Tmed2 regulates Smoothened trafficking and Hedgehog signalling

Hedgehog (HH) signalling plays a key role in embryonic pattering and stem cell differentiation. Compounds that selectively bind Smoothened (SMO) can induce cell death in mouse embryonic stem cells (ESCs). Here we perform a genetic screen in haploid ESCs and discover that SMO inhibits a cell death pathway that resembles dissociation induced death of human ESCs and Anoikis. In mouse ESCs, SMO acts through a G-protein coupled mechanism that is independent of GLI activation. Our screen also identifies the Golgi proteins Tmed2 and Tmed10. We show that TMED2 binds SMO and controls its abundance at the plasma membrane. In neural differentiation and neural tube pattering Tmed2 acts as a repressor of HH signalling strength. We demonstrate that the interaction between SMO and TMED2 is regulated by HH signalling suggesting SMO release form the ER-Golgi is critical for controlling G-protein and GLI mediated functions of mammalian HH signalling.