Tissue-specific activity of the pro-opiomelanocortin gene promoter

The pro-opiomelanocortin (POMC) gene is specifically expressed in corticotroph cells of the anterior pituitary. To define the POMC promoter sequences responsible for tissue-specific expression, we assessed POMC promoter activity by gene transfer into POMC-expressing pituitary tumor cells (AtT-20) and fibroblast L cells. The rat POMC promoter was only efficiently utilized and correctly transcribed in AtT-20 cells. 5'-End deletion analysis revealed two promoter regions required for activity in AtT-20 cells. When tested by fusion to a heterologous promoter, DNA fragments corresponding to both regions exhibited tissue-specific activity, suggesting the presence of at least two tissue-specific DNA sequence elements within the promoter. In summary, POMC promoter sequences from -480 to -34 base pairs appear sufficient to mimic the specificity of anterior pituitary expression.

Thyroid hormone stimulates rat pro-natriodilatin mRNA levels in primary cardiocyte cultures

Pro-natriodilatin (PND) is the precursor for atrial natriuretic peptide (ANP), a hormone which plays an important role in cardiovascular homeostasis. Since the effects of thyroid hormone (T3) on the cardiovascular and renal systems appear to mimic those elicited by ANP, we studied the effect of T3 on PND gene expression using rat neonatal cardiocytes in primary cultures. Treatment of cardiocytes for 48 h with T3 (5 X 10(-9) M) results in a maximal increase in PND mRNA levels; this increase is two fold in atrial and four fold in ventricular cell cultures. These results taken together with a previous report showing decreased plasma ANP in hypothyroid and increased plasma ANP in hyperthyroid rats suggest that at least some of the cardiovascular and renal effects of T3 may be mediated by a T3-dependent increase in PND gene expression.

Cloning and functional expression of the bovine natriuretic peptide receptor-B (natriuretic factor R1c subtype

We describe the isolation of a 3,276 base pair cDNA for the bovine natriuretic peptide receptor-B (NPR-B). Expression of this clone in Cos-P cells demonstrates that it encodes an agonist-dependent guanylyl cyclase. Porcine CNP stimulates the activity of this receptor up to 200-fold with an ED50 of 12 +/- 2 nM, whereas brain natriuretic peptide C-type natriuretic peptide (CNP) and atrial natriuretic factor (ANF) are less efficacious. In addition, ligand binding studies indicate that this receptor exhibits the pharmacology appropriate for the bovine NPR-B. CNP binds to Cos-P cell membranes expressing this clone with a Kd of 13 +/- 1 pM, and natriuretic peptides compete for [125I]-CNP binding with a rank order of pCNP > pBNP > rANF. Thus, the expressed receptor-guanylyl cyclase exhibits the expected pharmacological profile for ligand binding and cyclase activation of the bovine NPR-B receptor.

Absence of a bleeding tendency in severe acquired von Willebrand's disease. The role of platelet von Willebrand factor in maintaining normal hemostasis

A 67-year-old male with a prolonged activated partial thromboplastin time (APTT) of 43 seconds (normal, 25-40 seconds) was found to have laboratory features of von Willebrand's disease and IgA myeloma but had a normal bleeding time and no bleeding tendency. Plasma Factor VIII coagulant activity (F.VIII:C) was 80 U/L (0.08 U/mL), Factor VIII antigen (F.VIII:Ag) 70 U/L (0.07 U/mL), and von Willebrand's factor antigen (vWF:Ag) 50 U/L (0.05 U/mL) and ristocetin cofactor (vWF:RiCoF) 10 U/L (0.10 U/mL). The platelet vWF:Ag level was normal, whereas both platelet lysate and plasma vWF high molecular weight multimers were decreased. Patient plasma had no inhibitory effect on either F.VIII:C or vWF:RiCoF. However, when patient plasma was incubated with normal plasma, crossed immunoelectrophoresis for vWF:Ag demonstrated the presence of immune complexes. Infusion of 1-desamino-8-D-arginine vasopressin led to a transient correction of the plasma vWF:Ag multimer pattern. The survival of all components of vWF/F.VIII was decreased, as also occurred after cryoprecipitate. The levels of plasma F.VIII/vWF increased as the IgA values decreased after chemotherapy, whereas the platelet high molecular weight multimers remained decreased. The data suggest that the plasma vWF/F.VIII deficiency results from complexing of the IgA myeloma protein with vWF, resulting in premature clearance of the vWF/F.VIII complex. The absence of clinical bleeding likely results from the combination of a normal platelet vWF:Ag level and persistence of intermediate molecular weight vWF multimers.

Characterization of reticulofibroblastoid colonies (CFU-RF) derived from bone marrow and long-term marrow culture monolayers

The maintenance of hemopoietic precursors in long-term liquid bone marrow cultures (LTBMC) is associated with the presence of an adherent stromal layer composed of heterogeneous cell populations. We have used a culture assay to promote the growth of one of its cellular components and characterize its properties. Freshly obtained bone marrow cells and cells derived from the adherent layer of LTBMC were grown in methylcellulose-clotted plasma in the presence of phytohemagglutinin-stimulated leukocyte-conditioned medium (PHA-LCM), hydrocortisone (HC), and citrated normal human plasma. Both sources contained cells (CFU-RF) that gave rise to colonies of cells with a reticulofibroblastoid appearance. In the presence of HC, most colonies contained lipid-laden cells. Colonies could be further propagated as adherent layers when transferred into liquid cultures. These cells produced laminin, fibronectin, and collagen types I, III, IV, and V. They were negative for Von Willebrand factor VIII. The ability to synthesize laminin and collagen type IV distinguished these cells from a population of previously described bone marrow fibroblasts (CFU-F). The relationship of CFU-RF to hemopoietic precursors was investigated using patients with chronic myeloid leukemia and bone marrow transplant recipients. Cells within CFU-RF-derived colonies were uniformly negative for the Philadelphia chromosome, thus making it unlikely that they belonged to the malignant hemopoietic clone. CFU-RF-derived colonies in bone marrow transplant recipients were found to be exclusively of host origin. Both observations support the view that CFU-RF is not part of the repertoire of hemopoietic stem cells.

XhoI polymorphism at the human pronatriodilatin (hPND) gene locus

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Characterization of MENX-associated pituitary tumours

AIMS

The aim of this study is to evaluate the pathological features, serum hormone levels and ex vivo cultures of pituitary adenomas that occur in rats affected by MENX syndrome. MENX is multiple endocrine neoplasia syndrome caused by a germline mutation in the cell cycle inhibitor p27. Characterization of MENX adenomas is a prerequisite to exploit this animal model for molecular and translational studies of pituitary adenomas.

METHODS

We investigated MENX pituitary adenomas with immunohistochemistry, double immunofluorescence, electron microscopy, reverse transcription polymerase chain reaction (RT-PCR), measurement of serum hormone levels and ex vivo cultures.

RESULTS

Adenomas in MENX rats belong to the gonadotroph lineage. They start from 4 months of age as multiple neoplastic nodules and progress to become large lesions that efface the gland. Adenomas are composed of chromophobic cells predominantly expressing the glycoprotein alpha-subunit (αGSU). They show mitotic activity and high Ki67 labelling. A few neoplastic cells co-express gonadotropins and the transcription factor steroidogenic factor 1, together with growth hormone or prolactin and Pit-1, suggesting that they are not fully committed to one cell lineage. Ex vivo cultures show features similar to the primary tumour.

CONCLUSIONS

Our results suggest that p27 function is critical to regulate gonadotroph cells growth. The MENX syndrome represents a unique model to elucidate the physiological and molecular mechanisms mediating the pathogenesis of gonadotroph adenomas.

Repression of virus-induced interferon A promoters by homeodomain transcription factor Ptx1

Interferon A (IFN-A) genes are differentially expressed after virus induction. The differential expression of individual IFN-A genes is modulated by substitutions in the proximal positive virus responsive element A (VRE-A) of their promoters and by the presence or absence of a distal negative regulatory element (DNRE). The functional feature of the DNRE is to specifically act by repression of VRE-A activity. With the use of the yeast one-hybrid system, we describe here the identification of a specific DNRE-binding protein, the pituitary homeobox 1 (Ptx1 or Pitx1). Ptx1 is detectable in different cell types that differentially express IFN-A genes, and the endogenous Ptx1 protein binds specifically to the DNRE. Upon virus induction, Ptx1 negatively regulates the transcription of DNRE-containing IFN-A promoters, and the C-terminal region, as well as the homeodomain of the Ptx1 protein, is required for this repression. After virus induction, the expression of the Ptx1 antisense RNA leads to a significant increase of endogenous IFN-A gene transcription and is able to modify the pattern of differential expression of individual IFN-A genes. These studies suggest that Ptx1 contributes to the differential transcriptional strength of the promoters of different IFN-A genes and that these genes may provide new targets for transcriptional regulation by a homeodomain transcription factor.

TaqI polymorphism at the 3' end of the human pronatriodilatin gene (hPND)

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Identification of novel factor VIII inhibitor epitopes using synthetic peptide arrays

OBJECTIVES

Mapping the antibody-binding sites on the factor VIII (FVIII) protein opens the prospect of studying the development of FVIII inhibitors and the alteration of inhibitor specificities over time. This paper describes a novel approach to the mapping of FVIII antibody-binding sites.

METHODS

Immobilized synthetic peptide arrays covering 80% of the complete 2351 amino acid sequence of factor VIII (FVIII) were used to determine epitope specificity of 6 alloantibodies and 3 autoantibodies inhibitory to FVIII activity. This detailed assessment was carried out using a modified enzyme-linked immunosorbent assay with plasma from normal persons or hemophilia A patients without inhibitors as negative controls.

RESULTS

Antibody-combining sites could be differentiated in both a qualitative and quantitative manner and were patient-specific. Highly reactive peptides were restricted to specific sites in the A1-A3 and C1-C2 domains and were not proximal to known proteolytic cleavage sites. Free peptides incubated in vitro with the plasmas of 3 patients significantly reduced residual inhibitor titers in a dose-dependent manner.

CONCLUSION

This technique permits the study of the development and specificity of FVIII inhibitors, can detect and differentiate between inhibitory and noninhibitory antibodies using immobilized or free peptides respectively, permits correlation of antibody-combining sites with inhibition of FVIII activity and provides a basis for the development of inhibitor adsorption or neutralization technology.

Regulatory elements of the pro-opiomelanocortin gene: pituitary specificity and glucocorticoid repression

A short 543-bp fragment o f the pro-opiomelanocortin gene is sufficient for pituitary-specific expression and, in the anterior pituitary gland, for repression of pro-opiomelanocortin transcription by glucocorticoids. Within this 5'-flanking fragment of the gene, multiple regulatory elements contribute to tissue-specific expression and a single glucocorticoid receptor binding site acts as a "negative glucocorticoid response element." The current model for glucocorticoid repression depends on the mutually exclusive binding of the glucocorticoid receptor and of a positive transcription factor, the chicken ovalbumin upstream promoter element transcription factor, to overlapping DNA sequences within the negative glucocorticoid response element.

Blood monocytes from most human immunodeficiency virus type 1-infected patients do not carry proviral DNA

In blood, the CD4+ T cells of patients with human immunodeficiency virus type 1 (HIV-1) harbor HIV-1; however, whether the CD4+ blood monocytes carry the virus is controversial. Tissue macrophages are known to be infected. To determine in blood monocytes from HIV-1-seropositive patients contain HIV-1, we separated monocytes and T-cell subsets by using monoclonal antibodies bound to magnetic beads and by monocyte adherence to glass. Monocytes were cultured with macrophage colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, and interleukin-3. After 14 days in culture, cells were analyzed for the presence of HIV-1 antigen and multinucleated giant cells (MGCs). Freshly isolated cell subsets were analyzed for HIV-1 proviral DNA by PCR with modified env (SK68i and SK69i2) and gag (SK145i and SK150) primers. We found that (i) monocytes cultured without depletion of CD4+ T cells (11 of 11 patients) were HIV-1 antigen positive and showed dramatically increased spontaneous formation of MGCs (ii) monocytes cultured after depletion of CD4+ T cells (three experiments) were HIV-1 antigen negative and showed markedly decreased MGC formation, and (iii) in specimens from 14 patients subsequently analyzed by PCR, purified CD4+ T cells were positive for HIV-1 proviral DNA in all patients. In 11 of 14 patients (79%), the monocyte fractions were HIV-1 proviral DNA negative, while in the remaining 3 patients, the monocytes were positive for HIV-1 proviral DNA. In conclusion, the major reservoir for HIV-1 infection in human peripheral blood is the CD4+ T cell (14 of 14 cases).(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of a partial prostaglandin endoperoxide H synthase-1 deficiency in a patient with a bleeding disorder

Thromboxane A2 (TXA2), synthesized in platelets, is a powerful aggregating agent and vasoconstrictor. To induce platelet aggregation, the platelets' enzyme, prostaglandin endoperoxide H synthase-1 (PGHS-1), first converts arachidonic acid (AA) into prostaglandin H2 (PGH2). PGH2 is then converted by the enzyme thromboxane synthase into TXA2. Finally, TXA2 is secreted and can activate the TXA2 receptor on the platelet surface. The importance of TXA2 in haemostasis has been demonstrated by the presence of a bleeding tendency in patients showing an inherited defect in the TXA2 production pathway. We studied an 18-year-old woman with a lifelong bleeding disorder, moderate thrombocytopenia (55-71 x 109/l) and a prolonged bleeding time (12.5 min). Her platelets aggregated in the presence of both PGH2 and a stable TXA2 analogue, but did not aggregate in the presence of AA. The activity of PGHS-1 in platelets, measured using thin-layer chromatography and radioactive counting of TXA2 formation from [14C]-AA, was reduced to 13% of the activity measured in control subjects. PGHS-1 protein levels, measured using Western blot analysis, were also markedly reduced to 10% of control values. Such levels of PGHS-1 enzyme were too low to sustain platelet aggregation in the patient, even if the enzyme was active. The PGHS-1 protein level was also reduced in the patient's immortalized B lymphocytes, suggesting a systemic expression defect. Northern blot analysis was then carried out with poly (A)+ RNA extracted from the patient's immortalized B lymphocytes. PGHS-1 mRNA was detected as a 2.8-kb band in both the patient and control. The intensity of the band representing the patient's PGHS-1 mRNA was similar to that of the control subject. The Northern blot result suggests a normal transcriptional rate of the PGHS-1 gene for the patient. Therefore, the defect responsible for the reduced levels of PGHS-1 protein is probably post-transcriptional.

Opposite ability of pre-TCR and alpha beta TCR to induce apoptosis

In early CD4(-)CD8(-) pro-thymocytes, signaling through the pre-TCR is crucial for survival and differentiation into CD4(+)CD8(+) cells. At this more mature stage, interactions between alphabetaTCR and self-Ag/MHC complexes in turn lead either to cell survival and differentiation (positive selection) or to cell death (negative selection). Intrinsic differences must therefore exist between pre-TCR signals in CD4(-)CD8(-) thymocytes and alphabetaTCR signals in CD4(+)CD8(+) cells, since only the latter can mediate a death signal. In this work, we directly compared the capability of pre-TCR and alphabetaTCR to induce apoptosis in a CD4(-)CD8(-) thymoma cell line following receptor cross-linking with mAbs. Cross-linking of alphabetaTCR triggered high levels of programmed cell death, mimicking the negative selection signal usually induced in CD4(+)CD8(+) thymocytes. In contrast, pre-TCR was very inefficient at inducing apoptosis upon cross-linking, despite similar levels of surface receptor expression. Importantly, inefficient apoptosis induction by the pre-TCR did not result from its weak association with TCRzeta chain, since TCRs containing alpha-pTalpha chimeric chains, binding weakly to TCRzeta, were still able to induce apoptosis. Although similar tyrosine phosphorylation and calcium influx were induced after either pre-TCR or alphabetaTCR cross-linking, the two pathways diverged at the level of Fas ligand induction. Among putative transcription factors involved in Fas ligand mRNA induction, Nur77 and NFAT transcriptional activities were readily induced after alphabetaTCR, but not pre-TCR, stimulation. Together, these results support the view that the structure of the pre-TCR and alphabetaTCR directly influences their apoptosis-inducing capabilities by activating distinct signaling pathways.

Expression and mutation analysis of Tpit in the canine pituitary gland and corticotroph adenomas

Pituitary-dependent hyperadrenocorticism (PDH) in dogs is caused by a pituitary corticotroph adenoma. Although PDH is a common disorder in dogs, little is known about the underlying pathogenesis. In the pituitary glands of humans and mice, the pro-opiomelanocortin (POMC)-expressing cell lineages, the corticotrophs and melanotrophs, have a specific marker in common, the T-box transcription factor Tpit (Tbx19), which is obligate for POMC expression. Tpit also regulates the late differentiation of the corticotrophs and melanotrophs, and therefore may contribute to the pathogenesis of the corticotroph adenomas. The aim of this study was to perform an expression and mutation analysis of Tpit in the normal canine pituitary and in corticotroph adenomas. The distribution of the Tpit protein in the pituitary gland was studied with immunohistochemistry and the expression of the gene with RT-PCR. The coding region of Tpit cDNA from 14 dogs with PDH was screened for mutations. Tpit was expressed in corticotroph and melanotroph cells of the normal and adenomatous canine pituitary, and remained present in non-adenomatous corticotrophs of pituitaries from PDH dogs. No tumor-specific mutation in the Tpit cDNA from the corticotroph adenomas was found. However, a missense polymorphism in the highly conserved DNA-binding domain, the T-box, was discovered in one dog. It is concluded that Tpit can be used as a reliable marker for the corticotroph and melanotroph cells in the canine pituitary tissue and that mutations in the Tpit gene are unlikely to play a major role in the pathogenesis of canine corticotroph adenomas.