Palmitoyl Acyltransferase Activity of ZDHHC13 Regulates Skin Barrier Development Partly by Controlling PADi3 and TGM1 Protein Stability.

Deficiency of the palmitoyl-acyl transferase ZDHHC13 compromises skin barrier permeability and renders mice susceptible to environmental bacterial infection and inflammatory dermatitis. It had been unclear how the lack of ZDHHC13 proteins resulted in cutaneous abnormalities. In this study, we first demonstrate that enzymatic palmitoylation activity, rather than protein scaffolding, by ZDHHC13 is essential for skin barrier integrity, showing that knock-in mice bearing an enzymatically dead DQ-to-AA ZDHHC13 mutation lost their hair after weaning cyclically, recapitulating knockout phenotypes of skin inflammation and dermatitis. To establish the ZDHHC13 substrates responsible for skin barrier development, we employed quantitative proteomic approaches to identify protein molecules whose palmitoylation is tightly controlled by ZDHHC13. We identified over 300 candidate proteins that could be classified into four biological categories: immunological disease, skin development and function, dermatological disease, and lipid metabolism. Palmitoylation of three of these candidates-loricrin, peptidyl arginine deiminase type III, and keratin fiber crosslinker transglutaminase 1-by ZDHHC13 was confirmed by biochemical assay. Palmitoylation was critical for in vivo protein stability of the latter two candidates. Our findings reveal the importance of protein palmitoylation in skin barrier development, partly by promoting envelope protein crosslinking and the filaggrin processing pathway.

CBAP modulates Akt-dependent TSC2 phosphorylation to promote Rheb-mTORC1 signaling and growth of T-cell acute lymphoblastic leukemia.

High-frequency relapse remains a clinical hurdle for complete remission of T-cell acute lymphoblastic leukemia (T-ALL) patients, with heterogeneous dysregulated signaling profiles-including of Raf-MEK-ERK and Akt-mTORC1-S6K signaling pathways-recently being implicated in disease outcomes. Here we report that GM-CSF/IL-3/IL-5 receptor common ß-chain-associated protein (CBAP) is highly expressed in human T-ALL cell lines and many primary tumor tissues and is required to bolster leukemia cell proliferation in tissue culture and for in vivo leukemogenesis in a xenograft mouse model. Downregulation of CBAP markedly restrains expansion of leukemia cells and alleviates disease aggravation of leukemic mice. Transcriptomic profiling and molecular biological analyses suggest that CBAP acts upstream of Ras and Rac1, and functions as a modulator of both Raf-MEK-ERK and Akt-mTORC1 signaling pathways to control leukemia cell growth. Specifically, CBAP facilitated Akt-dependent TSC2 phosphorylation in cell-based assays and in vitro analysis, decreased lysosomal localization of TSC2, and elevated Rheb-GTP loading and subsequent activation of mTORC1 signaling. Taken together, our findings reveal a novel oncogenic contribution of CBAP in T-ALL leukemic cells, in addition to its original pro-apoptotic function in cytokine-dependent cell lines and primary hematopoietic cells, by demonstrating its functional role in the regulation of Akt-TSC2-mTORC1 signaling for leukemia cell proliferation. Thus, CBAP represents a novel therapeutic target for many types of cancers and metabolic diseases linked to PI3K-Akt-mTORC1 signaling.

CBAP functions as a novel component in chemokine-induced ZAP70-mediated T-cell adhesion and migration.

Activated chemokine receptor initiates inside-out signaling to transiently trigger activation of integrins, a process involving multiple components that have not been fully characterized. Here we report that GM-CSF/IL-3/IL-5 receptor common beta-chain-associated protein (CBAP) is required to optimize this inside-out signaling and activation of integrins. First, knockdown of CBAP expression in human Jurkat T cells caused attenuated CXC chemokine ligand-12 (CXCL12)-induced cell migration and integrin α4ß1- and αLß2-mediated cell adhesion in vitro, which could be rescued sufficiently upon expression of murine CBAP proteins. Freshly isolated CBAP-deficient primary T cells also exhibited diminution of chemotaxis toward CC chemokine ligand-21 (CCL21) and CXCL12, and these chemokines-induced T-cell adhesions in vitro. Adoptive transfer of isolated naive T cells demonstrated that CBAP deficiency significantly reduced lymph node homing ability in vivo. Finally, migration of T cell-receptor-activated T cells induced by inflammatory chemokines was also attenuated in CBAP-deficient cells. Further analyses revealed that CBAP constitutively associated with both integrin ß1 and ZAP70 and that CBAP is required for chemokine-induced initial binding of the talin-Vav1 complex to integrin ß1 and to facilitate subsequent ZAP70-mediated dissociation of the talin-Vav1 complex and Vav1 phosphorylation. Within such an integrin signaling complex, CBAP likely functions as an adaptor and ultimately leads to activation of both integrin α4ß1 and Rac1. Taken together, our data suggest that CBAP indeed can function as a novel signaling component within the ZAP70/Vav1/talin complex and plays an important role in regulating chemokine-promoted T-cell trafficking.

WSSV infection activates STAT in shrimp.

Although the JAK/STAT signaling pathway is usually involved in antiviral defense, a recent study suggested that STAT might be annexed by WSSV (white spot syndrome virus) to enhance the expression of a viral immediate early gene in infected shrimps. In the present study, we clone and report the first full-length cDNA sequence for a crustacean STAT from Penaeus monodon. Alignment and comparison with the deduced amino acid sequences of other STATs identified several important conserved residues and functional domains, including the DNA binding domain, SH2 domain and C-terminal transactivation domain. Based on these conserved sequences, a phylogenetic analysis suggested that shrimp STAT belongs to the ancient STAT family, while the presence of the functional domains suggested that shrimp STAT might share similar functions and regulating mechanisms with the well-known STATs isolated from model organisms. Real-time PCR showed a decreased transcription level of shrimp STAT after WSSV infection, but a Western blot analysis using anti-phosphorylated STAT antibody showed an increased level of phosphorylated (activated) STAT in the lymphoid organ of shrimp after WSSV infection. We further show that a primary culture of lymphoid organ cells from WSSV-infected shrimp resulted in activated STAT being translocated from the cytoplasm to the nucleus. This report provides experimental evidence that shrimp STAT is activated in response to WSSV infection. Our results support an earlier finding that WSSV does not disrupt JAK/STAT pathway, but on the contrary benefits from STAT activation in the shrimp host.