23136

EPB41L3

BACKGROUND: epithelial-to mesenchymal transition (EMT) involves in metastasis, causing loss of epithelial polarity. Metastasis is the major cause of carcinoma-induced death, but mechanisms are poorly understood. Here we identify differentially expressed in adenocarcinoma of the lung-1 (DAL-1), a protein belongs to the membrane-associated cytoskeleton protein 4.1 family, as an efficient suppressor of EMT in lung cancer. METHODS: The relationship between DAL-1 and EMT markers were analyzed by using immunohistochemistry in the clinical lung cancer tissues. Quantitative real-time PCR and western blot were used to characterize the expression of the EMT indicator mRNAs and proteins in DAL-1 overexpressed or knockdown cells. DAL-1 combined proteins were assessed by co-immunoprecipitation. RESULTS: DAL-1 levels were strongly reduced even lost in lymph node metastasis and advanced pathological stage of human lung carcinomas. Overexpression of DAL-1 altered the expression of numerous EMT markers, such as E-cadherin, beta-catenin Vimentin and N-cadherin expression, meanwhile changed the morphological shape of lung cancer cells, and whereas silencing DAL-1 had an opposite effect. DAL-1 directly combined with E-cadherin promoter and regulated its expression that could be the reason for impairing EMT and decreasing cell migration and invasion. Strikingly, HSPA5 was found as DAL-1 direct binding protein. CONCLUSIONS: These results suggest that tumor suppressor DAL-1 could also attenuate EMT and be important for tumor metastasis in the early transformation process in lung cancer.

Metastasis is the primary cause of death in lung cancer patients and EMT (epithelial-mesenchymal transition) promotes metastasis. Previous study revealed that DAL-1 (differentially expressed in adenocarcinoma of the lung) could attenuate EMT and metastasis in non-small cell lung cancer (NSCLC). Further study proved that HSPA5 (heat shock protein 5), which has a promoting effect on EMT, could bind to DAL-1. In this study, the mRNA and protein expression levels of target molecules were detected by RTq-PCR and western blot assays, the migration and invasion abilities were examined by Transwell migration and invasion assay, and the proliferation ability was measured by CCK-8 assay. We revealed that DAL-1 was downregulated while HSPA5 was upregulated in NSCLC and found the protein of DAL-1 and HSPA5 co-localized in the cytoplasm and nucleus. We demonstrated that DAL-1 can suppress the expression of HSPA5 on mRNA and protein levels, and decrease EMT, migration, invasion and proliferation abilities by down-regulating HSPA5. Furthermore, we discovered that DAL-1 plays a role in inhibiting PI3K/Akt/Mdm2 signaling pathway by suppressing HSPA5.