Editors' ChoiceDevelopmental Biology

Allosteric regulation of Warts

Sci. Signal.  05 Jan 2016:
Vol. 9, Issue 409, pp. ec2
DOI: 10.1126/scisignal.aaf1721

Warts (Wts) is part of the core kinase cassette of the Hippo growth control pathway. When phosphorylated by Hippo, Wts prevents the transcriptional coactivator Yorkie from stimulating the expression of genes required for cell proliferation. The Mob family protein Mats is required for Wts activation by Hippo. In the Drosophila melanogaster wing imaginal disc, the atypical myosin Dachs, which is recruited to the membrane by engagement of the protocadherins Fat (Ft) and Dachsous (Ds), inhibits Wts activation, thus promoting cell proliferation and tissue growth. In wing discs expressing an intramolecular fluorescence resonance energy transfer reporter in which the acceptor and donor were fused to opposite ends of Wts (Wts-FRET), Vrabioiu and Struhl found that Wts existed in two conformations in vivo: a closed conformation in which the two fluorescent moieties were close to one another and an open conformation in which they were far apart. At the periphery of the disc, where Dachs is strongly asymmetrically localized within cells, Wts-FRET preferentially adopted the closed conformation; in the center of the disc, where Dachs is only weakly asymmetrically localized within cells, Wts-FRET was predominantly in the open conformation. Hippo-mediated phosphorylation was not required for conformational switching of Wts, because the relative abundance of the open and closed conformations of Wts-FRET did not differ between wild-type wing disc cells and clones of cells lacking Hippo or Expanded, a protein required for Hippo activity. Indeed, the distribution of closed and open conformations across the disc was not affected by mutating the Hippo phosphorylation site in the Wts-FRET sensor. In mats mutant clones or when mats was knocked down by RNA interference, a higher proportion of the Wts-FRET was in the closed conformation. A variant of the Wts-FRET sensor that cannot interact with Mats also preferentially adopted the closed conformation in wing discs. Experiments using mutant clones, ectopic overexpression, or knockdown of Ft, Ds, or Dachs demonstrated that activation of either Ft or Ds promoted the closed conformation of Wts-FRET in a manner that depended on Dachs. Experiments in wing discs with dachs and mats single- or double-mutant clones indicated that Mats was required for the open state of Wts-FRET, even in the absence of Dachs. Thus, Mats promotes the transition of Wts from a closed, inactive conformation to an open conformation, and Dachs either reverses or inhibits this switch. These findings suggest that Wts exists in at least three states: a closed, inactive conformation; an open conformation that is competent to be phosphorylated by Hippo; and an active, phosphorylated state (see Manning and Harvey). These findings also illustrate how Wts activity can be attenuated independently of Hippo regulation to promote tissue growth.

A. M. Vrabioiu, G. Struhl, Fat/Dachsous signaling promotes Drosophila wing growth by regulating the conformational state of the NDR kinase Warts. Dev. Cell 35, 737–749 (2015). [PubMed]

S. A. Manning, K. F. Harvey, Warts opens up for activation. Dev. Cell 35, 666–668 (2015). [PubMed]