KBTBD7 regulates Wnt/PCP signaling by targeting Vangl proteins for endoplasmic reticulum-associated degradation via Vangl-p97/VCP direct interaction

Abstract

Wnt/Planar Cell Polarity (PCP) signaling is a pivotal mechanism coordinating diverse polarized cell behaviors and governing a wide range of tissue morphogenetic processes. Wnt/PCP signaling is under tight control to ensure accurate signaling activity for normal physiological functions, but the underlying molecular mechanisms remain largely unknown. Mutations in two dedicated core PCP components Vangl1 and Vangl2 have been identified in human birth defects (e. g. neural tube defects), whereas their abnormal activation has been implicated in various cancers. Here, I identified that the Cullin-RING ubiquitin ligase (CRL) CUL3-KBTBD7 negatively regulated PCP signaling by targeting the four-pass transmembrane proteins Vangl for degradation through the ubiquitin-proteasome system (UPS). KBTBD7, the substrate recognition protein in CRL3 complex, directly interacts with Vangl via Kelch repeats, resulting in Vangl ubiquitination and endoplasmic reticulum-associated degradation (ERAD). Interestingly, KBTBD7-induced Vangl2 ubiquitination and ERAD are dependent on p97/VCP, the key ERAD regulator for substrate extraction from the ER to the cytosol. p97/VCP directly interacts with Vangl2 via a highly conserved VCP-interacting motif (VIM) and recruits KBTBD7 from the cytosol to the ER, enabling efficient KBTBD7-Vangl2 interaction and ubiquitination. Moreover, I found that Wnt5a/CK1-induced basal phosphorylation of Vangl2 in the ER protects Vangl2 from KBTBD7-induced ubiquitination and degradation, leading to the efficient docking of Vangl2 to the plasma membrane, which highlights the importance of Wnt and ERAD in controlling the quality and activity of PCP signaling molecules. I further showed that KBTBD7 overexpression in zebrafish degraded Vangl2 and caused convergent extension (CE) defect, a typical Wnt/PCP signaling-defective phenotype in vertebrates. Using breast cancer cells and xenograft mouse model, I demonstrated a suppressive effect of KBTBD7 in inhibiting mammary tumor growth and metastasis via degrading Vangl proteins. The low expression level of KBTBD7 is significantly associated with poor outcomes in patients with breast cancers. In summary, my findings reveal a novel regulatory mechanism of Wnt/PCP signaling through p97/VCP-CRL3KBTBD7-mediated and ERAD-dependent Vangl ubiquitination and degradation, suggesting a potential new approach to modulate this signaling pathway for the therapeutic benefit of breast cancer patients.