The multi-faceted nature of 15 CFTR exonic variations: Impact on their functional classification and perspectives for therapy

BACKGROUND

The majority of variants of unknown clinical significance (VUCS) in the CFTR gene are missense variants. While change on the CFTR protein structure or function is often suspected, impact on splicing may be neglected. Such undetected splicing default of variants may complicate the interpretation of genetic analyses and the use of an appropriate pharmacotherapy.

METHODS

We selected 15 variants suspected to impact CFTR splicing after in silico predictions on 319 missense variants (214 VUCS), reported in the CFTR-France database. Six specialized laboratories assessed the impact of nucleotide substitutions on splicing (minigenes), mRNA expression levels (quantitative PCR), synthesis and maturation (western blot), cellular localization (immunofluorescence) and channel function (patch clamp) of the CFTR protein. We also studied maturation and function of the truncated protein, consecutive to in-frame aberrant splicing, on additional plasmid constructs.

RESULTS

Six of the 15 variants had a major impact on CFTR splicing by in-frame (n = 3) or out-of-frame (n = 3) exon skipping. We reclassified variants into: splicing variants; variants causing a splicing defect and the impairment of CFTR folding and/or function related to the amino acid substitution; deleterious missense variants that impair CFTR folding and/or function; and variants with no consequence on the different processes tested.

CONCLUSION

The 15 variants have been reclassified by our comprehensive approach of in vitro experiments that should be used to properly interpret very rare exonic variants of the CFTR gene. Targeted therapies may thus be adapted to the molecular defects regarding the results of laboratory experiments.

Bone status in a mouse model of genetic hemochromatosis

Genetic hemochromatosis is a cause of osteoporosis; mechanisms leading to iron-related bone loss are not fully characterized. We assessed the bone phenotype of HFE (-/-) male mice, a mouse model of hemochromatosis. They had a phenotype of osteoporosis with low bone mass and alteration of the bone microarchitecture.

INTRODUCTION

Genetic hemochromatosis is a cause of osteoporosis. However, the mechanisms leading to iron-related bone loss are not fully characterized. Recent human data have not supported the hypothesis of hypogonadism involvement. The direct role of iron on bone metabolism has been suggested.

METHODS

Our aim was to assess the bone phenotype of HFE (-/-) male mice, a mouse model of human hemochromatosis, by using microcomputed tomography and histomorphometry. HFE (-/-) animals were sacrificed at 6 and 12 months and compared to controls.

RESULTS

There was a significant increase in hepatic iron concentration and bone iron content in HFE (-/-) mice. No detectable Perls' staining was found in the controls' trabeculae. Trabecular bone volume (BV/TV) was significantly lower in HFE (-/-) mice at 6 and 12 months compared to the corresponding wild-type mice: 9.88 ± 0.82% vs 12.82 ± 0.61% (p = 0.009) and 7.18 ± 0.68% vs 10.4 ± 0.86% (p = 0.015), respectively. In addition, there was an impairment of the bone microarchitecture in HFE (-/-) mice. Finally, we found a significant increase in the osteoclast number in HFE (-/-) mice: 382.5 ± 36.75 vs 273.4 ± 20.95 ¢/mm(2) (p = 0.004) at 6 months and 363.6 ± 22.35 vs 230.8 ± 18.7 ¢/mm(2) (p = 0.001) at 12 months in HFE (-/-) mice vs controls.

CONCLUSION

Our data show that HFE (-/-) male mice develop a phenotype of osteoporosis with low bone mass and alteration of the microarchitecture. They suggest that there is a relationship between bone iron overload and the increase of the osteoclast number in these mice. These findings are in accordance with clinical observations in humans exhibiting genetic hemochromatosis and support a role of excess iron in relation to genetic hemochromatosis in the development of osteoporosis in humans.

Absence of VHL gene alteration and high VEGF expression are associated with tumour aggressiveness and poor survival of renal-cell carcinoma

Background:

The von Hippel–Lindau gene (VHL) alteration, a common event in sporadic clear-cell renal-cell carcinoma (CCRCC), leads to highly vascularised tumours. Vascular endothelial growth factor (VEGF) is the major factor involved in angiogenesis, but the prognostic significance of both VHL inactivation and VEGF expression remain controversial. The aims of this study were to analyse the relationship between VHL genetic and epigenetic alterations, VHL expression and VEGF tumour or plasma expression, and to analyse their respective prognostic value in patients with CCRCC.

Methods:

A total of 102 patients with CCRCC were prospectively analysed. Alterations in VHL were determined by sequencing, Multiplex Ligation-dependent Probe Amplification (MLPA) and methylation-specific MLPA. Expression of pVHL and VEGF was determined by immunohistochemistry. Plasma VEGF was measured by enzyme-linked immunosorbent assay (ELISA).

Results:

VHL mutation, deletion and promoter methylation were identified in 70, 76 and 14 cases, respectively. Overall, at least one VHL-gene alteration occurred in 91 cases (89.2%). Both VEGF tumour and plasma expression appeared to be decreased in case of VHL alteration. Median progression-free survival and CCRCC-specific survival were significantly reduced in patients with wild-type VHL or altered VHL and high VEGF expression, which, therefore, represent two markers of tumour aggressiveness in CCRCC.

Conclusion:

Stratifying CCRCCs according to VHL and VEGF status may help tailor therapeutic strategy.

Use of carbonic anhydrase IX (CAIX) expression and Von Hippel Lindau (VHL) gene mutation status to predict survival in renal cell carcinoma

5042

Background: VHL gene mutations induce the expression of CAIX, and previous studies have shown that low CAIX results in worse prognosis for RCC. We attempt to further describe the relationship between CAIX expression, VHL gene mutations and tumor characteristics. Methods: Radical nephrectomy was performed in 100 patients at 2 centers. Genomic DNA was extracted from frozen tumor samples using the QIAmp DNA mini kit. Four amplimers covering the whole coding sequence of the VHL gene were synthesized by PCR and sequenced by Big Dye. Mutation bearing sequences were confirmed by a second round of sequencing. The monoclonal antibody M75 was used to score the expression of the CAIX protein. Life table, Kaplan-Meier and Cox regression analyses addressed RCC-specific mortality (RCC-SM). Results: VHL mutations were identified in 58 patients (58%) and CAIX tumor expression ranged from 0% to 100%. Low CAIX expression (<85%) was associated with absence of VHL mutation (p=0.02), larger tumors (p=0.002), higher T stage (p=0.007), nodal metastases (p=0.001) and higher Fuhrman grade (p=0.006). Absence of VHL mutation was associated with worse ECOG (p=0.005), higher T stage (p=0.01) and presence of nodal (p=0.03) and distant metastases (p=0.02). Categorically-coded, CAIX was a statistically significant predictor of RCC-SM (p=0.002), while VHL mutation approached statistical significance (p=0.08) and a trend was observed for worse survival when VHL was not mutated. Patients with both high CAIX and VHL mutation had better survival (95.9% 1 year and 6 year median survival) than their counterparts with low CAIX expression and absence of VHL mutation (62.9% 1 year and 1.5 year median survival) (p<0.001). In Cox regression analyses, neither CAIX (p=0.06) nor VHL (p=0.4) achieved independent predictor status, when adjusted for age, gender, TNM stage, tumor size, Fuhrman and ECOG. Conclusions: Low CAIX expression is associated with the absence of VHL mutation and aggressive tumor characteristics, and is a statistically significant predictor of poor prognosis in patients with clear cell RCC.

No significant financial relationships to disclose.

Interleukin-6 and vascular endothelial growth factor release by renal cell carcinoma cells impedes lymphocyte-dendritic cell cross-talk

Anti-tumour T cell response requires antigen presentation via efficient immunological synapse between antigen presenting cells, e.g. dendritic cells (DC), and specific T cells in an adapted Th1 cytokine context. Nine renal cell carcinoma (RCC) primary culture cells were used as sources of tumour antigens which were loaded on DC (DC-Tu) for autologous T cell activation assays. Cytotoxic activity of lymphocytes stimulated with DC-Tu was evaluated against autologous tumour cells. Assays were performed with 75 grays irradiated tumour cells (Tu irr) and with hydrogen peroxide +/- heat shock (Tu H(2)O(2) +/- HS) treated cells. DC-Tu irr failed to enhance cytotoxic activity of autologous lymphocytes in seven of 13 assays. In all these defective assays, irradiated tumour cells displayed high interleukin (IL)-6 and vascular endothelial growth factor (VEGF) release. Conversely, when tumour cells released low IL-6 levels (n = 4), DC-Tu irr efficiently enhanced CTL activity. When assays were performed with the same RCC cells treated with H(2)O(2) + HS, DC-Tu stimulation resulted in improved CTL activity. H(2)O(2) + HS treatment induced post-apoptotic cell necrosis of tumour cells, totally abrogated their cytokine release [IL-6, VEGF, transforming growth factor (TGF)-beta1] and induced HSP70 expression. Taken together, data show that reduction in IL-6 and VEGF release in the environment of the tumour concomitantly to tumour cell HSP expression favours induction of a stronger anti-tumour CTL response.

Biological significance of serum VEGF measurement in renal cell carcinoma

4596

Background: VEGF plays an important role in Renal Cell Carcinoma (RCC) tumor angiogenesis and is a relevant molecular target. Our objective was to correlate serum VEGF measurement to clinical, biological and pathological variables in renal tumors. Methods: 206 patients who were operated for a renal tumor at our institution were prospectively assessed for serum VEGF measurement (enzyme-linked immunosorbent assay, R&D systems). Informed consent was obtained in all cases. Symptoms at presentation, pre-operative biology (haemoglobin, WBC count, platelet count, serum creatinin, calcemia, CRP, ASAT, ALAT, gamma-glutamyltransferase (γGT), Alkaline Phosphatases), TNM stage, Fuhrman grade and final pathology (benign vs malignant histology, histologic subtype) were systematically recorded. Qualitative and quantitative variables were compared by using Chi-square (Fischer exact test) and Student t tests, respectively. Results: There were 128 males (62.1%) and 78 females (37.9%). 185 tumors were malignant at histology (89.8%) including 155 tumors with clear cell histology (83.8%). Median serum VEGF level was 361 ng/ml (41–3090). Mean serum VEGF was not significantly different between benign and malignant tumors as well as between clear cell and non clear cell carcinomas (p: 0.4 and 0.8 respectively). Serum VEGF was strongly associated with symptoms, T Stage (p: 0.0001), N Stage (p: 0.004), Fuhrman grade (p: 0.007) and tumor necrosis (p: 0.004) but not with M Stage (p: 0.3). Serum VEGF was also found to be strongly associated with: haemoglobin, CRP, platelet count (p: 0.0001) and Alkaline phosphatases (p: 0.001). A weaker association was found between serum VEGF and γGT, ASAT (p: 0.05) or ALAT (p: 0.09). Finally serum VEGF was associated with cancer specific survival (p: 0.01). Conclusion: Serum VEGF is strongly associated with most usual clinical, biological and pathological prognostic parameters in RCC. Serum VEGF measurement should be further evaluated for prognostic purpose as well as for treatment monitoring.

No significant financial relationships to disclose.

Pilot study of VHL mutation analysis to predict response to interleukin-2 in patients with metastatic renal cell carcinoma

14539

Background: More than 300 different mutations have been described in von Hippel-Lindau (VHL) families and nearly 100 in sporadic RCC. In familial cases, there is an excess of mutations in exon 3 and exon 1, whereas mutations are evenly distributed in sporadic cases. Recent evidence suggests the importance of genotype/phenotype correlations with different VHL gene mutations contributing to a tumor’s unique biological behavior. We performed a pilot study to compare the incidence and type of VHL mutation in IL-2 complete responders (CR) and non-responders (NR). Methods: Genomic DNA was extracted from 20 frozen clear cell tumour samples (10 CR and 10 NR) using Qiamp DNA mini kits (Qiagen). Four amplimers covering the entire coding sequence and three exon/intron junctions of the VHL gene were synthesized by PCR. PCR products were subsequently purified and were sequenced using Big Dye Primer Cycle Sequencing kit (Perkin-Elmer Applied Biosystems) and an automated DNA sequencer (Perkin-Elmer Applied Biosystems). Point mutation detection was performed on DNA sequencing gels from colored peak chromatograms. Mutation bearing sequences were confirmed by a second round of PCR and sequencing. Results: In the CR patients, only 2 out of 10 samples (20%) had evidence of a VHL mutation. These VHL mutations included a false sense mutations in exon 2, comprised of a C to T transition at position 646 in the cDNA, creating a stop codon, and a frameshift mutation in exon 1 introducing in one allele an abnormal stop codon at the beginning of exon 3 potentially leading to a shorter protein product. In the 10 non-responder samples, there was also a 2 out of 10 (20%) incidence of VHL mutations. These mutations included a complex 12 nucleotide deletion in the third exon in the a domain of the protein, and a G deletion in the first exon introducing a premature stop codon. Conclusions: In this small pilot study of metastatic RCC patients, there were relatively few VHL gene mutations, and VHL mutations did not appear to correlate with response to IL-2 therapy. This study, however, does not assess inactivation of VHL genes due to hypermethylation. An expanded genetic profile to evaluate IL-2 responders versus non-responders using 500k SNP Chips is underway.

No significant financial relationships to disclose.

Relationship between VHL mutation status, tumor VEGF expression and plasma VEGF measurement in sporadic renal cell carcinoma

4602

Background: The relationship between VHL mutation status and prognosis in renal cell carcinoma (RCC) remains controversial. The aim of this study was to evaluate prospectively the association between VHL status, tumor VEGF expression, plasma VEGF levels and usual prognostic parameters in RCC. Methods: 70 patients with clear cell RCCs were included in this study. Genomic DNA was extracted using the QIAmp DNA mini kit (Qiagen) from frozen tumor samples. Four amplimers covering the whole coding sequence and exon/intron junctions of the VHL gene were synthetized by PCR followed by Big Dye sequencing (Applied Biosystems). Mutation bearing sequences were confirmed in a second round of PCR and sequencing reactions. Tumor VEGF expression was determined by immunohistochemistry and plasma VEGF was measured by enzyme-linked immunosorbent assay (Quantikine immunoassay, R&D systems). Results were expressed in pg/ml. Qualitative and quantitative variables were compared by using Chi-square (Fischer exact test) and Student t tests, respectively. Results: A VHL mutation was found in 46 cases (65.7%). VHL mutations were localized in exon 1, 2 and 3 in 23, 16 and 7 cases respectively. Median tumor VEGF expression was 45% (5–100). Median plasma VEGF was 104 pg/ml (13–1430). A significant association was found between VHL mutation and N stage (p: 0.01), Fuhrman grade, symptoms at presentation (p: 0.02) or tumor size (p: 0.007). A VHL mutation was found in 83.5% of low grade (G1–2) and 80% of incidental tumors respectively. A trend towards more frequent VHL mutations was observed in T1 tumors (87% mutation rate, p: 0.07) and in good performance status patients. Interestingly, VEGF tumor expression and plasma VEGF levels were not significantly different among patients with tumors having or not mutated VHL (p: 0.7). Conclusion: VHL mutations are more frequent in small incidental low stage or low grade tumors. Although VHL inactivation was not specifically determined in this study, we failed to show any association between VHL mutational status and VEGF tumor or plasma expression suggesting that other pathways than the VHL/HIF axis are required for explaining the angiogenic phenotype of RCC.

No significant financial relationships to disclose.

Effect of sodium butyrate on doxorubicin resistance and expression of multidrug resistance genes in thyroid carcinoma cells

ATP-binding cassette (ABC) transporters [P-glycoprotein and multidrug resistance (MDR)-associated proteins (MRPs)] confer MDR to tumor cells. In this work, we investigated doxorubicin resistance in three thyroid carcinoma cell lines. The effects of sodium butyrate (NaB) on doxorubicin-induced cytotoxicity and on transcription of three MDR genes were also studied. Thyroid cell lines established from anaplastic (8505C) and two poorly differentiated follicular (FTC 238 and FTC 133) cancers were cultured for 24 or 48 h in the presence of NaB (0, 0.25, 0.5 and 1 mM) alone or combined with increased doses of doxorubicin. Cytotoxicity was assessed using the MTT test. MDR1, MRP1 and MRP2 mRNA expression was studied by RT-PCR. After a 24- or 48-h incubation, doxorubicin alone induced cytotoxicity in the three cell lines. NaB significantly (p<0.0001) increased the doxorubicin-induced cytotoxicity. MRP1 transcripts were expressed in the three non-treated cell lines. MDR1 and MRP2 mRNAs were both present in 8505C, but absent in FTC 133 or FTC 238 cell lines, respectively. Treatment with NaB for 24 or 48 h induced no change in MRP1 and MRP2 levels, but increased MDR1 expression in 8505C and FTC 238 cell lines comparably to alkaline phosphatase activity. In conclusion, MRP1 and sometimes MDR1 and MRP2 are expressed in the tested cell lines. NaB potentiates doxorubicin-induced cytotoxicity independently of the ABC transporters. The combination of doxorubicin and NaB might have clinical implications for thyroid cancer therapy.

Hyperferritinemia revealing Gaucher's disease

Hyperferritinemia is frequently observed during Gaucher's disease but has never been described as an initial manifestation. We report the case of a 57-year-old woman without a previous medical history who presented with hyperferritinemia and IgG monoclonal gammopathy. The diagnostic procedure was negative except for the bone marrow biopsy, which revealed Gaucher's cells. Low beta-glucocerebrosidase activity in leukocytes confirmed the diagnosis of adult Gaucher's disease. We discuss the differential diagnosis and the mechanisms of hyperferritinemia in this disease.

Identification of an endogenous RNA transcribed from the antisense strand of the HFE gene

Hereditary haemochromatosis is an autosomal recessive disease which results in iron overload, and it is the most frequently inherited disorder in Caucasian populations. The gene involved (HFE) has recently been identified, and it encodes an MHC class I-like molecule. A 2.7 kb cDNA has been isolated, whereas the HFE gene expression is characterized by an almost ubiquitous mRNA of 4.1 kb in size. The difference between this transcript and the isolated cDNA has not yet been explained. Thus, the 5' end of the HFE gene is still undefined and very little is known about the regulation of its expression. By searching this end, we isolated an antisense transcript originating from the same gene locus. Further investigations (rapid amplification of cDNA ends, RT-PCR experiments and dbEST screening) indicated that this RNA spans exon 1, exon 2, part of intron 1 of the HFE gene and approximately 1 kb upstream of it. This HFE antisense transcript is polyadenylated but displays no open reading frame. A ribonuclease A protection assay definitively demonstrated the biological existence of the HFE antisense RNA, which appears to be expressed in all of the tissues and cell lines tested. Furthermore, in vitro coupled transcription-translation experiments revealed that the HFE expression is decreased by this antisense RNA, indicating that it may play a critical role in the regulation of the HFE gene expression.

Low penetrant hemochromatosis phenotype in eight families: no evidence of modifiers in the MHC region

The gene responsible for hemochromatosis (HFE) has been identified on the short arm of chromosome 6, 4.5 Mb telomeric to HLA-A. A major mutation C282Y is closely correlated with the disease, as it accounts for 68 to 100\% of the cases of hemochromatosis. Nevertheless, some C282Y homozygotes subjects have no clinical or biological expression of the disease. Moreover, in Northern European populations a large discrepancy is observed between the number of C282Y homozygotes and the number of diagnosed hemochromatosis patients, suggesting incomplete penetrance of the mutation. To localize and identify the modifying genes, we investigated eight families including C282Y homozygous relatives showing no clinical signs of the disease, in addition to the hemochromatosis patients. Genomic DNA from 20 C282Y homozygotes (10 patients and 10 siblings presenting no or minor biological abnormalities) were studied. Five polymorphisms from the HFE gene were determined by PCR restriction. Extended haplotypes of the 6p21.3 region were constructed with 10 microsatellite markers. All the C282Y homozygotes shared the same HFE polymorphism. The haplotypes presented no significant difference between the probands and their unaffected relatives. These studies suggest that neither HFE polymorphism nor genes surrounding HFE are able to modulate HFE expression.

Identification of three novel mutations in the dystrophin gene detected by the heteroduplex/SSCA screening procedure. Mutations in brief no. 222. Online

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are X-linked neuromuscular disorders associated with alterations in the dystrophin gene. Analysis of 45 DMD/BMD patients has identified 18 patients with no deletion in the dystrophin gene. Heteroduplex analysis (HD), single strand conformation analysis (SSCA), and subsequent sequencing, identified five mutations and nine polymorphisms. Three out of the 5 mutations (780C>G, 2501-1g-->t, 9812 9813ins9800-9812) are first reported here. Furthermore we compare the relative efficiencies of the two alternatives methods (HD and SSCA) for screening sequence alterations.

The HFE gene undergoes alternate splicing processes

The MHC class I-related HFE gene appears to be involved in iron metabolism, but its pathogenic mechanism in hemochromatosis remains unknown. Furthermore, very little is known about the regulation of its expression. Hybridization of human tissue Northern blots revealed five different HFE mRNAs, indicating that HFE gene transcription is subject to alternative processes. cDNA selection and RT-PCR performed on HeLa cells clearly demonstrated the occurrence of either differential termination or splicing in HFE transcription. Among the numerous molecules identified, two may have a genuine biological significance.

Use of Chinese hamster ovary cell lines transfected with cloned human thyrotropin receptor for the measurement of thyroid-stimulating antibodies: advantages and difficulties

We compared the activities of thyroid-stimulating antibodies (TSAb) as measured with two cell lines (JP26 and JP26/26) transfected with cloned human thyrotropin (TSH) receptor and the values for TSAb measured on human thyrocytes cultures. Sera were obtained from patients with Graves' disease, before, during and after therapy with carbimazole (1-methyl-2-thio-3-carbethoxyimidazole). The activities of TSAb performed with the three assays correlated significantly. The TSAb technique using JP26/26 cells was as sensitive as the method performed on human thyrocyte cultures since positive TSAb values were found in 45 out of 47 (95.7%) newly diagnosed patients, in 100% of patients who relapsed after drug withdrawal and in none in remission. When the JP26 cell line was used, sensitivity decreased as the detection rate was only 53.2 and 55.5% before treatment and in case of relapse, respectively. The TSH receptors analysis showed a receptor density two times higher for JP26/26 than for JP26. JP26/26 cells provide similar diagnostic information on human thyrocytes in patients with Graves' disease. Moreover with these cells, the procedure for cell culture is less cumbersome and precision is better. However, rigorous culture conditions are required to maintain TSH receptor expression in transfected cells.

[Molecular genetics of hemochromatosis]

Hemochromatosis is a recessive disorder of iron metabolism characterized by progressive iron loading of parenchymal organs, which accounts for clinical complications such as cirrhosis, diabetes mellitus, cardiopathy, endocrine dysfunctions and arthropathy. Clinical complications, which usually develop after the third or fourth decade of life, can be fatal but may be prevented by phlebotomy if iron excess is detected at a very early stage. The hemochromatosis gene (HFE), located 4.5 megabases telomeric to the HLA-A locus, encodes an HLA class I like protein and two missense mutations, C282Y and H63D in complete disequilibrium have been identified within this gene. Due to its high frequency in the general population, the involvement of H63D in the pathogenesis of the disease remains controversial, and it might correspond to a minor mutation. Conversely, the C282Y mutation is tightly linked to the disease, as it accounts for 80 to 100% of the hemochromatosis cases in Northern Europe. The lower frequency observed, in the patients, in Italy and South of France led to imagine either the implication of other mutations or of other genes. The C282Y mutation is absent in Asia and Africa and is present in the general population with a decreasing gradient of frequency from Northern to Southern Europe. The prevalence of the disease was usually estimated to be 3% but the observed frequency of the C282Y homozygotes is 5% in our breton population raising the question of the penetrance of the disease, and consequently the use of the genotypic test for its systematic screening. As HFE encodes a membrane protein similar to HLA class I protein, its contribution to iron overload is not obvious. The normal protein is predicted to to be expressed at the cell surface in association with beta 2-microglobulin, a localization for which C282Y is critical as it disrupts this association. This protein has also been shown to form a stable complex with the transferrin receptor leading to a decreased affinity for transferrin. A better knowledge of its function will help to decipher iron and different metal-ions metabolism. Although the exact role of the HFE protein is unknown, the genotypic test allows the clinicians to ascertain their diagnosis and genetic counselling.

Prevalence of the C282Y mutation in Brittany: penetrance of genetic hemochromatosis?

Hemochromatosis (GH) is an inborn error of iron metabolism, characterized by progressive iron loading that, if untreated, causes high morbidity and death. The gene responsible for the disease (HFE), located 4.5 megabases telomeric to the HLA-A locus, encodes a protein homologous to class I MHC molecules. A main mutation, C282Y, has been identified within the gene. Although hemochromatosis is considered as the most frequent inherited disease in the populations of Northern European origin, its prevalence in Brittany had not been evaluated yet. In this issue we report the C282Y mutation frequency in a cohort of 1000 newborns from maternity hospitals of the four breton départements. The homozygote frequency was 5/1000 and heterozygote frequency was 12%; such high frequencies raise the question of the penetrance of the disease and the relevance of systematic genotypic screening for hemochromatosis.

A 1200-kilobase transcription map encompassing the D6S105 locus at 6p21.3

The gene content of the MHC class I telomerically adjacent region, in linkage disequilibrium with hereditary hemochromatosis, has not been well characterized yet. In the present work, we established three bacterial clone contigs, including mainly P1-derived artificial chromosomes. These contigs cover 89% of the 1.2-Mb 6p-subtelomeric region encompassing locus D6S105. Terminal exon trapping was applied to selected clones from these contigs. Forty-six independent terminal exons were identified and mapped within the region, 2 of which matched perfectly to expressed sequence tags. These 3' exons are all expressed in human fetal brain but differentially expressed in four tissues and two cell lines. The high number of exons identified indicates that the high gene density observed in the MHC class I region extends to this telomerically adjacent region.

A candidate gene for hemochromatosis: frequency of the C282Y and H63D mutations

The gene whose alteration causes hereditary hemochromatosis (HFE according to the international nomenclature) was, more than 20 years ago, shown to map to 6p21.3. It has since escaped all efforts to identify it by positional cloning strategies. Quite recently, a gene named HLA-H was reported as being responsible for the disease. Two missense mutations, Cys282Tyr (C282Y) and His63Asp (H63D), were observed, but no proof was produced that the gene described is the hemochromatosis gene. To validate this gene as the actual site of the alteration causing hemochromatosis, we decided to look for the two mutations in 132 unrelated patients from Brittany. Our results indicate that more than 92% of these patients are homozygous for the C282Y mutation, and that all 264 chromosomes but 5 carry either mutation. These findings confirm the direct implication of HLA-H in hemochromatosis.

Structural analysis of CFTR gene in congenital bilateral absence of vas deferens

Congenital bilateral absence of the vas deferens (CBAVD) is found in most males with cystic fibrosis (CF), but this malformation can be observed without any pulmonary or digestive features. We have analyzed 13 exons of the CF gene in a cohort of 25 CBAVD patients. Among the 50 chromosomes studied, 24 mutations were identified: delta F508 (14 cases), R117H (7 cases), R1070W (2 cases), 621 + 1 G --> T (1 case), and A1067V (1 case). Except for delta F508, the most frequent mutations (R117H, R1070W) were not observed in the CF group (109 patients) studied in our laboratory. We discuss the significance of these results.

Structural analysis of CFTR gene in congenital bilateral absence of vas deferens

Congenital bilateral absence of the vas deferens (CBAVD) is found in most males with cystic fibrosis (CF), but this malformation can be observed without any pulmonary or digestive features. We have analyzed 13 exons of the CF gene in a cohort of 25 CBAVD patients. Among the 50 chromosomes studied, 24 mutations were identified: delta F508 (14 cases), R117H (7 cases), R1070W (2 cases), 621 + 1 G --&gt; T (1 case), and A1067V (1 case). Except for delta F508, the most frequent mutations (R117H, R1070W) were not observed in the CF group (109 patients) studied in our laboratory. We discuss the significance of these results.

Tat-induced lesions in transgenic mice do not correlate with the HIV-1 LTR transactivation

The product of the tat gene is the most potent transcriptional trans-activator of the HIV-1 LTR (Human Immunodeficiency Virus type 1 Long Terminal Repeat) and might be predicted to be one of the HIV-1 proteins involved in the pathogenesis of AIDS-associated tumors. Deciphering its role in vivo may imply generation of transgenic mouse models displaying different spectra of tat expression. However, it remains difficult to correlate the mRNA expression, the protein production and the eventual pathological consequences in the animal. Our goal in this work was to elaborate a binary transgenic system allowing such an approach, the correlation of the transgene expression in different tissues and the production of the Tat protein, tested as a trans-activator in vivo, with its pathogenic effects. No direct linkage was evident between the degree of transactivation and pathogenesis. Indeed, only benign lesions were observed in malpighian epithelia, where the production of the Tat protein was clearly evidenced by its transactivating property.

French CF family genotype analysis shows that the R297Q mutation is a rare polymorphism

The authors describe a cystic fibrosis family genotype analysis showing that the R297Q amino acid change is a rare polymorphism rather than a deleterious mutation as previously reported. Indeed in this family two healthy subjects have the following genotypes: delta F508/R297Q and N1303K/R297Q.

In vitro manipulation of early mouse embryos induces HIV1-LTRlacZ transgene expression

We report here that the transcriptional activity of early mouse embryos is affected by their manipulation and culture in vitro, using transgenic embryos that express the reporter gene lacZ. We examined the pattern of expression of the lacZ gene fused to the human immunodeficiency virus type 1 long terminal repeat during the preimplantation stages. Transgene expression is induced as early as the two-cell stage in embryos developed in vitro, while there is no constitutive expression at the same stage in embryos developed in vivo. We have established a relation between this inducible expression occurring in vitro and an oxidative stress phenomenon. Indeed, when the culture medium is supplemented with antioxidants such N-acetyl-cysteine or CuZn-superoxide dismutase the transgene expression is markedly reduced. We also present evidence that the transgene expression in vitro coincides with the onset of the embryonic genome activation as attested by the synthesis of the 70 × 10(3) M(r) protein complex. Therefore, this transgene expression could prove to be a useful tool in our understanding of the molecular mechanisms involved in this crucial developmental event.

Dispensable role of the NF-kappa B sites in the UV-induction of the HIV-1 LTR in transgenic mice

We have previously reported the epidermis-specific expression of the HIV-1 LTR in transgenic mice and its induction by UV-B rays. To dissect the underlying mechanism of the UV induction of the LTR in mice, we developed two approaches. We first demonstrated by gel mobility shift analysis, using mice epidermal extracts, that the NF-kappa B sites of the HIV-1 LTR were one of the targets of the UV induction. The Sp-1 sites and the potential AP-1 sites of the LTR were not involved in this phenomenon. The transient transfection assays of modified LTR in HeLa cells also demonstrated the involvement of the NF-kappa B sites in the UV induction and were consistent with previously published data. Secondly, to study the regulation acting on an integrated gene, we generated transgenic mice carrying the lacZ gene under the control of the partially deleted LTR. All the transgenic lines and unexpectedly those carrying the LTR deleted for the kappa B sites displayed a UV-inducible epidermal expression. This suggests that, in mice, the UV induction might be mediated through other sites than the kappa B sites and may also depend on changes of the chromatin state.