Journal
DEVELOPMENT
Volume 135, Issue 7, Pages 1347-1353Publisher
COMPANY BIOLOGISTS LTD
DOI: 10.1242/dev.009936
Keywords
STAT; Dictyostelium; tyrosine phosphatase; stress; DIF-1
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Funding
- NIGMS NIH HHS [R01 GM037830, R01 GM024279, R01 GM037830-22, R01 GM024279-30, R01 GM084227] Funding Source: Medline
- Wellcome Trust [053640/Z/98beta] Funding Source: Medline
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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.
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