The long non-coding RNA LINC00707 interacts with Smad proteins to regulate TGF signaling and cancer cell invasion

Background Long non-coding RNAs (lncRNAs) regulate cellular processes by interacting with RNAs or proteins. Transforming growth factor beta (TGF beta) signaling via Smad proteins regulates gene networks that control diverse biological processes, including cancer cell migration. LncRNAs have emerged as TGF beta targets, yet, their mechanism of action and biological role in cancer remain poorly understood.Methods Whole-genome transcriptomics identified lncRNA genes regulated by TGF beta. Protein kinase inhibitors and RNA-silencing, in combination with cDNA cloning, provided loss- and gain-of-function analyses. Cancer cell-based assays coupled to RNA-immunoprecipitation, chromatin isolation by RNA purification and protein screening sought mechanistic evidence. Functional validation of TGF beta-regulated lncRNAs was based on new transcriptomics and by combining RNAscope with immunohistochemical analysis in tumor tissue.Results Transcriptomics of TGF beta signaling responses revealed down-regulation of the predominantly cytoplasmic long intergenic non-protein coding RNA 707 (LINC00707). Expression of LINC00707 required Smad and mitogen-activated protein kinase inputs. By limiting the binding of Kruppel-like factor 6 to the LINC00707 promoter, TGF beta led to LINC00707 repression. Functionally, LINC00707 suppressed cancer cell invasion, as well as key fibrogenic and pro-mesenchymal responses to TGF beta, as also attested by RNA-sequencing analysis. LINC00707 also suppressed Smad-dependent signaling. Mechanistically, LINC00707 interacted with and retained Smad proteins in the cytoplasm. Upon TGF beta stimulation, LINC00707 dissociated from the Smad complex, which allowed Smad accumulation in the nucleus. In vivo, LINC00707 expression was negatively correlated with Smad2 activation in tumor tissues.Conclusions LINC00707 interacts with Smad proteins and limits the output of TGF beta signaling, which decreases LINC00707 expression, thus favoring cancer cell invasion.EZy4eavcmbb38C5oFYKmkjVideo AbstractConclusionsLINC00707 interacts with Smad proteins and limits the output of TGF beta signaling, which decreases LINC00707 expression, thus favoring cancer cell invasion.EZy4eavcmbb38C5oFYKmkjVideo Abstract