Isolation of the human genes encoding the Pyst1 and Pyst2 phosphatases: Characterisation of Pyst2 as a cytosolic dual-specificity MAP kinase phosphatase and its catalytic activation by both MAP and SAP kinases

We have isolated the human genes encoding the Pyst1 (MKP-3) and Pyst2 (MKP- X) MAP kinase phosphatases. Both genes consist of three exons interrupted b y two introns and lack an intron which is conserved in all the other member s of this gene family characterised to date. This reinforces the conclusion that Pyst1 and Pyst2 are members of a distinct and structurally homologous subfamily of dual-specificity (Thr/Tyr) MAP kinase phosphatases. We find t hat Pyst2 mRNA is constitutively expressed in a wide variety of human cell lines including those derived from ovarian, bladder and breast cancers. Whi le there is no evidence for inducible expression of Pyst2 mRNA in human ski n fibroblasts in response to cellular stress, Pyst2 mRNA levels are moderat ely increased in response to serum stimulation. Pyst2 protein is predominan tly cytosolic when expressed in COS-1 cells. In common with Pyst1, Pyst2 sh ows substrate selectivity for the classical p42 (ERK2) isoform of MAP kinas e both in vitro and in vivo, displaying much reduced activity towards stres s activated MAP kinase isoforms such as JNK-1 and p38/RK. Pyst2 binds p42 M AP kinase in vivo and both MAP kinase binding and substrate selectivity cor relate with the ability of different recombinant MAP and SAP kinases to cau se catalytic activation of the Pyst2 phosphatase in vitro.