HOPX functions as a tumour suppressor in head and neck cancer.

Lee Fah Yap,Paul G Murray,Pathmanathan Rajadurai,Robert J Hollows,Wenbin Wei,Ravindran Gokulan,Narayanan Prepageran,Ian C Paterson,San Jiun Chai,Victor Lopes,Joe B White,Sathya Narayanan Patmanathan,Keith D Hunter,Yew Toong Liew,Daniel W Lambert,C Max Robinson,Sook Ling Lai

doi:10.1038/srep38758

Abstract

Head and neck squamous cell carcinoma (HNSCC) is generalized term that encompasses a diverse group of cancers that includes tumours of the oral cavity (OSCC), oropharynx (OPSCC) and nasopharynx (NPC). Genetic alterations that are common to all HNSCC types are likely to be important for squamous carcinogenesis. In this study, we have investigated the role of the homeodomain-only homeobox gene, HOPX, in the pathogenesis of HNSCC. We show that HOPX mRNA levels are reduced in OSCC and NPC cell lines and tissues and there is a general reduction of HOPX protein expression in these tumours and OPSCCs. HOPX promoter methylation was observed in a subset of HNSCCs and was associated with a worse overall survival in HPV negative tumours. RNAseq analysis of OSCC cells transfected with HOPX revealed a widespread deregulation of the transcription of genes related to epithelial homeostasis and ectopic over-expression of HOPX in OSCC and NPC cells inhibited cell proliferation, plating efficiency and migration, and enhanced sensitivity to UVA-induced apoptosis. Our results demonstrate that HOPX functions as a tumour suppressor in HNSCC and suggest a central role for HOPX in suppressing epithelial carcinogenesis.

Highlights

reverse transcription quantitative PCR (RT-qPCR) analyses were performed to determine the mRNA levels of HOPX in a series of oral squamous cell carcinoma (OSCC) and Nasopharyngeal carcinoma (NPC) cell lines and tissues
In OSCC, compared to three cultures of normal oral keratinocytes, HOPX expression was markedly reduced in immortalized oral keratinocytes (n = 1), immortal cell lines derived from oral dysplasia tissues (n = 4) and SCCs (n = 11; Fig. 1A)
lysophosphatidic acid (LPA) can induce SRF whose activity is inhibited by HOPX17 and we have previously shown that LPA is a motility factor for both OSCC and NPC cells

Summary

Introduction

The HOPX-βpromoter contains CpG islands that are methylated in various cancers leading to down-regulation of HOPX expression, strongly suggesting that HOPX functions as a tumour suppressor[8,10,11]. We have extended these observations and show for the first time that the expression of HOPX is markedly down-regulated in three different subtypes of HNSCC, namely OSCC, NPC and OPSCC. Analysis of The Cancer Genome Atlas (TCGA) HNSCC dataset showed that hypermethylation of the HOPX-βpromoter occurs in a sub-set of HNSCCs and this was associated with worse overall survival in HPV negative HNSCCs. Ectopic expression of HOPX in OSCC cells revealed that HOPX loss was associated with the deregulated transcription of genes involved in epithelial homeostasis. Our results point to a central role for HOPX in suppressing epithelial carcinogenesis

Methods

Results

Conclusion