c-Cbl-Mediated Neddylation Antagonizes Ubiquitination and Degradation of the TGF-β Type II Receptor

Abstract

Transforming growth factor β (TGF-β) is a potent antiproliferative factor in multiple types of cells. Deregulation of TGF-β signaling is associated with the development of many cancers, including leukemia, though the molecular mechanisms are largely unclear. Here, we show that Casitas B-lineage lymphoma (c-Cbl), a known proto-oncogene encoding an ubiquitin E3 ligase, promotes TGF-β signaling by neddylating and stabilizing the type II receptor (TβRII). Knockout of c-Cbl decreases the TβRII protein level and desensitizes hematopoietic stem or progenitor cells to TGF-β stimulation, while c-Cbl overexpression stabilizes TβRII and sensitizes leukemia cells to TGF-β. c-Cbl conjugates neural precursor cell-expressed, developmentally downregulated 8 (NEDD8), a ubiquitin-like protein, to TβRII at Lys556 and Lys567. Neddylation of TβRII promotes its endocytosis to EEA1-positive early endosomes while preventing its endocytosis to caveolin-positive compartments, therefore inhibiting TβRII ubiquitination and degradation. We have also identified a neddylation-activity-defective c-Cbl mutation from leukemia patients, implying a link between aberrant TβRII neddylation and leukemia development.

Signaling Receptors for TGF-β Family Members

“…In addition, TbRII was recently shown to be modified also by the ubiquitin-like molecule NEDD8 (neural precursor cell-expressed, developmentally down-regulated 8) by the E3 ligase c-Cbl (Zuo et al 2013). c-Cbl is known as a ubiquitin E3 ligase and a negative modulator of many tyrosine kinase receptors, but has been shown to be capable also of neddylating the epidermal growth factor (EGF) receptor (Oved et al 2006).…”

“…Neddylation of TbRII at Lys556 and Lys567 was found to promote endocytosis of the receptor to early endosomes and to prevent its endocytosis to caveolin-positive compartments, thereby inhibiting degradation of TbRII (see further below). Interestingly, a neddylation-defective c-Cbl mutant was found in leukemias, suggesting that TbRII neddylation is important to inhibit leukemia progression (Zuo et al 2013).…”

The covalent modifier Nedd8 is critical for the activation of Smurf1 ubiquitin ligase in tumorigenesis

“…Smurf1 can be neddylated by itself or by other Nedd8 ligase(s). Among the currently known Nedd8 ligases (that is, Dcn1, Roc1/ Rbx1, MDM2, IAPs and c-Cbl) 6,13,23,25,[39][40][41][42] , only MDM2 was demonstrated to interact with Smurf1 (ref. 43).…”

“…Modification of CRLs by the ubiquitin-like Nedd8 (neural precursor cell-expressed developmentally downregulated protein 8), called neddylation, has been demonstrated to be essential for their activation 1,5 . In addition, non-cullin proteins such as p53, EGFR, pVHL, ribosomal proteins, Parkin, E2F-1 and TGFb II receptor have been shown to be neddylated as well [6][7][8][9][10][11][12][13] .…”

“…For example, Roc1/ Rbx1 and Dcn1 function synergistically to promote Nedd8 transfer from Ubc12 to Cullins 23,24 . MDM2, c-Cbl and IAPs have also been demonstrated to function as Nedd8 ligases to promote ligation to non-Cullin proteins 6,7,13,25 . All of the characterized Nedd8 E3s belong to the scaffold-type.…”