First published online December 22, 2008
Development 136, 203e (2009)
© The Company of Biologists Limited
Phosphorylation balancing act in Hh signalling
Hedgehog (Hh) signalling, which mediates many important developmental
processes, is regulated by the phosphorylation state of both the
seven-transmembrane protein Smoothened (Smo) and the Zn-finger transcription
factor Ci/Gli. In Drosophila, multiple kinases are involved in Smo
and Ci phosphorylation. Now, Jia and co-workers report that the
serine/threonine protein phosphatases PP4 and PP2A also regulate Hh signalling
by controlling Smo and Ci dephosphorylation, respectively (see
p. 307). By examining
wing development, they show that RNAi knockdown of PP4 increases Smo
phosphorylation and accumulation, which leads to increased Hh signalling
activity. Other experiments suggest that Hh normally promotes Smo
phosphorylation, at least in part, by downregulating the Smo-PP4 interaction,
which is mediated by the kinesin-related protein Costal 2. The researchers
also provide evidence that PP2A is a Ci phosphatase and that it upregulates
the signalling activity of full-length Ci, the form of Ci that activates Hh
target genes. Thus, they conclude, multiple phosphatases - as well as multiple
kinases - regulate the Hh signalling cascade.

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Related articles in Development:
- PP4 and PP2A regulate Hedgehog signaling by controlling Smo and Ci phosphorylation
- Hongge Jia, Yajuan Liu, Wei Yan, and Jianhang Jia
Development 2009 136: 307-316.
[Abstract]
[Full Text]