Tumour necrosis factor-stimulated gene (TSG)-6 controls epithelial–mesenchymal transition of proximal tubular epithelial cells

Abstract

Progressive renal disease is characterized by accumulation of extracellular matrix in the renal cortex. Proximal tubular cells (PTC) may contribute to disease through a process of epithelial–mesenchymal-transition (EMT): phenotypic change, disruption of the tubular basement membrane and migration into the interstitium. Hyaluronan (HA) synthesis and its extracellular organization by hyaladherins affect cell fate in other systems: this study investigated the role of the hyaladherin, tumour necrosis factor-stimulated gene (TSG)-6, in PTC EMT triggered in vitro by transforming growth factor (TGF)β1. TGFβ1 triggered the loss of PTC epithelial phenotype with 60% decreased expression of E-cadherin and 2–3-fold induction of alpha-smooth muscle actin (α-sma). It also increased the expression of TSG-6, HA-synthase-(HAS)2 and the HA-receptor, CD44, to a peak at 8–12 h, remaining elevated thereafter. Immuno-localization of HA demonstrated that unstimulated PTC assembled HA in cables and that treatment with TGFβ1 initiated cable disassembly with formation of dense HA-pericellular coats. Stable knockdown of TSG-6 with short-hairpin-RNA increased E-cadherin and HAS2 expression, produced loose HA-pericellular coats, HA cables were absent and cell migration was slowed. Treatment of transfectants with TGFβ1 did not induce α-sma, alter E-cadherin, pericellular-HA or migration but did induce HAS2. This was dependent on the expression of CD44 and was inhibited by CD44-specific siRNA. In summary, TSG-6 was central to EMT through effects on HA macromolecular structure and through CD44-dependent triggering of cell responses. These findings suggest that controlling the assembly of HA by proximal tubular cells may be a novel approach towards intervention in renal disease.