Antitumorigenic effect of Wnt 7a and Fzd 9 in non-small cell lung cancer cells is mediated through ERK-5-dependent activation of peroxisome proliferator-activated receptor γ

The Wnt pathway is critical for normal development, and mutation of specific components is seen in carcinomas of diverse orgins. The role of this pathway in lung tumorigenesis has not been clearly established. Recent studies from our laboratory indicate that combined expression of the combination of Wnt 7a and Frizzled 9 (Fzd 9) in Non-small Cell Lung Cancer (NSCLC) cell lines inhibits transformed growth. We have also shown that increased expression of peroxisome proliferator-activated receptor gamma(PPAR gamma) inhibits transformed growth of NSCLC and promotes epithelial differentiation of these cells. The goal of this study was to determine whether the effects of Wnt 7a/Fzd 9 were mediated through PPAR gamma. We found that Wnt 7a and Fzd 9 expression led to increased PPAR gamma activity. This effect was not mediated by altered expression of the protein. Wnt 7a and Fzd 9 expression resulted in activation of ERK5, which was required for PPAR gamma activation in NSCLC. SR 202, a known PPAR gamma inhibitor, blocked the increase in PPAR gamma activity and restored anchorage-independent growth in NSCLC expressing Wnt 7a and Fzd 9. SR 202 also reversed the increase in E-cadherin expression mediated by Wnt 7a and Fzd 9. These data suggest that ERK5-dependent activation of PPAR gamma represents a major effector pathway mediating the anti-tumorigenic effects of Wnt 7a and Fzd 9 in NSCLC.