A functional variant in microRNA-196a2 is associated with susceptibility of colorectal cancer in a Chinese population.

BACKGROUND AND AIMS: MicroRNAs (miRNA) can act as oncogenes or tumor suppressors. Polymorphisms present in pri-, pre- and mature miRNAs can potentially modulate the expression of hundreds of genes, broadly affecting miRNA function. Notably, the rs11614913 SNP in miR-196a2 has been implicated in carcinogenesis, but its association with colorectal cancer (CRC) remains unexplored. We performed a case-control study to investigate the genetic association between this functional SNP and CRC susceptibility and progression. METHODS: We genotyped the rs11614913 SNP in 252 CRC patients and 543 healthy controls by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). In addition, we examined miR-196a expression level in colorectal cancer tissues (n = 50) obtained from the studied CRC patients. RESULTS: Frequency of the CC genotype was higher in CRC patients than controls, implying that the subjects with the CC genotype or C allele containing genotypes (CT and CC) have a higher risk of CRC. However, no significant association between this polymorphism and CRC progression was observed. Expression analysis revealed that rs11614913 CC or carrying at least one C allele was associated with a significantly increased level of mature miR-196a (p = 0.010 or = 0.022). CONCLUSIONS: The present study provides the first evidence that miR-196a2 polymorphism may contribute to CRC susceptibility in a Chinese population through modulating mature miR-196a expression.

Pharmacological inhibition of AKT sensitizes MCF-7 human breast cancer-initiating cells to radiation.

BACKGROUND: Caner-initiating cells (CICs or cancer stem cells) have been shown both experimentally and clinically to be resistant to radiation. The mechanism underlying radioresistance remains unclear. METHODS: In the present study, we screened 51 genes which are potentially important in mediating radioresistance of breast CICs. RESULTS: The expression of AKT1 and AKT2 at protein and mRNA levels was dramatically increased among the screened genes by 8 Gy radiation treatment in MCF-7 mammosphere cells (predominantly CD24(-/low)/CD44(+) CICs), but not in the bulk population of MCF-7 cells (predominantly CD24(+)/CD44(+)). Using apoptosis and clonogenic survival assays, we found pharmacological inhibition of AKT with selective inhibitors of AKT sensitized MCF-7 mammosphere cells, but not MCF-7 monolayer cells to radiation. CONCLUSION: The present findings suggest that treatment with AKT inhibitors prior to ionizing radiation treatment may be a potential benefit to patients with breast cancer, in particular to eradiate breast CICs.

STAT1 promotes radioresistance of CD44(+)/CD24(-/low) cells in breast cancer.

Breast cancer-initiating cells are a relatively radioresistant subpopulation of breast cancer cells. However, the mechanism of this radioresistance is still unclear. This study aimed to investigate the effect of radiation on the levels of signal transducer and activator of transcription 1 (STAT1) in mammospheres of cancer-initiating cells and monolayer cultures of MCF-7 cells. We isolated CD44(+)/CD24(-/low) cancer-initiating cells from MCF-7 cells and propagated them as mammospheres. Next we used realtime quantitative reverse-transcriptase polymerase chain reaction to examine the mRNA level of STAT1 in mammospheres of breast cancer-initiating cells and monolayer cultures of MCF-7 cells. The apoptosis rate and surviving fraction using clonogenic assays was observed after treating the cells with a STAT1 inhibitor. After irradiation, the STAT1 level in the mammospheres was higher than that in the monolayer cultures. STAT1 inhibitor treatment did not cause significant changes in the apoptosis rate and surviving fraction in the MCF-7 monolayer cultures. However, the inhibitor treatment caused significant differences in the apoptosis rate and surviving fraction in mammospheres. Our study provides the first evidence that STAT1 signaling contributes to radioresistance in breast cancer-initiating cells and reveals STAT1 as a promising target to reduce radioresistance and enhance the efficacy of radiotherapy for breast cancer.

[Effects of radiosensitivity and X-ray dose on miR-7 expression in nasopharyngeal carcinoma].

OBJECTIVE: To investigate the effects of radiosensitivity and X-ray dose on the expression of miR-7 in nasopharyngeal carcinoma (NPC) cells. METHODS: Low radiosensitive NPC cells CNE-1 and high radiosensitive NPC cells CNE-2 were exposed to 0, 2 and 8 Gy X-ray. The total RNAs of the cell lines were extracted 10 h after radiation for reverse transcription of miR-7 and 18S rRNA by stem-loop primer and random hexamers, respectively. The non-irradiated CNE-1 cells served as the control sample and the relative quantity of the expression level was calculated after real-time PCR using SyBR green. RESULTS: miR-7 expression differed significantly between CNE-1 and CNE-2 cells (4.49-/+3.62 vs 1.29-/+1.10, F=135.483, P<0.001). The radiation dose also significantly affected the expression of miR-7 in NPC cells (F=39.565, P<0.001). CNE-1 cells with a 2 Gy exposure had the highest expression level of miR-7, while the non-irradiated CNE-1 cells had the lowest expression. CNE-2 cells exposed to 2 Gy X-ray had the lowest expression level of miR-7 and the non-irradiated CNE-2 cells had the highest. CONCLUSION: Radiosensitivity and radiation dose of X-ray have significant effect on the expression of miR-7 in NPC cells, indicating that miR-7 plays an important role in radioresistance of NPC cells to X-ray, and suppressed miR-7 expression may elevate the radiosensitivity of NPC cells.