Abstract
BackgroundFusion proteins have unique oncogenic properties and their identification can be useful either as diagnostic or therapeutic targets. Next generation sequencing data have previously shown a fusion gene formed between Rad51C and ATXN7 genes in the MCF7 breast cancer cell line. However, the existence of this fusion gene in colorectal patient tumor tissues is largely still unknown.MethodsWe evaluated for the presence of Rad51C-ATXN7 fusion gene in colorectal tumors and cells by RT-PCR, PCR, Topo TA cloning, Real time PCR, immunoprecipitation and immunoblotting techniques.ResultsWe identified two forms of fusion mRNAs between Rad51C and ATXN7 in the colorectal tumors, including a Variant 1 (fusion transcript between Rad51C exons 1–7 and ATXN7 exons 6–13), and a Variant 2 (between Rad51C exons 1–6 and ATXN7 exons 6–13). In silico analysis showed that the Variant 1 produces a truncated protein, whereas the Variant 2 was predicted to produce a fusion protein with molecular weight of 110 KDa. Immunoprecipitation and Western blot analysis further showed a 110 KDa protein in colorectal tumors. 5-Azacytidine treatment of LS-174 T cells caused a 3.51-fold increase in expression of the fusion gene (Variant 2) as compared to no treatment controls evaluated by real time PCR.ConclusionIn conclusion we found a fusion gene between DNA repair gene Rad51C and neuro-cerebral ataxia Ataxin-7 gene in colorectal tumors. The in-frame fusion transcript of Variant 2 results in a fusion protein with molecular weight of 110 KDa. In addition, we found that expression of fusion gene is associated with functional impairment of Fanconi Anemia (FA) DNA repair pathway in colorectal tumors. The expression of Rad51C-ATXN7 in tumors warrants further investigation, as it suggests the potential of the fusion gene in treatment and predictive value in colorectal cancers.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-016-0527-1) contains supplementary material, which is available to authorized users.
Highlights
Fusion proteins have unique oncogenic properties and their identification can be useful either as diagnostic or therapeutic targets
RTPCR specific primers were designed with forward primer spanning exon-5 of Rad51C and reverse primer located in exon-8 of ATXN7
The cDNA containing exons 5–7 of Rad51C and exons 6-8 of ATXN7 was amplified by one step RT-PCR using primers (LF-F and LF-R; Additional file 1: Table S1) that produced either two amplicons with size of 376 bp, and 316 bp as shown in Fig. 1a, or one product with size of 376 bp (Fig. 1b)
Summary
Fusion proteins have unique oncogenic properties and their identification can be useful either as diagnostic or therapeutic targets. The cancer genome is characterized by mutations, deletions, amplification, chromosomal translocations and microsatellite instability. Notable examples are TMPRSS2-ERG in prostate cancer, and EML4-ALK fusion in non-small-cell lung tumors [1,2,3]. At the molecular level some fusion genes are formed by DNA alterations as seen with ALK-C2orf fusion in colorectal cancers [6]. Of therapeutic value is that inhibition of one of the genes could in some cases be enough to affect the overall activity of the fusion gene, as has been observed with oncogenic KIF5B-RET, Kalvala et al Molecular Cancer (2016) 15:47 where the cells expressing the fusion gene are sensitive to multi-kinase inhibitors which inhibit RET [7,8,9]
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