RNA helicase DHX9 may be a therapeutic target in lung cancer and inhibited by enoxacin

Abstract

RNA helicase DHX9 is a member of human RNA enzymes. Previous studies have reported that DHX9 is highly expressed in various types of malignant tumor. However, its role in the progression of lung cancer remains to be fully clarified. The present study aims to investigate the oncogenic role of DHX9 in serum, tissues and lung cancer cell lines in vitro. We used RNA interference to downregulate DHX9 expression in A549 cells using a small interfering RNA lentiviral vector. Subsequently, enoxacin was used to inhibit cell proliferation, and this effect was detected using MTT. The results showed that DHX9 was overexpressed in the serum and tissues of lung cancer, especially in small cell lung cancer. Though enoxacin suppressed the proliferation of NSCLC cells, the inhibition effect was diminished when DHX9 was knocked down. In conclusion, the present study provided evidence suggesting that DHX9 was overexpressed in lung cancer and may contribute to the growth of lung cancer, and enoxacin may inhibit the proliferation based on DHX9. Thus DHX9 may be used as a diagnostic marker and a potential therapeutic target for the treatment of NSCLC.

Keywords: DHX9; enoxacin; lung cancer.

Figure 1

Serum DHX9 level in patients of lung cancer and controls. A. The serum level of DHX9 was highly expressed in tumor patients especially in SCLC patients, *P<0.01. B. ROC analysis for serum DHX9 for distinguishing lung cancer patients from benign lung diseases. C. Stage III or IV patients had significantly higher DHX9 than those with I or II stages (P<0.05). And patients with higher smoking index had higher DHX9 level (P<0.05), *P<0.05.

Figure 2

DHX9 level in tissues and cell lines. A. The level of DHX9 was higher in small cell lung cancer cell line H446 than NCSCL cell lines A549 and PC9. B. DHX9 was highly expressed in tumor tissues than compared normal tissues, and there were two bands in tumor tissues. C. DHX9 displayed two isoforms: one isoform of Mr~140,000 in the normal tissues, and one of Mr~128,000 in the tumor tissue or tumor cell lines. In addition, the two bands were similar to those in the tumor tissues when we mixed the lysates of normal tissue and H446 cell lines. D. Immunohistochemistry showed that DHX9 was highly expressed in tumor tissues than in normal controls.

Figure 3

Knockdown of DHX9 in NSCLC cell lines A549. A. Western Blot showed that DHX9 was knocked down by shRNA. B. qPCR showed that the mRNA of DHX9 was knocked down by shRNA. *P<0.01. ShRNA1 was the strongest blocker. C. DHX9 was knocked down by shRNA1.

Figure 4

DHX9 may be inhibited by enoxacin. A. DHX9 was cut down by enoxacin in a dose-response relationship. B, C. MTT showed that enoxacin significantly inhibited the proliferation of A549 cells. D. The IC50 of enoxacin in DHX9-shRNA-A549 was higher than A549 or NC-shRNA-A549 (IC50: 49.04 ug/ml vs 25.52 ug/ml vs 28.66 ug/ml, P<0.05), *P<0.05.