Non-canonical Wnt Signaling Induces Ubiquitination and Degradation of Syndecan4

Abstract

Dynamic regulation of cell adhesion receptors is required for proper cell migration in embryogenesis, tissue repair, and cancer. Integrins and Syndecan4 (SDC4) are the main cell adhesion receptors involved in focal adhesion formation and are required for cell migration. SDC4 interacts biochemically and functionally with components of the Wnt pathway such as Frizzled7 and Dishevelled. Non-canonical Wnt signaling, particularly components of the planar cell polarity branch, controls cell adhesion and migration in embryogenesis and metastasic events. Here, we evaluate the effect of this pathway on SDC4. We have found that Wnt5a reduces cell surface levels and promotes ubiquitination and degradation of SDC4 in cell lines and dorsal mesodermal cells from Xenopus gastrulae. Gain-and loss-of-function experiments demonstrate that Dsh plays a key role in regulating SDC4 steady-state levels. Moreover, a SDC4 deletion construct that interacts inefficiently with Dsh is resistant to Wnt5a-induced degradation. Non-canonical Wnt signaling promotes monoubiquitination of the variable region of SDC4 cytoplasmic domain. Mutation of these specific residues abrogates ubiquitination and results in increased SDC4 steadystate levels. This is the first example of a cell surface protein ubiquitinated and degraded in a Wnt/Dsh-dependent manner.Cell adhesion and migration are key processes for embryogenesis, inflammatory response, tissue repair, and cancer. Cell migration is a very dynamic process that requires the continuous assembly and disassembly of the cell surface complexes mediating cell-cell and cell-extracellular matrix adhesion (1, 2). Integrins and Syndecans are the main cell adhesion receptors involved in focal adhesion (FA) 5 formation and cell-extracellular matrix communication (3). FA formation of cells plated on fibronectin requires the specific engagement and synergism between ␣5␤1 integrin and Syndecan4 (SDC4)(3, 4).SDC4 is a cell surface heparan sulfate proteoglycan that activates intracellular signaling cascades through activation of PKC␣ (4). SDC4 overexpression or knockout compromises cell migration in normal (5) and tumorigenic cells (6). More recently it was demonstrated that SDC4 is required for localization of Rac1 and membrane protrusion formation at the leading edge to allow celldirected migration (7). In normal and tumorigenic cells, endocytosis and recycling of integrins modulate FA turnover and proper cell migration (8, 9). Which extracellular cues regulate the stability and turnover of FA receptors, in particular of SDC4, is a key question to understand cell migration.Wnt proteins constitute a large family of secreted glycoproteins that can activate diverse intracellular signaling pathways in a context-dependent manner. Wnt5a is known to promote polarized cell migration by activating a non-canonical Wnt pathway through the tyrosine kinase Ror2 receptor and c-Jun N-terminal kinase (10 -12). Wnt5a increases cell migration and invasiveness of tumorigenic cells by activation of FA kinase, PKC, Rac1, and promoti...

Ubiquitin-specific Protease 9x Deubiquitinates and Stabilizes the Spinal Muscular Atrophy Protein-Survival Motor Neuron

“…The 26 S proteasome usually degrades polyubiquitinated proteins conjugated with at least tetra-Ub (64). Mono-and oligo-ubiquitination (multiple mono-ubiquitinations) are also able to target proteins for proteasomal degradation (65)(66)(67)(68)(69). However, mono-Ub and short Ub chains have much weaker proteasomal binding affinity than that of poly-Ub chains, this might explain why SMN⌬7 is more rapidly degraded than SMN by the 26 S proteasome.…”

ICAP-1 monoubiquitination coordinates matrix density and rigidity sensing for cell migration through ROCK2- MRCKα balance

“…Tunable post-translational modifications may control ICAP-1 functions enabling the cell to adapt its migratory response. As ubiquitylation is emerging as important for cell migration dynamics and cell contractility (Carvallo et al, 2010;Sahai et al, 2007;Schaefer et al, 2012;Su et al, 2013;Wang et al, 2003), we addressed whether ubiquitylation may control ICAP-1 functions, enabling the cell to adapt its migratory response. Here, we show that ICAP-1 is monoubiquitylated by SMAD ubiquityl regulatory factor 1 (Smurf1).…”

Non-canonical ubiquitin-based signals for proteasomal degradation

“…For instance, monoubiquitylation of paired box 3 (PAX3), an important regulator of muscle differentiation, on a specific lysine residue (437 or 475) by the ubiquitin ligase TAF1 (Boutet et al, 2010), targets this protein for proteasomal degradation (Boutet et al, 2007). Similarly, syndecan 4 (SDC4), a cell adhesion receptor that is required for cell migration, becomes monoubiquitylated in its cytoplasmic domain in a WNT-and DSH-dependent manner and is subsequently degraded by the proteasome (Carvallo et al, 2010). Furthermore, proteasomal processing of the NF-B precursor p105 to the active subunit p50 requires its modification by several single ubiquitin moieties on a cluster of lysine residues that reside in the C-terminal half of the molecule (Kravtsova-Ivantsiv et al, 2009).…”