Mouse major satellite DNA is prone to eccDNA formation via DNA Ligase IV-dependent pathway

Elevated levels of extrachromosomal circular DNA (eccDNA or spcDNA) are closely associated with genomic instability and aging. Despite extensive studies, the mechanism of its generation in mammalian cells is unknown. We report here that mouse major satellite DNA (MSD) is prone to eccDNA formation and that the resulting molecules are multimeres of the basic repeat. Extrachromosomal circular major satellite (ECMS) DNA constitutes the majority of eccDNA in B16 mouse melanoma cells and is highly abundant in other mouse cells. Production of these molecules is enhanced in proliferating cells, suggesting that processes associated with DNA replication are involved in their appearance. Using siRNA technique we show that DNA Ligase IV is engaged in ECMS synthesis. Based on our findings we propose a novel two-step model for eccDNA formation in mammalian cells.

The impact of GP IIb/IIIa inhibitors during primary percutaneous coronary intervention in acute myocardial infarction patients

The use of glycoprotein (GP) IIb/IIIa inhibitors during percutaneous coronary interventions (PCI) in the acute phase of myocardial infarction (AMI) is still a matter of debate. The aim of the present study was to compare the outcomes of patients with acute ST-segment elevation myocardial infarction who underwent primary PCI and were concomitantly treated with GP IIb/IIIa inhibitors with those who were not treated with these drugs. Between January 1996 and November 2003, a total of 418 consecutive patients underwent PCI in the setting of ST-segment elevation AMI. At the operator's discretion, 287 patients were concomitantly treated with GP IIb/IIIa inhibitors and 115 patients were not. Angiographic success and final TIMI 3 flow in the infarct-related artery was achieved more frequently in patients treated with GP IIb/IIIa inhibitors (90% vs. 77%; p=0.001). The in-hospital composite endpoint of death, reinfarction and bleeding complications was significantly better in patients treated with GP IIb/IIIa inhibitors (4% vs. 12%; p=0.005). Furthermore, the adjusted 12-month survival rate was significantly better in these patients (RR: 2.99, CI: 1.29-6.9; p=0.01). Therefore, adjunctive therapy with GP IIbIIIa inhibitors during primary PCI is associated with improved short-term outcomes and one-year survival without an increased risk of bleeding.

Unusual cause of partially reversible severe cardiovascular autonomic failure

We report an unusual case of partially reversible severe cardiovascular autonomic system failure in a patient with double primary malignancies. The patient presented with severe orthostatic hypotension preceding the detection of lymphoma and lung cancer. The patient had autonomic failure on presentation. One year after surgery and chemotherapy, there was a gradual improvement in both symptoms and autonomic function simultaneously. We conclude that paraneoplastic severe autonomic failure can be reversible.

Significance of elevated cardiac troponin after percutaneous coronary interventions

Assays for cardiac troponin have become a standard for the diagnosis of myocardial damage. Due to their high sensitivity, minor myocardial injury can be frequently detected following percutaneous coronary interventions (PCI). Minor elevations in cardiac enzymes after apparently successful PCI are rather common and even modest increases in creatine kinase myocardial band (CK-MB) elevation identify a population with worse long-term prognosis compared to patients with no enzyme elevation. The significance of troponin elevation in acute coronary syndromes and its prognostic implications on short- and long-term clinical outcomes were previously demonstrated in several clinical studies. Conversely, data regarding troponin elevation after an apparently successful PCI is limited and their relevance in terms of predicting clinical outcomes remains unclear. Given the higher sensitivity of troponin essays, the incidence of troponin elevation after PCI is higher than that of CK-MB. In this review we discuss the significance and implications of post-procedural troponin elevation.

Role of nitric oxide in the regulation of cerebral blood flow in humans: chemoregulation versus mechanoregulation

BACKGROUND

From animal studies it emerged that nitric oxide is important for the modulation of CO2-mediated cerebral blood flow (CBF chemoregulation) but not for the pressor-dependent mechanism (mechanoregulation). This hypothesis was tested in 18 healthy subjects.

METHODS AND RESULTS

Peak velocity (PV), diastolic velocity (DV), and mean velocity (MV) were measured by transcranial Doppler of the middle cerebral artery. Chemoregulation was assessed during normocapnia, hypocapnia, and after inhaled mixture of 95% O2+5% CO2. Mechanoregulation was evaluated by incremental doses of phenylephrine. Measurements were repeated during infusion of sodium nitroprusside (SNP). Regional cerebrovascular resistance (CVR) was calculated as mean blood pressure (BP)/MV. SNP infusion decreased mean BP by 7 mm Hg and CVR decreased from 1.38+/-0.08 to 1.29+/-0.09 mm Hg/cm x s(-1); P=0.01, resulting in unaffected CBF. Phenylephrine (25 to 250 microg) caused a similar increase in BP in a dose-response fashion before and during SNP infusion. Despite the increments in BP and CVR, CBF remained unaffected. During hyperventilation (end-tidal CO2 approximately 24 mm Hg), CVR increased by 75+/-3% and PV and DV decreased by 27+/-2% and 43+/-2%, respectively (P<0.001 for all). SNP infusion blunted the vasoconstrictive effect of hypocapnia; CVR increased only by 57+/-5%, and PV and DV decreased by 23+/-2% and 35+/-3%, respectively, (P<0.05 for all). Similarly, SNP augmented the vasodilatory effect of hypercapnia.

CONCLUSIONS

Exogenous nitric oxide donor affects the basal cerebral vascular tone without affecting the CBF mechanoregulation. However, it selectively affects only the chemoregulatory mechanism (CO2-dependent). Thus, the CO2-NO axis is a cardinal pathway for CBF regulation in humans.

Uniquely conserved non-translated regions are involved in generation of the two major transcripts of protein phosphatase 2Cbeta

Partial cDNAs of different isoforms of protein phosphatase 2Cbeta (PP2Cbeta or PPM1B) have been characterized in mammals. We disclose here the full cDNAs of two major PP2Cbeta isoforms from human, rat and mouse. These cDNAs (2.6 and 3.3 kb) are able to encode 53 kDa (PP2Cbetal) and 43 kDa (PP2Cbetas) polypeptides, respectively. The isoforms are co-expressed ubiquitously with the highest level in skeletal muscle, as assessed by Northern-blot analysis. Western and in situ analyses using monoclonal antibodies against PP2Cbeta confirmed the existence of two isoforms in the cytoplasm. Comparative sequence analysis revealed that both cDNAs consist of six exons with an alternate usage of the 3' exons that underlies the differences between them. The genomic structure of PP2Cbeta is similar to that of other PP2C paralogs and includes a non-coding first exon followed by a large intron and a large second exon that encoded most of the catalytic domain. Both variants of the ending exon include large non-coding regions. All non-translated regions (NTRs) are highly conserved between the orthologous genes, indicating their regulatory function. The 5'-NTR is long (379 bp), includes upstream start codons and is predicted to contain stable secondary structures. Such features inhibit translation initiation by the scanning mechanism. Introduction of this NTR element into a bi-luciferase expression-cassette enabled expression of the second cistron, suggesting that it might serve as an internal ribosome entry site, or it contains a cryptic promoter. Overexpression of PP2Cbeta under CMV-promoter in 293 cells led to cell-growth arrest or cell death.

Protein phosphatase 2Calpha expression in normal human tissues: an immunohistochemical study

Protein phosphatase (PP2Calpha) is a member of the mammalian serine threonine-specific protein phosphatases family. We produced monoclonal antibodies against the recombinant PP2Calpha and evaluated the immunoreactivity of normal human tissues. The reactivity was strong in normal skin, the digestive tract, lung, kidney, breast, prostate, endocrine glands, and brain, while it was moderate in the ovary, testis, and liver. Epithelial cells revealed high levels of PP2Calpha expression, but stromal cells, including fibroblasts and endothelial cells, showed no or little PP2Calpha expression. Given the broad reactivity in endocrine and secreting epithelial cells, we propose that PP2Calpha expression might contribute to secretory cell function.

c-Cbl is a suppressor of the neu oncogene

A rodent oncogenic mutant of the Neu receptor tyrosine kinase is a useful experimental model because overexpression of the respective receptor, namely HER2/ErbB-2, in human malignancies is associated with relatively aggressive diseases. Here we show that the oncogenic form of Neu is constitutively associated with the product of the c-cbl proto-oncogene and is part of a large complex that includes the phosphoinositide 3-kinase and Shc. Ectopic expression of c-Cbl, a ubiquitin-protein isopeptide ligase specific to activated tyrosine kinases, causes rapid removal of Neu from the cell surface and severely reduces signaling downstream of oncogenic Neu. c-Cbl-induced down-regulation of Neu involves covalent attachment of ubiquitin molecules and requires the carboxyl-terminal domain of Neu. The negative effect of c-Cbl is antagonized by v-Cbl, a virus-encoded oncogenic truncated form of c-Cbl. In an in vivo model, infection of a Neu-transformed neuroblastoma with a c-Cbl-encoding retrovirus caused enhanced down-regulation of Neu and correlated with tumor retardation. Our results implicate c-Cbl in negative regulation of Neu and offer a potential target for treatment of HER2/ErbB-2-positive human malignancies.

Ubiquitin ligase activity and tyrosine phosphorylation underlie suppression of growth factor signaling by c-Cbl/Sli-1

Receptor desensitization is accomplished by accelerated endocytosis and degradation of ligand-receptor complexes. An in vitro reconstituted system indicates that Cbl adaptor proteins directly control downregulation of the receptor for the epidermal growth factor (EGFR) by recruiting ubiquitin-activating and -conjugating enzymes. We infer a sequential process initiated by autophosphorylation of EGFR at a previously identified lysosome-targeting motif that subsequently recruits Cbl. This is followed by tyrosine phosphorylation of c-Cbl at a site flanking its RING finger, which enables receptor ubiquitination and degradation. Whereas all three members of the Cbl family can enhance ubiquitination, two oncogenic Cbl variants, whose RING fingers are defective and phosphorylation sites are missing, are unable to desensitize EGFR. Our study identifies Cbl proteins as components of the ubiquitin ligation machinery and implies that they similarly suppress many other signaling pathways.

The association between melatonin and sleep stages in normal adults and hypogonadal men

The role of melatonin in normal sleep-wake regulation has been inferred from the temporal relationships between its cycle and the 24 h cycle in sleep propensity. Pharmacological doses of melatonin were reported to have sleep-inducing effects in insomniacs. The current study investigated the relationship between melatonin and sleep stages in groups of hypogonadal men with abnormal melatonin levels. We were also interested in examining what would happen to these relationships during testosterone replacement therapy. Male patients with hypogonadotropic hypogonadism (IGD, n = 6), constitutional delayed puberty (DP, n = 6), and Klinefelter's syndrome (KS, n = 5) before and during testosterone replacement therapy were studied. Six patients with KS and normal testosterone levels were also studied. Results were compared with those obtained in normal controls (n = 6). Serum samples were obtained at 15 min intervals from 1900-0700h in a controlled light-dark environment with simultaneous polysomnographic sleep recordings. Serum melatonin levels were the highest in IGD and DP and lowest in KS patients. A lower percentage of sleep stage 2 and higher percentage of stage 3/4 were observed in IGD and DP groups while KS patients had higher percentage of stage 2 and lower percentage of stage 3/4 as compared to controls. Slow wave sleep was the highest in IGD and the lowest in KS groups. Serum melatonin levels were lowest in KS groups. Serum melatonin levels were lowest in sleep stage 3/4, higher in stage 2 and highest in REM sleep when all groups were combined and averaged together. However, in the IGD group, melatonin levels were actually lowest in REM sleep. Also in the KS group, melatonin levels were lower in REM than during sleep stage 2. Serum melatonin levels were lowest in sleep stage 3/4 in all groups, higher in stage 2, and highest in REM sleep. During waking periods, melatonin levels were the highest in untreated IGD, DP and KS patients. Testosterone treatment given to these patients, although normalized, their melatonin levels did not statistically significantly change these correlations. These data demonstrate that relative melatonin concentrations are associated with sleep stages in hypogonadal and normal men. The results also indicate that the association between melatonin and the reproductive hormones are independent of the synchronizing effects of melatonin on sleep homeostasis.

Telomeric repeats on small polydisperse circular DNA (spcDNA) and genomic instability

Small polydisperse circular DNA (spcDNA) is a heterogeneous population of extrachromosomal circular molecules present in a large variety of eukaryotic cells. Elevated amounts of total spcDNA are related to endogenous and induced genomic instability in rodent and human cells. We suggested spcDNA as a novel marker for genomic instability, and speculated that spcDNA might serve as a mutator. In this study, we examine the presence of telomeric sequences on spcDNA. We report for the first time the appearance of telomeric repeats in spcDNA molecules (tel-spcDNA) in rodent and human cells. Restriction enzyme analysis indicates that tel-spcDNA molecules harbor mostly, if not exclusively, telomeric repeats. In rodent cells, tel-spcDNA levels are higher in transformed than in normal cells and are enhanced by treatment with carcinogen. Tel-spcDNA is also detected in some human tumors and cell lines, but not in others. We suggest, that its levels in human cells may be primarily related to the amount of the chromosomal telomeric sequences. Tel-spcDNA may serve as a unique mutator, through specific mechanisms related to the telomeric repeats, which distinguish it from the total heterogeneous spcDNA population. It may affect telomere dynamics and genomic instability by clastogenic events, alterations of telomere size and sequestration of telomeric proteins.

ErbB tyrosine kinases and the two neuregulin families constitute a ligand-receptor network

The recently isolated second family of neuregulins, NRG2, shares its primary receptors, ErbB-3 and ErbB-4, and induction of mammary cell differentiation with NRG1 isoforms, suggesting functional redundancy of the two growth factor families. To address this possibility, we analyzed receptor specificity of NRGs by using an engineered cellular system. The activity of isoform-specific but partly overlapping patterns of specificities that collectively activate all eight ligand-stimulatable ErbB dimers was revealed. Specifically, NRG2-alpha [corrected], like NRG1-beta [corrected], emerges as a narrow-specificity ligand, whereas NRG2-beta [corrected] is a pan-ErbB ligand that binds with different affinities to all receptor combinations, including those containing ErbB-1, but excluding homodimers of ErbB-2. The latter protein, however, displayed cooperativity with the direct NRG receptors. Apparently, signaling by all NRGs is funneled through the mitogen-activated protein kinase (MAPK). However, the duration and potency of MAPK activation depend on the identity of the stimulatory ligand-receptor ternary complex. We conclude that the NRG-ErbB network represents a complex and nonredundant machinery developed for fine-tuning of signal transduction.

Abnormal melatonin secretion in hypogonadal men: the effect of testosterone treatment

OBJECTIVE

We have recently demonstrated that GnRH deficient male patients have increased nocturnal melatonin secretion, whereas hypergonadotrophic hypogonadal males have decreased melatonin levels. We were interested in determining whether testosterone (T) treatment (when T levels were well matched with pubertal control values) has an effect on melatonin secretory profiles in these patients.

DESIGN

Prospective, controlled.

SUBJECTS

Six male patients with idiopathic hypogonadotrophic hypogonadism (IGD), six males with hypergonadotrophic hypogonadism due to Klinefelter's syndrome (KS) and seven controls. Patients were examined before and during the administration of 250 mg testosterone enanthate/month for four months.

MEASUREMENTS

Serum samples for melatonin levels were obtained every 15 minutes from 1990 to 0700 h in a controlled light-dark environment. The results of FSH, LH, T and oestradiol (E2) (determined at hourly intervals) and melatonin profiles, were compared with the pre-treatment values in each group, and with values obtained in the control group.

RESULTS

All 12 patients had low pre-treatment T levels (1.4 +/- 0.7 in IGD and 2.0 +/- 0.4 in KS vs. 19.8 +/- 2.3 nmol/l in controls) and attained normal levels after four months of T treatment (19.5 +/- 7 in IGD and 22.7 +/- 3.8 nmol/l in KS). Serum LH, FSH and E2 levels (11 +/- 4 IU/l, 24 +/- 10 IU/l and 113 +/- 12 pmol/l, respectively) were still elevated in KS during T treatment as compared with values in controls (2 +/- 1 IU/l, 2 +/- 1 IU/l and 67 +/- 4 pmol/l, respectively). In IGD, serum LH (0.12 +/- 0.1 IU/l) and FSH (0.16 +/- 0.2 IU/l) levels during T treatment were suppressed. Pretreatment melatonin levels in IGD were greater than those in age-matched pubertal controls while in KS, melatonin levels were lower than values in controls. Melatonin levels were equal in all 12 hypogonadal patients and controls when T levels were well matched. Mean (+/- SD) dark-time melatonin levels decreased from 286 +/- 18 to 157 +/- 26 pmol/l in IGD and increased from 92 +/- 19 to 183 +/- 48 pmol/l in KS (vs 178 +/- 59 pmol/l in controls). The integrated melatonin values decreased in IGD (from 184 +/- 14 to 102 +/- 21 pmol/min. 1 x 10(3)) and increased in KS (from 64 +/- 13 to 123 +/- 40, vs. 116 +/- 39 pmol/min. 1 x 10(3) in controls). No correlations were found between melatonin and LH, FSH or E2 levels.

CONCLUSIONS

These data indicate that male patients with GnRH deficiency have increased nocturnal melatonin secretion while in hypergonadotrophic hypogonadal males melatonin secretion is decreased. Testosterone treatment normalized melatonin concentrations in these patients. Taken together, the results suggest that GnRH, gonadotrophins and gonadal steroids modulate pineal melatonin in humans.

Small polydispersed circular DNA (spcDNA) in human cells: association with genomic instability

Small Polydispersed Circular DNA (spcDNA) was suggested to be associated with genetically unstable cells. However, until now, qualitative and quantitative research has been limited due to the lack of efficient methods for detection and analysis. We developed a two-dimensional (2-D) neutral-neutral gel electrophoresis assay for the identification, characterisation and quantitation of spcDNA. Using this method, we established the relation of spcDNA to genetic and induced genomic instability in human cells, both in vitro and in vivo. Enhanced amounts of spcDNA were found in genetically unstable cells and tissues. spcDNA was detected in a tumor cell-line (HeLa) and in tumor tissue (colon carcinoma) as well as in fibroblasts derived from patients suffering from the genomic instability disease, Fanconi's Anemia. We failed to detect spcDNA in the genetically stable normal human fibroblasts. However, following treatment with the initiating carcinogen MNNG, an induction of spcDNA was observed. The level of spcDNA was quantified according to mitochondrial DNA (mtDNA) standards. In light of these findings, we discuss the possible role of spcDNA as a marker and an enhancer of genomic instability.

Decreased nocturnal melatonin secretion in patients with Klinefelter's syndrome

OBJECTIVE

We have recently demonstrated that GnRH deficient male patients have increased nocturnal melatonin secretion which decreases to normal levels during testosterone treatment. The results suggested that sex steroids, rather than LH, modulate pineal melatonin in an inverse fashion. The purpose of this study was to characterize circulating melatonin levels in untreated males with hypergonadotrophic hypogonadism due to Klinefelter's syndrome (KS).

DESIGNS

Prospective, controlled.

SUBJECTS

Eleven patients with Klinefelter's syndrome and seven controls. Patients were subdivided into two groups: (1) with low testosterone, and (2) with normal testosterone levels.

MEASUREMENTS

Serum samples for melatonin concentrations were obtained every 15 minutes from 1900 to 0700 h in a controlled light-dark environment.

RESULTS

All patients had elevated FSH, LH and oestradiol (E2) levels. Mean (+/-SD) dark time nocturnal melatonin levels were significantly lower in low testosterone KS (92 +/- 19 pmol/l) compared with 146 +/- 42 pmol/l in normal testosterone KS and 179 +/- 59 pmol/l in controls (P < 0.02). A similar pattern was observed for the mean (+/-SD) peak melatonin levels (165 +/- 41, 236 +/- 59 and 293 +/- 89 pmol/l) in low testosterone KS, normal testosterone KS and controls, respectively (P < 0.01). Integrated nocturnal melatonin secretion values (AUC) were also lower in low testosterone KS (64 +/- 13) compared with 96 +/- 26 in normal testosterone KS and 116 +/- 39 pmol/min 1 x 10(3) in controls (P < 0.02). The time of melatonin peak and the time of the nocturnal melatonin rise as well as the light-time mean (+/-SD) serum melatonin levels were similar in all three groups. No correlations were found between melatonin and LH, FSH, or E2 levels.

CONCLUSIONS

Melatonin secretion is decreased in male patients with low testosterone hypergonadotrophic hypogonadism whereas in normal testosterone Klinefelter's syndrome patients, melatonin secretory profiles are normal. The results suggest that the suppression of melatonin secretion in these patients is mediated by GnRH (either directly or indirectly) and/or oestradiol.

A hierarchical network of interreceptor interactions determines signal transduction by Neu differentiation factor/neuregulin and epidermal growth factor

The ErbB family includes four homologous transmembrane tyrosine kinases. Whereas ErbB-1 binds to the epidermal growth factor (EGF), both ErbB-3 and ErbB-4 bind to the Neu differentiation factors (NDFs, or neuregulins), and ErbB-2, the most oncogenic family member, is an orphan receptor whose function is still unknown. Because previous lines of evidence indicated the existence of interreceptor interactions, we used ectopic expression of individual ErbB proteins and their combinations to analyze the details of receptor cross talks. We show that 8 of 10 possible homo-and heterodimeric complexes of ErbB proteins can be hierarchically induced by ligand binding. Although ErbB-2 binds neither ligand, even in a heterodimeric receptor complex, it is the preferred heterodimer partner of the three other members, and it favors interaction with ErbB-3. Selective receptor overexpression in human tumor cells appears to bias the hierarchical relationships. The ordered network is reflected in receptor transphosphorylation, ErbB-2-mediated enhancement of ligand affinities, and remarkable potentiation of mitogenesis by a coexpressed ErbB-2. The observed superior ability of ErbB-2 to form heterodimers, in conjunction with its uniquely high basal tyrosine kinase activity, may explain why ErbB-2 overexpression is associated with poor prognosis.

Nocturnal secretory patterns of melatonin, luteinizing hormone, prolactin and cortisol in male patients with gonadotropin-releasing hormone deficiency

To clarify whether disorders of gonadotropin releasing hormone (GnRH) deficiency are associated with altered melatonin and pituitary hormones secretory patterns, we studied male patients with hypogonadotropic hypogonadism (IGD; n = 6), delayed puberty (DP; n = 7) and age-matched pubertal controls (n = 7). Serum samples for the determination of melatonin, luteinizing hormone (LH), prolactin and cortisol levels were obtained at 15 min intervals from 1900 to 0700 in a controlled light-dark environment, complete bed-rest and fasting with simultaneous sleep recordings. Mean (+/- SD) dark-time melatonin levels were significantly higher in IGD (286 +/- 26 pmol/L) and DP (205 +/- 44 pmol/L) compared with 178 +/- 64 pmol/L in controls (P < 0.003). So were the mean (+/- SD) peak melatonin levels (453 +/- 63, 346 +/- 106 and 292 +/- 96 pmol/L) in IGD, DP and controls, respectively (P < 0.03). Integrated nocturnal melatonin (AUC) values were also higher in IGD and DP (184 +/- 15 and 134 +/- 28 pmol/min/L x 10(3)) compared with 116 +/- 42 pmol/min/L x 10(3) in controls (P < 0.003). The time of onset of the nocturnal melatonin rise was observed earlier in IGD and DP patients as compared to controls. No correlations were found between melatonin and LH levels, between melatonin and prolactin levels, or between melatonin and cortisol levels. These data indicate that melatonin secretion is enhanced in male patients with GnRH deficiency. The lack of correlation between melatonin and LH suggest that circulating gonadal steroids, rather than LH, modulate melatonin secretion in a reverse fashion.

Abnormal melatonin secretion in male patients with hypogonadism

Recently we have demonstrated that melatonin secretion is increased in untreated male patients with GnRH deficiency. Testosterone administration to these patients decreased melatonin secretion to normal levels. These data, however, did not exclude a gonadotropic effect on melatonin secretion. To further elucidate whether gonadal steroids and/or gonadotropins modulate melatonin secretion in humans we compared untreated young males with hypogonadotropic hypogonadism (IGD, n = 6), and hypergonadotropic hypogonadism caused by KlinEfelter's syndrome (KS, n = 11) to normal pubertal male controls (n = 7). KS patients were subdivided into two groups: KS-1, with low testosterone; and KS-2, with normal testosterone levels. Serum samples for melatonin concentrations were obtained every 15 min from 7 PM to 7 AM in a controlled light-dark environment with simultaneous sleep recordings. All KS patients had elevated gonadotropin levels and decreased melatonin levels. Mean (+/- SD) dark-time nocturnal melatonin levels in KS-1 were 92 +/- 21 pmol/L and were 146 +/- 46 pmol/L in KS-2 compared with 178 +/- 64 pmol/L in controls. Integrated nocturnal melatonin secretion values (AUC) were 64 +/- 14 pmol/min x L x 10(3) in KS-1 and 96 +/- 29 pmol/min x L x 10(3) in KS-2 compared with 116 +/- 42 pmol/min x L x 10(3) in controls. All IGD patients had low gonadotropin and testosterone levels. Their dark-time melatonin levels (286 +/- 26 pmol/L) and the AUC values (184 +/- 15 pmol/min/L x 10(3)) were increased. These data indicate that melatonin secretion is increased in male patients with GnRH deficiency and decreased in low testosterone hypergonadotropic hypogonadal patients. Taken together, our results suggest that both gonadotropins and gonadal steroids modulate melatonin secretion in humans.

Diversification of Neu differentiation factor and epidermal growth factor signaling by combinatorial receptor interactions

The ErbB family includes two receptors, ErbB-1 and ErbB-3, that respectively bind to epidermal growth factor and Neu differentiation factor, and an orphan receptor, ErbB-2. Unlike ErbB-1 and ErbB-2, the intrinsic tyrosine kinase of ErbB-3 is catalytically impaired. By using interleukin-3-dependent cells that ectopically express the three ErbB proteins or their combinations, we found that ErbB-3 is devoid of any biological activity but both ErbB-1 and ErbB-2 can reconstitute its extremely potent mitogenic activity. Transactivation of ErbB-3 correlates with heterodimer formation and is reflected in receptor phosphorylation and the transregulation of ligand affinity. Inter-receptor interactions enable graded proliferative and survival signals: heterodimers are more potent than homodimers, and ErbB-3-containing complexes, especially the ErbB-2/ErbB-3 heterodimer, are more active than ErbB-1 complexes. Nevertheless, ErbB-1 signaling displays dominance over ErbB-3 when the two receptors are coexpressed. Although all receptor combinations activate the mitogen-activated protein kinases ERK and c-Jun kinase, they differ in their rate of endocytosis and in coupling to intervening signaling proteins. It is conceivable that combinatorial receptor interactions diversify signal transduction and confer double regulation, in cis and in trans, of the superior mitogenic activity of the kinase-defective ErbB-3.