Although the number of mice that were injected with the TE-1HM-siATF4 cells did not significantly differ from that of the mice that were injected with TE-1HMSCR, when the presence of tumor nodules was macroscopically examined, the mice that had been implanted with the TE-1HMSCR cells showed more liver and lung metastases compared with those that had been implanted with the TE-1HM-siATF4 cells. This may be due to an insufficient number of mice in each group. Subsequently, the mice that were implanted with the TE-1HM-SCR cells did show statistically significant increases in liver and lung metastases compared with those that had been implanted with the TE-1HM-siATF4 cells following a repetition of the in vivo experiment using 10 mice per group. In the present study, we showed that ATF4 is frequently upregulated in ESCC tissues compared with non-cancerous epithelial samples. In addition, MRS 2179 tetrasodium salt clinical evidence indicated that ATF4 overexpression correlates with TNM stage and lymph node metastasis. Furthermore, the Kaplan-Meier analysis showed that the patients with ESCC and positive ATF4 expression had significantly worse prognoses than those with negative ATF4 expression. A multivariate analysis revealed that ATF4 expression was an independent prognostic factor for survival after surgical resection. These clinical data strongly suggest that ATF4 contributes to the progression and metastasis of ESCC. Emerging but limited evidence ML 337 suggests that ATF4 regulates the metastasis of tumor cells. It has been reported that the induction of the metastasis-associated gene LAMP3 occurs as a consequence of the activation of the PERK/eIF2a/ATF4-arm of the unfolded protein response and is independent of HIF-1a. Additionally, hypoxia-induced ATF4 has been found in circulating tumor cells but not in their parental cells. In breast cancer, the PERK/ATF4/LAMP3-arm of the UPR is an additional pathway mediating hypoxia-induced tumor cell migration. In this study, our in vitro and in vivo data demonstrate that the overexpression of ATF4 promotes the migration and invasion of ESCC cells with low metastatic potential, while the silencing of ATF4 suppresses the migration and invasion of ESCC cells with high metastatic potential. Thus, these data suggest that ATF4 is an important downstream mediator of metastasis that functions via multiple mechanisms and is, therefore, a valuable therapeutic target. Tumor cells must successful undergo a series of sequential and selective events to metastasize, including detachment, migration, local invasion, intravasation, survival in the circulatory system, extravasation, and regrowth in distant metastatic organs. In fact, degradation of the ECM is an essential step in tumor invasion and metastasis, which is mainly regulated by MMPs.