APM2 is a novel mediator of cisplatin resistance in a variety of cancer cell types regardless of p53 or MMR status.

Cisplatin is one of the most widely used chemotherapeutics in the world today. Unfortunately, chemoresistance often develops hindering the effectiveness of the drug. Mismatch-repair (MMR) and p53 have previously been shown to be important determinants of cisplatin resistance and can contribute to cisplatin resistance clinically. Here, we have used cDNA microarray to identify several genes as up or downregulated in a previously described, cisplatin resistant, clone of the HCT116 cell line (HCT116-K). On follow-up, one gene, APM2, was found to promote cisplatin resistance when overexpressed in sensitive HCT116 clones. Furthermore, silencing APM2 in a panel of cell lines encompassing all combinations of p53 status and MMR proficiency (HCT116-K, HCT116, SW620, MCF7, PC-3 and OV2008) resulted in sensitization regardless of these 2 factors. In addition, silencing APM2 stably using shRNA also resulted in the sensitization of cells to cisplatin. More importantly, cisplatin inhibited the growth of APM2 silenced tumor xenografts (HCT116-K or OV2008 cells) significantly better than it inhibited the growth of xenografts carrying nontargeting control shRNAs. These findings represent a novel strategy that could be exploited to overcome cisplatin resistance in patients regardless of p53 status or ability to perform MMR.

Transcriptomic profiling of radiation-resistant or -sensitive human colorectal cancer cells: acute effects of a single X-radiation dose.

We previously isolated several clones that were closely-related genetically from a human colorectal tumor (HCT116) cell line. These clones displayed significantly different X-radiation response phenotypes. In this paper, we investigated how a single dose of X-radiation modulated the transcriptomic profiles of either the radiation-resistant (HCT116Clone2_XRR) or the radiation-sensitive (HCT116CloneK_XRS) clone when each was compared to a reference clone, HCT116Clone10_control. The latter represented a control clone that displayed a similar X-radiation response as the parental HCT116 cells. Pooled RNAs were obtained from HCT116Clone2_XRR, HCT116CloneK_XRS or HCT116Clone10_control cells either before or at 10 min, 6 or 24 h after treatment with 4-Gy X-radiation. Transcriptomic profiles were assessed by cDNA microarrays. At least three independent experiments were carried out for each time point and statistical analysis was performed by paired t-test (p<0.05). From 19,200 genes/ESTs examined, we identified only 120 genes/ESTs that were differentially expressed at any one of these four time points. Interestingly, different patterns of gene modulation were observed between the radiation-sensitive and radiation-resistant clones. However, the fold changes of gene modulation were generally small (2-3 fold). Surprisingly, only 12.7% of 79 genes involved in DNA damage sensor/repair and cell cycle and between 2.6 and 9.2% of 76 genes involved in apoptosis, were significantly modulated in these early time points following irradiation. By comparison, up to 10% of 40 known housekeeping genes were differentially expressed. Thus in our experimental model, we were able to detect the up-regulation or down-regulation of mostly novel genes and/or pathways in the acute period (up to 24 h) following a single dose of 4-Gy X-radiation.

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

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 (XRRA1) (GenBank BK000541). Here, we present the first report on the molecular cloning, genomic characterization and over-expression of the XRRA1 gene. RESULTS: We found that XRRA1 was expressed predominantly in testis of both human and macaque. cDNA microarray analysis showed three-fold higher expression of XRRA1 in macaque testis relative to other tissues. We further cloned the macaque XRRA1 cDNA (GenBank AB072776) and a human XRRA1 splice variant from HCT116Clone2_XRR (GenBank AY163836). In silico analysis revealed the full-length human XRRA1, mouse, rat and bovine Xrra1 cDNAs. The XRRA1 gene comprises 11 exons and spans 64 kb on chromosome 11q13.3. Human and macaque cDNAs share 96% homology. Human XRRA1 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 XRRA1 after XR in HCT116 clones manifesting significantly different XR responses. Further, we found that XRRA1 was expressed in most tumor cell types. Surprisingly, mouse Xrra1 was detected in mouse embryonic stem cells R1. CONCLUSIONS: Both XRRA1 cDNA and protein are highly conserved among mammals, suggesting that XRRA1 may have similar functions. Our results also suggest that the genetic modulation of XRRA1 may affect the XR responses of HCT116 clones and that XRRA1 may have a role in the response of human tumor and normal cells to XR. XRRA1 might be correlated with cancer development and might also be an early expressed gene.