Background and Aims: The epithelial mesenchymal transition (EMT) is an important mechanism for cancer progression and metastasis, and the recent studies have shown that paired related homeobox 1 (PRRX1) is a critical transcription factor of promoting EMT. The previous studies of the authors demonstrated that the PRRX1 expression is increased in gastric cancer, which is closely related to the poor prognosis of patients. This study was conducted to further investigate the relations of PRRX1 promoting proliferation and metastasis of gastric cancer cells with the EMT and associates signaling pathway, so as to provide approaches for prevention and treatment of the recurrence and metastasis of gastric cancer. 
Methods: The PRRX1 expressions in normal human gastric mucosal GES-1 cells, and gastric cancer SGC 7901 and MNK45 cells were detected by Western blot analysis. The MNK45 cells were infected with PRRX1 overexpression lentivirus (PRRX1 overexpression group) or empty lentivirus (negative control group), with the untreated MNK45 cells as blank control, and then, the migration ability of the cells was detected by Transwell assay, and the expressions of PRRX1, TGF-β1, Smad2 and EMT markers, as well as the changes in these protein expressions after intervention of the TGF-β/Smad2 pathway inhibitor SB-431542 were determined by Western blot analysis. Eight nude mice were randomized into two groups, and then subcutaneously transplanted with PRRX1 overexpression lentivirus infected MNK45 cells (PRRX1 overexpression group) or empty lentivirus infected MNK45 cells (negative control group), and then, the growth properties of the tumor xenografts in the two groups of mice were observed.
Results: The PRRX1 expression in either gastric cancer SGC7901 or MNK45 cells was significantly higher than that in normal gastric mucosal GES-1 cells, and in SGC7901 cells was higher than that in MNK45 cells (all P<0.05). Compared with blank control group, the migration ability was significantly enhanced, the protein expressions of PRRX1, TGF-β1, Smad2 and the mesenchymal marker vimentin were significantly increased, while the expression of epithelial marker E-cadherin was significantly decreased in PRRX1 overexpression group (all P<0.05); no significant changes in expressions of above proteins were noted in negative control group (all P>0.05). In MNK45 cells of the PRRX1 overexpression group after SB-431542 treatment, the expressions of PRRX1 and TGF-β1 were unaffected (both P>0.05), but the increasing in Smad2 and vimentin expressions and the decreasing in E-cadherin expression were significantly suppressed (all P<0.05). Both volume growth rate and weight of tumor xenograft in nude mice of PRRX1 overexpression group were greater than those of negative control group (all P<0.05).
Conclusion: Overexpression of PRRX1 can promote the growth and metastasis of gastric cells, and the mechanism may be probably associated with its inducing the activation of TGF-β/Smad2 pathway and thereby promoting the EMT process. The interventions on PRRX1 overexpression and TGF-β/Smad2 pathway may be new approaches for prevention and treatment of the recurrence and metastasis of gastric cancer.