Altered localization of Drosophila Smoothened protein activates Hedgehog signal transduction.
Hedgehog (Hh) signaling is critical for many developmental events and must be restrained to prevent cancer. A transmembrane protein, Smoothened (Smo), is necessary to transcriptionally activate Hh target genes. Smo activity is blocked by the Hh transmembrane receptor Patched (Ptc). The reception of a Hh signal overcomes Ptc inhibition of Smo, activating transcription of target genes. Using Drosophila salivary gland cells in vivo and in vitro as a new assay for Hh signal transduction, we investigated the regulation of Hh-triggered Smo stabilization and relocalization. Hh causes Smo to move from internal membranes to the cell surface. Relocalization is protein synthesis-independent and occurs within 30 min of Hh treatment. Ptc and the kinesin-related protein Costal2 (Cos2) cause internalization of Smo, a process that is dependent on both actin and microtubules. Disruption of endocytosis by dominant negative dynamin or Rab5 prevents Smo internalization. Fly versions of Smo mutants associated with human tumors are constitutively present at the cell surface. Forced localization of Smo at the plasma membrane activates Hh target gene transcription. Conversely, trapping of activated Smo mutants in the ER prevents Hh target gene activation. Control of Smo localization appears to be a crucial step in Hh signaling in Drosophila.
Departments of Developmental Biology and Genetics, Howard Hughes Medical Institute, Beckman Center B300, Stanford University School of Medicine, Stanford, California 94305-5329, USA.
Alan Jian
AJ
Zhu
Limin
L
Zheng
Kaye
K
Suyama
Matthew P
MP
Scott
D000818:Animals; D004330:Drosophila / Q000196:embryology / Q000378:metabolism*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D017930:Genes, Reporter; D053823:Hedgehog Proteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012469:Salivary Glands / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D000072086:Smoothened Receptor; D015533:Transcriptional Activation
D029721:Drosophila Proteins; D053823:Hedgehog Proteins; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D011993:Recombinant Fusion Proteins; D000072086:Smoothened Receptor; C070844:ptc protein, Drosophila; C100664:smo protein, Drosophila; C077245:hh protein, Drosophila