In vivo functions of the patched protein: requirement of the C terminus for target gene inactivation but not Hedgehog sequestration.

The membrane protein Patched (Ptc) is a key regulator of Hedgehog (Hh) signaling in development and is mutated in human tumors. Ptc opposes Hh-induced gene transcription and sequesters Hh protein. To dissect these functions, we tested partially deleted forms of Ptc in Drosophila. Deletion of either half of Ptc abolishes all function while coexpression of the halves restores nearly full activity. Deletion of the final 156 residues of Ptc permits Hh sequestration but abolishes inhibition of Hh targets. This deletion has dominant-negative activity, promoting target gene activation in a ligand-independent manner. We observe little or no association of full-length or partially deleted Ptc with the membrane protein Smoothened in Drosophila cultured cells.