In a previous genome-wide gene expression profiling analysis using an invasion cancer cell lines model, we have identified Slug was selectively overexpressed in the highly invasive cancer cells. Here, we investigated the clinical significance of Slug in lung adenocarcinoma and the role of Slug in the process of cancer cell invasion and metastasis. Real-time quantitative reverse transcription PCR was used to investigate Slug mRNA in surgically resected lung adenocarcinoma of 54 patients. There were no differences in age, gender, disease stage, tumor status and lymph node metastasis between the high and low Slug expression group. High expression of Slug mRNA in lung cancer tissue was significantly associated with post-operative relapse (P = 0.03) and shorter patient survival (P < 0.001). Multivariate analysis using the Cox regression model, Slug mRNA expression (P = 0.02), stage of disease (P = 0.01) and age (P = 0.002) were the significant prognostic factors for survival, whereas Slug mRNA expression (P = 0.002) and stage of disease (P < 0.001) were significant factors for predicting recurrence. We overexpressed Slug in a lung adenocarcinoma cell line with very low Slug levels and investigated the in vitro and in vivo effects of Slug expression. The overexpression of Slug enhanced xenograft tumor growth and increased microvessel counts in angiogenesis assay. Both inducible and constitutive overexpression of Slug suppressed the expression of E-cadherin and increased the in vitro invasive ability. Overexpression of Slug did not affect the cancer cell migration on wound assay. Zymography revealed increased MMP-2 activity in Slug overexpressed cells. ELISA, RT-PCR and immunohistochemistry confirmed the increase of MMP-2 proteins and mRNA in Slug overexpressed cells and xenograft tumors. In conclusion, Slug expression can predict the clinical outcome of lung adenocarcinoma patients. Increase of cancer cell invasion by Slug is mediated through the suppression of E-cadherin and up-regulation of MMP-2. Slug is a novel invasion-promoting gene in lung adenocarcinoma.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]