A comparative study of circulating microRNAs in nasopharyngeal carcinoma patients

Abstract

Nasopharyngeal carcinoma (NPC) is squamous cell carcinoma derived from the

epithelial layer of nasopharynx. The incidence is high in Southern China and

South-east Asia. In Hong Kong, the prevalent of NPC subtype is undifferentiated

NPC and is in close association with Epstein-Barr virus (EBV). MicroRNAs

(miRNAs) are small non-coding RNAs. They play vital roles in regulating gene

expression at post-transcriptional level. EBV also expresses viral miRNAs but the

function remains unclear. In NPC diagnosis and monitoring, circulating EBV

DNA level has been commonly used. However, in some cases, EBV DNA is

below the detection threshold in the plasma of NPC patients making it impossible

to be used in continuous monitoring of the patients. This study aimed to evaluate

whether miRNAs (both NPC-derived and EBV-derived miRNAs) could be used

as candidate circulating markers for disease monitoring.

Candidate gene approach was used to select suitable circulating miRNA markers

for NPC patients. Four candidate miRNAs including miR-21, miR-1301, miRBART7

and miR-BART22 were examined. The expression levels were first

validated in paired NPC tissues and normal counterparts. Furthermore, circulating

miRNA levels were evaluated in the plasma of NPC and normal individuals. To

examine the changes of miRNA in response to radiotherapy, changes of

circulating miRNA were monitored in 13 NPC patients before and after

radiotherapy. In addition, functional assay in cell proliferation was performed to

validate the potential role of the candidate miRNA in the pathogenesis of

undifferentiated NPC.

Of the 4 candidate miRNAs, miR-BART7 was consistently over-expressed in

both tumor tissues and plasma samples of NPC. In addition, circulating miRBART7

was also detected in NPC patients in case of the plasma EBV DNA levels

below the detection threshold. In response to radiotherapy, 10 of 13 (76.92%)

patients had decreasing circulating miR-BART7 in the plasma samples collected

at 3 month after radiotherapy. Furthermore, introducing miR-BART7 mimics into

the undifferentiated NPC cell line HONE1 and normal nasopharyngeal-derived

epithelial cell cultures NP69 and NP460 resulted in significant increases in cell

proliferation rates of all the 3 cell lines.

To summarize, miR-BART7 expression was significantly higher in NPC patients

as a potential oncogenic miRNA. Evaluating the miR-BART7 levels is a possible

screening approach in NPC diagnosis and post-treatment monitoring. The

oncogenic role of miR-BART7 in the development of undifferentiated NPC

deserves further investigation.