BACKGROUNDEpithelial-mesenchymal transition is a cellular process characterized by the loss of cell adhesion, inhibition of E-cadherin expression, and increased cell mobility. Cells without Napsin A are susceptible to transition. Further studies are required to investigate whether this transition can be reversed by restoration of Napsin A.

METHODSA Napsin A expression vector PLJM1-Napsin A plasmid was constructed and then transfected into the epithelial cell line A549 by lentivirus transfection to obtain A549-PLJM1-Napsin A cell line. Cell proliferation was assayed by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide and cell cycle was measured by flow cytometry. The E-cadherin, type I collagen, and focal adhesion kinase mRNA level was detected by reverse transcription-polymerase chain reaction. The Napsin A, E-cadherin, type I collagen, and focal adhesion kinase protein level in A549 cells was detected by Western blotting.

RESULTSTransforming growth factor-b1 induced epithelial-mesenchymal transition in A549 cells, as demonstrated by significant reduction of E-cadherin mRNA and protein levels (P < 0.01) as well as up-regulation of type I collagen (P < 0.01). Transfection of Napsin A in A549 cells can partially block the transforming growth factor-b1-regulated expression of E-cadherin and type I collagen (P < 0.01). In addition, transforming growth factor-b1-induced cell proliferation was inhibited by Napsin A (P < 0.01). Further study demonstrated that Napsin A caused G(0)/G(1) arrest and inhibited the expression of focal adhesion kinase (P < 0.01), a key protein in the integrin signaling pathway, in the in vitro epithelial-mesenchymal transition model.

CONCLUSIONSSustained Napsin A expression in A549 cells can inhibit the transforming growth factor-b1-induced epithelial-mesenchymal transition. This may be due to the Napsin A-mediated inhibition of focal adhesion kinase expression and integrin signaling pathway.