eP330 - DHX15 as a Tumor Suppressor in Colon Cancer

Purpose/Background: We used a screening method to identify genes involved in transforming neural stem cells into glioma-initiating cells and found DEAH (Asp-Glu-Ala-His) box helicase 15 (DHX15) as a candidate tumor suppressor gene in glioma. We have also conducted preliminary research on mutations in this gene with the theme of glioma.DHX15 is an outstanding member of the DEAD-box RNA helicase subfamily in the DExD/H helicase family. It plays an important role in RNA splicing and the innate immune system against viral infections. We previously revealed that DHX15 acts as a tumor suppressor in glioma. In glioma, DHX15 is an antitumor gene, and its Ia–Ib and III–IV motifs, but not its ATPase activity, play important roles in its growth-inhibitory function (Ito S, Sakamoto K, et al. Br J Cancer. 2017).DHX15 is involved in tumorigenesis, both as a tumor promoting factor in acute lymphoblastic leukemia , lung cancer and prostate cancer; and as a tumor suppressor in glioma, hepatocellular carcinoma and gastric cancer. mTORC1 is involved in DHX15-mediated regulation of autophagy and that DHX15 inhibits proliferation of hepatocellular carcinoma (HCC) cells by suppressing autophagy (Zhao M, Ying L, Wang R, et al. Front Med. 2020). We then aimed to elucidate the role of DHX15 gene mutations in CRC onset and progression. Although its role in CRC remains unknown, DHX15 expression level may positively correlate with patient’s prognosis (Fan L, Guo X, Zhang J, et al. Rev Esp Enferm Dig. 2023), suggesting that DHX15 also acts as a tumor suppressor gene in colon cancer. In this study, we aimed to examine the role of DHX15 in colon cancer.Methods/Interventions: GFP-positive cells were observed through Incucyte live-cell imaging analysis for 2 days. DHX15 expression was examined by immunohistochemical (IHC) staining using the tumor tissue and the adjacent normal-appearing tissue. We also investigated the involvement of NF-κB, Wnt-β catenin signaling, and autophagy by means of a luciferase assay and IHC.Results/Outcomes: HCT116, SW480, Caco2, and DLD1 colon cancer cell lines were cotransfected with DHX15- and GFP-expressing plasmids. DHX15 significantly reduced the cell number of all the identified colon cancer cell lines (HCT116: p = 0.0007, SW480: p = 0.02, Caco2: p = 0.001, DLD1: p = 0.04). DHX15 was also expressed in human colon cancer tissues. Its level (mainly distributed in the cytoplasm) was higher in tumor tissues than in the adjacent normal-appearing tissues. IHC showed that DHX15 was mainly located within the nucleus of transfected HCT116, SW480, Caco2, and DLD1 cells. The number of AC3-positive apoptotic cells was comparable between the control and DHX15-transfected cells. Notably, Ki67-positive proliferating cells were significantly reduced in HCT116, SW480, and DLD1 after transfection (HCT116: p = 0.021, SW480: p = 0.039, Caco2: p = 0.09, DLD1: p = 0.002). These findings indicate that DHX15 suppressed the growth of colon cancer cell lines by reducing the proliferation. DHX15 overexpression significantly exhibited less LC3 puncta in DLD1.(p=0.04)Conclusion/

Discussion: DHX15 may act as a tumor suppressor gene in colon cancer. The existence of a relationship between DHX15 and autophagy inhibition may be related to the anti-tumor effect of DHX15. Further research is needed to elucidate the molecular mechanism of DHX15 on CRC.