The vacuolating cytotoxin VacA produced by Helicobacter pylori causes massive cellular vacuolation in vitro and gastric tissue damage in vivo, leading to gastric ulcers, when administered intragastrically. Here we report that mice deficient in protein tyrosine phosphatase receptor type Z (Ptprz, also called PTP-zeta or RPTP-beta, encoded by Ptprz) do not show mucosal damage by VacA, although VacA is incorporated into the gastric epithelial cells to the same extent as in wild-type mice. Primary cultures of gastric epithelial cells from Ptprz+/+ and Ptprz-/- mice also showed similar incorporation of VacA, cellular vacuolation and reduction in cellular proliferation, but only Ptprz+/+ cells showed marked detachment from a reconstituted basement membrane 24 h after treatment with VacA. VacA bound to Ptprz, and the levels of tyrosine phosphorylation of the G protein-coupled receptor kinase-interactor 1 (Git1), a Ptprz substrate, were higher after treatment with VacA, indicating that VacA behaves as a ligand for Ptprz. Furthermore, pleiotrophin (PTN), an endogenous ligand of Ptprz, also induced gastritis specifically in Ptprz+/+ mice when administered orally. Taken together, these data indicate that erroneous Ptprz signaling induces gastric ulcers.

The CRMP (collapsin response mediator protein) family is thought to play key roles in growth cone guidance during neural development. The four members (CRMP1-4) identified to date have been demonstrated to form hetero-multimeric structures through mutual associations. In this study, we cloned a novel member of this family, which we call CRMP5, by the yeast twohybrid method. This protein shares relatively low amino acid identity with the other CRMP members (49 -50%) and also with dihydropyrimidinase (51%), whereas CRMP1-4 exhibit higher identity with each other (68 -75%), suggesting that CRMP5 might be categorized into a third subfamily. The mouse CRMP5 gene was located at chromosome 5 B1. Northern blot and in situ hybridization analyses indicated that CRMP5 is expressed throughout the nervous system similarly to the other members (especially CRMP1 and CRMP4) with the expression peak in the first postnatal week. Association experiments using the yeast two-hybrid method and coimmunoprecipitation showed that CRMP5 interacts with dihydropyrimidinase and all the CRMPs including itself, except for CRMP1, although the expression profile almost overlaps with that of CRMP1 during development. These results suggest that CRMP complexes in the developing nervous system are classifiable into two populations that contain either CRMP1 or CRMP5. This indicates that different complexes may have distinct functions in shaping the neural networks.

Acetylation is mediated by acetyltransferases and deacetylases, and occurs not only on histones but also on diverse proteins. Although histone acetylation in chromatin structure and transcription has been well studied, the biological roles of non-histone acetylation remain elusive. Histone deacetylase 6 (Hdac6), a member of the histone deacetylase (HDAC) family, is a unique deacetylase that localizes to cytoplasm and functions in many cellular events by deacetylating non-histone proteins including α-tubulin, Hsp90, and cortactin. Since robust expression of Hdac6 is observed in brain, it would be expected that Hdac6-mediated reversible acetylation plays essential roles in CNS. Here we demonstrate the crucial roles of Hdac6 deacetylase activity in the expression of emotional behavior in mice. We found that Hdac6-deficient mice exhibit hyperactivity, less anxiety, and antidepressant-like behavior in behavioral tests. Moreover, administration of Hdac6-specific inhibitor replicated antidepressant-like behavior in mice. In good agreement with behavioral phenotypes of Hdac6-deficient mice, Hdac6 dominantly localizes to the dorsal and median raphe nuclei, which are involved in emotional behaviors. These findings suggest that HDAC6-mediated reversible acetylation might contribute to maintain proper neuronal activity in serotonergic neurons, and also provide a new therapeutic target for depression.

Receptor-type protein tyrosine phosphatases (RPTPs) are considered to transduce extracellular signals across the membrane through changes in their PTP activity, however, our understanding of the regulatory mechanism is still limited. Here, we show that pleiotrophin (PTN), a natural ligand for protein tyrosine phosphatase receptor type Z (Ptprz) (also called PTPf/ RPTPb), inactivates Ptprz through oligomerization and increases the tyrosine phosphorylation of substrates for Ptprz, G proteincoupled receptor kinase-interactor 1 (Git1) and membrane associated guanylate kinase, WW and PDZ domain containing 1 (Magi1). Oligomerization of Ptprz by an artificial dimerizer or polyclonal antibodies against its extracellular region also leads to inactivation, indicating that Ptprz is active in the monomeric form and inactivated by ligand-induced oligomerization.

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Protein-tyrosine phosphatase receptor type Z (Ptprz) has multiple substrate proteins, including G protein-coupled receptor kinase-interactor 1 (Git1), membrane-associated guanylate kinase, WW and PDZ domain-containing 1 (Magi1), and GTPase-activating protein for Rho GTPase (p190RhoGAP). We have identified a dephosphorylation site at Tyr-1105 of p190RhoGAP; however, the structural determinants employed for substrate recognition of Ptprz have not been fully defined. In the present study, we revealed that Ptprz selectively dephosphorylates Git1 at Tyr-554, and Magi1 at Tyr-373 and Tyr-858 by in vitro and cell-based assays. Of note, the dephosphorylation of the Magi1 Tyr-858 site required PDZ domain-mediated interaction between Magi1 and Ptprz in the cellular context. Alignment of the primary sequences surrounding the target phosphotyrosine residue in these three substrates showed considerable similarity, suggesting a consensus motif for recognition by Ptprz. We then estimated the contribution of surrounding individual amino acid side chains to the catalytic efficiency by using fluorescent peptides based on the Git1 Tyr-554 sequence in vitro. The typical substrate motif for the catalytic domain of Ptprz was deduced to be Glu/Asp-Glu/Asp-Glu/Asp-Xaa-Ile/ Val-Tyr(P)-Xaa (Xaa is not an acidic residue). Intriguingly, a G854D substitution of the Magi1 Tyr-858 site matching better to the motif sequence turned this site to be susceptible to dephosphorylation by Ptprz independent of the PDZ domainmediated interaction in cells. Furthermore, we found by database screening that the substrate motif is present in several proteins, including paxillin at Tyr-118, its major phosphorylation site. Expectedly, we verified that Ptprz efficiently dephosphorylates paxillin at this site in cells. Our study thus provides key insights into the molecular basis for the substrate recognition of Ptprz.Protein-tyrosine phosphorylation is a dynamic process governed by the balanced actions of protein-tyrosine kinases (PTKs), 2 and protein-tyrosine phosphatases (PTPs), and critical to the regulation of numerous physiological processes (for review, see Ref. 1). The specificity of the signal transduction depends on the ability of each PTK or PTP to phosphorylate or dephosphorylate precisely particular sites on specific substrates, respectively. Elucidation of the specificity for individual PTPs has been an important subject of investigation; however, even the identification of PTP substrates is still methodologically difficult. To our knowledge, substrate specificity of PTPs has been characterized only for PTP1B (2).Receptor-like PTPs (RPTPs) are a structurally and functionally diverse family of enzymes comprised of eight subfamilies. PTP receptor type Z (Ptprz, also called PTP or RPTP␤) is a RPTP classified in the R5 subfamily together with Ptprg (PTP␥). Three isoforms of Ptprz are generated by alternative splicing from a single Ptprz gene: the two transmembrane isoforms Ptprz-A and Ptprz-B and the secretory isoform Ptprz-S (also known as phosphacan...

Protein tyrosine phosphatase receptor type Z (Ptprz/PTPzeta/RPTPbeta) is a receptor-like protein tyrosine phosphatase (RPTP) preferentially expressed in the brain. ErbB4 is a member of the ErbB-family tyrosine kinases known as a neuregulin (NRG) receptor. Both are known to bind to postsynaptic density-95 (PSD95) on the second and the first/second PDZ (PSD95/Disc large/zona occludens1) domains, respectively, through the PDZ-binding motif of their carboxyl termini. Here we report a functional interaction between Ptprz and ErbB4. An intracellular carboxyl-terminal region of Ptprz pulled-down PSD95 and ErbB4 from an adult rat synaptosomal preparation. ErbB4 and Ptprz showed co-localization in cell bodies and apical dendrites of neurons in the prefrontal cortex. In HEK293T cells, phosphorylation of ErbB4 was raised by co-expression of PSD95, which was repressed by additional expression of Ptprz. In vitro experiments using the whole intracellular region (ICR) of ErbB4 also showed that PSD95 stimulates the autophosphorylation of ErbB4, and that the ICR of Ptprz dephosphorylates ErbB4 independent of the presence of PSD95. Taken together with the finding that the tyrosine phosphorylation level of ErbB4 was increased in Ptprz-deficient mice, these results suggest that Ptprz has a role in suppressing the autoactivation of ErbB4 by PSD95 at the postsynaptic density in the adult brain.