Abstract
WNT-5A, a key player in embryonic development and post-natal homeostasis, has been associated with a myriad of pathological conditions including malignant, fibroproliferative and inflammatory disorders. Previously, we have identified WNT-5A as a transcriptional target of TGF-β in airway smooth muscle cells and demonstrated its function as a mediator of airway remodeling. Here, we investigated the molecular mechanisms underlying TGF-β-induced WNT-5A expression. We show that TGF-β-activated kinase 1 (TAK1) is a critical mediator of WNT-5A expression as its pharmacological inhibition or siRNA-mediated silencing reduced TGF-β induction of WNT-5A. Furthermore, we show that TAK1 engages p38 and c-Jun N-terminal kinase (JNK) signaling which redundantly participates in WNT-5A induction as only simultaneous, but not individual, inhibition of p38 and JNK suppressed TGF-β-induced WNT-5A expression. Remarkably, we demonstrate a central role of β-catenin in TGF-β-induced WNT-5A expression. Regulated by TAK1, β-catenin is required for WNT-5A induction as its silencing repressed WNT-5A expression whereas a constitutively active mutant augmented basal WNT-5A abundance. Furthermore, we identify Sp1 as the transcription factor for WNT-5A and demonstrate its interaction with β-catenin. We discover that Sp1 is recruited to the WNT-5A promoter in a TGF-β-induced and TAK1-regulated manner. Collectively, our findings describe a TAK1-dependent, β-catenin- and Sp1-mediated signaling cascade activated downstream of TGF-β which regulates WNT-5A induction.
Highlights
WNT-5A is a member of the Wingless/integrase 1 (WNT) family of secreted glycoproteins
We have shown that TGF-b induces WNT-5A expression in airway smooth muscle cells where it mediates the expression of extracellular matrix proteins (ECM) [16]
We observed that pharmacological inhibition of SMAD3 (SIS3; 3 mM), Rhoassociated protein kinase (ROCK) (Y27632; 1 mM), phosphatidylinositol 3-kinase (PI3K) (LY294002; 3 mM), glycogen synthase kinase (GSK) -3 (SB216763; 10 mM) and protein kinase C (PKC) (BIM; 3 mM), failed to reduce
Summary
WNT-5A is a member of the Wingless/integrase 1 (WNT) family of secreted glycoproteins. There are 19 WNT ligands known in humans that act through 10 Frizzled (FZD) receptors, low-density lipoprotein receptor-related protein (LRP) 5/6 coreceptors and many non-FZD receptors, including ROR1, ROR2, RYK [1]. WNT signaling is broadly subdivided into two main streams- canonical (b-catenin-dependent) and non-canonical (bcatenin-independent) WNT signaling. In the canonical signaling, binding of a WNT ligand to a FZD receptor and LRP5/6 coreceptors activates signaling mechanisms resulting in stabilization of the transcriptional co-activator b-catenin, leading to its accumulation in the cytosol. Stabilized b-catenin translocates to the nucleus where it partners with the T-cell factor/lymphoid enhancer-binding factor (TCF/LEF) transcription factors and activates target gene transcription. Non-canonical WNT signaling functions exclusive of b-catenin and LRP5/6 and involves a multitude of pathways regulating gene transcription, cytoskeletal reorganization, cell polarity and cell movements. WNT/Ca2+ and WNT/planar cell polarity (PCP) are the best characterized noncanonical WNT signaling pathways among others.
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