title: 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.
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.
authors.affiliation: Department of Oral Pathology, College of Dentistry, Howard University, Washington DC, USA.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Zhejiang Cancer Hospital, Zhejiang Cancer Research Institute, Hangzhou, Zhejiang, China.
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Ling
authors.affiliation: Department of Oral Pathology, College of Dentistry, Howard University, Washington DC, USA.
authors.forename: Yubin
authors.initials: Y
authors.lastname: Hao
authors.affiliation: Department of Oral Pathology, College of Dentistry, Howard University, Washington DC, USA.
authors.forename: Xiaowu
authors.initials: X
authors.lastname: Pang
authors.affiliation: Sanford Burnham Prebys Medical Discovery Institute, Orlando, Florida, USA.
authors.forename: Xianlin
authors.initials: X
authors.lastname: Han
authors.affiliation: Department of Otolaryngology, Head and Neck Surgery, Johns Hopkins University, San Diego, California, USA.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Califano
authors.affiliation: Department of Oral Pathology, College of Dentistry, Howard University, Washington DC, USA.|Department of Radiology, College of Medicine, Howard University, Washington DC, USA.
authors.forename: Liang
authors.initials: L
authors.lastname: Shan
authors.affiliation: Department of Oral Pathology, College of Dentistry, Howard University, Washington DC, USA.|Cancer Center, Howard University, Washington DC, USA.
authors.forename: Xinbin
authors.initials: X
authors.lastname: Gu
mesh_terms: D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D016147:Genes, Tumor Suppressor; D006258:Head and Neck Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D064593:Heterografts; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D035683:MicroRNAs / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D000077195:Squamous Cell Carcinoma of Head and Neck; D014162:Transfection; D000099157:Sphingosine Kinase
chemical_list: D035683:MicroRNAs; D017853:Phosphotransferases (Alcohol Group Acceptor); D000099157:Sphingosine Kinase; C509207:MIRN124 microRNA, human
keywords: BcL-2 family; ceramide; head and neck cancer; miR-124; sphingosine kinase 1