Cost-effective and sensitive aptasensor with guanine chemiluminescence detection capable of simply quantifying thrombin in human serum was developed using thrombin aptamer (TBA), one of the G-quadruplex DNA aptamers, without expensive nanoparticles and complicated procedures. Guanines of G-quadruplex TBA-conjugated carboxyfluorescein (6-FAM) bound with thrombin do not react with 3,4,5-trimethoxylphenylglyoxal (TMPG) in the presence of tetra-n-propylammonium hydroxide (TPA), whereas guanines of free TBA- and TBA-conjugated 6-FAM immobilized on the surface of graphene oxide rapidly react with TMPG to emit light. Thus, guanine chemiluminescence in 5% human serum with thrombin was lower than that without thrombin when TBA-conjugated 6-FAM was added in two samples and incubated for 20 min. In other words, the brightness of guanine chemiluminescence was quenched due to the formation of G-quadruplex TBA-conjugated 6-FAM bound with thrombin in a sample. High-energy intermediate, capable of emitting dim light by itself, formed from the reaction between guanines of TBA and TMPG in the presence of TPA, transfers energy to 6-FAM to emit bright light based on the principle of chemiluminescence energy transfer (CRET). G-quadruplex TBA aptasensor devised using the rapid interaction between TBA-conjugated 6-FAM and thrombin quantified trace levels of thrombin without complicated procedures. The limit of detection (LOD = background + 3 × standard deviation) of G-quadruplex TBA aptasensor with good linear calibration curve, accuracy, precision, and recovery was as low as 12.3 nM in 5% human serum. Using the technology reported in this research, we expect that various types of G-quadruplex DNA aptasensors capable of specifically sensing a target molecule such as ATP, HIV, ochratoxin, potassium ions, and thrombin can be developed.

Stress-induced phosphoprotein1 (STIP1) is a candidate biomarker in epithelial ovarian cancer (EOC). In this study, we investigated in detail the expression of STIP1, as well as its functions, in EOC. STIP1 expression was assessed by immunohistochemistry (IHC) and the results were compared with clinicopathologic factors, including survival data. The effects of STIP1 gene silencing via small interfering RNA (siRNA) were examined in EOC cells and a xenograft model. The expression of STIP1 protein in EOC was significantly higher than in the other study groups (P < 0.001), and this increase of expression was significantly associated with tumor stage (P = 0.005), tumor grade (P = 0.029), and lymph node metastasis (P = 0.020). In multivariate analysis, overall survival in EOC was significantly shorter in cases with high STIP1 expression (HR = 2.78 [1.01-7.63], P = 0.047). STIP1 silencing in EOC cells resulted in inhibition of cell proliferation and invasion. In addition, in vivo experiments using STIP1 siRNA clearly showed a strong inhibition of tumor growth and a modulation of expression of prosurvival and apoptotic genes, further suggesting that STIP1 silencing can prevent cell proliferation and invasion. In conclusion, increased STIP1 expression is associated with poor survival outcome in EOC, and STIP1 may represent a useful therapeutic target in EOC patients.

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