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Oncotarget. 2017 Apr 11;8(15):25005-25020. doi: 10.18632/oncotarget.15334.

MiR-124 acts as a tumor suppressor by inhibiting the expression of sphingosine kinase 1 and its downstream signaling in head and neck squamous cell carcinoma.

Author information

1
Department of Oral Pathology, College of Dentistry, Howard University, Washington DC, USA.
2
Zhejiang Cancer Hospital, Zhejiang Cancer Research Institute, Hangzhou, Zhejiang, China.
3
Sanford Burnham Prebys Medical Discovery Institute, Orlando, Florida, USA.
4
Department of Otolaryngology, Head and Neck Surgery, Johns Hopkins University, San Diego, California, USA.
5
Department of Radiology, College of Medicine, Howard University, Washington DC, USA.
6
Cancer Center, Howard University, Washington DC, USA.

Abstract

By analyzing the expression profile of microRNAs in head and neck squamous cell carcinomas (HNSCC), we found that the expression level of miR-124 was 4.59-fold lower in tumors than in normal tissues. To understand its functions, we generated a miR-124-expressing subline (JHU-22miR124) and a mock vector-transfected subline (JHU-22vec) by transfecting the mimic of miR-124 into JHU-22 cancer cells. Restored expression of miR-124 in JHU-22miR124 cells led to reduced cell proliferation, delayed colony formation, and decreased tumor growth, indicating a tumor-suppressive effect of miR-124. Subsequent target search revealed that the 3'-UTR of SphK1 mRNA carries a complementary site for the seed region of miR-124. SphK1 was also detected to be overexpressed in HNSCC cell lines, but down-expressed in JHU-22miR124 cells and tumor xenografts. These results suggest that SphK1 is a target of miR-124. To confirm this finding, we constructed a 3'-UTR-Luc-SphK1 vector and a binding site-mutated luciferase reporter vector. Co-transfection of 3'-UTR-Luc-SphK1 with miR-124 expression vector exhibited a 9-fold decrease in luciferase activity compared with mutated vector, suggesting that miR-124 inhibits SphK1 activity directly. Further studies on downstream signaling demonstrated accumulation of ceramide, increased expression of the pro-apoptotic Bax, BAD and PARP, decreased expression of the anti-apoptotic Bcl-2 and Bcl-xL, and enhanced expression of cytochrome c and caspase proteins in JHU-22miR124 compared with JHU-22vec cells and tumor xenografts. We conclude that miR-124 acts as a tumor suppressor in HNSCC by directly inhibiting SphK1 activity and its downstream signals.

KEYWORDS:

BcL-2 family; ceramide; head and neck cancer; miR-124; sphingosine kinase 1

PMID:
28212569
PMCID:
PMC5421905
DOI:
10.18632/oncotarget.15334
[Indexed for MEDLINE]
Free PMC Article

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