Up-regulation of Fibronectin in Oesophageal Squamous Cell Carcinoma is Associated with Activation of the Erk Pathway

Fibronectin (FN) was found to be up-regulated in human oesophageal squamous cell carcinoma (ESCC) by cDNA microarray analysis in our laboratory. In order to elucidate the chronology of FN expression at various stages of oesophageal carcinogenesis, RT-PCR, immunohistochemistry and Western blot analysis were carried out on ESCC tissue samples with different pathological characteristics. FN was mainly localized in the interstitial tissues, and its up-regulation in ESCC was significantly associated with the depth of invasion by carcinoma (R = 0.803, p < 0.01). To investigate its relationship with the Erk pathway further, pRaf-1 and pErk-1/2 expression were also analysed in ESCC. Activation of Erk1/2 and Raf was identified in 63.3% and 60.3% of the tumour specimens, respectively, whereas normal mucosal epithelial tissues were negative. Moreover, a close association was observed between pErk-1/2 expression and the differentiation grade (R = -0.421, p = 0.002): pErk-1/2 signal was greater in poorly differentiated tissues than in well and moderately differentiated tissues. Co-expression of FN and pErk-1/2 was found at the invasive front of tumour nests by double immunofluorescence staining and there was a statistical correlation between the expression of FN and pErk-1/2 (p < 0.05). In the cell line EC9706, plasma FN was able to phosphorylate Raf and further activate Erk, but it did not alter MMP-2 protein expression or activity, indicating that MMP-2 may not be the downstream target gene of the Erk pathway. All the above data suggest that the up-regulation of FN contributes to the later stage of oesophageal carcinogenesis, and that activation of the Erk pathway may be involved in the roles of FN in ESCC.