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PNAS 106 (25): 10183-10188

Copyright © 2009 by the National Academy of Sciences.


Kinase activity-independent regulation of cyclin pathway by GRK2 is essential for zebrafish early development

Xi Jiang, Peng Yang, and Lan Ma1

State Key Laboratory of Medical Neurobiology and Pharmacology Research Center, Shanghai Medical College and Institutes of Brain Science, Fudan University, Shanghai 200032, China

Edited by Robert J. Lefkowitz, Duke University Medical Center, Durham, NC, and approved April 24, 2009

Received for publication December 1, 2008.

Abstract: G protein-coupled receptor (GPCR) kinases (GRKs) are known as a family of serine/threonine kinases that function as key regulators of GPCRs, as well as other types of receptors. Extensive studies of GRKs at the cellular and organismal levels have led to a consensus that GRK-catalyzed phosphorylation of receptors is the primary mechanism underlying their physiological functions. Here, we report that down-regulation of GRK2 in zebrafish embryos with GRK2 morpholino results in developmental early arrest and, interestingly, that this arrest can be rescued by exogenous expression of a GRK2 kinase-dead mutant, K220R. A physical interaction between GRK2 and cyclin B1 regulator patched homolog 1 (PTCH1), stimulated by Hedgehog (Hh), rather than GRK2-mediated phosphorylation of downstream targets, appears as the underlying mechanism. We identify residues 262–379 as the PTCH1-binding region (BP). Interaction of GRK2, K220R, and BP with PTCH1 reduces the association of PTCH1 with cyclin B1 and disrupts PTCH1-mediated inhibition of cyclin B1 nuclear translocation, whereas the PTCH1-binding deficient GRK2 mutant ({Delta}312–379) does not. Cell cycle and cell proliferation assays show that overexpressing PTCH1 remarkably inhibited cell growth and this effect could be attenuated by GRK2, K220R, or BP, but not {Delta}312–379. In vivo studies show that BP, as well as the nuclear-localizing cyclin B1 mutant, is effective in rescuing the early arrest phenotype in GRK2 knockdown embryos, but {Delta}312–379 is not. Our data thus reveal a novel kinase activity-independent function for GRK and establish a role for GRK2 as a cell-cycle regulator during early embryonic development.

Key Words: cyclin B1 • early arrest • embryonic development • G protein-coupled receptor kinase • PTCH1

Author contributions: X.J. and L.M. designed research; X.J. and P.Y. performed research; X.J., P.Y., and L.M. analyzed data; and X.J. and L.M. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

This article contains supporting information online at

1To whom correspondence should be addressed. E-mail: lanma{at}

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