The long noncoding RNA <i>VIM-AS1</i> and nucleoporin Nup358/RanBP2 regulate SMAD nuclear accumulation during TGF-β signaling

The transforming growth factor β (TGF-β) pathway is a developmental signaling network that regulates tissue homeostasis and malfunctions in human diseases, including cancer. TGF-β signals via two receptors, which activate SMAD and alternative signaling pathways. We show that TGF-β induces the expression of the mammalian long noncoding RNA (lncRNA) VIM-AS1 (Vimentin antisense RNA1) variant-2 (v.2) via a transcriptional SMAD-GATA6-SPI1 complex. VIM-AS1 v.1 and v.2 localize in different cell compartments, including the nuclear border. Unbiased whole transcriptomic analysis and functional gain and loss of function assays establish that VIM-AS1 v.2 enhances TGF-β signaling. Mechanistically, VIM-AS1 v.2 interacts with the nucleoporin Nup358/RanBP2, contributing to the binding of Nup358/RanBP2 to SMAD2/3 and enhancing SMAD nuclear accumulation. In the context of cancer biology, VIM-AS1 did not affect the antiproliferative actions of TGF-β, yet had an impact on the epithelial-mesenchymal transition gene program, and increased the invasion and motility of tumor cells, whereas its silencing sensitized cancer cells to chemotherapeutic agents. The molecular mechanism highlights how a lncRNA can modulate the nuclear pore's capacity to import SMAD complexes, by facilitating their capture by Nup358/RanBP2 and thereby enhancing nuclear accumulation of SMADs with distinct isoform composition, thus promoting selectively TGF-β signaling responses.