An essential role for Grk2 in Hedgehog signalling downstream of Smoothened. (4th April 2016)

• Record Type: Journal Article
• Authors: Zhao, Zhonghua; Lee, Raymond Teck Ho; Pusapati, Ganesh V; Iyu, Audrey; Rohatgi, Rajat; Ingham, Philip W
• Is Part Of: EMBO reports. Volume 17:Number 5(2016:May)
• Page Start: 739
• Page End: 752
• Publication Date: 2016-04-04
• Subjects: Grk2 -- Hedgehog signalling -- phosphorylation -- PKA -- Smo; Molecular biology -- Periodicals; Molecular Biology -- Periodicals; Molecular biology; Periodicals; 572.8
• DOI: 10.15252/embr.201541532
• Languages: English
• ISSNs: 1469-221X

Abstract

Abstract: The G‐protein‐coupled receptor kinase 2 (adrbk2/GRK2) has been implicated in vertebrate Hedgehog (Hh) signalling based on the effects of its transient knock‐down in mammalian cells and zebrafish embryos. Here, we show that the response to Hh signalling is effectively abolished in the absence of Grk2 activity. Zebrafish embryos lacking all Grk2 activity are refractory to both Sonic hedgehog (Shh) and oncogenic Smoothened (Smo) activity, but remain responsive to inhibition of cAMP‐dependent protein kinase (PKA) activity. Mutation of the kinase domain abrogates the rescuing activity of grk2 mRNA, suggesting that Grk2 acts in a kinase‐dependent manner to regulate the response to Hh. Previous studies have suggested that Grk2 potentiates Smo activity by phosphorylating its C‐terminal tail (CTT). In the zebrafish embryo, however, phosphomimetic Smo does not display constitutive activity, whereas phospho‐null mutants retain activity, implying phosphorylation is neither sufficient nor necessary for Smo function. Since Grk2 rescuing activity requires the integrity of domains essential for its interaction with GPCRs, we speculate that Grk2 may regulate Hh pathway activity by downregulation of a GPCR. Synopsis: Loss of zebrafish Grk2 eliminates all responses to Hh signalling during embryogenesis, but phospho‐null mutants of Smo retain significant activity, suggesting that Smo is not the principal target of Grk2. Grk2 is essential for all responses to Hh signalling in the zebrafish embryo. Phosphorylation of Grk2/CK1 sites in the Smo CTT is neither necessary nor sufficient for its activation. Grk2 regulates Hh signalling downstream of Smo, possibly via an unidentified GPCR. Abstract : Loss of zebrafish Grk2 eliminates all responses to Hh signalling during embryogenesis, but phospho‐null mutants of Smo retain significant activity, suggesting that Smo is not the principal target of Grk2.