72 X.-Q. Zhang et al. some hepatocytes (data not given) and for all Purkinje cells (Figure 1D). Furthermore, if KCa3.1 only represents one of several substrates of PHPT1 the signal from the channel-bound enzyme may be weak compared to all other signals. In conclusion, in the present immunohistochem- ical study the expression of PHPT1 has been investigated in mouse embryo and adult mouse organs. At the same time, in the HPR project, the PHPT1 expression in human tissues, cancers, and cell lines has been investigated. The expression in various tissues was essentially similar in the two species. Of particular interest was the finding that tissues where the epithelial cells have a short half-life were strongly stained, which suggests that PHPT1 is involved in cell proliferation. Acknowledgements Xiao-Qun Zhang and Ulla Beckman Sundh con- tributed equally in the project. The assistance of A˚ sa Haglund, Sima Koria, and Elvy Netzel are gratefully acknowledged. Declaration of interest: The authors report no conﬂicts of interest. The authors alone are respon- sible for the content and writing of the paper. References 1. Cohen P. The role of protein phosphorylation in human health and disease. The Sir Hans Krebs Medal Lecture. Eur J Biochem. 2001;268:5001 10. 2. Hunter T. Signalling*2008 and beyond. Cell. 2000;100: 113 27. 3. Boyer PD, DeLuca M, Ebner KE, Hultquist DE, Peter JB. Identiﬁcation of phosphohistidine in digests from a probable intermediate of oxidative phosphorylation. J Biol Chem. 1962;237:3306 8. 4. Matthews HR. Protein kinases and phosphatases that act on histidine, lysine, or arginine residues in eukaryotic proteins: a possible regulator of the mitogen-activated protein kinase cascade. Pharmacol Ther. 1995;67:323 50. 5. Besant PG, Attwood PV. Mammalian histidine kinases. Biochim Biophys Acta. 2005;1754:281 90. 6. Huang J, Wei Y, Kim Y, Osterberg L, Matthews HR. Puriﬁcation of a protein histidine kinase from the yeast Saccharomyces cerevisiae. The ﬁrst member of this class of protein kinases. J Biol Chem. 1991;266:9023 31. 7. Ek P, Pettersson G, Ek B, Gong F, Li JP, Zetterqvist O¨ . Identiﬁcation and characterization of a mammalian 14-kDa phosphohistidine phosphatase. Eur J Biochem. 2002;269: 5016 23. 8. Klumpp S, Krieglstein J. Phosphorylation and dephosphor- ylation of histidine residues in proteins. Eur J Biochem. 2002;269:1067 71. 9. Ma¨urer A, Wieland T, Meissl F, Niroomand F, Mehringer R, Krieglstein J, et al. The b-subunit of G proteins is a substrate of protein histidine phosphatase. Biochem Biophys Res Commun. 2005;334:1115 20. 10. Klumpp S, Bechmann G, Ma¨urer A, Selke D, Krieglstein J. ATPcitrate lyase as a substrate of protein histidine phospha- tase in vertebrates. Biochem Biophys Res Commun. 2003;306:110 5. 11. Srivastava S, Zhdanova O, Di L, Albaqumi M, Wulff H, Skolnik EY. Protein histidine phosphatase 1 negatively regulates CD4 T cells by inhibition the K channel KCa3.1. Proc Natl Acad Sci U S A. 2008;105:14441 6. 12. van Vlierberghe P, Meijerink JP, Lee C, Ferrando AA, Look AT, van Wering ER, et al. A new recurrent 9q34 duplication in pediatric T-cell acute lymphoblastic leukemia. Leukemia. 2006;20:1245 53. 13. Paul S, Amundsen S. Development of gene expression signatures for practical radiation biodosimetry. Int J Radiat Oncol Biol Phys. 2008;71:1236 44.