Function and molecular regulation of WNT‐5A expression by TGF‐β

Abstract

Disruption of WNT‐5A homeostasis has been linked to various disorders like fibrosis, cancer and inflammation with recent evidence implicating it in asthma. Here, we have investigated the function and molecular regulation of WNT‐5A expression in airway smooth muscle (ASM) cells by TGF‐β.Immortalized human ASM cells were used to measure mRNA by qRT‐PCR and protein abundance by immunoblotting.ASM cells expressed a variety of WNT ligands and Frizzled receptors which were differentially modulated by TGF‐β. WNT‐5A was the most abundant ligand expressed and showed ~4–16 fold upregulation in response to TGF‐β (2 ng/mL). Knockdown using siRNA demonstrated WNT‐5A requirement for TGF‐β‐induced collagen and fibronectin expression. TGF‐β induction of WNT‐5A appeared to require TGF‐β activated kinase (TAK)‐1 activity, as pharmacological inhibition of TAK‐1 with LL‐Z1640–2 (500 nM) prevented WNT5A expression. Interestingly, inhibition of ERK1/2 (U0126, 3μM), Smad3 (SIS3, 3μM) and β‐catenin/TCF (PKF115–584, 100 nM) augmented WNT‐5A expression suggesting a negative regulatory role.In conclusion, TGF‐β‐induced WNT‐5A expression mediates extracellular matrix expression by human ASM cells. WNT5A induction occurs via complex signaling cascades with TAK‐1 acting as a positive regulator, whereas ERK1/2, Smad3 and β‐catenin/TCF mediate a negative constraint.This study is funded by University of Groningen.