Ubiquitination and regulation of Smad7 in the TGF- β 1/Smad signaling of aristolochic acid nephropathy

Abstract

Aristolochic acid I (AAI) affects TGF-β1/Smad signaling, which causes AA nephropathy (AAN), but the mechanisms are not fully understood. We aimed to clarify whether Arkadia and UCH37 participate in TGF-β1/Smad signaling via Smad7, and the regulatory mechanisms of Smad7. One side, mice and cultured mouse renal tubular epithelial cells (RTECs) were treated with various AAI doses and concentrations, respectively; on the other side, RTECs were transfected with small interfering RNA (siRNA) expression vectors against Arkadia and UCH37 and then treated with 10 µg/ml AAI. And then detect the mRNA and protein levels of Smad7, UCH37, Arkadia and any other relative factors by RT-PCR and Western blotting. In kidney tissues and RTECs, the mRNA and protein levels of Smad7 decreased with increasing AAI doses concentrations by real-time PCR and Western blotting, whereas those of Arkadia, UCH37, Smad2, Smad3 and TβRI increased. Cells transfected with the Arkadia siRNA expression vector showed reduced mRNA and protein levels of vimentin, α-SMA, Smad2, Smad3 and TβRI after AAI treatment, while those of CK18 and Smad7 increased compared with those of untransfected RTECs. Conversely, cells transfected with the UCH37 siRNA expression vector showed the opposite effect on analyzed signaling molecules after AAI treatment. Arkadia and UCH37 participate in TGF-β1/Smad signaling-mediated renal fibrosis, and Smad7 blocks TGF-β1 signaling by inhibiting Smad2/Smad3 phosphorylation and enhancing the degradation of TβRI.

Enhancer of Zeste Homolog 2 Inhibition Attenuates Renal Fibrosis by Maintaining Smad7 and Phosphatase and Tensin Homolog Expression

“…39,55 In contrast, Smad7 blocks TGFb1 signaling by inhibiting Smad2/Smad3 phosphorylation and enhancing the degradation of TGFb-RI. 56,57 In this study, we observed that injury to the kidney increased expression of TGFb-RI and phosphorylation of Smad3 and decreased expression of Smad7, whereas treatment with the EZH2 inhibitor preserved Smad7 expression, which is accompanied by reduced Smad3 phosphorylation and TGFb-RI expression. These data strongly suggest that maintaining Smad7 stability is a critical mechanism by which EZH2 inhibition suppresses TGFb/Smad3 signaling.…”

Mitigated NSAID-induced apoptotic and autophagic cell death with Smad7 overexpression

“…4 , indomethacin led to significant repressed status of Smad7, rapid down-regulation of Smad7 consistent with its accelerated degradation. In the literature, aristolochic acid-induced nephropathy and streptozotocin-induced diabetic nephropathy were reported with significant ubiquitination of Smad7, ( 27 , 28 ) but never in NSAID-induced GI damages before our investigation. Though not investigated in the current study further, an important regulatory step involving specific ubiquitination by Smurfs (Smad-ubiquitin regulatory factors), members of the homologous to E6-associated protein C-terminus ubiquitin ligase family, mediates the proteasomal degradation of Smads and/or receptors.…”

RETRACTED: miR-363 Alleviates Detrusor Fibrosis via the TGF-β1/Smad Signaling Pathway by Targeting Col1a2 in Rat Models of STZ-Induced T2DM

“…33 The TGF-b1/Smad signaling pathway can control the strength and timing of downstream signals and also mediate the fibrosis of animal organs. 34 TGF-b1 can increase the expression of many fibrotic genes, including those expressing collagen extracellular matrix proteins and a-smooth muscle actin through the Smad2/3 signaling pathway. 35 Among the various regulatory factors, an increased level of TGF-b1 has the potential to stimulate bladder fibrosis.…”