In addition, Tir is inserted into the plasma membrane of the host cell in a hairpin loop structure. It is also possible that NleL is affecting Tir localization. Further studies are required to dissect the exact molecular mechanism on how the E3 ligase activity of NleL modulates the pedestal formation. However, its expression and function in ESCC remains unknown. In the present study, we have determined that ATF4 expression is frequently up-regulated in ESCC tissues compared with adjacent non-cancerous epithelial samples. Using a tissue microarray, we found that ATF4 overexpression correlated with the TNM stage and lymph node metastasis. In addition, positive ATF4 expression indicated poorer prognoses than negative ATF4 expression in patients with ESCC. Furthermore, we showed that ATF4 promoted the migration and invasion of ESCC cells both in vitro and in vivo. MMP-2 and MMP-7 are both essential for ATF4-induced ESCC cell invasion. Our findings highlight the importance of ATF4 dysfunction in promoting tumor progression and metastasis and implicate it as a potential therapeutic target for ESCC. To determine whether ATF4 can be used as a predictive factor of the clinical outcomes of ESCC patients, immunohistochemistry was performed using 168 paraffin-embedded primary tumor samples and paired adjacent non-cancerous samples. Positive immunoreactivity for ATF4 was observed primarily in the cytoplasm of carcinoma cells and non-cancerous epithelial cells. As summarized in Table 1, among all of the tumor samples that were analyzed, 30 demonstrated strong ATF4 staining, 43 showed moderate staining, 44 had weak staining, and 51 exhibited negative staining. In contrast, the majority of adjacent non-cancerous epithelial samples showed weak or negative staining for ATF4. Next, we explored the association between ATF4 protein expression and the clinicopathological characteristics of ESCC. The segregation of the patients into ATF4-positive and -negative groups did not reveal significant correlations with the clinicopathological parameters of age, sex, drinking habit, tumor site, or tumor differentiation. However, these groups did show significant correlations with TNM stage and lymph node metastasis. Furthermore, we investigated the correlation of ATF4 expression with prognostic data. As a result, we found that the patients with ATF4-positive ESCC had significantly worse prognoses than those that were ATF4-negative. Additionally, the overall survival rates of ATF4-positive patients were significantly lower than those that were ATF4-negative. The staining intensity of ATF4 significantly correlated with shorter overall survival times. As shown in Table 3, univariate analyses showed that overall survival correlated with TNM stage, lymph node metastasis, and ATF4 expression. Furthermore, a multivariate Cox regression analysis indicated that ATF4 expression and lymph node metastasis were independent prognostic factors for overall survival. The prognostic value of ATF4 protein expression in patient subgroups that were stratified according to tumor clinical stage was also analyzed.