The 30 kb deletion in the APOBEC3 cluster decreases APOBEC3A and APOBEC3B expression and creates a transcriptionally active hybrid gene but does not associate with breast cancer in the European population
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Katarzyna Klonowska1, Wojciech Kluzniak2, Bogna Rusak2, Anna Jakubowska2, Magdalena Ratajska3, Natalia Krawczynska3, Danuta Vasilevska4, Karol Czubak1, Marzena Wojciechowska1, Cezary Cybulski2, Jan Lubinski2 and Piotr Kozlowski1
1Department of Molecular Genetics, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland
2Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University, Szczecin, Poland
3Department of Biology and Medical Genetics, Medical University of Gdansk, Gdansk, Poland
4Department of Gynecology, Centre of Obstetrics and Gynecology, Vilnius University Hospital Santariskiu Klinikos, Vilnius, Lithuania
Piotr Kozlowski, email: [email protected], [email protected]
Keywords: APOBEC3B, hereditary breast cancer, MLPA, copy number variation (CNV), meta-analysis
Received: April 25, 2017 Accepted: June 10, 2017 Published: July 19, 2017
APOBEC3B, in addition to other members of the APOBEC3 gene family, has recently been intensively studied due to its identification as a gene whose activation in cancer is responsible for a specific pattern of massively occurring somatic mutations. It was recently shown that a common large deletion in the APOBEC3 cluster (the APOBEC3B deletion) may increase the risk of breast cancer. However, conflicting evidence regarding this association was also reported. In the first step of our study, using different approaches, including an in-house designed multiplex ligation-dependent probe amplification assay, we analyzed the structure of the deletion and showed that although the breakpoints are located in highly homologous regions, which may generate recurrent occurrence of similar but not identical deletions, there is no sign of deletion heterogeneity. This knowledge allowed us to distinguish transcripts of all affected genes, including the highly homologous canonical APOBEC3A and APOBEC3B, and the hybrid APOBEC3A/APOBEC3B gene. We unambiguously confirmed the presence of the hybrid transcript and showed that the APOBEC3B deletion negatively correlates with APOBEC3A and APOBEC3B expression and positively correlates with APOBEC3A/APOBEC3B expression, whose mRNA level is >10-fold and >1500-fold lower than the level of APOBEC3A and APOBEC3B, respectively. In the next step, we performed a large-scale association study in three different cohorts (2972 cases and 3682 controls) and showed no association of the deletion with breast cancer, familial breast cancer or ovarian cancer. Further, we conducted a meta-analysis that confirmed the lack of the association of the deletion with breast cancer in non-Asian populations.
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