Response gene to complement 32 interacts with Smad3 to promote epithelial-mesenchymal transition of human renal tubular cells

Guo X, Jose PA, Chen SY. Response gene to complement 32 interacts with Smad3 to promote epithelial-mesenchymal transition of human renal tubular cells. Am J Physiol Cell Physiol 300: C1426-C1432, 2011. First published February 9, 2011; doi: 10.1152/ajpcell.00204.2010.-Previous studies demonstrate that response gene to complement 32 (RGC-32) mediates transforming growth factor-beta(1)-induced epithelial-mesenchymal transition (EMT) of human renal proximal tubular cells. However, the mechanisms underlying RGC-32 function remain largely unknown. In the present study, we found that RGC-32 function in EMT is associated with Smad3. Coexpression of RGC-32 and Smad3, but not Smad2, induces a higher mesenchymal marker alpha-smooth muscle actin (alpha-SMA) protein expression as compared with RGC-32 or Smad3 alone, while knockdown of Smad3 using short hairpin interfering RNA blocks RGC-32-induced alpha-SMA expression. These data suggest that RGC-32 interacts with Smad3, but not Smad2, in the regulation of EMT. In addition to alpha-SMA, RGC-32 and Smad3 also synergistically activate the expression of extracellular matrix protein fibronectin and downregulate the epithelial marker E-cadherin. RGC-32 colocalizes with Smad3 in the nuclei of renal proximal tubular cells. Coimmunoprecipitation assays showed that Smad3, but not Smad2, physically interacts with RGC-32 in renal proximal tubular cells. Mechanistically, RGC-32 and Smad3 coordinate the induction of EMT by regulating the EMT regulators Slug and Snail. Taken together, our data demonstrate for the first time that RGC-32 interacts with Smad3 to mediate the EMT of human renal proximal tubular cells.