Assessment of the functional impact of germline BRCA1/2 variants located in non-coding regions in families with breast and/or ovarian cancer predisposition.

PURPOSE: The molecular mechanism of breast and/or ovarian cancer susceptibility remains unclear in the majority of patients. While germline mutations in the regulatory non-coding regions of BRCA1 and BRCA2 genes have been described, screening has generally been limited to coding regions. The aim of this study was to evaluate the contribution of BRCA1/2 non-coding variants. METHODS: Four BRCA1/2 non-coding regions were screened using high-resolution melting analysis/Sanger sequencing or next-generation sequencing on DNA extracted from index cases with breast and ovarian cancer predisposition (3926 for BRCA1 and 3910 for BRCA2). The impact of a set of variants on BRCA1/2 gene regulation was evaluated by site-directed mutagenesis, transfection, followed by Luciferase gene reporter assay. RESULTS: We identified a total of 117 variants and tested twelve BRCA1 and 8 BRCA2 variants mapping to promoter and intronic regions. We highlighted two neighboring BRCA1 promoter variants (c.-130del; c.-125C > T) and one BRCA2 promoter variants (c.-296C > T) inhibiting significantly the promoter activity. In the functional assays, a regulating region within the intron 12 was found with the same enhancing impact as within the intron 2. Furthermore, the variants c.81-3980A > G and c.4186-2022C > T suppress the positive effect of the introns 2 and 12, respectively, on the BRCA1 promoter activity. We also found some variants inducing the promoter activities. CONCLUSION: In this study, we highlighted some variants among many, modulating negatively the promoter activity of BRCA1 or 2 and thus having a potential impact on the risk of developing cancer. This selection makes it possible to conduct future validation studies on a limited number of variants.

[Recommendations for genetic testing and management of individuals genetically at-risk of cutaneous melanoma]. / Recommandations pour le diagnostic de prédisposition génétique au mélanome cutané et pour la prise en charge des personnes à risque.

Cutaneous melanoma is a multifactorial disease resulting from both environmental and genetic factors. Five susceptibility genes have been identified over the past years, comprising high-risk susceptibility genes (CDKN2A, CDK4, and BAP1 genes) and intermediate-risk susceptibility genes (MITF, and MC1R genes). The aim of this expert consensus was to define clinical contexts justifying genetic analyses, to describe the conduct of these analyses, and to propose surveillance recommendations. Given the regulatory constraints, it is recommended that dermatologists work in tandem with a geneticist. Genetic analysis may be prescribed when at least two episodes of histologically proven invasive cutaneous melanoma have been diagnosed before the age of 75 years in two 1st or 2nd degree relatives or in the same individual. The occurrence in the same individual or in a relative of invasive cutaneous melanoma with ocular melanoma, pancreatic cancer, renal cancer, mesothelioma or a central nervous system tumour are also indications for genetic testing. Management is based upon properly managed photoprotection and dermatological monitoring according to genetic status. Finally, depending on the mutated gene and the familial history, associated tumour risks require specific management (e.g. ocular melanoma, pancreatic cancer). Due to the rapid progress in genetics, these recommendations will need to be updated regularly.

Malformations, genetic abnormalities, and Wilms tumor.

BACKGROUND: Wilms Tumor (WT) can occur in association with tumor predisposition syndromes and/or with clinical malformations. These associations have not been fully characterized at a clinical and molecular genetic level. This study aims to describe clinical malformations, genetic abnormalities, and tumor predisposition syndromes in patients with WT and to propose guidelines regarding indications for clinical and molecular genetic explorations. PROCEDURE: This retrospective study analyzed clinical abnormalities and predisposition syndromes among 295 patients treated for WT between 1986 and 2009 in a single pediatric oncological center. RESULTS: Clinically identified malformations and predisposition syndromes were observed in 52/295 patients (17.6%). Genetically proven tumor predisposition syndromes (n = 14) frequently observed were syndromes associated with alterations of the chromosome WT1 region such as WAGR (n = 6) and Denys-Drash syndromes (n = 3), syndromes associated with alterations of the WT2 region (Beckwith-Wiedeman syndrome, n = 3), and Fanconi anemia (n = 2). Hemihypertrophy and genito-urinary malformations (n = 12 and n = 16, respectively) were the most frequently identified malformations. Other different syndromes or malformations (n = 10) were less frequent. Median age of WT diagnosis was significantly earlier for children with malformations than those without (27 months vs. 37 months, P = 0.0009). There was no significant difference in terms of 5-year EFS and OS between WT patients without or with malformations. CONCLUSIONS: The frequency of malformations observed in patients with WT underline the need of genetic counseling and molecular genetic explorations for a better follow-up of these patients, with a frequently good outcome. A decisional tree, based on clinical observations of patients with WT, is proposed to guide clinicians for further molecular genetic explorations.

Short-term psychological impact of the BRCA1/2 test result in women with breast cancer according to their perceived probability of genetic predisposition to cancer.

BACKGROUND: The effect of BRCA1/2 gene test result on anxiety, depression, cancer-related thought intrusion or avoidance and perceived control over cancer risk was assessed in breast cancer (BC) patients, according to their perceived probability of genetic predisposition to cancer. METHODS: Two hundred and forty-three (89% response rate) women with BC completed questionnaires after an initial genetic counselling visit (T1), of which 180 (66%) completed questionnaires again after receiving the BRCA1/2 results (T2). The discrepancy between women's perceived probability of cancer genetic predisposition at T1 and the geneticist's computed estimates was assessed. RESULTS: In all, 74% of women received a negative uninformative (NU), 11% a positive BRCA1/2 and 15% an unclassified variant (UV) result. On hierarchical regression analysis, in women with a positive BRCA1/2 result (vs NU or UV), a lower perceived probability of cancer genetic predisposition than objective estimates at T1 predicted lower levels of anxiety at T2 (ß=-0.28; P<0.01), whereas in women receiving a UV result (vs NU or positive BRCA1/2), a lower perceived probability of cancer genetic predisposition than objective estimates at T1 predicted higher levels of anxiety (ß=0.20; P<0.01), depression (ß=0.19; P<0.05) and intrusion (ß=0.18; P<0.05) at T2. CONCLUSION: The type of BRCA1/2 test result differently affects distress according to women's perceived probability of genetic predisposition before testing.

The complete BRCA2 gene and mutations in chromosome 13q-linked kindreds.

Breast carcinoma is the most common malignancy among women in developed countries. Because family history remains the strongest single predictor of breast cancer risk, attention has focused on the role of highly penetrant, dominantly inherited genes in cancer-prone kindreds (1). BRCA1 was localized to chromosome 17 through analysis of a set of high-risk kindreds (2), and then identified four years later by a positional cloning strategy (3). BRCA2 was mapped to chromosomal 13q at about the same time (4). Just fifteen months later, Wooster et al. (5) reported a partial BRCA2 sequence and six mutations predicted to cause truncation of the BRCA2 protein. While these findings provide strong evidence that the identified gene corresponds to BRCA2, only two thirds of the coding sequence and 8 out of 27 exons were isolated and screened; consequently, several questions remained unanswered regarding the nature of BRCA2 and the frequency of mutations in 13q-linked families. We have now determined the complete coding sequence and exonic structure of BRCA2 (GenBank accession #U43746), and examined its pattern of expression. Here, we provide sequences for a set of PCR primers sufficient to screen the entire coding sequence of BRCA2 using genomic DNA. We also report a mutational analysis of BRCA2 in families selected on the basis of linkage analysis and/or the presence of one or more cases of male breast cancer. Together with the specific mutations described previously, our data provide preliminary insight into the BRCA2 mutation profile.

Rare germline large rearrangements in the BRCA1/2 genes and eight candidate genes in 472 patients with breast cancer predisposition.

Hereditary breast cancers account for up to 5-10 % of breast cancers and a majority are related to the BRCA1 and BRCA2 genes. However, many families with breast cancer predisposition do not carry any known mutations for BRCA1 and BRCA2 genes. We explored the incidence of rare large rearrangements in the coding, noncoding and flanking regions of BRCA1/2 and in eight other candidate genes--CHEK2, BARD1, ATM, RAD50, RAD51, BRIP1, RAP80 and PALB2. A dedicated zoom-in CGH-array was applied to screen for rearrangements in 472 unrelated French individuals from breast-ovarian cancer families that were being followed in eight French oncogenetic laboratories. No new rearrangement was found neither in the genomic regions of BRCA1/2 nor in candidate genes, except for the CHEK2 and BARD1 genes. Three heterozygous deletions were detected in the 5' and 3' flanking regions of BRCA1. One large deletion introducing a frameshift was identified in the CHEK2 gene in two families and one heterozygous deletion was detected within an intron of BARD1. The study demonstrates the usefulness of CGH-array in routine genetic analysis and, aside from the CHEK2 rearrangements, indicates there is a very low incidence of large rearrangements in BRCA1/2 and in the other eight candidate genes in families already explored for BRCA1/2 mutations. Finally, next-generation sequencing should bring new information about point mutations in intronic and flanking regions and also medium size rearrangements.

Tumor BRCA testing can reveal a high tumor mutational burden related to POLE pathogenic variants.

OBJECTIVE: Tumors harboring a POLE pathogenic variant, associated with high tumor mutational burden, are good candidates for immunotherapy. However, POLE pathogenic variants are not currently screened in routine clinical practice. Can these tumors be identified by means of an already available test? METHODS: We describe seven tumors harboring a POLE pathogenic variant, among eight patients with tumors harboring multiple BRCA1/2 variants (from 4 to 20). All patients were managed at Institut Curie, Paris. Five patients were selected because of unexpected tumor BRCA testing results with multiple variants and another three patients were selected because of a POLE pathogenic variant detected by large tumor testing. We looked for other tumor variants by Next-Generation Sequencing in tumors harboring multiple BRCA1/2 variants, and for multiple BRCA1/2 variants in tumors harboring a POLE pathogenic variant. RESULTS: Four of the five tumors selected because of multiple BRCA1/2 variants exhibited a POLE pathogenic variant, and all three tumors selected for POLE pathogenic variants exhibited multiple BRCA1/2 variants. CONCLUSIONS: Tumor BRCA testing could be a way to detect tumors harboring a highly mutagenic POLE pathogenic variant.

PEL: an unbiased method for estimating age-dependent genetic disease risk from pedigree data unselected for family history.

Providing valid risk estimates of a genetic disease with variable age of onset is a major challenge for prevention strategies. When data are obtained from pedigrees ascertained through affected individuals, an adjustment for ascertainment bias is necessary. This article focuses on ascertainment through at least one affected and presents an estimation method based on maximum likelihood, called the Proband's phenotype exclusion likelihood or PEL for estimating age-dependent penetrance using disease status and genotypic information of family members in pedigrees unselected for family history. We studied the properties of the PEL and compared with another method, the prospective likelihood, in terms of bias and efficiency in risk estimate. For that purpose, family samples were simulated under various disease risk models and under various ascertainment patterns. We showed that, whatever the genetic model and the ascertainment scheme, the PEL provided unbiased estimates, whereas the prospective likelihood exhibited some bias in a number of situations. As an illustration, we estimated the disease risk for transthyretin amyloid neuropathy from a French sample and a Portuguese sample and for BRCA1/2 associated breast cancer from a sample ascertained on early-onset breast cancer cases.

Epidemiological, clinical, paraclinical and molecular study of a cohort of 102 patients affected with autosomal recessive progressive cerebellar ataxia from Alsace, Eastern France: implications for clinical management.

While Friedreich's ataxia (FRDA) and ataxia telangiectasia (AT) are known to be the two most frequent forms of autosomal recessive cerebellar ataxia (ARCA), knowledge on the other forms of ARCA has been obtained only recently, and they appear to be rarer. Little is known about the epidemiological features and the relative frequency of the ARCAs and only few data are available about the comparative features of ARCAs. We prospectively studied 102 suspected ARCA cases from Eastern France (including 95 from the Alsace region) between 2002 and 2008. The diagnostic procedure was based on a sequential strategic scheme. We examined the clinical, paraclinical and molecular features of the large cohort of patients and compared features and epidemiology according to molecular diagnosis. A molecular diagnosis could be established for 57 patients; 36 were affected with FRDA, seven with ataxia plus oculomotor apraxia type 2 (AOA2), four with AT, three with ataxia plus oculomotor apraxia type 1 (AOA1), three with Marinesco-Sjögren syndrome, two with autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS), one with ataxia with vitamin E deficiency (AVED) and one with autosomal recessive cerebellar ataxia type 2 (ARCA2). The group of patients with no identified mutation had a significantly lower spinocerebellar degeneration functional score corrected for disease duration (SDFS/DD ratio; p = 0.002) and comprised a significantly higher proportion of cases with onset after 20 years (p < 0.01). Extensor plantar reflexes were rarer and cerebellar atrophy was more frequent in the group of patients with a known non-Friedreich ARCA compared to all other patients (p < 0.0001 and p = 0.0003, respectively). Lower limb areflexia and electroneuromyographic evidences of peripheral neuropathy were more frequent in the Friedreich ataxia group than in the group with a known non-Friedreich ataxia and were more frequent in the later group than in the group with no identified mutation (p = 0.0001 and p = 0.01, respectively). The overall prevalence of ARCA in Alsace is 1/19,000. We can infer the prevalence of FRDA in Alsace to be 1/50,000 and infer that AT is approximately eight times less frequent than FRDA. MSS, AOA2 and ARSACS appear only slightly less frequent than AT. Despite the broad variability of severity, Friedreich ataxia patients are clinically distinct from the other forms of ARCA. Patients with no identified mutation have more often a pure cerebellar degenerative disease or a spastic ataxia phenotype. It appears that ARCA cases can be divided into two major groups of different prognosis, an early-onset group with a highly probable genetic cause and an adult-onset group with better prognosis for which a genetic cause is more difficult to prove but not excluded. ARCAs are rare, early-disabling and genetically heterogeneous diseases dominated by FRDA. Several of the recently identified ARCAs, such as AVED, ARSACS, AOA1, AOA2 and MSS, have a prevalence close to AT and should be searched for extensively irrespective of ethnic origins. The strategic scheme is a useful tool for the diagnosis of ARCAs in clinical practice.

Establishment and characterisation of a new breast cancer xenograft obtained from a woman carrying a germline BRCA2 mutation.

BACKGROUND: The BRCA2 gene is responsible for a high number of hereditary breast and ovarian cancers, and studies of the BRCA2 biological functions are limited by the lack of models that resemble the patient's tumour features. The aim of this study was to establish and characterise a new human breast carcinoma xenograft obtained from a woman carrying a germline BRCA2 mutation. METHODS: A transplantable xenograft was obtained by grafting a breast cancer sample into nude mice. The biological and genetic profiles of the xenograft were compared with that of the patient's tumour using histology, immunohistochemistry (IHC), BRCA2 sequencing, comparative genomic hybridisation (CGH), and qRT-PCR. Tumour response to standard chemotherapies was evaluated. RESULTS: Histological profile identified the tumour as a basal-like triple-negative breast cancer. Targeted BRCA2 DNA sequencing of the xenograft showed the presence of the mutation previously identified in the carrier. Comparative genomic hybridisation array profiles of the primary tumour and the xenograft revealed a high number of similar genetic alterations. The therapeutic assessment of the xenograft showed sensitivity to anthracyclin-based chemotherapy and resistance to docetaxel. The xenograft was also highly sensitive to radiotherapy and cisplatin-based treatments. CONCLUSIONS: This study describes a new human breast cancer xenograft obtained from a BRCA2-mutated patient. This xenograft provides a new model for the pre-clinical drug development and for the exploration of the drug response biological basis.

[Cancer genetic predisposition: current events and perspectives in 2010]. / Prédispositions génétiques aux cancers: actualités et perspectives en 2010.

Studies performed during these last 30 years have had a major impact on the understanding of carcinogenesis. They have opened a new field: cancer genetic predisposition. At the present time, most of the cancer predispositions linked to the alteration of one gene, associated with a high risk of cancer and with a specific phenotype have been identified. About 70 genes have been identified and have led to genetic testing. The indication of genetic testing, the management of at risk patients require the establishment of guidelines. The next challenge is the identification of cancer susceptibility genes associated with low risk or modifying the effect of treatment.

[Genetic testing in the context of the revision of the French law on bioethics]. / Les tests génétiques à l'heure de la deuxième révision des lois de bioéthique.

This article focuses on six questions raised by genetic testing in human: (1) the use of genetic tests, (2) information given to relatives of patients affected with genetic disorders, (3) prenatal and preimplantatory diagnosis for late onset genetic diseases and the use of pangenomic tests in prenatal diagnosis, (4) direct-to-consumer genetic testing, (5) population screening in the age of genomic medicine and (6) incidental findings when genetic testing are used.

Molecular basis of the Li-Fraumeni syndrome: an update from the French LFS families.

We have performed an extensive analysis of TP53 in 474 French families suggestive of Li-Fraumeni syndrome (LFS), including 232 families fulfilling the Chompret criteria. We identified a germline alteration of TP53 in 82 families (17%), in 67/232 of the families fulfilling the Chompret criteria (29%) and in 15/242 which did not fulfil these criteria (6%). Most of the alterations corresponded to missense mutations (67%), and we identified in four families genomic deletions removing the entire TP53 locus, the promoter and the non-coding exon 1, or exons 2-10. These results represent a definitive argument demonstrating that LFS results from TP53 haplodeficiency. The mean ages of tumour onset were significantly different between patients harbouring TP53 missense mutations and other types of alterations, missense mutations being associated with a 9 year earlier tumour onset. These results confirm that missense mutations not only inactivate p53 but also have an additional oncogenic effect. Germline alterations of TP53 that lead exclusively to loss of function are therefore associated with a later age of tumour onset and the presence of such mutations should be considered in atypical LFS families with tumours diagnosed after 40 years.

Rapid progression of prostate cancer in men with a BRCA2 mutation.

Men with BRCA2 mutations have been found to be at increased risk of developing prostate cancer. There is a recent report that BRCA2 carriers with prostate cancer have poorer survival than noncarrier prostate cancer patients. In this study, we compared survival of men with a BRCA2 mutation and prostate cancer with that of men with a BRCA1 mutation and prostate cancer. We obtained the age at diagnosis, age at death or current age from 182 men with prostate cancer from families with a BRCA2 mutation and from 119 men with prostate cancer from families with a BRCA1 mutation. The median survival from diagnosis was 4.0 years for men with a BRCA2 mutation vs 8.0 years for men with a BRCA1 mutation, and the difference was highly significant (P<0.01). It may be important to develop targeted chemotherapies to treat prostate cancer in men with a BRCA2 mutation.

Does nonsense-mediated mRNA decay explain the ovarian cancer cluster region of the BRCA2 gene?

BRCA2 (BReast CAncer susceptibility gene 2) germline mutation carriers are at increased risk for breast and ovarian cancers. Mutations occurring in the ovarian cancer cluster region (OCCR) are linked to higher ovarian cancer and/or lower breast cancer risk(s) than mutations occurring elsewhere in BRCA2. Most BRCA2 germline mutations introduce premature termination codons (PTCs), making their mRNAs likely targets of nonsense-mediated mRNA decay (NMD), a mechanism that eliminates PTC-bearing transcripts to prevent expression of truncated proteins. Contradictory evidence exists regarding whether NMD can be triggered by PTCs located far upstream of the nearest exon-exon junction (EEJ). Since the OCCR comprises a major portion of the 4.9 kb exon 11 of BRCA2, we investigated if transcripts bearing PTCs in this large exon are unable to trigger NMD, and if this might contribute to the phenotypic difference associated with the OCCR. We examined cDNA from 18 carriers of PTC-introducing germline mutations located throughout BRCA2, and found that PTC-bearing transcripts were 1.4-3.3-fold less prevalent than their nonmutated counterparts irregardless of PTC position. We conclude that NMD can recognize PTCs up to 4.5 kb upstream of the nearest EEJ, demonstrating that a general inability of NMD to recognize PTCs in exon 11 is unlikely to explain the genotype-phenotype correlation associated with the OCCR.

Impact of the MDM2 SNP309 and p53 Arg72Pro polymorphism on age of tumour onset in Li-Fraumeni syndrome.

Li-Fraumeni syndrome, resulting from p53 (TP53) germline mutations, represents one of the most devastating genetic predispositions to cancer. Recently, the MDM2 SNP309 (T-->G variation) was shown to be associated with accelerated tumour formation in p53 mutation carriers. The impact of the common p53 codon 72 polymorphism on cancer risk remains controversial. We therefore investigated the effect of these two polymorphisms in 61 French carriers of the p53 germline mutation. The mean age of tumour onset in MDMD2 SNP309 G allele carriers (19.6 years) was significantly different from that observed in patients homozygous for the T allele (29.9 years, p<0.05). For the p53 codon 72 polymorphism, the mean age of tumour onset in Arg allele carriers (21.8 years) was also different from that of Pro/Pro patients (34.4 years, p<0.05). We observed a cumulative effect of both polymorphisms because the mean ages of tumour onset in carriers of the MDM2G and p53Arg alleles (16.9 years) and those with the MDM2T/T and p53Pro/Pro genotypes (43 years) were clearly different (p<0.02). Therefore, our results confirm the impact of the MDM2 SNP309 G allele on the age of tumour onset in germline p53 mutation carriers, and suggest that this effect may be amplified by the p53 72Arg allele. Polymorphisms affecting p53 degradation therefore represent one of the rare examples of modifier genetic factors identified to date in mendelian predispositions to cancer.

The contribution of germline rearrangements to the spectrum of BRCA2 mutations.

BACKGROUND: Few germline BRCA2 rearrangements have been described compared with the large number of germline rearrangements reported in the BRCA1 gene. However, some BRCA2 rearrangements have been reported in families that included at least one case of male breast cancer. OBJECTIVE: To estimate the contribution of large genomic rearrangements to the spectrum of BRCA2 defects. METHODS: Quantitative multiplex PCR of short fluorescent fragments (QMPSF) was used to screen the BRCA2 gene for germline rearrangements in highly selected families. QMPSF was previously used to detect heterozygous deletions/duplications in many genes including BRCA1 and BRCA2. RESULTS: We selected a subgroup of 194 high risk families with four or more breast cancers with an average age at diagnosis of < or = 50 years, who were recruited through 14 genetic counselling centres in France and one centre in Switzerland. BRCA2 mutations were detected in 18.6% (36 index cases) and BRCA1 mutations in 12.4% (24 index cases) of these families. Of the 134 BRCA1/2 negative index cases in this subgroup, 120 were screened for large rearrangements of BRCA2 using QMPSF. Novel and distinct BRCA2 deletions were detected in three families and their boundaries were determined. We found that genomic rearrangements represent 7.7% (95% confidence interval 0% to 16%) of the BRCA2 mutation spectrum. CONCLUSION: The molecular diagnosis of breast cancer predisposition should include screening for BRCA2 rearrangements, at least in families with a high probability of BRCA2 defects.

Comparing ataxias with oculomotor apraxia: a multimodal study of AOA1, AOA2 and AT focusing on video-oculography and alpha-fetoprotein.

Whether the recessive ataxias, Ataxia with oculomotor apraxia type 1 (AOA1) and 2 (AOA2) and Ataxia telangiectasia (AT), can be distinguished by video-oculography and alpha-fetoprotein level remains unknown. We compared 40 patients with AOA1, AOA2 and AT, consecutively referred between 2008 and 2015 with 17 healthy subjects. Video-oculography revealed constant impairments in patients such as cerebellar signs, altered fixation, impaired pursuit, hypometric saccades and abnormal antisaccades. Horizontal saccade latencies could be highly increased reflecting oculomotor apraxia in one third of patients. Specific distinctive alpha-fetoprotein thresholds were determined for AOA1 (7-15 µg/L), AOA2 (15-65 µg/L) and AT (>65 µg/L). Early age onset, severe walking disability, movement disorders, sensori-motor neuropathy and cerebellar atrophy were all shared. In conclusion, alpha-fetoprotein level seems to permit a distinction while video-oculography does not and therefore is not mandatory, even if an appropriate oculomotor examination remains crucial. Our findings are that AOA1, AOA2 and AT form a particular group characterized by ataxia with complex oculomotor disturbances and elevated AFP for which the final diagnosis is relying on genetic analysis. These findings could guide genetic analysis, assist reverse-phenotyping and provide background for the interpretation of the numerous variants of unknown significance provided by next-generation sequencing.

Structural organization and expression of human MTUS1, a candidate 8p22 tumor suppressor gene encoding a family of angiotensin II AT2 receptor-interacting proteins, ATIP.

The Mitochondrial Tumor suppressor 1 (MTUS1) gene is a newly identified candidate tumor suppressor gene at chromosomal position 8p22. We report here that MTUS1 encodes a family of proteins whose leader member (ATIP1) was previously isolated in our laboratory as a novel interacting partner of the angiotensin II AT2 receptor involved in growth inhibition (Nouet, JBC 279: 28989-97, 2004). The MTUS1 gene contains 17 coding exons distributed over 112 kb of genomic DNA. Alternative exon usage generates three major transcripts (ATIP1, ATIP3 and ATIP4), each showing different tissue distribution. ATIP polypeptides are identical in their carboxy-terminal region carrying four coiled-coil domains. In their amino-terminal portion, ATIP polypeptides exhibit distinct motifs for localisation in the cytosol, nucleus or cell membrane, suggesting that MTUS1 gene products may be involved in a variety of intracellular functions in an AT2-dependent and independent manner. ATIP1 is ubiquitous and highly expressed in the brain. ATIP3 is the major transcript in tissues (prostate, bladder, breast, ovary, colon) corresponding to cancer types with frequent loss of heterozygosity at 8p22. Interestingly, ATIP4 is a brain-specific transcript highly abundant in the cerebellum and fetal brain. High evolutionary conservation of ATIP amino-acid sequences suggests important biological roles for this new family of proteins in tumor suppression and/or brain function.

Mutation analysis of the 8p22 candidate tumor suppressor gene ATIP/MTUS1 in hepatocellular carcinoma.

A high frequency of allelic loss affecting chromosome 8p and a minimal region of deletion at p21-22 have been previously reported in hepatocellular carcinoma (HCC), suggesting that at least one tumor suppressor gene is present in this region. In this study, we assessed whether the angiotensin II AT2 receptor interacting protein (ATIP)/mitochondrial tumor suppressor gene (MTUS1), a gene newly identified at position 8p22, may be a candidate tumor suppressor gene mutated in HCC. We searched for alterations in the 17 coding exons of ATIP/MTUS1 by means of denaturating high-performance liquid chromatography and sequencing, in 51 HCC tumors and 58 cell lines for which loss of heterozygosity status was known. Five major nucleotide substitutions were identified, all located in exons used by the ATIP3 transcript which is the only ATIP transcript variant expressed in liver. These nucleotide variations result in amino-acid substitution or deletion of conserved structural motifs (nuclear localisation signal, polyproline motif, leucine zipper) and also affect exonic splicing enhancer motifs and physiological splice sites, suggesting potential deleterious effects on ATIP3 function and/or expression.