Splicing y susceptibilidad a cáncer

Splicing and genetic susceptibility to cancer

Room B-8

Head: Eladio A. Velasco (Staff Scientist CSIC) -CV: cvn_20180704_eavs

Lab members:

Beatriz Díez Gómez (Research Technician CSIC)

Eugenia Fraile Bethencourt (Predoctoral Fellowship – Universidad de Valladolid)

Alberto Valenzuela Palomo (BRIDGES)

                                                                               [Miguel Ángel Santos. Agencia Photogenic. Valladolid]

Line of Research

Our interest is focused on Hereditary Breast and Ovarian Cancer (HBOC) syndrome that is characterized by a high genetic heterogeneity and whose predisposing spectrum has not been elucidated yet. So far there have been identified inactivating mutations in at least 25 responsible genes, including BRCA1, BRCA2, TP53 (Li-Fraumeni disease), STK11 (Peutz-Jeghers syndrome), PTEN (Cowden syndrome), CDH1, PALB2, ATM, CHEK2, BARD1, Abraxas, XRCC2, MUTY, BRIP1RAD50, RAD51C, RAD51D and NBS1. Most of them are involved in the DNA repair pathway in order to keep the genomic integrity. The two principal genes, BRCA1 and BRCA2, account for only 16% of familial risk of breast cancer, whereas the rest of the genes participate with less than 10% to the inherited susceptibility to HBOC. Genetic testing of BRCA1 and BRCA2 provides essential information for the clinical management of HBOC families since it allows the detection of asymptomatic mutation carriers and facilitates preventive decision-making. In a recent study (Michailidou et al, 2013), associations between 41 loci and breast cancer were identified by GWAS. However, about 50% of the relative risk to breast cancer would not have been explained yet. It has been estimated that up to 1,000 loci could be involved in the disease.

On the other hand, 15-20% of patients carry a BRCA1/2 DNA variant of unknown clinical significance (UVs) since it is not known whether they are neutral or disease-causing, hampering genetic diagnostic and, therefore, disease prevention. Pathogenic mutations are often predicted on the basis of their impact on protein function but other gene expression steps, such as transcription and splicing, can be disrupted and involved in a disease. Intron removal (splicing) is guided by a large number of splicing factors, ribonucleoproteins and a complex array of sequences including acceptor and donor sites, polypyrimidine tract and branch point, as well as exonic and intronic splicing enhancers and silencers that stimulate or repress exon inclusion into the mature mRNA, respectively. Consequently, all these elements are potential targets of spliceogenic.

Frequency_Frequency

These alterations remain often hidden as suitable assays to characterize them are not available. Reclassification of a DNA variant as deleterious represents an advance in disease prevention since it increases the number of patients and families who may benefit from tailored prevention protocols, contributes to a better knowledge of the genes and mechanisms of pathogenicity of HBOC and will even allow the development of new alternative therapies. Our main line of research aims to investigate the role of mis-splicing of breast cancer genes in HBOC. Hybrid minigenes in splicing reporter plasmid are our main tool of the laboratory. They constitute a useful technology for both, the basic knowledge of splicing regulatory mechanisms and the study of the correlation between mutation, defective splicing and disease. In fact, we have developed and patented a new splicing vector, pSAD (Splicing And Disease; patent #P201231427: “Plasmid pSAD for splicing functional assays”), where there have been constructed a complete set of BRCA1 and BRCA2 minigenes that cover 45 out of the 50 exons of both genes so that we can potentially assay any candidate variant to study its impact on splicing. Actually, we have already analyzed hundreds of variants by minigene assays. The identification of abnormal splicing patterns in BRCA1 and BRCA2 as well as other predisposing genes will contribute to elucidate the genetic susceptibility spectrum of breast/ovarian cancer.

The largest minigene ever reported with BRCA2 exons 19 to 27.

Minigene with BRCA2 exons 14 to 20

We have set up a splicing-minigene facility to study any human gene under the splicing viewpoint. In fact, we have already developed minigenes of MLH1 (Lynch syndrome), SERPINA1 (Severe Alpha-1 Antitrypsin Deficiency), COL1A1 (Osteogenesis Imperfecta) and CHD7 (Intellectual Disability).

OBJECTIVES

                The main objective of our line of research is to clarify the genetic susceptibility landscape of HBOC. As a translational research laboratory we aim that our findings have an impact on patient’s health by improving the molecular diagnostics and prevention of this disease.

The specific goals can be divided in two main topics:

  1. Correlation between gene expression alterations of the two principal responsible genes and BRCA1 y BRCA2, and hereditary breast cancer in two steps:
    1. Transcription: Analysis of BRCA promoters, map of regulatory elements, and identification of germline regulatory mutations in HBOC patients.
    2. Pre-mRNA processing (splicing):
      • Study of the correlation between mutations, aberrant splicing patterns of breast cancer genes and HBOC.
      • Regulation of large exons of BRCA1 and BRCA2 and implications in the disease
      • Study of the regulation of exons with non-canonical GC donor site of DNA repair genes such as BRCA2, FANCA and PALB2.
  2. Genetic epidemiology of HBOC:
    1. Distribution of mutations in predisposing genes in the Spanish population (Castilla y León).
    2. Characterization of prevalent founder mutations in Castilla y León. Identification of the common ancestor haplotype.
    3. Identification of new HBOC genes in high risk BRCAX patients.

Financial Support

  • Instituto de Salud Carlos III. Ministerio de Economía y Competitividad. Proyecto de Investigación en Salud, Referencia:  PI17/00227 (2018-2020). "Aberrant splicing in hereditary breast cancer: Functional analysis of  susceptibility genes by hybrid minigenes" . Total amount: 99.220 €.
  • European Commision, Project ID 634935 (2015-2020): "Breast Cancer Risk after Diagnostic Gene Sequencing (BRIDGES)".
  • Instituto de Salud Carlos III. Ministerio de Economía y Competitividad. Proyecto de Investigación en Salud, Project ID PI13/01749 (2014-2016): "Alterations of transcription and splicing of the BRCA1 and BRCA2 genes and genetic susceptibility to Breast and Ovarian Cancer".  Total amount: 74.838,5 €.
  • Consejería de Educación, Junta de Castilla y León (Project ID CSI090U14): "Impact of transcriptional and splicing regulatory mutations of tumor-suppressor genes on molecular diagnostics and prevention of breast cancer"

Relevant publications

  • Montalban G, Fraile-Bethencourt E, López-Perolio I, Pérez-Segura P, Infante M, Durán M, Alonso-Cerezo MC, López-Fernández A, Diez O, de la Hoya M, Velasco EA, Gutiérrez-Enríquez S (2018). Characterization of spliceogenic variants located in regions linked to high levels of alternative splicing: BRCA2 c.7976+5G > T as a case study. Human Mutation 2018 Jul 3. doi: 10.1002/humu.23583.  Pubmed
  • Fraile-Bethencourt E, Valenzuela-Palomo A, Díez-Gómez B, Acedo A, Velasco EA (2018). Identification of 8 spliceogenic variants in BRCA2 exon 16 by minigene assays. Frontiers in Genetics 2018, 9: 188. DOI: 10.3389/fgene.2018.00188. https://www.frontiersin.org/articles/10.3389/fgene.2018.00188/full
  • Fraile-Bethencourt E, Valenzuela-Palomo A, Díez-Gómez B, Infante M, Durán M, Marcos G, Lastra E, Gómez-Barrero S, Velasco EA (2018). Genetic dissection of the BRCA2 promoter and transcriptional impact of DNA variants. Breast Cancer Research and Treatment 2018. DOI: 10.1007/s10549-018-4826-7. https://www.ncbi.nlm.nih.gov/pubmed/29766361
  • Fraile-Bethencourt E, Díez-Gómez B, Velásquez-Zapata V, Acedo A, Sanz DJ, Velasco EA (2017). Functional classification of DNA variants by hybrid minigenes: Identification of 30 spliceogenic variants of BRCA2 exons 17 and 18. PLoS Genetics 13(3):e1006691. doi: 10.1371/journal.pgen.1006691. http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1006691
  • Acedo A, Hernández-Moro C, Curiel-García Á, Díez-Gómez B, Velasco EA. (2015). Functional Classification of BRCA2 DNA Variants by Splicing Assays in a Large Minigene with 9 Exons. Human Mutation 36: 210–221.
  • Lara B, Martínez MT, Blanco I, Hernández-Moro C, Velasco EA, Ferrarotti I, Rodriguez-Frias F, Perez L, Vazquez I, Alonso J, Posada M, Martínez-Delgado B. 2014. Severe alpha-1 antitrypsin deficiency in composite heterozygotes inheriting a new splicing mutation QOMadrid. Respiratory Research 15: 125.
  • Ruiz de Garibay G, Acedo A, García-Casado Z, Gutiérrez-Enríquez S, Tosar A, Romero A, Garre P, Llort G, Thomassen M, Díez O, Pérez-Segura P, Eduardo Díaz-Rubio E, Velasco EA, Caldés T, de la Hoya M. (2014). Capillary Electrophoresis Analysis of Conventional Splicing Assays: IARC Analytical and Clinical Classification of 31 BRCA2 Genetic Variants. Human Mutation 35: 53-57.
  • Infante M, Duran M, Acedo A, Sánchez-Tapia EM, Díez-Gómez B, Barroso A, Garcia-Gonzalez M, Feliubadalo L, Lasa A, de la Hoya M; Esteban-Cardeñosa E; Díez O; Martínez-Bouzas C; Godino J; Teulé A; Osorio A; Lastra E; Gonzalez-Sarmiento R, Miner C, Velasco EA (2013). The highly prevalent BRCA2 mutation c.2808_2811del (3036delACAA) is located in a mutational hotspot and has multiple origins. Carcinogenesis 34: 2505-2511
  • Blanco A, de la HM, Osorio A, Diez O, Miramar MD, Infante M, Martinez-Bouzas C, Torres A, Lasa A, Llort G, Brunet J, Grana B, Perez SP, Garcia MJ, Gutierrez-Enriquez S, Carracedo A, Tejada MI, Velasco EA, Calvo MT, Balmana J, Benitez J, Caldes T, Vega A (2013) Analysis of PALB2 Gene in BRCA1/BRCA2 Negative Spanish Hereditary Breast/Ovarian Cancer Families with Pancreatic Cancer Cases. PLoS One 8:e67538.
  • Perez-Cabornero L, Infante M, Velasco E, Lastra E, Miner C, Duran M (2013) Evaluating the Effect of Unclassified Variants Identified in MMR Genes Using Phenotypic Features, Bioinformatics Prediction, and RNA Assays. J Mol Diagn 15:380-390
  • Acedo A, Sanz DJ, Duran M, Infante M, Perez-Cabornero L, Miner C, Velasco EA (2012) Comprehensive splicing functional analysis of DNA variants of the BRCA2 gene by hybrid minigenes. Breast Cancer Res 14:R87
  • Perez-Cabornero L, Infante M, Velasco E, Lastra E, Acedo A, Miner C, Duran M (2011) Frequency of rearrangements in Lynch syndrome cases associated with MSH2: characterization of a new deletion involving both EPCAM and the 5' part of MSH2. Cancer Prev Res (Phila) 4:1556-1562
  • Sanz DJ, Acedo A, Infante M, Duran M, Perez-Cabornero L, Esteban-Cardenosa E, Lastra E, Pagani F, Miner C, Velasco EA (2010) A high proportion of DNA variants of BRCA1 and BRCA2 is associated with aberrant splicing in breast/ovarian cancer patients. Clin Cancer Res 16:1957-1967
  • Infante M, Duran M, Lasa A, Acedo A, de la HM, Esteban-Cardenosa E, Sanz DJ, Perez-Cabornero L, Lastra E, Miner C, Velasco EA (2010) Two founder BRCA2 mutations predispose to breast cancer in young women. Breast Cancer Res Treat 122:567-571
  • Infante M, Duran M, Acedo A, Perez-Cabornero L, Sanz DJ, Garcia-Gonzalez M, Beristain E, Esteban-Cardenosa E, de la HM, Teule A, Vega A, Tejada MI, Lastra E, Miner C, Velasco EA (2010) BRCA1 5272-1G>A and BRCA2 5374delTATG are founder mutations of high relevance for genetic counselling in breast/ovarian cancer families of Spanish origin. Clin Genet 77:60-69
  • Perez-Cabornero L, Velasco E, Infante M, Sanz D, Lastra E, Hernandez L, Miner C, Duran M (2009) A new strategy to screen MMR genes in Lynch Syndrome: HA-CAE, MLPA and RT-PCR. Eur J Cancer 45:1485-1493.
  • Milne RL, Osorio A, Cajal TR, Vega A, Llort G, de la HM, Diez O, Alonso MC, Lazaro C, Blanco I, Sanchez-de-Abajo A, Caldes T, Blanco A, Grana B, Duran M, Velasco E, et al. (2008) The average cumulative risks of breast and ovarian cancer for carriers of mutations in BRCA1 and BRCA2 attending genetic counseling units in Spain. Clin Cancer Res 14:2861-2869
  • Velasco E, Infante M, Duran M, Perez-Cabornero L, Sanz DJ, Esteban-Cardenosa E, Miner C (2007) Heteroduplex analysis by capillary array electrophoresis for rapid mutation detection in large multiexon genes. Nat Protoc 2:237-246
 
IBGM

Instituto De Biología Y Genética Molecular.
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