EGFL6, a potential novel ligand of EGFR, play roles in Nasopharyngeal cacinoma metastasis through establishing invasive and long-distant metastatic niche by paracrine and autocrine

Abstract

Distant metastasis is the leading cause of treatment failure in Nasopharyngeal carcinoma (NPC). Our study focused on the searching of potential targets for NPC metastasis treatment. cDNA microarray was applied in this screening. We compared gene expression level in metastatic NPC, non-metastatic NPC and inflammatory cases with different bioinformatic methods. EGFL6 was chosen for further study. The over-expression of EGFL6 was confirmed in NPC cell lines and 63% of the metastatic cases(n = 7/11, 3 years follow-up) by Q-PCR. EGFL6 was identified as an independent prognostic index for NPC distant metastasis survival prognostic, P = 0.023 (n = 96, QPCR). As a follicle stem cell specifically expressed secretion protein, EGFL6 showed its powerful strength in promoting cell migration and especially the formation of aggressive morphology in the matrix-gel based three-dimensional culture. With the overexpression of secreting EGFL6, CNE2 cells formed the follicle-like structure but with more aggressive leading edge, which invaded deep into the matrix-gel instead of forming single layer epithelial structure. EGFL6 overexpressed SUNE1 cells breakthrough the restriction of its regular sphere structure, and migrated for more spaces. In vivo study also showed that EGFL6 dramatically increased the tumorigenisis in subcutaneous injection assay and the growth of metastatic tumor in the mice tail vein injection experiment. Mechanism study showed that EGFL6 was a potential novel ligand of EGFR. Our resulted demonstrated that EGFL6 could bind to EGFR and caused its phosphorylation, which activated EGFR and leaded to its internalization. c-Src was subsequently phosphorylated, and the MAPK/ERK signalling cascade was activated. The EGFL6 bound cells down-regulated their expression of E-cadherin and loosed the connection with the adjacent cells, strength their F-actin and vimentin towards the direction they migrated, which indicated a transition from epithelial to mesenchymal characteristic. Further study is on going to investigate the potential of EGFL6 as a therapeutic target for NPC metastatic treatment. In conclusion, we found that EGFL6 was a potential novel ligand of EGFR, which played roles in NPC metastasis through establishing invasive and long-distant metastatic cancer niche by paracrine and autocrine.