However, the role of menin in tumorigenesis and its physiological functions are not known. Here, we show that menin inactivation by antisense RNA antagonizes transforming growth factor type beta-mediated cell growth inhibition. Menin interacts with Smad3, and antisense menin suppresses transforming growth factor type beta-induced and Smad3-induced transcriptional activity by inhibiting Smad3/4-DNA binding at specific transcriptional regulatory sites. These results implicate a mechanism of tumorigenesis by menin inactivation.

Skeletal responsiveness to parathyroid hormone in pseudohypoparathyroidism

BACKGROUND

Although there have been some case reports suggesting that bone in patients with pseudohypoparathyroidism (PHP) might respond to parathyroid hormone (PTH), no information is available as to whether serum PTH concentration is related to bone metabolic markers or to bone mineral density (BMD) in PHP.

OBJECTIVE

To address these relationships, by comparing intact serum PTH, bone metabolic markers and BMD in patients with PHP with those in patients with idiopathic hypoparathyroidism (IHP) and postoperative hypoparathyroidism (OHP).

METHODS

Intact serum PTH, bone metabolic markers (osteocalcin, tartrate-resistant acid phosphatase, pyridinoline, deoxypyridinoline) and BMD by dual-energy X-ray absorptiometry or single-photon absorptiometry were measured in patients with PHP Ia (n=2) and PHP Ib (n=8). The results were compared with those in patients with IHP (n=5) and OHP (n=14).

RESULTS

All bone metabolic markers measured were present in significantly greater amounts in patients with PHP Ib than in those with IHP+OHP. The Z score (standard deviation of average BMD at each age) of the BMD of femoral neck was significantly lower in patients with PHP Ib than in those with IHP+OHP. The Z scores of BMD of lumbar spine and radius were also lower in patients with PHP Ib than in those with IHP+OHP, but the difference was not significant. Moreover, the intact serum PTH concentrations were significantly and positively related to bone metabolic marker levels in all patients, and the intact serum PTH concentrations were significantly and negatively related to BMD of lumbar spine in PHP patients.

CONCLUSIONS

These results suggest that PTH stimulates bone turnover in PHP Ib patients, resulting in a relatively lower BMD in PHP Ib patients than in IHP+OHP patients. The present study indicates that bones of most cases of PHP could respond to PTH.

Testosterone inhibits osteoclast formation stimulated by parathyroid hormone through androgen receptor

Androgens play an important role in the regulation of bone metabolism in animals and humans. The present study was performed to investigate whether androgens would affect osteoclast formation stimulated by parathyroid hormone (PTH) in mouse bone cell cultures and its mechanism. Testosterone as well as alpha-dihydrotestosterone (DHT) concentration-dependently inhibited osteoclast formation induced by PTH-(1-34). 10(-8) M ICI 182780, an estrogen receptor inhibitor, did not affect PTH-induced osteoclast formation antagonized by 10(-8) M testosterone, although it completely antagonized the effects of 10(-8) M 17beta-estradiol. Moreover, 3 microM 4-androsten-4-ol-3,17-dione, an aromatase inhibitor, did not affect PTH-induced osteoclast formation antagonized by testosterone. Hydroxyflutamide, an androgen receptor antagonist, concentration-dependently antagonized the inhibitory effects of testosterone as well as DHT on PTH-stimulated osteoclast formation. In conclusion, the present study first demonstrated that testosterone inhibited osteoclast formation stimulated by PTH through the androgen receptor, but not through the production of intrinsic estrogen in mouse bone cell cultures.

Determinants of bone mineral density and spinal fracture risk in postmenopausal Japanese women

The present study analyzed the factors that determine bone mineral density (BMD) and predict spinal fracture risk in postmenopausal Japanese women. Two hundred and five postmenopausal Japanese women aged 48-84 years (mean age 64 years) were enrolled in the cross-sectional study. BMD of the lumbar spine, femoral neck and total body as well as body composition were measured by dual-energy X-ray absorptiometry (DXA). Mid-radial BMD was measured by single-photon absorptiometry. We also determined serum levels of insulin-like growth factor (IGF)-I, IGF binding protein-2, -3 and osteocalcin as well as urinary levels of pyridinoline (Pyr), deoxy-Pyr (D-Pyr) and growth hormone. Multiple regression analysis revealed that lean body mass (LBM) was positively correlated with BMD at all sites. In contrast, femoral neck BMD was highly related to fat mass as well as LBM, although fat mass was not an independent correlate of total body and mid-radial BMD. LBM and urinary D-Pyr were crucial determinants at all sites except the mid-radius in stepwise regression analysis. Fat mass and serum IGF-I were determinants of femoral neck and mid-radial BMD, respectively. In terms of reproductive history, parity affected lumbar BMD. Factors affecting BMD differed according to the site. On the other hand, lumbar BMD as well as serum levels of IGF-I and albumin were selected as predictors of spinal fracture risk in multiple logistic regression analysis. Lumbar BMD, serum IGF-I and LBM were selected in women with lumbar BMD above 0.727 g/cm2. In conclusion, the present study indicates that LBM is a more important determinant of BMD than fat mass at any site except the femoral neck. Age, serum IGF-I and urinary D-Pyr were also determinants of BMD, dependent on the regions measured. Lumbar BMD and LBM as well as serum levels of IGF-I and albumin were useful markers which predicted the risk of osteoporotic spinal fractures in postmenopausal Japanese women.

Structure-function study and anti-HIV activity of synthetic peptide analogues derived from viral chemokine vMIP-II

The viral macrophage inflammatory protein II (vMIP-II) shows a broad spectrum interaction with both CC and CXC chemokine receptors including CCR5 and CXCR4, two principal coreceptors for the cellular entry of human immunodeficiency virus type 1 (HIV-1). Recently, we have shown that a synthetic peptide derived from the N-terminus of vMIP-II, designated as V1, is a potent antagonist of CXCR4 but not CCR5 [Zhou, N., et al. (2000) Biochemistry 39, 3782-3787]. In this study, we synthesized a series of new peptides derived from other regions of vMIP-II and characterized their binding activities with both CXCR4 and CCR5. The results provided further support for the notion that the N-terminus of vMIP-II is the major determinant for CXCR4 recognition and that vMIP-II probably interacts with other chemokine receptors such as CCR5 with different sequence and conformational determinants. To understand the structure-function relationship of V1 peptide, its solution conformation was studied using circular dichroism spectroscopy, which showed a random conformation similar to that of the corresponding N-terminus in native vMIP-II. In addition, we synthesized a series of mutant analogues of V1 containing alanine, glycine, or phenylalanine substitution at various positions. Residues Val-1, Arg-7, and Lys-9 of V1 peptide were found to be critical for receptor interaction, because single alanine replacement at these positions dramatically decreased peptide binding to CXCR4. In contrast, alanine or phenylalanine substitution at Cys-11 led to significant enhancement in peptide affinity for CXCR4. Finally, we showed that V1 peptide inhibits HIV-1 replication in CXCR4(+) T-cell lines. These studies provide new insights into the structure-function relationship of V1 peptide and demonstrate that this peptide may be a lead for the development of therapeutic agents.

Estrogen modulates osteoblast proliferation and function regulated by parathyroid hormone in osteoblastic SaOS-2 cells: role of insulin-like growth factor (IGF)-I and IGF-binding protein-5

Although there is clinical evidence showing that combined therapy with parathyroid hormone (PTH) and estrogen is additively effective in increasing the bone mass of patients with osteoporosis, the mechanism of the interaction between these hormones remains unclear. The present study was performed to determine whether estrogen would affect osteoblast proliferation and function modulated by PTH in human osteoblastic SaOS-2 cells. Human PTH-(1-34) significantly inhibited [(3)H]thymidine (TdR) incorporation, which was attenuated by 24 h pretreatment with 10(-10) to 10(-7) M 17 beta-estradiol (17 beta-E(2)) in a concentration-dependent manner. PTH significantly stimulated alkaline phosphatase (ALP) activity, collagen synthesis and type-1 procollagen mRNA expression after pretreatment with 17 beta-E(2 )in these cells. Tamoxifen, an anti-estrogen, antagonized these 17 beta-E(2)-induced effects. Pretreatment with insulin-like growth factor-I (IGF-I) mimicked estrogen action, and coincubation of 3 microg/ml anti-IGF-I antibody antagonized the effects of 17 beta-E(2 )as well as those of IGF-I. In the presence of 17 beta-E(2 )pretreatment, PTH strongly stimulated IGF-binding protein (IGFBP)-5 mRNA expression in these cells, and recombinant IGFBP-5 increased type-1 procollagen mRNA expression and ALP activity. In conclusion, estrogen attenuates PTH-induced inhibition of osteoblast proliferation and PTH stimulates osteoblast function in the presence of estrogen pretreatment. IGF-I and/or IGFBP-5 seemed to be involved in the estrogen-induced modulation of PTH action on osteoblast proliferation and function.

Short stature caused by a natural growth hormone antagonist

Severe short stature in a male child due to a single mutation in the GH-1 gene was first reported in 1996 by Takahashi et al. [N Engl J Med 1996;334:432-436]. This missense mutation was predicted to convert codon 77 from arginine (R) to cysteine (C). The child's chronological age was 4 years and 11 months, and his bone age 2 years and 6 months, i.e., equal to only 51% of his chronological age. Body proportions were normal except for the prominent forehead and saddle nose. Pituitary size was normal on magnetic resonance imaging examinations. Serum IGF-1, IGFBP-3 and GHBP were all decreased or at the lower limit of the normal range. Nocturnal urinary growth hormone (GH) excretion was high. Isoelectric focusing analysis revealed the presence of an abnormal GH peak in addition to the normal one. The R77C mutant GH possessed a 6 times greater affinity to GHBP than the wild-type GH, and inhibited tyrosine phosphorylation in IM-9 cells 10 times more potently than the wild-type GH, showing an antagonistic or a dominant negative action. In agreement with the antagonistic property of the mutant GH exhibited, the child did not show any increase in serum IGF-1 levels after exogenous hGH administration. It should be noted that the child in this study is not a typical case of Kowarski syndrome in which endogenous GH is found to be simply bioinactive, as in the patient we recently described elsewhere. Therefore, this patient's condition should be categorized as a new syndrome of short stature caused by a natural GH antagonist.

Cloning and characterization of the 5'-flanking region of the human prolactin-releasing peptide receptor gene

Recently a novel peptide which specifically stimulates the secretion of prolactin (PRL) was found and named PRL-releasing peptide (PrRP). To evaluate the regulation of human (h) PrRP-receptor (PrRP-R) gene expression, we cloned the 5'-flanking region of the hPrRP-R gene and determined the nucleotide sequence of 4.0 kilobase pairs (kb) upstream from the translation start site. Analysis of the hPrRP-R transcripts by means of 5'-rapid amplification of cDNA ends suggested that the hPrRP-R gene had multiple transcription start sites between -429 and -365 from the translation start site. There is no typical TATA or CAAT but a GC box and putative binding sites for several transcription factors including Pit-1 and pituitary homeobox 1 (Ptx1). However, transient transfection studies using a luciferase reporter gene demonstrated that 5'-flanking region exerts promoter activity in several non-pituitary cell lines as well as in GH(3) cells. The GC box located from -467 to -457 was identified as an important region for the basal expression of the hPrRP-R gene. Knowledge of the promoter region of the hPrRP-R gene, which was obtained in the present study, will facilitate the clarification of its transcriptional regulation.

Methylglyoxal induces G:C to C:G and G:C to T:A transversions in the supF gene on a shuttle vector plasmid replicated in mammalian cells

We previously reported that the majority of base-pair substitutions induced by an endogenous mutagen, methylglyoxal, were G:C-->T:A transversions and G:C-->A:T transitions in wild-type and nucleotide excision repair (NER)-deficient (uvrA or uvrC) Escherichia coli strains. To investigate the mutation spectrum of methylglyoxal in mammalian cells and to compare the spectrum with those detected in other experimental systems, we analyzed mutations in a bacterial suppressor tRNA (supF) gene in the shuttle vector plasmid pMY189. We treated pMY189 with methylglyoxal and immediately transfected it into simian COS-7 cells. The cytotoxicity and the mutation frequency (MF) increased according to the dose of methylglyoxal. In the mutants induced by methylglyoxal, multi-base deletions were predominant (50%), followed by base-pair substitutions (35%), in which 89% of the substitutions occurred at G:C sites. Among them, G:C-->C:G and G:C-->T:A transversions were predominant. The overall distribution of methylglyoxal-induced mutations detected in the supF gene was different from that for the spontaneous mutations. These results suggest that methylglyoxal may take part in causing G:C-->C:G and G:C-->T:A transversions in vivo.

Multifocal fibrosclerosis as a possible cause of panhypopituitarism with central diabetes insipidus

Multifocal fibrosclerosis denotes a combination of similar fibrous disorders occurring at different anatomical sites. We encountered a 53-year-old male patient with orbital pseudotumor, chronic paranasal sinusitis, fibrous nodules of the lungs, intracranial pachymeningitis, and panhypopituitarism with central diabetes insipidus (DI) as a possible manifestation of multifocal fibrosclerosis. It has been reported that intracranial pachymeningitis or orbital pseudotumor associated with multifocal fibrosclerosis could invade the sella turcica causing a variety of anterior and/or posterior pituitary dysfunctions. In our case, intracranial pachymeningitis apparently involved the pituitary stalk and gland. Isolated gonadotropin deficiency, in addition to central DI, preceded panhypopituitarism. Although panhypopituitarism with central DI due to multifocal fibrosclerosis is quite rare and only one case has ever been reported, this systemic fibrotic disorder can be a possible cause of panhypopituitarism with central DI.

Profiling of Caenorhabditis elegans proteins using two-dimensional gel electrophoresis and matrix assisted laser desorption/ionization-time of flight-mass spectrometry

The nematode Caenorhabditis elegans (C. elegans) is the first animal whose whole 97 Mb genome sequence, encoding ca. 19000 open reading frames (ORF's), has been essentially determined. We tried to establish a 2-DE map of the nematode proteome by means of two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). A soluble protein fraction of mixed stages of the worm, wild-type strain N2, was applied to 2-D PAGE. After Coomassie Brilliant Blue (CBB) staining, 1200 spots were detected and 140 major spots were excised from the gel and subjected to in-gel digestion with Achromobacter protease I (lysyl endopeptidase). Resulting peptides were analyzed by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) followed by peptide mass fingerprinting for protein identification. With this approach we have obtained a two-dimensional electrophoresis (2-DE) protein map in which 69 spots were localized as landmarks for comparison of expression profiles to elucidate the basis of various biological events.

Stimulation by eicosapentaenoic acids of leptin mRNA expression and its secretion in mouse 3T3-L1 adipocytes in vitro

Recent evidence indicates that both leptin and eicosapentaenoic acids (EPA) improve insulin sensitivity. In the present study, we examined the effect of EPA on endogenous leptin expression in 3T3-L1 adipocytes to clarify whether the EPA's effect is exerted through leptin expression. EPA caused a time- and dose-dependent increase of leptin mRNA levels in 3T3-L1 adipocytes. Leptin mRNA expression was significantly increased up to 309.4 +/- 17.0% of the control by 24 h (P < 0.01; n = 6). Leptin secretion was also significantly increased up to 193.3 +/- 12.1% of the control by 24 h (P < 0.01; n = 6). EPA is a ligand for peroxisome proliferator-activated receptors (PPARs) with the highest affinity to PPARalpha. We examined the effect on leptin expression of clofibrate, a ligand for PPARalpha, bezafibrate, for PPARbeta, or troglitazone, for PPARgamma, to clarify whether these ligands for PPARs could mimic EPA-induced stimulation of leptin expression. Neither clofibrate nor bezafibrate affected leptin mRNA expression, whereas troglitazone significantly suppressed leptin mRNA expression. On the other hand, inhibition by 6-diazo-5-oxo-l-norleucine of the rate-limiting enzyme in hexosamine biosynthesis blunted EPA-induced stimulation of leptin mRNA expression and its secretion. These data suggest that EPA up-regulates leptin gene expression and its secretion probably through a hexosamine biosynthetic pathway.

[Relationship between fatty liver and coronary risk factors]

Fatty liver is a common finding in abdominal ultrasonographic examination in health check-ups, but the relationship between fatty liver and so-called coronary risk factors has rarely been investigated from the viewpoint of prevention of coronary heart disease. The purpose of the present study was to elucidate such a relationship by comparing the coronary risk factors with and without fatty liver by using data from health check-ups for the mid-management and management staff of a manufacturing company. The majority (77.1%) of those with fatty liver in the present study were categorized as "normal" or "marginally obese" and only a small portion (22.9%) were categorized as "obese" according to the classification of the body mass index. The group of subjects with fatty liver had significantly lower mean HDL-cholesterol and higher levels of fasting blood sugar, HDL/total cholesterol ratio, triglyceride, uric acid and transaminases, than those parameters in subjects without fatty liver, even after adjustment for age and body-mass index. The blood pressure (both systolic and diastolic) and total cholesterol level did not show any significant difference after controlling the covariates. Our results indicated that fatty liver has a close correlation with the majority of coronary risk factors causing atheroscleotic diseases, and most of these relationships are independent of total body mass. Our results regarding fatty liver are a help to occupational health personnel when advising workers to reduce their own risk of atherogeic diseases.

Formation of 5-formyl-2'-deoxycytidine from 5-methyl-2'-deoxycytidine in duplex DNA by Fenton-type reactions and gamma-irradiation

5-methyl-2'-deoxycytidine (5-Me-dC) is formed by the enzymatic methylation of dC, primarily in CpG sequences in DNA, and is involved in the regulation of gene expression. In the present study, 5-Me-dC and double-stranded DNA fragments containing 5-Me-dC were either gamma-irradiated or aerobically treated with Fenton-type reagents, Fe(II)-EDTA, Fe(II)-nitrilotriacetic acid, Fe(III)-EDTA-H(2)O(2)-catechol or ascorbic acid-H(2)O(2) under neutral conditions. The formation of 5-formyl-2'-deoxycytidine (5-CHO-dC) was observed upon treatment of both 5-Me-dC and DNA fragments containing 5-Me-dC. The yields of 5-CHO-dC from 5-Me-dC and those of 5-formyl-2'-deoxyuridine from dT were comparable. These results suggest that 5-Me-dC in DNA is as susceptible to oxidation as dT in cells, and raise the possibility that 5-CHO-dC may contribute to the high mutagenic rate observed in CpG sequences in genomic DNA.

In vitro processing of amyloid precursor protein by cathepsin D

The formation of beta A4 amyloid in the brains of individuals with Alzheimer's disease requires the proteolytic cleavage of amyloid precursor protein. Several lines of evidence suggest that cathepsin D, the major lysosomal/endosomal aspartic protease, may be involved in this process. In this work, we used a sensitive in vitro method of detection to investigate the role of cathepsin D in the proteolytic processing of a 100-amino acid C-terminal fragment (C100) inclusive of beta A4 and cytoplasmic domain of APP. Digestion of C100 with cathepsin D resulted in cleavage at the amyloidogenic gamma-cleavage sites. This occurred preferentially at Thr43-Val44 and at Ala42-Thr43, generating full length beta A4 43 and beta A4 42 amyloid peptides, respectively. Cathepsin D was also found to cleave the substrate at the following nonamyloidogenic sites; Leu34-Met35, Thr48-Leu49 and Leu49-Val50. A high concentration of cathepsin D resulted in cleavage also occurring at Phe19-Phe20, Phe20-Ala21 and Phe93-Phe94 of the C100, suggesting that these sites are somewhat less sensitive to the action of cathepsin D. Digestion of C100 using different solublizing agents indicated that the cleavage of C100 by cathepsin D is greatly influenced by the structural integrity of the substrate. However, our results suggest that cathepsin D could generate the pathogenic beta A4 amyloid peptides from its precursor in vitro, which may indicate a role in the amyloidogenesis of Alzheimer's disease.

The C422F mutation of the growth hormone receptor gene is not responsible for short stature

A missense mutation, C422F, was identified in the intracellular domain of GH receptor (GHR) in a Japanese short boy. Although this mutation was previously reported in a patient with GH insensitivity syndrome (GHIS), it has not been clear whether this mutation causes GH insensitivity. To clarify the effect of this mutation on GH signal transduction, mutant GHR was expressed in CHO cells, and its functional properties were investigated. There were no significant differences in GH-induced tyrosine phosphorylation of STAT5b (signal transducer and activator of transcription) between wild-type GHR (GHR-wt)- and mutant GHR (GHR-C422F)-expressing cells. Moreover, STAT5-mediated transcriptional activation of GHR-C422F-expressing cells was comparable to that of GHR-wt-expressing cells. These findings indicated that the C422F mutation of GHR affected neither GH-induced tyrosine phosphorylation nor the transcriptional activation of STAT5. In addition, the analysis of genotypes and phenotypes of his family revealed that body heights of family members with heterozygous or homozygous C422F mutations were all within normal ranges, with the single exception of the proband. These in vitro and in vivo results indicate that the C422F missense mutation of GHR is a polymorphism that does not result in GHIS.

Cell cycle regulation of menin expression

The multiple endocrine neoplasia type 1 gene product, menin, interacts with Jun D. The physiological role of menin in cell cycle control and the manner in which its inactivation contributes to tumorigenesis remain unknown. In the present study, the expression of menin was examined at various cell cycle stages in GH4C1 cells, a rat pituitary cell line. Cells synchronized at the G1-S-phase boundary expressed menin at a lower level than G0-G1-synchronized cells. The expression of menin increased as the cells entered S phase, at which time Jun D expression also increased. In contrast, cells synchronized at the G2-M phase expressed lower levels of menin. At G0-G1, G1-S, and G2-M phases of the cell cycle, menin was found predominantly in the nucleus. In summary, we show that in pituitary cells, menin is a nuclear protein whose expression is cell-cycle regulated. The data suggest that menin has an important role in cell growth regulation.