Transforming growth factor-β1 induces the non-classical secretion of peroxiredoxin-I in A549 cells

Recent studies found that peroxiredoxin-I (Prx-I) is secreted from A549 cells although it does not contain a signal peptide and is known to be a cytosolic protein. Transforming growth factor-β1 (TGF-β1) treatment dramatically enhanced Prx-I secretion from A549 cells, and this effect was not inhibited by brefeldin A. Further investigation revealed that A549 cells constitutively secrete TGF-β1. Furin, a TGF-β1-converting enzyme, was also highly activated in A549 cells. Ectopic expression of α1-antitrypsin Portland (α1-PDX), a potent furin inhibitor, blocked both TGF-β1 activation and Prx-I secretion. Our findings collectively suggest that non-classical secretion of Prx-I is induced by TGF-β1, which is constitutively activated by furin in A549 cells.