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Hedgehog signalling activity of Smoothened requires phosphorylation by protein kinase A and casein kinase I


The Hedgehog (Hh) family of secreted proteins governs cell growth and patterning in animal development1. The Hh signal is transduced by the seven-transmembrane protein Smoothened (Smo); however, the mechanism by which Smo is regulated remains largely unknown. Here we show that protein kinase A (PKA) and casein kinase I (CKI) regulate Smo cell-surface accumulation and activity in response to Hh. Blocking PKA or CKI activity in the Drosophila wing disc prevents Hh-induced Smo accumulation and attenuates pathway activity, whereas increasing PKA activity promotes Smo accumulation and pathway activation. We show that PKA and CKI phosphorylate Smo at several sites, and that phosphorylation-deficient forms of Smo fail to accumulate on the cell surface and are unable to transduce the Hh signal. Conversely, phosphorylation-mimicking Smo variants show constitutive cell-surface expression and signalling activity. Furthermore, we find that the levels of Smo cell-surface expression and activity correlate with its levels of phosphorylation. Our data indicate that Hh induces progressive Smo phosphorylation by PKA and CKI, leading to elevation of Smo cell-surface levels and signalling activity.

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Figure 1: Positive regulation of Smo accumulation and Hh signalling by PKA and CKI.
Figure 2: Phosphorylation of Smo by PKA and CKI.
Figure 3: Hh signalling activity of Smo variants.
Figure 4: Regulation of Smo cell-surface accumulation by phosphorylation and models for kinase regulation of Smo activity.


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We thank D. Kalderon, S. Cohen, P. Beachy, R. Holmgren and G. Struhl for reagents, and K. Wharton and H. Kramer for comments. This work was supported by grants from NIH, Leukemia and Lymphoma Society Scholar Program to J.J., who is a Eugene McDermott Endowed Scholar of Biomedical Science at UTSW.

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Correspondence to Jin Jiang.

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Supplementary Figures

This file contains figures and legends for Supplementary Fig. S1 (rescuing smo mutant phenotypes by Smo variants), Fig. S2 (regulation of Smo cell surface accumulation by phosphorylation in S2 cells), Fig. S3 (cell surface accumulation of wild type Smo and SmoSD123 in wing discs) and Fig. S4 (effects of overexpressing phosphorylation deficient forms of Smo on accumulation of wild type Smo in wing discs). (DOC 3122 kb)

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Jia, J., Tong, C., Wang, B. et al. Hedgehog signalling activity of Smoothened requires phosphorylation by protein kinase A and casein kinase I. Nature 432, 1045–1050 (2004).

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