Editors' ChoiceMAP Kinase

A Tether and A Phosphatase

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Science's STKE  23 May 2000:
Vol. 2000, Issue 33, pp. tw2
DOI: 10.1126/stke.2000.33.tw2

In order for signals to be transmitted from the MAP kinase pathway into the nucleus, the activated kinase must physically translocate into the nucleus. Phosphorylation of the MAP kinase leads to its ability to translocate into the nucleus; however, the signal for redistribution to the cytoplasm is less well understood. Mattison and Ota took advantage of the model organism Saccharomyces cerevisiae to study the mechanism of transport into and out of the nucleus. Redistribution of the stress-activated MAP kinase, Hog1p, from the nucleus to the cytoplasm is not dependent on dephosphorylation by the nuclear protein phosphatase, Ptp2, or the cytoplasmic phosphatase, Ptp3. Under conditions of very high osmotic stress, the accumulation of Hog1p in the nucleus was diminished in yeast lacking Ptp2 and was increased in yeast lacking Ptp3. Furthermore, overexpression of catalytically inactive forms of the phosphatases led to alterations in the distribution of Hog1p: inactive Ptp2 shifted Hog1p to the nucleus and inactive Ptp3 shifted Hog1p to the cytoplasm. These data along with the in vitro binding of the phosphatases with Hog1p suggest that these phosphatases serve dual roles: They dephosphorylate the Hog1p to inactivate the kinase, and they serve as nuclear (Ptp2) and cytoplasmic (Ptp3) tethers that contribute to controlling the subcellular localization of the Hog1p. This second function is independent of the phosphatase activity of Ptp2 and Ptp3 and may occur through binding sites separate from those that mediate dephosphorylation.

Mattison, C.P., and Ota, I.M. (2000) Two protein tyrosine phosphatases, Ptp2 and Ptp3, modulate the subcellular localization of the Hog1 MAP kinase in yeast. Genes Dev. 14: 1229-1235. [Abstract] [Full Text]