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First published online 27 February 2008
doi: 10.1242/dev.009936

Development 135, 1347-1353 (2008)
Published by The Company of Biologists 2008
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Evidence that DIF-1 and hyper-osmotic stress activate a Dictyostelium STAT by inhibiting a specific protein tyrosine phosphatase

Tsuyoshi Araki1,*, Judith Langenick1,*, Marianne Gamper2,3, Richard A. Firtel2 and Jeffrey G. Williams1,{dagger}

1 University of Dundee, College of Life Sciences, Dow Street, Dundee DD1 5EH, UK.
2 University of California, San Diego, Natural Sciences Building Room 6111, 9500 Gilman Drive, La Jolla, CA 92093-0380, USA.
3 Biomedical Research Foundation (SBF), Lauchefeld 31, CH-9548 Matzingen, Switzerland.

{dagger} Author for correspondence (e-mail: j.g.williams{at}dundee.ac.uk)

Accepted 18 January 2008

STATc becomes tyrosine phosphorylated and accumulates in the nucleus when Dictyostelium cells are exposed to the prestalk cell inducer Differentiation inducing factor 1 (DIF-1), or are subjected to hyper-osmotic stress. We show that the protein tyrosine phosphatase PTP3 interacts directly with STATc and that STATc is refractory to activation in PTP3 overexpressing cells. Conversely, overexpression of a dominant inhibitor of PTP3 leads to constitutive tyrosine phosphorylation and ectopic nuclear localisation of STATc. Treatment of cells with DIF-1 or exposure to hyper-osmotic stress induces a decrease in biochemically assayable PTP3 activity and both agents also induce serine-threonine phosphorylation of PTP3. These observations suggest a novel mode of STAT activation, whereby serine-threonine phosphorylation of a cognate protein tyrosine phosphatase results in the inhibition of its activity, shifting the phosphorylation-dephosphorylation equilibrium in favour of phosphorylation.

Key words: STAT, Dictyostelium, Tyrosine phosphatase, Stress, DIF-1


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STAT activation: DIF-ining a new mechanism

Development 2008 135: e705. [Full Text]  





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