Smoothened signal transduction is promoted by G protein-coupled receptor kinase 2.
Deregulation of the Sonic hedgehog pathway has been implicated in an increasing number of human cancers. In this pathway, the seven-transmembrane (7TM) signaling protein Smoothened regulates cellular proliferation and differentiation through activation of the transcription factor Gli. The activity of mammalian Smoothened is controlled by three different hedgehog proteins, Indian, Desert, and Sonic hedgehog, through their interaction with the Smoothened inhibitor Patched. However, the mechanisms of signal transduction from Smoothened are poorly understood. We show that a kinase which regulates signaling by many "conventional" 7TM G-protein-coupled receptors, G protein-coupled receptor kinase 2 (GRK2), participates in Smoothened signaling. Expression of GRK2, but not catalytically inactive GRK2, synergizes with active Smoothened to mediate Gli-dependent transcription. Moreover, knockdown of endogenous GRK2 by short hairpin RNA (shRNA) significantly reduces signaling in response to the Smoothened agonist SAG and also inhibits signaling induced by an oncogenic Smoothened mutant, Smo M2. We find that GRK2 promotes the association between active Smoothened and beta-arrestin 2. Indeed, Gli-dependent signaling, mediated by coexpression of Smoothened and GRK2, is diminished by beta-arrestin 2 knockdown with shRNA. Together, these data suggest that GRK2 plays a positive role in Smoothened signaling, at least in part, through the promotion of an association between beta-arrestin 2 and Smoothened.
Meloni
Alison R
AR
Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA.
Fralish
Gregory B
GB
Kelly
Patrick
P
Salahpour
Ali
A
Chen
James K
JK
Wechsler-Reya
Robert J
RJ
Lefkowitz
Robert J
RJ
Caron
Marc G
MG
D000818:Animals; D019390:Arrestins / Q000235:genetics / Q000378:metabolism; D002417:Cattle; D002460:Cell Line; D006801:Humans; D051379:Mice; D015513:Oncogene Proteins / Q000378:metabolism; D011485:Protein Binding; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D000072086:Smoothened Receptor; D015534:Trans-Activators / Q000378:metabolism; D000071676:Zinc Finger Protein GLI1; D051552:beta-Adrenergic Receptor Kinases / Q000235:genetics / Q000378:metabolism*; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins
C000605254:ARRB2 protein, human; C000605258:Arrb2 protein, mouse; D019390:Arrestins; D015513:Oncogene Proteins; D043562:Receptors, G-Protein-Coupled; C491022:Smo protein, mouse; D000072086:Smoothened Receptor; D015534:Trans-Activators; D000071676:Zinc Finger Protein GLI1; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins; D051552:beta-Adrenergic Receptor Kinases