Exogenous induction of unphosphorylated PTEN reduces TGFβ-induced extracellular matrix expressions in lung fibroblasts

Transforming growth factor β (TGFβ) plays an important role in regulating aberrant extracellular matrix (ECM) production from alveolar/epithelial cells (AECs) and fibroblasts in pulmonary fibrosis. Although the tumor suppressor gene phosphatase and tensin homologue deleted from chromosome 10 (PTEN) can negatively control many TGFβ-activated signaling pathways via the phosphatase activity, hyperactivation of the TGFβ-related signaling pathways is often observed in fibrosis. Loss of PTEN expression might cause TGFβ-induced ECM production. In addition, TGFβ was recently shown to induce loss of PTEN enzymatic activity by phosphorylating the PTEN C-terminus. Therefore, we hypothesized that exogenous transfer of unphosphorylated PTEN (PTEN4A) might lead to reduce TGFβ-induced ECM expression in not only epithelial cells but also fibroblasts. Adenovirus-based exogenous PTEN4A induction successfully reduced TGFβ-induced fibronectin expression and retained β-catenin at the cell membrane in human epithelial cells. Exogenous unphosphorylated PTEN also attenuated TGFβ-induced ECM production and inhibited TGFβ-induced β-catenin translocation in a human fibroblast cell line and in mouse primary isolated lung fibroblasts. Conversely, TGFβ-induced α-smooth muscle actin expression did not seem to be inhibited in these fibroblasts. Our data suggest that exogenous administration of unphosphorylated PTEN might be a promising strategy to restore TGFβ-induced loss of PTEN activity and reduce aberrant TGFβ-induced ECM production from epithelial cells and fibroblasts in lung fibrosis as compared with wild-type PTEN induction.