Elsevier

Developmental Biology

Volume 337, Issue 1, 1 January 2010, Pages 99-109
Developmental Biology

Regulation of Smoothened by Drosophila G-protein-coupled receptor kinases

https://doi.org/10.1016/j.ydbio.2009.10.014Get rights and content
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Abstract

The Hedgehog (Hh) signaling pathway plays a conserved and essential role in regulating development and homeostasis of numerous tissues. Cytoplasmic signaling is initiated by Smoothened (Smo), a G-protein-coupled receptor (GPCR) family member, whose levels and activity are regulated by the Hh receptor Patched (Ptc). In response to Hh binding to Ptc, Ptc-mediated repression of Smo is relieved, leading to Smo activation, surface accumulation, and downstream signaling. We find that downregulation of Drosophila Smo protein in Hh-responding imaginal disc cells is dependent on the activity of G-protein-coupled receptor kinase 2 (Gprk2). By analyzing gain- and null loss-of-function phenotypes, we provide evidence that Gprk2 promotes Smo internalization subsequent to its activation, most likely by direct phosphorylation. Ptc-dependent regulation of Smo accumulation is normal in gprk2 mutants, indicating that Gprk2 and Ptc downregulate Smo by different mechanisms. Finally, we show that both Drosophila G-protein-coupled receptor kinase orthologues, Gprk1 and Gprk2, act in a partially redundant manner to promote Hh signaling. Our results suggest that Smo is regulated by distinct Ptc-dependent and Gprk2-dependent trafficking mechanisms in vivo, analogous to constitutive and activity-dependent regulation of GPCRs. G-protein-coupled receptor kinase activity is also important for efficient downstream signaling.

Keywords

Hedgehog signaling
G-protein-coupled receptor kinase
Protein trafficking
Patched
Smoothened
Drosophila melanogaster

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