Beta-1,4-galactosyltransferase-3 deficiency suppresses the growth of immunogenic tumors in mice.

Background: Beta-1,4-galactosyltransferase-3 (B4GALT3) belongs to the family of beta-1,4-galactosyltransferases (B4GALTs) and is responsible for the transfer of UDP-galactose to terminal N-acetylglucosamine. B4GALT3 is differentially expressed in tumors and adjacent normal tissues, and is correlated with clinical prognosis in several cancers, including neuroblastoma, cervical cancer, and bladder cancer. However, the exact role of B4GALT3 in the tumor immune microenvironment (TIME) remains unclear. Here, we aimed to elucidate the function of B4GALT3 in the TIME. Methods: To study the functions of B4GALT3 in cancer immunity, either weakly or strongly immunogenic tumor cells were subcutaneously transplanted into wild-type (WT) and B4galt3 knockout (KO) mice. Bone marrow transplantation and CD8+ T cell depletion experiments were conducted to elucidate the role of immune cells in suppressing tumor growth in B4galt3 KO mice. The cell types and gene expression in the tumor region and infiltrating CD8+ T cells were analyzed using flow cytometry and RNA sequencing. N-glycosylated proteins from WT and B4galt3 KO mice were compared using the liquid chromatography tandem mass spectrometry (LC-MS/MS)-based glycoproteomic approach. Results: B4galt3 KO mice exhibited suppressed growth of strongly immunogenic tumors with a notable increase in CD8+ T cell infiltration within tumors. Notably, B4galt3 deficiency led to changes in N-glycan modification of several proteins, including integrin alpha L (ITGAL), involved in T cell activity and proliferation. In vitro experiments suggested that B4galt3 KO CD8+ T cells were more susceptible to activation and displayed increased downstream phosphorylation of FAK linked to ITGAL. Conclusion: Our study demonstrates that B4galt3 deficiency can potentially boost anti-tumor immune responses, largely through enhancing the influx of CD8+ T cells. B4GALT3 might be suppressing cancer immunity by synthesizing the glycan structure of molecules on the CD8+ T cell surface, as evidenced by the changes in the glycan structure of ITGAL in immune cells. Importantly, B4galt3 KO mice showed no adverse effects on growth, development, or reproduction, underscoring the potential of B4GALT3 as a promising and safe therapeutic target for cancer treatment.

A degron system targeting endogenous PD-1 inhibits the growth of tumor cells in mice.

Recently, targeted protein degradation systems have been developed using the ubiquitin-proteasome system. Here, we established Programmed cell death-1 (PD-1) knockdown mice as a model system for subjecting endogenous mouse proteins to the small molecule-assisted shutoff (SMASh) degron system. SMASh degron-tagged PD-1-mCherry in Jurkat cells and CD3+ splenocytes were degraded by the NS3/4A protease inhibitors, asunaprevir (ASV) or grazoprevir (GRV). Growth of MC-38 colon adenocarcinoma cells injected in Pdcd1-mCherry-SMASh homozygous knock-in (KI) mice was repressed by ASV or GRV. Moreover, growth of MC-38 cells was suppressed in wild-type mice transplanted with KI bone marrow cells after GRV treatment. This is the first study to use a degron tag targeting an endogenous mouse protein in vivo. Our experimental system using the SMASh degron may be employed for treating diseases and characterizing the cellular functions of essential proteins.

Galactosyl carbohydrate residues on hematopoietic stem/progenitor cells are essential for homing and engraftment to the bone marrow.

The role of carbohydrate chains in leukocyte migration to inflamed sites during inflammation and trafficking to the lymph nodes under physiological conditions has been extensively characterized. Here, we report that carbohydrate chains also mediate the homing and engraftment of hematopoietic stem/progenitor cells (HSPCs) to the bone marrow (BM). In particular, we found that transplanted BM cells deficient in ß-1,4-galactosyltransferase-1 (ß4GalT-1) could not support survival in mice exposed to a lethal dose of irradiation. BM cells obtained from mice deficient in ß4GalT-1 showed normal colony-forming activity and hematopoietic stem cell numbers. However, colony-forming cells were markedly rare in the BM of recipient mice 24 h after transplantation of ß4GalT-1-deficient BM cells, suggesting that ß4GalT-1 deficiency severely impairs homing. Similarly, BM cells with a point mutation in the UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase gene, encoding a key enzyme in sialic acid biosynthesis, showed mildly impaired homing and engraftment abilities. These results imply that the galactosyl, but not sialyl residues in glycoproteins, are essential for the homing and engraftment of HSPCs to the BM. These findings suggest the possibility of modifying carbohydrate structures on the surface of HSPCs to improve their homing and engraftment to the BM in clinical application.

Lactosylceramide synthases encoded by B4galt5 and 6 genes are pivotal for neuronal generation and myelin formation in mice.

It is uncertain which ß4-galactosyltransferase (ß4GalT; gene name, B4galt), ß4GalT-5 and/or ß4GalT-6, is responsible for the production of lactosylceramide (LacCer) synthase, which functions in the initial step of ganglioside biosynthesis. Here, we generated conditional B4galt5 knockout (B4galt5 cKO) mice, using Nestin-Cre mice, and crossed these with B4galt6 KO mice to generate B4galt5 and 6 double KO (DKO) mice in the central nervous system (CNS). LacCer synthase activity and major brain gangliosides were completely absent in brain homogenates from the DKO mice, although LacCer synthase activity was about half its normal level in B4galt5 cKO mice and B4galt6 KO mice. The DKO mice were born normally but they showed growth retardation and motor deficits at 2 weeks and died by 4 weeks of age. Histological analyses showed that myelin-associated proteins were rarely found localized in axons in the cerebral cortex, and axonal and myelin formation were remarkably impaired in the spinal cords of the DKO mice. Neuronal cells, differentiated from neurospheres that were prepared from the DKO mice, showed impairments in neurite outgrowth and branch formation, which can be explained by the fact that neurospheres from DKO mice could weakly interact with laminin due to lack of gangliosides, such as GM1a. Furthermore, the neurons were immature and perineuronal nets (PNNs) were poorly formed in DKO cerebral cortices. Our results indicate that LacCer synthase is encoded by B4galt5 and 6 genes in the CNS, and that gangliosides are indispensable for neuronal maturation, PNN formation, and axonal and myelin formation.

Characterization of Innate and Adaptive Immune Responses in PYNOD-Deficient Mice.

PYNOD (also called NLRP10) is a member of the nucleotide-binding domain and leucine-rich repeat containing family. Many members of this family play important roles in the activation and/or regulation of immune and inflammatory responses. We previously showed that PYNOD inhibits the IL-1ß secretion in response to microbial infection in PYNOD-transgenic mice. In this study, we generated PYNOD-knockout (KO) mice and further investigated PYNOD's role in the innate and adaptive immune responses. Similar to wild-type macrophages, PYNOD-KO macrophages produced IL-1ß and induced pyroptosis, a caspase-1-dependent programmed cell death, in response to various inflammasome activators and microbial infection. In addition, the PYNOD deficiency did not significantly affect the proliferation or cytokine production of T cells, the delayed-type hypersensitivity responses, the anti-tumor immunity, the Ag-specific Ab production, the cytotoxicity of NK cells, or the maturation, Ag-presenting capacity, or elicited migration of dendritic cells. Furthermore, the steady-state skin self-antigen transport to regional lymph nodes was not impaired in PYNOD-KO mice, suggesting that PYNOD is dispensable for steady-state dendritic cell migration. These results suggested that PYNOD is dispensable for the regulation of innate and adaptive immune responses in mice, unless PYNOD's expression is highly induced under certain conditions.

New insights into the role of Jmjd3 and Utx in axial skeletal formation in mice.

Jmjd3 and Utx are demethylases specific for lysine 27 of histone H3. Previous reports indicate that Jmjd3 is essential for differentiation of various cell types, such as macrophages and epidermal cells in mice, whereas Utx is involved in cancer and developmental diseases in humans and mice, as well as Hox regulation in zebrafish and nematodes. Here, we report that Jmjd3, but not Utx, is involved in axial skeletal formation in mice. A Jmjd3 mutant embryo (Jmjd3Δ18/Δ18), but not a catalytically inactive Utx truncation mutant (Utx-/y), showed anterior homeotic transformation. Quantitative RT-PCR and microarray analyses showed reduced Hox expression in both Jmjd3Δ18/Δ18 embryos and tailbuds, whereas levels of Hox activators, such as Wnt signaling factors and retinoic acid synthases, did not decrease, which suggests that Jmjd3 plays a regulatory role in Hox expression during axial patterning. Chromatin immunoprecipitation analyses of embryo tailbud tissue showed trimethylated lysine 27 on histone H3 to be at higher levels at the Hox loci in Jmjd3Δ18/Δ18 mutants compared with wild-type tailbuds. In contrast, trimethylated lysine 4 on histone H3 levels were found to be equivalent in wild-type and Jmjd3Δ18/Δ18 tailbuds. Demethylase-inactive Jmjd3 mutant embryos showed the same phenotype as Jmjd3Δ18/Δ18 mice. These results suggest that the demethylase activity of Jmjd3, but not that of Utx, affects mouse axial patterning in concert with alterations in Hox gene expression.-Naruse, C., Shibata, S., Tamura, M., Kawaguchi, T., Abe, K., Sugihara, K., Kato, T., Nishiuchi, T., Wakana, S., Ikawa, M., Asano, M. New insights into the role of Jmjd3 and Utx in axial skeletal formation in mice.

AP-1B-mediated protein sorting regulates polarity and proliferation of intestinal epithelial cells in mice.

BACKGROUND & AIMS: In epithelial cells, protein sorting mechanisms regulate localization of plasma membrane proteins that generate and maintain cell polarity. The clathrin-adaptor protein (AP) complex AP-1B is expressed specifically in polarized epithelial cells, where it regulates basolateral sorting of membrane proteins. However, little is known about its physiological significance. METHODS: We analyzed the intestinal epithelia of mice deficient in Ap1m2 (Ap1m2(-/-) mice), which encodes the AP-1B µ1B subunit, and compared it with 129/B6/CD1 littermates (controls). Notch signaling was inhibited by intraperitoneal injection of dibenzazepine, and ß-catenin signaling was inhibited by injection of IWR1. Intestinal tissue samples were collected and analyzed by immunofluorescence analysis. RESULTS: Ap1m2(-/-) mice developed intestinal epithelial cell hyperplasia. The polarity of intestinal epithelial cells was disrupted, as indicated by the appearance of ectopic microvilli-like structures on the lateral plasma membrane and mislocalization of basolateral membrane proteins, including the low-density lipoprotein receptor and E-cadherin. The E-cadherin-ß-catenin complex therefore was disrupted at the adherens junction, resulting in nuclear translocation of ß-catenin. This resulted in up-regulation of genes regulated by ß-catenin/transcription factor 4 (Tcf4) complex, and increased the proliferation of intestinal epithelial cells. CONCLUSIONS: AP-1B is required for protein sorting and polarization of intestinal cells in mice. Loss of AP-1B in the intestinal epithelia results in mislocalization of E-cadherin, activation of ß-catenin/Tcf4 complex, proliferation, and hyperplasia.

EXTL2, a member of the EXT family of tumor suppressors, controls glycosaminoglycan biosynthesis in a xylose kinase-dependent manner.

Mutant alleles of EXT1 or EXT2, two members of the EXT gene family, are causative agents in hereditary multiple exostoses, and their gene products function together as a polymerase in the biosynthesis of heparan sulfate. EXTL2, one of three EXT-like genes in the human genome that are homologous to EXT1 and EXT2, encodes a transferase that adds not only GlcNAc but also N-acetylgalactosamine to the glycosaminoglycan (GAG)-protein linkage region via an α1,4-linkage. However, both the role of EXTL2 in the biosynthesis of GAGs and the biological significance of EXTL2 remain unclear. Here we show that EXTL2 transfers a GlcNAc residue to the tetrasaccharide linkage region that is phosphorylated by a xylose kinase 1 (FAM20B) and thereby terminates chain elongation. We isolated an oligosaccharide from the mouse liver, which was not detected in EXTL2 knock-out mice. Based on structural analysis by a combination of glycosidase digestion and 500-MHz (1)H NMR spectroscopy, the oligosaccharide was found to be GlcNAcα1-4GlcUAß1-3Galß1-3Galß1-4Xyl(2-O-phosphate), which was considered to be a biosynthetic intermediate of an immature GAG chain. Indeed, EXTL2 specifically transferred a GlcNAc residue to a phosphorylated linkage tetrasaccharide, GlcUAß1-3Galß1-3Galß1-4Xyl(2-O-phosphate). Remarkably, the phosphorylated linkage pentasaccharide generated by EXTL2 was not used as an acceptor for heparan sulfate or chondroitin sulfate polymerases. Moreover, production of GAGs was significantly higher in EXTL2 knock-out mice than in wild-type mice. These results indicate that EXTL2 functions to suppress GAG biosynthesis that is enhanced by a xylose kinase and that the EXTL2-dependent mechanism that regulates GAG biosynthesis might be a "quality control system" for proteoglycans.

Large-scale identification of target proteins of a glycosyltransferase isozyme by Lectin-IGOT-LC/MS, an LC/MS-based glycoproteomic approach.

Model organisms containing deletion or mutation in a glycosyltransferase-gene exhibit various physiological abnormalities, suggesting that specific glycan motifs on certain proteins play important roles in vivo. Identification of the target proteins of glycosyltransferase isozymes is the key to understand the roles of glycans. Here, we demonstrated the proteome-scale identification of the target proteins specific for a glycosyltransferase isozyme, ß1,4-galactosyltransferase-I (ß4GalT-I). Although ß4GalT-I is the most characterized glycosyltransferase, its distinctive contribution to ß1,4-galactosylation has been hardly described so far. We identified a large number of candidates for the target proteins specific to ß4GalT-I by comparative analysis of ß4GalT-I-deleted and wild-type mice using the LC/MS-based technique with the isotope-coded glycosylation site-specific tagging (IGOT) of lectin-captured N-glycopeptides. Our approach to identify the target proteins in a proteome-scale offers common features and trends in the target proteins, which facilitate understanding of the mechanism that controls assembly of a particular glycan motif on specific proteins.

Endothelial PI3K-C2α, a class II PI3K, has an essential role in angiogenesis and vascular barrier function.

The class II α-isoform of phosphatidylinositol 3-kinase (PI3K-C2α) is localized in endosomes, the trans-Golgi network and clathrin-coated vesicles; however, its functional role is not well understood. Global or endothelial-cell-specific deficiency of PI3K-C2α resulted in embryonic lethality caused by defects in sprouting angiogenesis and vascular maturation. PI3K-C2α knockdown in endothelial cells resulted in a decrease in the number of PI3-phosphate-enriched endosomes, impaired endosomal trafficking, defective delivery of VE-cadherin to endothelial cell junctions and defective junction assembly. PI3K-C2α knockdown also impaired endothelial cell signaling, including vascular endothelial growth factor receptor internalization and endosomal RhoA activation. Together, the effects of PI3K-C2α knockdown led to defective endothelial cell migration, proliferation, tube formation and barrier integrity. Endothelial PI3K-C2α deficiency in vivo suppressed postischemic and tumor angiogenesis and diminished vascular barrier function with a greatly augmented susceptibility to anaphylaxis and a higher incidence of dissecting aortic aneurysm formation in response to angiotensin II infusion. Thus, PI3K-C2α has a crucial role in vascular formation and barrier integrity and represents a new therapeutic target for vascular disease.

Glycoprotein hyposialylation gives rise to a nephrotic-like syndrome that is prevented by sialic acid administration in GNE V572L point-mutant mice.

Mutations in the key enzyme of sialic acid biosynthesis, UDP-N-acetylglucosamine 2-epimerase/N-acetyl-mannosamine kinase, result in distal myopathy with rimmed vacuoles (DMRV)/hereditary inclusion body myopathy (HIBM) in humans. Sialic acid is an acidic monosaccharide that modifies non-reducing terminal carbohydrate chains on glycoproteins and glycolipids, and it plays an important role in cellular adhesions and interactions. In this study, we generated mice with a V572L point mutation in the GNE kinase domain. Unexpectedly, these mutant mice had no apparent myopathies or motor dysfunctions. However, they had a short lifespan and exhibited renal impairment with massive albuminuria. Histological analysis showed enlarged glomeruli with mesangial matrix deposition, leading to glomerulosclerosis and abnormal podocyte foot process morphologies in the kidneys. Glycan analysis using several lectins revealed glomerular epithelial cell hyposialylation, particularly the hyposialylation of podocalyxin, which is one of important molecules for the glomerular filtration barrier. Administering Neu5Ac to the mutant mice from embryonic stages significantly suppressed the albuminuria and renal pathology, and partially recovered the glomerular glycoprotein sialylation. These findings suggest that the nephrotic-like syndrome observed in these mutant mice resulted from impaired glomerular filtration due to the hyposialylation of podocyte glycoproteins, including podocalyxin. Furthermore, it was possible to prevent the nephrotic-like disease in these mice by beginning Neu5Ac treatment during gestation.

Gene knockout and metabolome analysis of carnitine/organic cation transporter OCTN1.

PURPOSE: Solute carrier OCTN1 (SLC22A4) is an orphan transporter, the physiologically important substrate of which is still unidentified. The aim of the present study was to examine physiological roles of OCTN1. METHODS: We first constructed octn1 gene knockout (octn1 ( -/- )) mice. Metabolome analysis was then performed to identify substrates in vivo. The possible association of the substrate identified with diseased conditions was further examined. RESULTS: The metabolome analysis of blood and several organs indicated complete deficiency of a naturally occurring potent antioxidant ergothioneine in octn1 ( -/- ) mice among 112 metabolites examined. Pharmacokinetic analyses after oral administration revealed the highest distribution to small intestines and extensive renal reabsorption of [(3)H]ergothioneine, both of which were much reduced in octn1 ( -/- ) mice. The octn1 ( -/- ) mice exhibited greater susceptibility to intestinal inflammation under the ischemia and reperfusion model. The blood ergothioneine concentration was also much reduced in Japanese patients with Crohn's disease, compared with healthy volunteers and patients with another inflammatory bowel disease, ulcerative colitis. CONCLUSIONS: These results indicate that OCTN1 plays a pivotal role for maintenance of systemic and intestinal exposure of ergothioneine, which could be important for protective effects against intestinal tissue injuries, providing a possible diagnostic tool to distinguish the inflammatory bowel diseases.

Impairment of embryonic cell division and glycosaminoglycan biosynthesis in glucuronyltransferase-I-deficient mice.

We have revealed that in Caenorhabditis elegans, non-sulfated chondroitin is required for normal cell division and cytokinesis at an early developmental stage, whereas heparan sulfate is essential for embryonic morphogenesis in the later stages of development. To clarify the roles of chondroitin sulfate and heparan sulfate in early embryogenesis in mammals, we generated glucuronyltransferase-I (GlcAT-I) knock-out mice by gene targeting. GlcAT-I is an enzyme required for the synthesis of both chondroitin sulfate and heparan sulfate. Here we report that mice with a deletion of GlcAT-I showed remarkable reduction of the synthesis of chondroitin sulfate and heparan sulfate and embryonic lethality before the 8-cell stage because of failed cytokinesis. In addition, treatment of wild-type 2-cell embryos with chondroitinase ABC had marked effects on cell division, although many heparitinase-treated embryos normally developed to blastocysts. Taken together, these results suggest that chondroitin sulfate in mammals, as with non-sulfated chondroitin in C. elegans, is indispensable for embryonic cell division.

S1P(2), the G protein-coupled receptor for sphingosine-1-phosphate, negatively regulates tumor angiogenesis and tumor growth in vivo in mice.

Sphingosine-1-phosphate (S1P) has been implicated in tumor angiogenesis by acting through the G(i)-coupled chemotactic receptor S1P(1). Here, we report that the distinct receptor S1P(2) is responsible for mediating the G(12/13)/Rho-dependent inhibitory effects of S1P on Akt, Rac, and cell migration, thereby negatively regulating tumor angiogenesis and tumor growth. By using S1P(2)(LacZ/+) mice, we found that S1P(2) was expressed in both tumor and normal blood vessels in many organs, in both endothelial cells (EC) and vascular smooth muscle cells, as well as in tumor-associated, CD11b-positive bone marrow-derived cells (BMDC). Lewis lung carcinoma or B16 melanoma cells implanted in S1P(2)-deficient (S1P(2)(-/-)) mice displayed accelerated tumor growth and angiogenesis with enhanced association of vascular smooth muscle cells and pericytes. S1P(2)(-/-) ECs exhibited enhanced Rac activity, Akt phosphorylation, cell migration, proliferation, and tube formation in vitro. Coinjection of S1P(2)(-/-) ECs and tumor cells into wild-type mice also produced a relative enhancement of tumor growth and angiogenesis in vivo. S1P(2)(-/-) mice were also more efficient at recruiting CD11b-positive BMDCs into tumors compared with wild-type siblings. Bone marrow chimera experiments revealed that S1P(2) acted in BMDCs to promote tumor growth and angiogenesis. Our results indicate that, in contrast to endothelial S1P(1), which stimulates tumor angiogenesis, S1P(2) on ECs and BMDCs mediates a potent inhibition of tumor angiogenesis, suggesting a novel therapeutic tactic for anticancer treatment.

Important role of heparan sulfate in postnatal islet growth and insulin secretion.

Heparan sulfate (HS) binds with several signaling molecules and regulates ligand-receptor interactions, playing an essential role in embryonic development. Here we showed that HS was intensively expressed in pancreatic islet beta-cells after 1 week of age in mice. The enzymatic removal of HS in isolated islets resulted in attenuated glucose-induced insulin secretion with a concomitant reduction in gene expression of several key components in the insulin secretion machinery. We further depleted islet HS by inactivating the exostosin tumor-like 3 gene specifically in beta-cells. These mice exhibited abnormal islet morphology with reduced beta-cell proliferation after 1 week of age and glucose intolerance due to defective insulin secretion. These results demonstrate that islet HS is involved in the regulation of postnatal islet maturation and required to ensure normal insulin secretion.

Learning/memory impairment and reduced expression of the HNK-1 carbohydrate in beta4-galactosyltransferase-II-deficient mice.

The glycosylation of glycoproteins and glycolipids is important for central nervous system development and function. Although the roles of several carbohydrate epitopes in the central nervous system, including polysialic acid, the human natural killer-1 (HNK-1) carbohydrate, alpha2,3-sialic acid, and oligomannosides, have been investigated, those of the glycan backbone structures, such as Galbeta1-4GlcNAc and Galbeta1-3GlcNAc, are not fully examined. Here we report the generation of mice deficient in beta4-galactosyltransferase-II (beta4GalT-II). This galactosyltransferase transfers Gal from UDP-Gal to a nonreducing terminal GlcNAc to synthesize the Gal beta1-4GlcNAc structure, and it is strongly expressed in the central nervous system. In behavioral tests, the beta4GalT-II(-/-) mice showed normal spontaneous activity in a novel environment, but impaired spatial learning/memory and motor coordination/learning. Immunohistochemistry showed that the amount of HNK-1 carbohydrate was markedly decreased in the brain of beta4GalT-II(-/-) mice, whereas the expression of polysialic acid was not affected. Furthermore, mice deficient in glucuronyltransferase (GlcAT-P), which is responsible for the biosynthesis of the HNK-1 carbohydrate, also showed impaired spatial learning/memory as described in our previous report, although their motor coordination/learning was normal as shown in this study. Histological examination showed abnormal alignment and reduced number of Purkinje cells in the cerebellum of beta4GalT-II(-/-) mice. These results suggest that the Galbeta1-4GlcNAc structure in the HNK-1 carbohydrate is mainly synthesized by beta4GalT-II and that the glycans synthesized by beta4GalT-II have essential roles in higher brain functions, including some that are HNK-1-dependent and some that are not.

Both alleles of PSF1 are required for maintenance of pool size of immature hematopoietic cells and acute bone marrow regeneration.

Hematopoietic stem cells (HSCs) have a very low rate of cell division in the steady state; however, under conditions of hematopoietic stress, these cells can begin to proliferate at high rates, differentiate into mature hematopoietic cells, and rapidly reconstitute ablated bone marrow (BM). Previously, we isolated a novel evolutionarily conserved DNA replication factor, PSF1 (partner of SLD5-1), from an HSC-specific cDNA library. In the steady state, PSF1 is expressed predominantly in CD34(+)KSL (c-kit(+)/Sca-1(+)/Lineage(-)) cells and progenitors, whereas high levels of PSF1 expression are induced in KSL cells after BM ablation. In 1-year-old PSF1(+/-) mice, the pool size of stem cells and progenitors is decreased. Whereas young PSF1(+/-) mutant mice develop normally, are fertile, and have no obvious differences in hematopoiesis in the steady state compared with wild-type mice, intravenous injection of 5-fluorouracil (5-FU) is lethal in PSF1(+/-) mice, resulting from a delay in induction of HSC proliferation during ablated BM reconstitution. Overexpression studies revealed that PSF1 regulates molecular stability of other GINS components, including SLD5, PSF2, and PSF3. Our data indicate that PSF1 is required for acute proliferation of HSCs in the BM of mice.

The scaffold protein JSAP1 regulates proliferation and differentiation of cerebellar granule cell precursors by modulating JNK signaling.

Cerebellar granule cell precursors (GCPs) proliferate in the outer part of the external granular layer (EGL). They begin their differentiation by exiting the cell cycle and migrating into the inner part of the EGL. Here we report that JSAP1, a scaffold protein for JNK signaling pathways, is expressed predominantly in the post-mitotic GCPs of the inner EGL. JSAP1 knockdown or treatment with a JNK inhibitor enhances the proliferation of cultured GCPs, but the overexpression of wild-type JSAP1 leads to increased proportions of p27(Kip1)- and NeuN-positive cells, even with saturating concentrations of Sonic hedgehog (Shh), a potent GCP mitogen. However, these differentiation-promoting effects on GCPs are attenuated significantly in cells overexpressing a mutant JSAP1 that lacks the JNK-binding domain. Together, these data suggest that JSAP1 antagonizes the mitogenic effect of Shh on GCPs and promotes their exit from the cell cycle and differentiation, by modulating JNK activity.

Ablation of the scaffold protein JLP causes reduced fertility in male mice.

The specific and efficient activation of mitogen-activated protein kinase (MAPK) signaling modules is mediated, at least in part, by scaffold proteins. c-Jun NH(2)-terminal kinase (JNK)-associated leucine zipper protein (JLP) was identified as a scaffold protein for JNK and p38 MAPK signaling modules. JLP is expressed nearly ubiquitously and is involved in intracellular signaling pathways, such as the G(alpha13) and Cdo-mediated pathway, in vitro. To date, however, JLP expression has not been analyzed in detail, nor are its physiological functions well understood. Here we investigated the expression of JLP in the mouse testis during development. Of the tissues examined, JLP was strongest in the testis, with the most intense staining in the elongated spermatids. Since the anti-JLP antibody used in this study can recognize both JLP and sperm-associated antigen 9 (SPAG9), a splice variant of JLP that has been studied extensively in primates, we also examined its expression in macaque testis samples. Our results indicated that in mouse and primate testis, the isoform expressed at the highest level was JLP, not SPAG9. We also investigated the function of JLP by disrupting the Jlp gene in mice, and found that the male homozygotes were subfertile. Taken together, these observations may suggest that JLP plays an important role in testis during development, especially in the production of functionally normal spermatozoa.

Neural-specific ablation of the scaffold protein JSAP1 in mice causes neonatal death.

We previously identified c-Jun NH(2)-terminal kinase (JNK)/stress-activated protein kinase-associated protein 1 (JSAP1, also known as JNK-interacting protein 3) as a scaffolding factor for JNK intracellular signaling pathways. Targeted gene-disruption studies have shown that JSAP1-null mice are unable to breathe and die shortly after birth. Although neural defects might be responsible for their death, there has been no convincing evidence for this. Here we first generated genetically engineered mice carrying a loxP-flanked (floxed) jsap1 gene. To evaluate the validity of this deletion as a jsap1 conditional knockout (KO), we created mice in which the same exon was deleted in all cell lineages, and compared their phenotypes with those of the jsap1 conventional KO mice reported previously. The two KO lines showed indistinguishable phenotypes, i.e., neonatal death and morphological defects in the telencephalon, indicating that the conditional deletion was a true null mutation. We then introduced the floxed jsap1 deletion mutant specifically into the neural lineage, and found that the jsap1 conditional KO mice showed essentially the same phenotypes as the JSAP1-null mice. These results strongly suggest that the neonatal death of jsap1-deficient mice is caused by defects in the nervous system.