Post-transcriptional Up-regulation of Tsc-22 by Ybx1, a Target of miR-216a, Mediates TGF-β-induced Collagen Expression in Kidney Cells

Increased accumulation of extracellular matrix proteins and hypertrophy induced by transforming growth factor-beta 1 (TGF-beta)in renal mesangial cells (MC) are hallmark features of diabetic nephropathy. Although the post-transcriptional regulation of key genes has been implicated in these events, details are not fully understood. Here we show that TGF-beta increased microRNA-216a (miR-216a) levels in mouse MC, with parallel down-regulation of Ybx1, a miR-216a target and RNA-binding protein. TGF-beta also enhanced protein levels of Tsc-22 (TGF-beta-stimulated clone 22) and collagen type I alpha-2 (Col1a2) expression in MC through far upstream enhancer E-boxes by interaction of Tsc-22 with an E-box regulator, Tfe3. Ybx1 colocalized with processing bodies in MC and formed a ribonucleoprotein complex with Tsc-22 mRNA, and this complex formation was reduced by TGF-beta, miR-216a mimics, or Ybx1 shRNA to increase Tsc-22 protein levels but enhanced by miR-216a inhibitor oligonucleotides. Chromatin immunoprecipitation (ChIP) assays revealed that TGF-beta could increase the occupancies of Tsc-22 and Tfe3 on enhancer E-boxes of Col1a2. Co-immunoprecipitation assays revealed that TGF-beta promoted the interaction of Tsc-22 with Tfe3. These results demonstrate that post-transcriptional regulation of Tsc-22 mediated through Ybx1, a miR-216a target, plays a key role in TGF-beta -induced Col1a2 in MC related to the pathogenesis of diabetic nephropathy.