Identification and characterisation of inhibin beta A in nasopharyngeal carcinoma

Abstract

A high concern of nasopharyngeal carcinoma (NPC) from the southern China and also Hong Kong has been resulted due to its particular high incidence and endemicity. Besides Epstein-Barr virus (EBV) infection and non-viral environmental risk factors, genetic predisposition also plays an important role in NPC development. Radiotherapy with or without additional chemotherapy is the standard first-line treatment for non-metastatic NPC. Novel treatment modalities including targeted therapy and more recently immunotherapy have gradually emerged as new hopes of treatment. cDNA microarray was applied for searching genes related to the development of distant metastasis in NPC. Candidate genes were validated by qPCR with NPC diagnostic biopsies. In addition to the expression location of chromosome, inhibin beta A (INHBA) was selected for further study according to the relationship of gene expression levels and distant metastasis-free survival. Chromosome 7 is frequently amplified in NPC. It was revealed to be involved in the functioning of biological processes, for example cell proliferation, signalling pathways and transportation. Nevertheless, the role of genes on chromosomes 7 in NPC has not yet been understood. INHBA, the candidate gene chosen for further study is located at chromosome 7p14.1. It can form a disulphide-liked homodimer, activin A known as a member of TGF-beta superfamily. Similar to the role of TGF-beta in tumourigenesis, it exhibited both tumour promoting and suppressing functions in a diversified types of cancers. Cancer propagation and increased propensity for distant metastasis have been found in the overexpression of INHBA in cancers associated with activin A formation in advanced stage of cancers. In this study, oncogenic ability of INHBA was demonstrated in both in vitro and in vivo function assays. In the in vitro functional assays on overexpression of INHBA in NPC cell lines, INHBA promoted the tumourigenic ability of NPC cells, including cell foci formation, colony formation in soft agar, migration and invasion. The tumourigenicity of INHBA in NPC was further demonstrated by in vivo functional assay in xenograft nude mice. Tumourigenic function of INHBA was further confirmed by silencing INHBA by shRNA in NPC cell line. In vitro functional assay showed a significant inhibition of tumourigenesis in NPC with knockdown INHBA. A dramatic decrease in cell proliferation, cell foci formation, anchorage-independent growth, cell migration and invasion assays were also observed. Furthermore, tumour formation was significantly inhibited in animal models, and a great difference was observed by knockdown INHBA. This provided a strong evidence on the essential role of INHBA in tumourigenesis of NPC. Cells involved in metastatic tumours are believed to acquire all genetic alternations that are necessary for the maintenance of malignant phenotypes in cancer cells. With respect to the results of migration and invasion assays, the strong relationship between INHBA and metastatic ability of NPC further suggested that INHBA plays an essential role in NPC development. Further characterisation of INHBA in nasopharyngeal carcinogenesis may help identify an ideal target as a biomarker for prediction of NPC development and as a novel therapeutic target for NPC treatment.