Genetic, functional, and histopathological evaluation of two C-terminal BRCA1 missense variants

Lovelock, P. K., Healey, S., Au, W., Sum, E. Y. M., Tesoriero, A., Wong, E. M., Hinson, S., Brinkworth, R., Bekessy, A., Diez, O., Izatt, L., Solomon, E., Jenkins, M., Renard, H., Hopper, J., Waring, P., Tavtigian, S. V., Goldgar, D., Lindeman, G. J., Visvader, J. E., Couch, F. J., Henderson, B. R., Southey, M., Chenevix-Trench, G., Spurdle, A. B., & Brown, M. A. (2006) Genetic, functional, and histopathological evaluation of two C-terminal BRCA1 missense variants. Journal of Medical Genetics, 43(1), pp. 74-83.

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Abstract

Background: The vast majority of BRCA1 missense sequence variants remain uncharacterised for their possible effect on protein expression and function, and therefore are unclassified in terms of their pathogenicity. BRCA1 plays diverse cellular roles and it is unlikely that any single functional assay will accurately reflect the total cellular implications of missense mutations in this gene.

Objective: To elucidate the effect of two BRCA1 variants, 5236G>C (G1706A) and 5242C>A (A1708E) on BRCA1 function, and to survey the relative usefulness of several assays to direct the characterisation of other unclassified variants in BRCA genes.

Methods and Results: Data from a range of bioinformatic, genetic, and histopathological analyses, and in vitro functional assays indicated that the 1708E variant was associated with the disruption of different cellular functions of BRCA1. In transient transfection experiments in T47D and 293T cells, the 1708E product was mislocalised to the cytoplasm and induced centrosome amplification in 293T cells. The 1708E variant also failed to transactivate transcription of reporter constructs in mammalian transcriptional transactivation assays. In contrast, the 1706A variant displayed a phenotype comparable to wildtype BRCA1 in these assays. Consistent with functional data, tumours from 1708E carriers showed typical BRCA1 pathology, while tumour material from 1706A carriers displayed few histopathological features associated with BRCA1 related tumours.

Conclusions: A comprehensive range of genetic, bioinformatic, and functional analyses have been combined for the characterisation of BRCA1 unclassified sequence variants. Consistent with the functional analyses, the combined odds of causality calculated for the 1706A variant after multifactorial likelihood analysis (1:142) indicates a definitive classification of this variant as "benign". In contrast, functional assays of the 1708E variant indicate that it is pathogenic, possibly through subcellular mislocalisation. However, the combined odds of 262:1 in favour of causality of this variant does not meet the minimal ratio of 1000:1 for classification as pathogenic, and A1708E remains formally designated as unclassified. Our findings highlight the importance of comprehensive genetic information, together with detailed functional analysis for the definitive categorisation of unclassified sequence variants. This combination of analyses may have direct application to the characterisation of other unclassified variants in BRCA1 and BRCA2.

Impact and interest:

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ID Code: 89479
Item Type: Journal Article
Refereed: Yes
Keywords: adult, aged, article, bioinformatics, carboxy terminal sequence, centrosome, clinical article, controlled study, female, gene amplification, gene location, gene sequence, genetic analysis, genetic transfection, genetic variability, histopathology, human, human tissue, missense mutation, oncogene, pathogenicity, priority journal, transcription regulation, Australia, BRCA1 Protein, Breast Neoplasms, Genes, Reporter, Humans, Loss of Heterozygosity, Middle Aged, Models, Molecular, Mutation, Missense, Protein Processing, Post-Translational, Protein Transport, RNA Splicing, RNA Stability, Trans-Activation (Genetics), Transcription, Genetic, Transcriptional Activation, Mammalia, unclassified organisms
DOI: 10.1136/jmg.2005.033258
ISSN: 0022-2593
Divisions: Current > QUT Faculties and Divisions > Faculty of Health
Current > Institutes > Institute of Health and Biomedical Innovation
Copyright Owner: Copyright 2006 The Authors
Deposited On: 25 Oct 2015 23:54
Last Modified: 09 Jun 2016 02:07

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