Aberrant expression of nuclear prothymosin α contributes to epithelial-mesenchymal transition in lung cancer

Elevated expression of prothymosin α (ProT) is frequently observed in cancers, but the underlying molecular mechanism remains poorly understood. Here, we report the clinical relevance of ProT expression and its correlation with lung cancer progression. We have shown that ProT was highly expressed in early-stage lung cancer, exhibiting nuclear localization; on the contrary, a loss of nuclear ProT expression was detected in late-stage tumor specimens. Furthermore, the expression of nuclear ProT impaired lung cancer cell migration, suppressed TGF-β-induced epithelial-to-mesenchymal transition (EMT)-associated transcription factor expression, and inhibited in vivo tumor metastasis. The suppressive effect of ProT was further found to trigger Smad7 acetylation-dependent deregulation of TGF-β signaling. ProT enhanced Smad7 stability by promoting its lysine acetylation, thereby competing with the binding of Smad2 to the SNAI1, TWIST1, and ZEB1 promoters. Eventually, the binding of Smad7 in the presence of ProT resulted in reduced expression of the EMT transcription factors, leading to the inhibition of TGF-β-induced EMT and tumor metastasis. Collectively, this study unravels the role of ProT in lung cancer progression and highlights the potential of nuclear ProT as an indicator for monitoring tumor development.