The C-terminal cytoplasmic tail of hedgehog receptor Patched1 is a platform for E3 ubiquitin ligase complexes

The Sonic hedgehog (Shh) signaling pathway plays a crucial role in cell proliferation and differentiation via Patched1 (Ptc1), a 12-pass transmembrane receptor protein. The C-terminal cytoplasmic tail of Ptc1 can be cleaved to release the 7th intracellular domain (ICD7), whose function is still unclear. In this study, we found that the ICD7 fragment of Ptc1 associates with polyubiquitinated species. Using mass spectrometry, we identified a cluster of E3 ubiquitin ligase complex as novel Ptc1 ICD7-binding proteins. In particular, Ptc1 ICD7 interacted with most components of the Cullin-2 (CUL2)-based E3 ligase complex, including TCEB1 (EloC), TCEB2 (EloB), ZYG11B, and CUL2 itself. To address the significance of CUL2-based E3 ligase in Ptc1 function, we examined the effects of CUL2 knockdown on Shh-induced osteoblast differentiation in the mesenchymal stem cell line C3H10T1/2. Indeed, knockdown of CUL2 abolished the Shh-induced stem cell differentiation. These results suggest that CUL2-based E3 ligase complex may play a role in Shh- and Ptc1-dependent signaling pathways.