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Abstract Background As part of our investigation into the genetic basis of tumor cell radioresponse, we have isolated several clones with a wide range of responses to X-radiation (XR) from an unirradiated human colorectal tumor cell line, HCT116. Using human cDNA microarrays, we recently identified a novel gene that was down-regulated by two-fold in an XR-resistant cell clone, HCT116Clone2_XRR. We have named this gene as X-ray radiation resistance associated 1 (<it>XRRA1</it>) (GenBank BK000541). Here, we present the first report on the molecular cloning, genomic characterization and over-expression of the <it>XRRA1 </it>gene. Results We found that <it>XRRA1 </it>was expressed predominantly in testis of both human and macaque. cDNA microarray analysis showed three-fold higher expression of <it>XRRA1 </it>in macaque testis relative to other tissues. We further cloned the macaque <it>XRRA1 </it>cDNA (GenBank AB072776) and a human <it>XRRA1 </it>splice variant from HCT116Clone2_XRR (GenBank AY163836). <it>In silico </it>analysis revealed the full-length human <it>XRRA1</it>, mouse, rat and bovine <it>Xrra1 </it>cDNAs. The <it>XRRA1 </it>gene comprises 11 exons and spans 64 kb on chromosome 11q13.3. Human and macaque cDNAs share 96% homology. Human <it>XRRA1 </it>cDNA is 1987 nt long and encodes a protein of 559 aa. XRRA1 protein is highly conserved in human, macaque, mouse, rat, pig, and bovine. GFP-XRRA1 fusion protein was detected in both the nucleus and cytoplasm of HCT116 clones and COS-7 cells. Interestingly, we found evidence that COS-7 cells which over-expressed XRRA1 lacked Ku86 (Ku80, XRCC5), a non-homologous end joining (NHEJ) DNA repair molecule, in the nucleus. RT-PCR analysis showed differential expression of <it>XRRA1 </it>after XR in HCT116 clones manifesting significantly different XR responses. Further, we found that <it>XRRA1 </it>was expressed in most tumor cell types. Surprisingly, mouse <it>Xrra1 </it>was detected in mouse embryonic stem cells R1. Conclusions Both <it>XRRA1 </it>cDNA and protein are highly conserved among mammals, suggesting that <it>XRRA1 </it>may have similar functions. Our results also suggest that the genetic modulation of <it>XRRA1 </it>may affect the XR responses of HCT116 clones and that <it>XRRA1 </it>may have a role in the response of human tumor and normal cells to XR. <it>XRRA1 </it>might be correlated with cancer development and might also be an early expressed gene.</p

bmc genomics

Molecular cloning, genomic characterization and over-expression of a novel gene, XRRA1, identified from human colorectal cancer cell HCT116Clone2_XRR and macaque testis