Pregnant Women's perceptions of exposure to brominated flame retardants.

BACKGROUND: Recent media reports on human studies associating brominated flame retardants (BFRs) in household products in pregnancy with urogenital anomalies in boys and endocrine disruption in both sexes. We sought to explore the perceptions of pregnant women of brominated flame retardant (BFR) exposure, in light of recent media reports on the adverse health effects of BFR exposure prenatally. METHODS: Pregnant women were recruited for interviews through posters and pamphlets in prenatal clinics, prenatal fairs and community centres. Interviews were audiotaped and transcribed verbatim for Charmaz-based qualitative analysis supported by NVIVO 10™. RESULTS: Theoretical sufficiency was reached after analyzing the interviews of 23 pregnant women. Themes co-constructed were: I-Lack of Awareness of BFRs; II-Factors Influencing BFR Exposure; III-Responsibility; IV-Informed Choice. Almost all participants felt it was difficult to make informed choices to avoid BFRs, and wanted communication from clinicians and regulation from governments regarding decreasing BFR exposure. CONCLUSION: Pregnant women in Canada may be unaware of the potential risks of exposure to BFRs. Professional organizations and governments should further study risk associated with BFR exposure in pregnancy and provide educational materials for pregnant women and clinicians regarding BFR exposure.

Human growth hormone receptor (GHR) expression in obesity: II. Regulation of the human GHR gene by obesity-related factors.

BACKGROUND AND METHODS: In our previous analyses, we found significantly lower levels of growth hormone receptor (GHR) mRNA in adipose tissues of obese than in those of lean individuals, suggesting that idiopathic obesity involves GH resistance due to decreased GHR availability. To understand the mechanism(s) behind this downregulation, we performed an in silico analysis of the three most relevant GHR gene promoters, which revealed putative response elements (REs) for a number of obesity adipose-associated factors, including tumor necrosis factor-alpha (TNFα), hypoxia-inducible factor-1-alpha (HIF-1α) and glucocorticoids. We then characterized the dose-dependent effects of these factors on GHR expression in HEK293 cells and in mature human SGBS (Simpson-Golabi-Behmel syndrome) adipocytes using quantitative reverse transcriptase-PCR and assessed the function of their putative REs by luciferase-reporter assays, site-directed mutagenesis and chromatin immunoprecipitation (ChIP) assays. RESULTS: TNFα treatments significantly reduced GHR mRNA levels and GHR promoter activities at doses ≥ 10 ng ml(-1) in both cell lines. Transient overexpression of HIF-1α or exposure to the hypoxia mimetic CoCl(2) significantly increased GHR mRNA levels and promoter activities. Dexamethasone had biphasic effects: there was a significant increase in GHR mRNA levels at 10(-10) M and in promoter activities at 10(-10) and 10(-8) M, whereas a significant decrease in both mRNA levels and promoter activities occurred at 10(-6) M. Site-directed mutagenesis of the putative nuclear factor-κB, HIF-1α and glucocorticoid REs resulted in the loss of these effects, whereas ChIP analysis confirmed specific transcription factor-promoter interactions. CONCLUSIONS: Our results suggest that the increased activity of TNFα, HIF-1α and glucocorticoids in obese adipose tissues could alter GHR gene transcription through specific REs and that TNFα may be involved in the development of GH resistance.

Human growth hormone receptor (GHR) expression in obesity: I. GHR mRNA expression in omental and subcutaneous adipose tissues of obese women.

OBJECTIVES: Growth hormone (GH)-deficient individuals display increased adiposity that can be effectively reduced by GH therapy because of GH's lipolytic effects. However, similar GH treatments of individuals with idiopathic obesity (not associated with an endocrinopathy/syndrome) have had little success. We hypothesized that this form of obesity may be associated with GH resistance at the level of the adipocyte because of reduced GH receptor (GHR) expression. SUBJECTS AND METHODS: We studied GHR expression in omental and subcutaneous fat tissues from a cohort of 55 women ranging from lean to obese by various adiposity parameters. mRNA levels of total GHR and the dominant-negative truncated GHR(1-279) (trGHR) form were assayed by quantitative reverse transcriptase-PCR. Associations between adiposity measures and GHR levels as well as trGHR/GHR ratios were analyzed. RESULTS: Total GHR mRNA expression was 2-3-fold lower in omental as well as subcutaneous adipose tissues of obese compared with lean women (P ≤ 0.05-0.001). Lean individuals expressed higher GHR mRNA levels in omental fat compared with subcutaneous (P ≤ 0.01); in obese women, this depot-specific difference was lost. Omental and subcutaneous adipose GHR mRNA levels displayed significant negative correlations with a spectrum of indicators of obesity while, in subcutaneous fat, there was a significantly higher trGHR/GHR ratio with increasing adiposity (P ≤ 0.05). CONCLUSION: These results support our hypothesis that, with obesity, there is lower GHR expression in the adipocyte, and suggest one possible explanation why GH supplementation is not an effective treatment for individuals with idiopathic obesity.

Familial amyloid precursor protein mutants cause caspase-6-dependent but amyloid ß-peptide-independent neuronal degeneration in primary human neuron cultures.

Although familial Alzheimer disease (AD)-associated autosomal dominant mutants have been extensively studied, little is known about the underlying molecular mechanisms of neurodegeneration induced by these mutants in AD. Wild-type, Swedish or London amyloid precursor protein (APP) transfection in primary human neurons induced neuritic beading, in which several co-expressed proteins, such as enhanced green fluorescent protein, red fluorescent protein (RFP)-tau and RFP-ubiquitin, accumulated. APP-induced neuritic beading was dependent on caspase-6 (Casp6), because it was inhibited with 5 µM z-VEID-fmk or with dominant-negative Casp6. Neuritic beading was independent from APP-mediated amyloid ß-peptide (Aß) production, because the APPM596V (APP(MV)) mutant, which cannot generate Aß, still induced Casp6-dependent neuritic beading. However, the beaded neurons underwent Casp6- and Aß-dependent cell death. These results indicate that overexpression of wild-type or mutant APP causes Casp6-dependent but Aß-independent neuritic degeneration in human neurons. Because Casp6 is activated early in AD and is involved in axonal degeneration, these results suggest that the inhibition of Casp6 may represent an efficient early intervention against familial forms of AD. Furthermore, these results indicate that removing Aß without inhibiting Casp6 may have little effect in preventing the progressive dementia associated with sporadic or familial AD.

Effect of forkhead box O1 (FOXO1) on beta cell development in the human fetal pancreas.

AIMS/HYPOTHESIS: Recent studies have demonstrated that in adult murine beta cells the forkhead box O1 (FOXO1) transcription factor regulates proliferation and stress resistance. However, the role of FOXO1 during pancreatic development remains largely unknown. The present study aimed to characterise the expression of the FOXO1 transcription factor in the early to mid-gestation human fetal pancreas and to understand its role in islet cell development. METHODS: Human (8-21 week fetal age) pancreases were examined using immunohistological, quantitative RT-PCR and western blotting. Isolated human (18-21 week) fetal islet epithelial cell clusters were treated with insulin or glucose, or transfected with FOXO1 small interfering RNA (siRNA). RESULTS: Nuclear and cytoplasmic FOXO1 were widely produced during human fetal endocrine pancreatic development, co-localising in cells with the transcription factors pancreatic and duodenal homeobox 1 (PDX-1) and neurogenin 3 (NGN3) as well as cytokeratin 19 (CK19), insulin and glucagon. Treatment with exogenous insulin (50 nmol/l) induced the nuclear exclusion of FOXO1 in both cytokeratin 19 (CK19)(+) (p < 0.01) and insulin(+) cells (p < 0.05) in parallel with increased phospho-Akt (p < 0.05) production. siRNA knockdown of FOXO1 significantly increased the number of NGN3(+) (p < 0.01) and NK6 homeobox 1 (NKX6-1)(+) (p < 0.05) cells in parallel with increases in insulin gene expression (p < 0.03) and C-peptide(+) cells (p < 0.05) and reduced levels of hairy and enhancer of split 1 (HES1) (p < 0.01). CONCLUSIONS/INTERPRETATION: Our results indicate that FOXO1 may negatively regulate beta cell differentiation in the human fetal pancreas by controlling critical transcription factors, including NGN3 and NKX6-1. These data suggest that the manipulation of FOXO1 levels may be a useful tool for improving cell-based strategies for the treatment of diabetes.

Transcription factor expression in the developing human fetal endocrine pancreas.

AIMS/HYPOTHESIS: Morphological changes that occur during pancreatic endocrine cell differentiation have been shown in rodent systems to be dependent on sequential alterations in transcription factor expression. However, similar data for humans have been limited. The aim of the present study was to provide a connection between pancreatic morphology, transcription factor gene expression and protein localisation during human fetal development. METHODS: Human fetal pancreases were examined at early (8-12 weeks of fetal age), middle (14-16 weeks) and late (19-21 weeks) stages, using immunohistological, microarray and qRT-PCR analyses. RESULTS: We observed a significant decrease in pancreatic duodenal homeobox 1 (PDX-1)(+)/cytokeratin 19(+) cells (p < 0.001), with a simultaneous increase in PDX-1(+)/insulin(+) cells from 8 to 21 weeks (p < 0.05). Increased PDX-1/insulin co-localisation within islet clusters was noted, while no co-expression of PDX-1 with glucagon was found, suggesting that loss of PDX-1 is essential for alpha cell formation. Given that neurogenin 3 (NGN3) expression is critical for establishing the endocrine cell programme in the rodent pancreas, we examined its expression pattern and co-localisation in PDX-1(+), insulin(+) and glucagon(+) cells. Co-localisation of NGN3 with PDX-1, insulin and glucagon was noted during early development, with significant decreases in middle and late stages (p < 0.001). Our microarray and co-localisation analyses of transcription factors linked to NGN3 demonstrated that ISL1 transcription factor (ISL1), neurogenic differentiation 1 (NEUROD1), NK2 related transcription factor related, locus 2 (NKX2-2) and paired box gene 6 (PAX6) were upregulated during development and present in all four endocrine cell types, while NK6 related transcription factor related, locus 1 (NKX6-1) was expressed exclusively in beta cells. CONCLUSIONS/INTERPRETATION: This study is an important step towards identifying key molecular factors involved in development of the human fetal endocrine pancreas.

SGNE1/7B2 is epigenetically altered and transcriptionally downregulated in human medulloblastomas.

In a genome-wide screen using differential methylation hybridization (DMH), we have identified a CpG island within the 5' region and untranslated first exon of the secretory granule neuroendocrine protein 1 gene (SGNE1/7B2) that showed hypermethylation in medulloblastomas compared to fetal cerebellum. Bisulfite sequencing and combined bisulfite restriction assay were performed to confirm the methylation status of this CpG island in primary medulloblastomas and medulloblastoma cell lines. Hypermethylation was detected in 16/23 (70%) biopsies and 7/8 (87%) medulloblastoma cell lines, but not in non-neoplastic fetal (n=8) cerebellum. Expression of SGNE1 was investigated by semi-quantitative competitive reverse transcription-polymerase chain reaction and found to be significantly downregulated or absent in all, but one primary medulloblastomas and all cell lines compared to fetal cerebellum. After treatment of medulloblastoma cell lines with 5-aza-2'-deoxycytidine, transcription of SGNE1 was restored. No mutation was found in the coding region of SGNE1 by single-strand conformation polymorphism analysis. Reintroduction of SGNE1 into the medulloblastoma cell line D283Med led to a significant growth suppression and reduced colony formation. In summary, we have identified SGNE1 as a novel epigenetically silenced gene in medulloblastomas. Its frequent inactivation, as well as its inhibitory effect on tumor cell proliferation and focus formation strongly argues for a significant role in medulloblastoma development.

Caspase-1 activation of caspase-6 in human apoptotic neurons.

Active caspase-6 (Csp-6) induces cell death in primary cultures of human neurons and is abundant in the neuropathological lesions of Alzheimer's disease. However, the mode of Csp-6 activation is not known. Here, we show that the Csp-1 inhibitor, Z-YVAD-fmk specifically prevents activation of Csp-6 and cell death in human neurons. A transient increase in Csp-1-like activity and an increase in the p23Csp-1 subunit occur early after serum deprivation. Recombinant active Csp-1 (R-Csp-1) cleaves recombinant and neuronal pro-Csp-6 in vitro resulting in Csp-6 activity. However, R-Csp-1 does not induce cell death when microinjected in human neurons despite the inhibition of serum-deprivation induced cell death with a Csp-1 dominant negative construct. These results show that Csp-1 is an upstream positive regulator of Csp-6-mediated cell death in primary human neurons. Furthermore, these results suggest that the activation of Csp-1 must be accompanied by an apoptotic insult to induce Csp-6-mediated cell death.

Cellular prion protein inhibits proapoptotic Bax conformational change in human neurons and in breast carcinoma MCF-7 cells.

Prion protein (PrP) prevents Bcl-2-associated protein X (Bax)-mediated cell death, but the step at which PrP inhibits is not known. We first show that PrP is very specific for Bax and cannot prevent Bak (Bcl-2 antagonist killer 1)-, tBid-, staurosporine- or thapsigargin-mediated cell death. As Bax activation involves Bax conformational change, mitochondrial translocation, cytochrome c release and caspase activation, we investigated which of these events was inhibited by PrP. PrP inhibits Bax conformational change, cytochrome c release and cell death in human primary neurons and MCF-7 cells. Serum deprivation-induced Bax conformational change is more rapid in PrP-null cells. PrP does not prevent active caspase-mediated cell death. PrP does not colocalize with Bax in normal or apoptotic primary neurons and cannot prevent Bax-mediated cytochrome c release in a mitochondrial cell-free system. We conclude that PrP protects against Bax-mediated cell death by preventing the Bax proapoptotic conformational change that occurs initially in Bax activation.

No evidence for mutations or altered expression of the Suppressor of Fused gene (SUFU) in primitive neuroectodermal tumours.

The sonic hedgehog (Shh) and the Wnt signalling pathways are involved in the development of medulloblastomas (MBs), the most frequent malignant brain tumours in children. Components of these two developmental and cancer-associated pathways, including (Patched) PTCH, SMOH, adenomatous polyposis coli (APC), beta-catenin and AXIN1 show somatic mutations in sporadic MBs. In this study we analysed SUFU (human Suppressor of Fused), which acts as a negative regulator of both the Shh and Wnt signalling pathways and therefore represents a putative tumour suppressor gene, to find out if it is also involved in the pathogenesis of sporadic MBs. We screened 145 primitive neuroectodermal tumours (PNETs) including 90 classic MBs, 42 of the desmoplastic variant and two medullomyoblastomas as well as 11 MB cell lines for mutations using single-strand conformational polymorphism (SSCP) and sequencing analysis. 18% of the MBs exhibited allelic losses on chromosome 10q. In contrast to a previous report, in which truncating mutations of SUFU have been identified in 9% of MBs, we were not able to identify somatic mutations of SUFU in our large tumour panel. We uncovered single nucleotide polymorphisms (SNPs) in exon 4, 8, 11 and in intron 2 in the SUFU gene. Expression analysis by competitive reverse transcription-polymerase chain reaction (RT-PCR) revealed no difference in SUFU mRNA levels of both MB subtypes and normal foetal or adult cerebellar tissues. Our results indicate that genetic alterations of the SUFU gene, do not contribute significantly to the molecular pathogenesis of MBs.

Developmental changes in the expression of somatostatin receptors (1-5) in the brain, hypothalamus, pituitary and spinal cord of the human fetus.

The actions of somatostatin (SST) in the nervous system are mediated by specific high affinity SST receptors (SSTR1-5). However, the role of this hormone and the distribution of its receptor subtypes have not yet been defined in neural structures of the human fetus. We have analyzed four neural tissues (CNS, hypothalamus, pituitary and spinal cord) from early to midgestation for the expression of five human SSTR mRNAs, using a reverse transcription-polymerase chain reaction and Southern blot approach. These fetal neural tissues all express mRNA for multiple SSTR subtypes from as early as 16 weeks of fetal life but the developmental patterns of expression vary considerably. Transcripts for SSTR1 and SSTR2A are the most widely distributed, being expressed in all four neural tissues. SSTR2A is often the earliest transcript to be detected (7.5 weeks in CNS). SSTR3 mRNA is confined to the pituitary, hypothalamus, and spinal cord. SSTR4 is expressed in fetal brain, hypothalamus and spinal cord but not pituitary. SSTR5 mRNA is detectable in the pituitary and spinal cord by 14-16 weeks of fetal life. This mapping of SSTR mRNA expression patterns in human fetal neural tissues is an important first step toward our goal of determining the role of SST in the nervous system during early stages in human development.

Characterization of the growth hormone receptor in human dermal fibroblasts and liver during development.

Human tissues express growth hormone receptors (hGHR) by the 3rd mo of gestation. We assessed developmental changes in hGHR function in fibroblasts and liver, testing binding and hormonal response. Fetal cells showed low but reproducible hGH binding. No age-related changes occurred in fibroblasts (9 wk-34 yr). In contrast, there was a fourfold increase in hGH binding in postnatal liver, with a sixfold increase in hGHR mRNA. Both full-length and truncated hGHR mRNAs were detected in all livers. Cross-linking revealed a larger hGH/receptor complex in fetal liver. Fetal hepatocytes produced 10 times more insulin-like growth factor (IGF)-II than IGF-I, and responded to hGH (150 ng/ml) with a significant increase in IGF-II. Fetal hepatocytes secreted three IGF-binding proteins (IGFBPs), including IGFBP1, but not IGFBP3. hGH did not alter fetal hepatocyte IGFBPs but stimulated glucose uptake. Exposure of fibroblasts to hGH decreased hGH binding only in >1-yr postnatal fibroblasts, whereas treatment with dexamethasone (100-400 nM) increased binding only in postnatal cells. Thus, although fetal hepatocytes and fibroblasts possess functional hGHR, these receptors (and/or their signaling pathways) are immature or have adapted to the in utero environment.

Alu elements in human growth hormone receptor gene 5' untranslated region exons.

The human growth hormone receptor (hGHR) is encoded by exons 2-10 of the hGHR gene on chromosome 5p13.1-p12. There are several different 5' untranslated region (5'UTR) variants of hGHR mRNA (V1-V9) that all encode the same protein. We have recently mapped the V1-V9 5'UTR sequences within 40 kb of the 5' flanking region of the hGHR gene. Seven of the exons are clustered within two small modules, module A (V2-V9-V3) and module B (V7-V1-V4-V8), approximately 38 kb and approximately 18 kb respectively upstream of exon 2 of the coding region; V6 lies midway between the two modules and V5 is adjacent to exon 2. We now report the existence of two subvariant V3 exons, one upstream of module A (exon V3b) and one midway between module B and exon 2 (exon V3a/b). Both have sequences homologous to Alu elements. In addition, we determined the alternative splicing mechanisms that produce three different mRNAs from these exons: V3c (from the V3 exon in module A) or V3a and V3b (from a combination of exon V3 and the Alu-containing V3 subvariant exons). hGHR expression is under developmental- and tissue-specific regulation: module A-derived mRNAs are widely expressed in human tissues, while module B-derived mRNAs are only detectable in postnatal liver. Expression of the variant V3 mRNAs is similar to those from module A, being produced ubiquitously in human fetal and postnatal tissues, with V3c always the major variant detected. The Alu-containing mRNAs (V3a and V3b) are also detectable in baboon and rhesus tissues, in accordance with the finding of Alu elements throughout the primate genome. In summary, we have mapped the relative locations of two new 5'UTR exons within the 5' flanking region of the hGHR gene and described the derivation and expression patterns for two variant hGHR mRNAs from these primate-specific exons. The introduction of Alu elements has contributed to the evolution of the primate GHR gene as a highly complex transcriptional unit.

Galphas transcripts are biallelically expressed in the human kidney cortex: implications for pseudohypoparathyroidism type 1b.

Pseudohypoparathyroid type 1b patients are characterized by renal resistance to PTH in the absence of Albright's hereditary osteodystrophy or other endocrine abnormalities. Kindred studies have suggested that the cause of this resistance is a specific decrease in Galphas activity in renal proximal tubules due to paternal imprinting of Galphas. To test this, allelic expression of Galphas was analyzed in human fetal kidney cortex samples by RT-PCR assays. The results showed that, in contrast to the parent-specific expression of exon 1A and XLalphas (paternal) or NESP (maternal) mRNAs, Galphas transcripts are biallelically expressed in human kidney cortex. These data implicate abnormal imprinting of alternative regions within the GNAS1 locus as a more likely cause of pseudohypoparathyroid type 1b.

17-beta-estradiol induces an inhibitor of active caspases.

We have shown previously that caspase-6 activity is lethal to human neurons (LeBlanc et al., 1999; Zhang et al., 2000). Here we find that 17-beta-estradiol but not 17-alpha-estradiol prevents caspase-6-mediated neuronal cell death. 17-beta-estradiol-treated neuronal extracts directly inhibit recombinant active caspase-6, caspase-3, caspase-7, and caspase-8 in vitro. We conclude that 17-beta-estradiol induces a caspase inhibitory factor (CIF) that is preventing neuronal apoptosis. The induction of CIF occurs within 10 min of 17-beta-estradiol exposure to neurons, does not require de novo protein synthesis, and involves mitogen-activated protein kinase activation. The effect is antagonized by the estrogen receptor antagonist tamoxifen. In contrast, 17-beta-estradiol does not induce CIF or prevent caspase-mediated cell death in cultured astrocytes. CIF does not act through oxidation of the caspase active site. CIF activity copurifies with proteins of between 12 and 14 kDa in size. Our results indicate that 17-beta-estradiol induces an inhibitor of active caspases through a receptor-mediated nongenomic pathway and provide an additional mechanism for the neuroprotective action of 17-beta-estradiol that is likely highly relevant to the understanding of the role of estrogen against Alzheimer's disease.

GT repeat polymorphism in the 5' flanking region of the human growth hormone receptor gene.

A polymorphic GT dinucleotide repeat sequence has been identified in the 5' flanking region of the human growth hormone receptor (hGHR) gene on chromosome 5p13.1-p12, within the promoter region of the V9 5'UTR exon. Thirteen alleles have been identified in 50 non-related individuals, with an observed heterozygosity of 52%. The major allele contains 24 repeats, although a range of 19-32 repeats has been observed. Codominant segregation was demonstrated in five two-generation and two three-generation families. This marker may be useful in analysing the role of the hGHR gene in pre- and postnatal growth disorders.

Class III alleles of the variable number of tandem repeat insulin polymorphism associated with silencing of thymic insulin predispose to type 1 diabetes.

Type 1 diabetes results from autoimmune destruction of the insulin-producing pancreatic beta cells. The insulin gene (INS) is also expressed in human thymus, an ectopic expression site likely involved in immune tolerance. The IDDM2 diabetes susceptibility locus maps to a minisatellite composed of a variable number of tandem repeats situated 0.5 kb upstream of INS. Chromosomes carrying the protective long INS variable number of tandem repeats alleles (class III) produce higher levels of thymic INS mRNA than those with the predisposing, short class I alleles. However, complete silencing of thymic INS transcripts from the class III chromosome was found in a small proportion of heterozygous human thymus samples. We hypothesized that the specific class III alleles found on these chromosomes silence rather than enhance thymic insulin expression. To test the prediction that these alleles are predisposing, we developed a DNA fingerprinting method for detecting two putative "silencing" alleles found in two thymus samples (S1, S2). In a set of 287 diabetic children and their parents we found 13 alleles matching the fingerprint of the S1 or S2 alleles. Of 18 possible transmissions, 12 of the S1-S2 alleles were transmitted to the diabetic offspring, a frequency of 0.67, significantly higher than the 0.38 seen in the remaining 142 class III alleles; P = 0.025. This confirms our prediction and represents an additional level of correlation between thymic insulin and diabetes susceptibility, which supports a thymic enhancer effect of the INS variable number of tandem repeats as the mechanism of IDDM2 and refines the contribution of IDDM2 genotyping to diabetes risk assessment.

Evidence against GRB10 as the gene responsible for Silver-Russell syndrome.

Recent evidence shows that Silver-Russell syndrome (SRS), the major functional deficit of which is limited growth, both intrauterine and postnatal, is due to a double dose of a gene within 7p11.2-p13 that is normally expressed exclusively from the maternal copy. Of the several growth-related genes in this chromosomal region, only GRB10 has been demonstrated to be imprinted; however, imprinting was limited to brain and muscle and was incomplete. Using reverse-transcript PCR, we now confirm GRB10 imprinting in these two tissues is isoform-specific and, more importantly, demonstrate absence of imprinting in growth plate cartilage, the tissue most directly involved in linear growth. Thus, it is unlikely that GRB10 is the gene responsible for SRS.

Prion protein protects human neurons against Bax-mediated apoptosis.

The function of the cellular prion protein (PrP) is still poorly understood. We present here an unprecedented role for PrP against Bax-mediated neuronal apoptosis and show that PrP potently inhibits Bax-induced cell death in human primary neurons. Deletion of four octapeptide repeats of PrP (PrPDeltaOR) and familial D178N and T183A PrP mutations completely or partially eliminate the neuroprotective effect of PrP. PrP remains anti-apoptotic despite truncation of the glycosylphosphatidylinositol (GPI) anchor signal peptide, indicating that the neuroprotective form of PrP does not require the abundant cell surface GPI-anchored PrP. Our results implicate PrP as a potent and novel anti-apoptotic protein against Bax-mediated cell death.

Alternative promoter usage and splicing of ZNF74 multifinger gene produce protein isoforms with a different repressor activity and nuclear partitioning.

We have previously shown that ZNF74, a candidate gene for DiGeorge syndrome, encodes a developmentally expressed zinc finger gene of the Kruppel-associated box (KRAB) multifinger subfamily. Using RACE, RT-PCR, and primer extension on human fetal brain and heart mRNAs, we here demonstrate the existence of six mRNA variants resulting from alternative promoter usage and splicing. These transcripts encode four protein isoforms differing at their N terminus by the composition of their KRAB motif. One isoform, ZNF74-I, which corresponds to the originally cloned cDNA, was found to be encoded by two additional mRNA variants. This isoform, which contains a KRAB motif lacking the N terminus of the KRAB A box, was devoid of transcriptional activity. In contrast, ZNF74-II, a newly identified form of the protein that is encoded by a single transcript and contains an intact KRAB domain with full A and B boxes, showed strong repressor activity. Deconvolution immunofluorescence microscopy using transfected human neuroblastoma cells and nonimmortalized HS68 fibroblasts revealed a distinct subcellular distribution for ZNF74-I and ZNF74-II. In contrast to ZNF74-I, which largely colocalizes with SC-35 in nuclear speckles enriched in splicing factors, the transcriptionally active ZNF74-II had a more diffuse nuclear distribution that is more characteristic of transcriptional regulators. Taken with the previously described RNA-binding activity of ZNF74-I and direct interaction with a hyperphosphorylated form of the RNA polymerase II participating in pre-mRNA processing, our results suggest that the two ZNF74 isoforms exert different or complementary roles in RNA maturation and in transcriptional regulation.