The 3-beta-hydroxysteroid-Delta(8), Delta(7)-isomerase EBP inhibits cholesterylation of Smoothened

Hedgehog (Hh) pathway plays a central role in vertebrate embryonic development and carcinogenesis. The G-protein coupled receptor-like protein Smoothened (SMO) is one of the major members in Hh pathway. Covalent modification of cholesterol on the 95th asparagine (D95) of human SMO, which is regulated by Hh and PTCH1, is critical for SMO activation. However, it is not known whether SMO cholesterylation is regulated by other proteins. In this study, we identified Emopamil binding protein (EBP, also known as 3-beta-hydroxysteroid-Delta(8),Delta(7)-isomerase) as a SMO-interacting protein. Overexpression of EBP suppressed SMO cholesterylation and Hh pathway activity, whereas genetic disruption of EBP enhanced SMO cholesterylation and the downstream signaling. EBP-mediated inhibition of SMO cholesterylation was independent of its isomerase activity, but dependent on the C-terminus of EBP that was required for SMO binding. The X-linked dominant chondrodysplasia punctate 2 (CDPX2)-associated EBP mutants inhibited SMO cholesterylation too. Together, this study shows that EBP modulates SMO cholesterylation through direct binding and suggests a possible mechanism of CDPX2 pathogenesis.