Y-box protein-1 controls transforming growth factor-β1 translation in proximal tubular cells

Abstract

Transforming growth factor-beta1 (TGF-beta1) mRNA has low basal translational efficiency in proximal tubule cells; however, its translation is stimulated by profibrotic cytokines. We studied the role of the multifunctional Y-box protein-1 (YB-1) in regulating proximal tubule cell TGF-beta1 translation. Using RNA-electrophoretic mobility shift assays and ultraviolet crosslinking, we found two protein complexes of 50 and 100 kDa, which bound to the TGF-beta1 mRNA 5'-untranslated region. Supershift studies using antibodies to YB-1 showed that both sites contained YB-1 as did studies with recombinant YB-1, which demonstrated that it was sufficient to form both complexes. RNA competition experiments confirmed YB-1 binding to the two predicted binding sites; one with high affinity and the other with lower affinity. Strong basal YB-1 association with TGF-beta1 mRNA was found in proximal tubule cells, which decreased when platelet-derived growth factor was used to activate TGF-beta1 translation. In contrast, knockdown of proximal tubule cell YB-1 expression abrogated TGF-beta1 synthesis. Our results suggest that TGF-beta1 translation in proximal tubule cells requires YB-1 binding to a high-affinity site in the 5'-untranslated region of its mRNA; however, binding to a low-affinity site inhibits basal translation.

Y-Box Binding Protein-1 Mediates Profibrotic Effects of Calcineurin Inhibitors in the Kidney

“…Thus, YB-1 might be another important profibrotic factor induced by CsA, perhaps upstream but at least in a TGF-b-independent manner. Of note, YB-1 controls TGF-b translation in proximal tubular cells (17).…”

“…Another active role of YB-1 in fibrosis is accomplished by transcriptional control of the cellular content of a-smooth muscle actin (26) and Col1A (19,(27)(28)(29). Furthermore, in proximal tubular cells, YB-1 controls TGF-b1 translation (17), the most potent and ubiquitous profibrotic cytokine.…”

“…With its capacity to exhibit RNA-as well as DNAbinding properties, YB-1 controls the cellular content of multiple proteins. By means of RNA binding, YB-1 protects IL-2 and GM-CSF mRNA from degradation and controls TGF-b1 translation in proximal tubular cells (17). Furthermore, YB-1 is involved in mRNA processing (18).…”

Interaction of Hepatitis C Viral Proteins with Cellular Oncoproteins in the Induction of Liver Cancer

“…TGF-, a key cytokine in the activation of stellate cells and fibrosis, also cooperates with NS5A in polarity changes of hepatic precursor cells leading to the EMT [90]. EMT is also driven by many pathways and molecules such as TGF-1, the translation of which is regulated by YB-1 [92] and Wnt/Notch pathways, which were also shown to be involved in EMT [93]. Interestingly, YB-1 has been shown to bind to the promoters of a number of Wnt pathway genes; a fragment of YB-1 has been identified as a ligand for Notch 3 receptors [94,95].…”

The N-terminal Domain of the Y-box Binding Protein YB-1 Plays a Major Role in Cell Proliferation and Apoptosis

“…It is also involved in translational regulation of Cyclin D1, c-jun, mertk and PDGFR-β mRNA, by the PI3K-AKT pathway (Evdokimova et al, 2006). It is shown to be controlling transforming growth factor beta-1 (TGF-β1) translation in proximal tubular cells (Fraser et al, 2007).…”