Jagged/Notch signalling is required for a subset of TGFβ1 responses in human kidney epithelial cells

Abstract

The Jagged/Notch pathway has been implicated in TGFβ1 responses in epithelial cells in diabetic nephropathy and other fibrotic conditions in vivo. Here, we identify that Jagged/Notch signalling is required for a subset of TGFβ1-stimulated gene responses in human kidney epithelial cells in vitro. TGFβ1 treatment of HK-2 and RPTEC cells for 24h increased Jagged1 (a Notch ligand) and Hes1 (a Notch target) mRNA. This response was inhibited by co-incubation with Compound E, an inhibitor of γ-secretase (GSI), an enzyme required for Notch receptor cleavage and transcription regulation. In both cell types, TGFβ1-responsive genes associated with epithelial-mesenchymal transition such as E-cadherin and vimentin were also affected by γ-secretase inhibition, but other TGFβ1 targets such as connective tissue growth factor (CTGF) and thrombospondin-1 (THBS1) were not. TGFβ1-induced changes in Jagged1 expression preceded EMT-associated gene changes, and co-incubation with GSI altered TGFβ1-induced changes in cell shape and cytoskeleton. Transfection of cells with the activated, cleaved form of Notch (NICD) triggered decreased expression of E-cadherin in the absence of TGFβ1, but did not affect α-smooth muscle actin expression, suggesting differential requirements for Notch signalling within the TGFβ1-responsive gene subset. Increased Jagged1 expression upon TGFβ1 exposure required Smad3 signalling, and was also regulated by PI3K and ERK. These data suggest that Jagged/Notch signalling is required for a subset of TGFβ1-responsive genes, and that complex signalling pathways are involved in the crosstalk between TGFβ1 and Notch cascades in kidney epithelia.

The role of EMT in renal fibrosis

“…Other intracellular pathways and transcription factors such as Erk-1/2 and Wnt signalling are also thought to be involved in mediating EMT (Schramek et al 2003;Taki et al 2003). The Jagged/Notch signalling pathway has recently been implicated as an important regulator of EMT and renal fibrosis (Leask 2010;Nyhan et al 2010;Zavadil et al 2004) and Jagged/Notch-mediated EMT is associated with increased expression of Snail (Saad et al 2010). Future experiments will delineate whether any of these pathways can be targeted specifically for the treatment and prevention of renal fibrosis.…”

The role of TGF-β and epithelial-to mesenchymal transition in diabetic nephropathy

“…Using proximal tubule cell line models, HK2 and RPTEC cells, they demonstrated that the Jagged/Notch signalling pathway is activated in response to TGF-β1. Furthermore, the cytokine-evoked changes in Jagged 1 expression preceeded EMT associated gene changes in both E-cadherin and vimentin, effects which appeared to be dependent on Smad3 activity [36]. Therefore, TGF-β1 can modulate transcription of multiple target genes through the activation of at least one, or a cross talk of multiple signaling pathways.…”

Notch Intracellular Domain Expression in Various Skin Fibroproliferative Diseases

“…This process leads to increased myofibroblast accumulation and scarring11. Recent evidence has shown that the Notch signaling pathway promotes EMT via interactions with the TGF-β signaling pathway in the kidney tubular epithelium20.…”