The DUB family consists of approximately 120 members, which can cleave polyubiquitin chains or remove the ubiquitin moiety from target proteins, thus reversing the effect of ubiquitin ligases. The importance of addition of ubiquitin moieties for the function of PDGFRβ has been extensively investigated, while no deubiquitinating enzyme (DUB) that may regulate the levels of ubiquitination of PDGFRβ has been identified to date.ĭUBs have been implicated in the regulation of diverse cellular processes, such as cell cycle, signal transduction, apoptosis, DNA repair and chromatin remodelling. Ubiquitination of RTKs following ligand binding and phosphorylation is a hallmark of receptor-mediated endocytosis and serves to mediate interactions of RTKs with the sorting machineries at the cell surface and at endosomes. Ubiquitination is a post-translational modification of cellular proteins that plays important roles in, e.g., proteasomal degradation of proteins, intracellular trafficking, receptor internalization and downregulation, DNA repair and cell proliferation.

This results in internalization and activation of downstream signalling pathways at the plasma membrane as well as during endosomal trafficking and via translocation to the nucleus. PDGF isoforms bind to receptor tyrosine kinases (RTKs) α and β (PDGFRα and PDGFRβ, respectively), causing receptor dimerization and autophosphorylation. The platelet-derived growth factor (PDGF) isoforms are mitogens and chemotactic agents for smooth muscle cells, pericytes, fibroblasts and glial cells of the brain, regulating embryonic development, would healing, interstitial fluid pressure and blood–brain barrier. Thus, USP17- and USP4-mediated changes in ubiquitination of PDFGRβ lead to dysregulated signalling and transcription downstream of STAT3, resulting in defects in the control of cell proliferation. Deletion of USP17 was lethal to fibroblasts, while deletion of USP4 led to a decreased proliferative response to stimulation by PDGF-BB. Induction of USP17 promoted acute upregulation of the mRNA expression of STAT3-inducible genes STAT3, CSF1, junB and c-myc, while causing long-term changes in the expression of myc and CDKN1A. Induction of each of the DUBs in BJhTERT fibroblasts and U2OS osteosarcoma cells led to prolonged and/or shifted activation of STAT3 in response to PDGF-BB stimulation, which in turn led to increased transcriptional activity of STAT3. Deubiquitination of PDGFRβ did not affect its stability, but regulated the timing of its trafficking, whereby USP17 prolonged the presence of the receptor at the cell surface, while USP4 affected the speed of trafficking towards early endosomes. By overexpressing a panel of deubiquitinating enzymes (DUBs), we found that USP17 and USP4 efficiently deubiquitinate PDGF receptor β (PDGFRβ) and are able to remove both Lys63 and Lys48-linked polyubiquitin chains from the receptor. Ubiquitination of PDGFRs serves as a mark to direct the internalization and sorting of the receptors. Interaction of platelet-derived growth factor (PDGF) isoforms with their receptors results in activation and internalization of receptors, with a concomitant activation of downstream signalling pathways.

Finetune com