The Study Of RanBP7, 8 In TGF-β/BMP Signaling Pathway And Its Function In Human Lung Fibrosis Cells

RNAi(RNA interference)is a process of sequence-specific, post-transcriptional gene silencing in animals and plants initiated by double-stranded RNA that is homologous to the silenced gene and has proven as a novel approach to suppress gene expression specifically. In our study, we designed the specific RNA interference sequences targeting RanBP7 and RanBP8 and investigated the effects of RanBP7 and RanBP8 in TGF-βand BMP signaling and further examined the effects of RanBP8 in lung fibrosis.Signal transduction of the transforming growth factorβ(TGF-β)cytokines is mediated by an evolutionarily conserved mechanism. One key step of the TGF-βpathway is nuclear translocation of Smad proteins as a consequence of TGF-β-induced phosphorylation at their carboxy-termini. Here we identify RanBP7 and RanBP8 as critical components in transporting TGF-βand BMP-activated Smads into the nucleus. Using RNA interference(RNAi)technology to knockdown of Ran binding proteins 7 and 8(RanBP7 and 8), resulted in marked decrease in nuclear accumulation of Smadl in response to bone morphogenetic protein 2(BMP2) and of Smad2/3 in response to TGF-β. Therefore, we have identified new evolutionarily conserved proteins that play crucial roles in signal transduction of BMP and TGF-βinto the nucleus.RanBP7/8 interact with Smads regardless of their phosphorylation status. Our data also suggest that basal Smads may have multiple routes for nuclear import since depleting RanBP7/8 did not reduce the nuclear presence of Smads in unstimulated cells.TGF-βsignaling plays an important role in the pathogenesis of lung fibrosis, and blocking it can attenuate lung fibrosis, so we examine whether RanBP8 has relationship with lung fibrosis. MTT assay showed that HLF cell proliferation was inhibited but flow cytometry experiment showed that the percentage of HLF cell apoptosis was not changed after transfection of siRanBP8. These results implied that siRNA targeting RanBP8 may has exhibiting anti-fibrogenesis actions and future studies will be required.