Sequential Phosphorylation of Smoothened Transduces Graded Hedgehog Signaling

Sci. Signal., 5 July 2011
Vol. 4, Issue 180, p. ra43
DOI: 10.1126/scisignal.2001747

Sequential Phosphorylation of Smoothened Transduces Graded Hedgehog Signaling

  1. Ying Su*,
  2. Jason K. Ospina*,
  3. Junzheng Zhang*,
  4. Andrew P. Michelson,
  5. Adam M. Schoen, and
  6. Alan Jian Zhu
  1. Department of Cell Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
  1. To whom correspondence should be addressed. E-mail: zhua{at}
  • * These authors contributed equally to this work.


The correct interpretation of a gradient of the morphogen Hedgehog (Hh) during development requires phosphorylation of the Hh signaling activator Smoothened (Smo); however, the molecular mechanism by which Smo transduces graded Hh signaling is not well understood. We show that regulation of the phosphorylation status of Smo by distinct phosphatases at specific phosphorylated residues creates differential thresholds of Hh signaling. Phosphorylation of Smo was initiated by adenosine 3′,5′-monophosphate (cAMP)–dependent protein kinase (PKA) and further enhanced by casein kinase I (CKI). We found that protein phosphatase 1 (PP1) directly dephosphorylated PKA-phosphorylated Smo to reduce signaling mediated by intermediate concentrations of Hh, whereas PP2A specifically dephosphorylated PKA-primed, CKI-phosphorylated Smo to restrict signaling by high concentrations of Hh. We also established a functional link between sequentially phosphorylated Smo species and graded Hh activity. Thus, we propose a sequential phosphorylation model in which precise interpretation of morphogen concentration can be achieved upon versatile phosphatase-mediated regulation of the phosphorylation status of an essential activator in developmental signaling.


Y. Su, J. K. Ospina, J. Zhang, A. P. Michelson, A. M. Schoen, and A. J. Zhu, Sequential Phosphorylation of Smoothened Transduces Graded Hedgehog Signaling. Sci. Signal. 4, ra43 (2011).

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