Patched (Ptc) is a conserved 12-pass transmembrane protein receptor that plays an obligate negative regulatory role in the Hedgehog signaling pathway in insects and vertebrates. Patched is an essential gene in embryogenesis for proper segmentation in the fly embryo, mutations in which may be embryonic lethal. Patched functions as the receptor for the Hedgehog protein
Discovery
The original mutations in the
ptc gene were discovered in the fruit fly
Drosophila melanogaster by 1995
Nobel Laureates Eric F. Wieschaus and Christiane Nusslein-Volhard and colleagues, and the gene was independently cloned in 1989 by Joan Hooper in the laboratory of Matthew P. Scott, and by
Philip Ingham and colleagues.
Role in hedgehog signaling
Patched is part of a negative feedback mechanism for hedgehog signaling that helps shape the spatial gradient of signaling activity across tissues. In the absence of hedgehog, low levels of patched are sufficient to suppress activity of the signal transduction pathway. When hedgehog is present, its
cholesterol moiety binds to the sterol-sensing domain in patched, which then inhibits the activity of
smoothened. Smoothened is a G protein-coupled receptor, most of which is stored in membrane bound vesicles internally within the cell and which increases at the cell surface when hedgehog is present. Smoothened must be present on the
cell membrane in order for the Hedgehog signaling pathway to be activated. Among other genes, the transcription of the patched gene is induced by hedgehog signaling, with the accumulation of the patched protein limiting signaling through the Smoothened protein. Recent work implicates the
cilium in intracellular trafficking of hedgehog signaling components in vertebrate cells.
Role in disease
Mutated patched proteins have been implicated in a number of cancers including basal cell carcinoma,
medulloblastoma, and
rhabdomyosarcoma.
Hereditary
in the human patched homolog
PTCH1 cause autosomal dominant
Gorlin syndrome, which consists of overgrowth and hereditary disposition to cancer including basal cell carcinoma and medulloblastoma. Mice with mutations in mouse
PTCH1 similarly develop medulloblastoma.
