MicroRNA in Saliva and Serum is a Novel Biomarker for Oral Squamous Cell Carcinoma Patients

Kazuki Iwamoto , Department of Oral and Maxillofacial Surgery, Ehime University Graduate School of Medicine, Ehime, Japan
Koh-ichi Nakashiro , Department of Oral and Maxillofacial Surgery, Ehime University Graduate School of Medicine, Ehime, Japan
Norihiko Tokuzen , Department of Oral and Maxillofacial Surgery, Ehime University Graduate School of Medicine, Ehime, Japan
Hiroshi Tanaka , Department of Oral and Maxillofacial Surgery, Ehime University Graduate School of Medicine, Ehime, Japan
Hiroyuki Hamakawa , Department of Oral and Maxillofacial Surgery, Ehime University Graduate School of Medicine, Ehime, Japan
In oral squamous cell carcinoma (OSCC), there is no useful diagnostic and predictive biomarker. MicroRNAs (miRNAs) are small non-coding double-stranded RNA with size of approximately 22 nucleotides, and those inhibit protein translation by binding the 3’-untranslated region of target mRNAs. MiRNAs can act as tumor suppressor genes or oncogenes in human malignancies. Furthermore, it is known that miRNAs exist and circulate in many types of body fluids, saliva, serum, plasma, urine, semen and more1. These reports suggest the possibility that circulating miRNA in body fluid becomes a novel biomarker for OSCC patients. In this study, we have attempted to identify novel miRNA markers in saliva and serum for OSCC patients. We extracted and purified circulating miRNA in saliva and serum of OSCC patients and healthy volunteers, and then carried out miRNA microarray analysis. In salivary miRNA, we found that 20 miRNAs were significantly down-regulated more than 5-fold changes in OSCC patients compared to healthy volunteers, and no miRNA was up-regulated. On the other hand, 12 miRNAs were significantly down-regulated and 2 miRNAs were up-regulated in serum from OSCC patients. Subsequently, we examined the expression levels of these miRNAs in saliva and serum by real time quantitative RT-PCR. Among these miRNAs, miR-26a and miR-191 were significantly reduced in the serum of the patients. In breast cancer, it was reported that miR-26a function as a tumor-suppressive miRNA2 (TS-miR), and miR-191 function as an oncogenic miRNA. Then we transfected human OSCC cells (GFP-SAS) with synthetic mature miRNAs mimicking human miR-26a and miR-191 at the concentration of 20 nM. After transfection for 3 days, the growth of GFP-SAS cells was evaluated by WST-8 assay. MiR-26a significantly inhibited the growth of GFP-SAS cells but miR-191 did not. These results suggest that down-regulation of miR-26a and miR-191 in serum are novel markers for OSCC patients, and miR-26a may function as a tumor-suppressive miRNA in OSCC.

References

  1. Kosaka N, Iguchi H, Ochiya T, et al. Circulating microRNA in body fluid: a new potential biomarker for cancer diagnosis and prognosis. Cancer Sci. 2012;10:2087
  2. Gao J, Li L, Wu M, et al. MiR-26a inhibits proliferation and migration of breast cancer through repression of MCL-1. PLoS One. 2013;8:e65138.
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