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Fig. 2 | Molecular Cancer

Fig. 2

From: Noncoding RNAs related to the hedgehog pathway in cancer: clinical implications and future perspectives

Fig. 2

Three patterns of abnormal hedgehog signaling activation in cancer. Positive and negative regulatory components, Smo and Ptch are depicted in red and blue, respectively. a Type 1 - ligand independent oncogenic Hh pathway (autonomous). The gain-of-function mutant Smo (red asterisk) and the loss-of-function mutant Ptch or Sufu (blue asterisk) can activate the Hh signaling pathway. b Type 2 - ligand dependent oncogenic Hh pathway (autocrine or juxtacrine). The autocrine Hh ligand of tumor cells is taken up by the same tumor cells (autocrine) or adjacent tumor cells (juxtacrine), and stimulates the Hh signaling in cancer by interacting with Ptch and Smo. c Type 3/a - ligand dependent oncogenic Hh pathway (paracrine). This is the paracrine mode in which stromal cells take up the Hh ligand secreted by tumor cells, and then secrete some growth factors, such as VEGF and IGF, which provide a suitable environment for tumor cells growth. d Type 3/b - ligand dependent oncogenic Hh pathway (reverse paracrine). This is the reverse paracrine mode in which tumor cells directly take up the Hh ligand secreted by stromal cells, triggering cascade response of Hh signaling

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