Fig. 2: Schematic figure of the Hedgehog (Hh) pathway in vertebrates. | Cell Death & Disease

Fig. 2: Schematic figure of the Hedgehog (Hh) pathway in vertebrates.

From: Hedgehog signalling in the tumourigenesis and metastasis of osteosarcoma, and its potential value in the clinical therapy of osteosarcoma

Fig. 2

In vertebrates, there are three Hh ligands, Sonic hedgehog (Shh), Desert hedgehog (Dhh) and Indian hedgehog (Ihh); two 12-pass transmembrane receptors, Patched1 (PTCH1) and Patched2 (PTCH2); Smoothened (Smo); and three transcription factor glioma-associated oncogene homologues, GLI1, GLI2 and GLI3. a Off-state. In the absence of the Hh ligands, the cell surface receptor Patched (Ptch1 or Ptch2) binds to the class F G-protein-coupled receptor Smo and inhibits Smo activity, resulting in the inhibition of Hh signalling pathway activation. b On-state. In the presence of a Hh ligand (Shh, Ihh or Dhh), the Hh ligand binds to its receptor Ptch1 or Ptch2, initiating the classical Hh signalling pathway. Hh induces the phosphorylation of multiple Ser/Thr residues at the carboxy terminus of Smo, resulting in the release of the inhibition of Smo by Ptch. The activated Smo recruits and activates a cascade of cytoplasmic protein complexes to activate the Hh pathway. The target genes of the Hh pathway are transcribed and expressed

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