Transforming growth factor-ß signals promote progression of squamous cell carcinoma by inducing epithelial-mesenchymal transition and angiogenesis.

At present, the molecular mechanisms driving the progression and metastasis of oral squamous cell carcinoma (OSCC) remain largely uncharacterized. The activation of transforming growth factor-ß (TGF-ß) signaling in the tumor microenvironment has been observed in various types of cancer and has been implicated their progression by enhancing the migration and invasion of epithelial cancer cells. However, its specific roles in the oral cancer progression remain unexplored. In this study, we examined the effects of TGF-ß signaling on the murine squamous cell carcinoma, SCCVII cells in vitro and in vivo. The incubation of SCCVII cells with TGF-ß induced the activation of TGF-ß signals and epithelial-mesenchymal transition (EMT). Notably, the motility of SCCVII cells was increased upon the activation of the TGF-ß signaling. RNA sequencing revealed upregulation of genes related to EMT and angiogenesis. Consistent with these in vitro results, the inhibition of TGF-ß signals in SCCVII cell-derived primary tumors resulted in suppressed angiogenesis. Furthermore, we identified six candidate factors (ANKRD1, CCBE1, FSTL3, uPA, TSP-1 and integrin ß3), whose expression was induced by TGF-ß in SCCVII cells, and associated with poor prognosis for patients with head and neck squamous cell carcinoma. These results highlight the role of TGF-ß signals in the progression of OSCC via multiple mechanisms, including EMT and angiogenesis, and suggest novel therapeutic targets for the treatment of OSCC.

Inhibition of transforming growth factor-ß signals suppresses tumor formation by regulation of tumor microenvironment networks.

The tumor microenvironment (TME) consists of cancer cells surrounded by stromal components including tumor vessels. Transforming growth factor-ß (TGF-ß) promotes tumor progression by inducing epithelial-mesenchymal transition (EMT) in cancer cells and stimulating tumor angiogenesis in the tumor stroma. We previously developed an Fc chimeric TGF-ß receptor containing both TGF-ß type I (TßRI) and type II (TßRII) receptors (TßRI-TßRII-Fc), which trapped all TGF-ß isoforms and suppressed tumor growth. However, the precise mechanisms underlying this action have not yet been elucidated. In the present study, we showed that the recombinant TßRI-TßRII-Fc protein effectively suppressed in vitro EMT of oral cancer cells and in vivo tumor growth in a human oral cancer cell xenograft mouse model. Tumor cell proliferation and angiogenesis were suppressed in tumors treated with TßRI-TßRII-Fc. Molecular profiling of human cancer cells and mouse stroma revealed that K-Ras signaling and angiogenesis were suppressed. Administration of TßRI-TßRII-Fc protein decreased the expression of heparin-binding epidermal growth factor-like growth factor (HB-EGF), interleukin-1ß (IL-1ß) and epiregulin (EREG) in the TME of oral cancer tumor xenografts. HB-EGF increased proliferation of human oral cancer cells and mouse endothelial cells by activating ERK1/2 phosphorylation. HB-EGF also promoted oral cancer cell-derived tumor formation by enhancing cancer cell proliferation and tumor angiogenesis. In addition, increased expressions of IL-1ß and EREG in oral cancer cells significantly enhanced tumor formation. These results suggest that TGF-ß signaling in the TME controls cancer cell proliferation and angiogenesis by activating HB-EGF/IL-1ß/EREG pathways and that TßRI-TßRII-Fc protein is a promising tool for targeting the TME networks.

CD40 is expressed in the subsets of endothelial cells undergoing partial endothelial-mesenchymal transition in tumor microenvironment.

Tumor progression and metastasis are regulated by endothelial cells undergoing endothelial-mesenchymal transition (EndoMT), a cellular differentiation process in which endothelial cells lose their properties and differentiate into mesenchymal cells. The cells undergoing EndoMT differentiate through a spectrum of intermediate phases, suggesting that some cells remain in a partial EndoMT state and exhibit an endothelial/mesenchymal phenotype. However, detailed analysis of partial EndoMT has been hampered by the lack of specific markers. Transforming growth factor-ß (TGF-ß) plays a central role in the induction of EndoMT. Here, we showed that inhibition of TGF-ß signaling suppressed EndoMT in a human oral cancer cell xenograft mouse model. By using genetic labeling of endothelial cell lineage, we also established a novel EndoMT reporter cell system, the EndoMT reporter endothelial cells (EMRECs), which allow visualization of sequential changes during TGF-ß-induced EndoMT. Using EMRECs, we characterized the gene profiles of multiple EndoMT stages and identified CD40 as a novel partial EndoMT-specific marker. CD40 expression was upregulated in the cells undergoing partial EndoMT, but decreased in the full EndoMT cells. Furthermore, single-cell RNA sequencing analysis of human tumors revealed that CD40 expression was enriched in the population of cells expressing both endothelial and mesenchymal cell markers. Moreover, decreased expression of CD40 in EMRECs enhanced TGF-ß-induced EndoMT, suggesting that CD40 expressed during partial EndoMT inhibits transition to full EndoMT. The present findings provide a better understanding of the mechanisms underlying TGF-ß-induced EndoMT and will facilitate the development of novel therapeutic strategies targeting EndoMT-driven cancer progression and metastasis.

TGF-ß generates a population of cancer cells residing in G1 phase with high motility and metastatic potential via KRTAP2-3.

Transforming growth factor ß (TGF-ß) increases epithelial cancer cell migration and metastasis by inducing epithelial-mesenchymal transition (EMT). TGF-ß also inhibits cell proliferation by inducing G1 phase cell-cycle arrest. However, the correlation between these tumor-promoting and -suppressing effects remains unclear. Here, we show that TGF-ß confers higher motility and metastatic ability to oral cancer cells in G1 phase. Mechanistically, keratin-associated protein 2-3 (KRTAP2-3) is a regulator of these dual effects of TGF-ß, and its expression is correlated with tumor progression in patients with head and neck cancer and migratory and metastatic potentials of oral cancer cells. Furthermore, single-cell RNA sequencing reveals that TGF-ß generates two populations of mesenchymal cancer cells with differential cell-cycle status through two distinctive EMT pathways mediated by Slug/HMGA2 and KRTAP2-3. Thus, TGF-ß-induced KRTAP2-3 orchestrates cancer cell proliferation and migration by inducing EMT, suggesting motile cancer cells arrested in G1 phase as a target to suppress metastasis.

Transforming growth factor-ß-induced secretion of extracellular vesicles from oral cancer cells evokes endothelial barrier instability via endothelial-mesenchymal transition.

BACKGROUND: During metastasis, cancer cells undergo epithelial-mesenchymal transition (EMT) in response to transforming growth factor-ß (TGF-ß), which is abundant in the tumor microenvironment, and acquire invasive and metastatic potentials. Metastasis to distant organs requires intravascular invasion and extravasation of cancer cells, which is accompanied by the disruption of the adhesion between vascular endothelial cells. Cancer cell-derived extracellular vesicles (EVs) have been suggested to induce the destabilization of normal blood vessels at the metastatic sites. However, the roles of EVs secreted from cancer cells that have undergone EMT in the destabilization of blood vessels remain to be elucidated. In the present study, we characterized EVs secreted by oral cancer cells undergoing TGF-ß-induced EMT and elucidated their effects on the characteristics of vascular endothelial cells. METHODS: Induction of EMT by TGF-ß in human oral cancer cells was assessed using quantitative RT-PCR (qRT-PCR) and immunocytochemistry. Oral cancer cell-derived EVs were isolated from the conditioned media of oral cancer cells that were treated with or without TGF-ß using ultracentrifugation, and characterized using nanoparticle tracking analysis and immunoblotting. The effects of EVs on human umbilical artery endothelial cells were examined by qRT-PCR, cellular staining, and permeability assay. The significant differences between means were determined using a t-test or one-way analysis of variance with Tukey's multiple comparisons test. RESULTS: Oral cancer cells underwent EMT in response to TGF-ß as revealed by changes in the expression of epithelial and mesenchymal cell markers at both the RNA and protein levels. Oral cancer cells treated with TGF-ß showed increased EV production and altered EV composition when compared with untreated cells. The EVs that originated from cells that underwent EMT by TGF-ß induced endothelial-mesenchymal transition, which was characterized by the decreased and increased expression of endothelial and mesenchymal cell markers, respectively. EVs derived from oral cancer cells also induced intercellular gap formation which led to the loss of endothelial cell barrier stability. CONCLUSIONS: EVs released from oral cancer cells that underwent TGF-ß-induced EMT target endothelial cells to induce vascular destabilization. Detailed characterization of oral cancer-derived EVs and factors responsible for EV-mediated vascular instability will lead to the development of agents targeting metastasis.

Activation of ß2-adrenergic receptor signals suppresses mesenchymal phenotypes of oral squamous cell carcinoma cells.

Metastasis is a primary reason related to the mortality of oral squamous cell carcinoma (OSCC) patients. A program called epithelial-mesenchymal transition (EMT) has been shown to play a critical role in promoting metastasis in epithelium-derived carcinoma. During EMT, epithelial cancer cells acquire motile mesenchymal phenotypes and detach from primary tumors. Recent lines of evidence have suggested that EMT confers cancer cells with tumor-initiating ability. Therefore, selective targeting of EMT would lead to the development of effective therapeutic agents. In this study, using a chemical biology approach, we identified isoxsuprine, a ß2-adrenergic receptor (ß2-AR) agonist as a low-molecular-weight compound that interferes with the acquisition of mesenchymal phenotypes of oral cancer cells. Treatment of multiple types of oral cancer cells with isoxsuprine led to the downregulation of mesenchymal cell markers that was accompanied by reduced cell motility. Similar inhibitory effects were also observed for isoprenaline, a non-selective ß-adrenergic receptor (ß-AR) agonist. In addition, inhibition of cell migration upon treatment with isoxsuprine was reverted by a non-selective ß-AR antagonist, propranolol, and the CRISPR/Cas9 system-mediated deletion of the ß2-AR gene, suggesting that the effects exerted by isoxsuprine involved signals mediated by ß2-AR. In addition, in a subcutaneous xenograft model of oral cancer cells, the administration of isoxsuprine effectively suppressed primary tumor growth, suggesting ß2-AR signals to be a promising cancer therapeutic target for treatment of OSCC.

Targeting all transforming growth factor-ß isoforms with an Fc chimeric receptor impairs tumor growth and angiogenesis of oral squamous cell cancer.

Tumor progression is governed by various growth factors and cytokines in the tumor microenvironment (TME). Among these, transforming growth factor-ß (TGF-ß) is secreted by various cell types residing in the TME and promotes tumor progression by inducing the epithelial-to-mesenchymal transition (EMT) of cancer cells and tumor angiogenesis. TGF-ß comprises three isoforms, TGF-ß1, -ß2, and -ß3, and transduces intracellular signals via TGF-ß type I receptor (TßRI) and TGF-ß type II receptor (TßRII). For the purpose of designing ligand traps that reduce oncogenic signaling in the TME, chimeric proteins comprising the ligand-interacting ectodomains of receptors fused with the Fc portion of immunoglobulin are often used. For example, chimeric soluble TßRII (TßRII-Fc) has been developed as an effective therapeutic strategy for targeting TGF-ß ligands, but several lines of evidence indicate that TßRII-Fc more effectively traps TGF-ß1 and TGF-ß3 than TGF-ß2, whose expression is elevated in multiple cancer types. In the present study, we developed a chimeric TGF-ß receptor containing both TßRI and TßRII (TßRI-TßRII-Fc) and found that TßRI-TßRII-Fc trapped all TGF-ß isoforms, leading to inhibition of both the TGF-ß signal and TGF-ß-induced EMT of oral cancer cells, whereas TßRII-Fc failed to trap TGF-ß2. Furthermore, we found that TßRI-TßRII-Fc suppresses tumor growth and angiogenesis more effectively than TßRII-Fc in a subcutaneous xenograft model of oral cancer cells with high TGF-ß expression. These results suggest that TßRI-TßRII-Fc may be a promising tool for targeting all TGF-ß isoforms in the TME.

TNF-α enhances TGF-ß-induced endothelial-to-mesenchymal transition via TGF-ß signal augmentation.

The tumor microenvironment (TME) consists of various components including cancer cells, tumor vessels, cancer-associated fibroblasts (CAFs), and inflammatory cells. These components interact with each other via various cytokines, which often induce tumor progression. Thus, a greater understanding of TME networks is crucial for the development of novel cancer therapies. Many cancer types express high levels of TGF-ß, which induces endothelial-to-mesenchymal transition (EndMT), leading to formation of CAFs. Although we previously reported that CAFs derived from EndMT promoted tumor formation, the molecular mechanisms underlying these interactions remain to be elucidated. Furthermore, tumor-infiltrating inflammatory cells secrete various cytokines, including TNF-α. However, the role of TNF-α in TGF-ß-induced EndMT has not been fully elucidated. Therefore, this study examined the effect of TNF-α on TGF-ß-induced EndMT in human endothelial cells (ECs). Various types of human ECs underwent EndMT in response to TGF-ß and TNF-α, which was accompanied by increased and decreased expression of mesenchymal cell and EC markers, respectively. In addition, treatment of ECs with TGF-ß and TNF-α exhibited sustained activation of Smad2/3 signals, which was presumably induced by elevated expression of TGF-ß type I receptor, TGF-ß2, activin A, and integrin αv, suggesting that TNF-α enhanced TGF-ß-induced EndMT by augmenting TGF-ß family signals. Furthermore, oral squamous cell carcinoma-derived cells underwent epithelial-to-mesenchymal transition (EMT) in response to humoral factors produced by TGF-ß and TNF-α-cultured ECs. This EndMT-driven EMT was blocked by inhibiting the action of TGF-ßs. Collectively, our findings suggest that TNF-α enhances TGF-ß-dependent EndMT, which contributes to tumor progression.

TGF-beta and TNF-alpha cooperatively induce mesenchymal transition of lymphatic endothelial cells via activation of Activin signals.

Lymphatic systems play important roles in the maintenance of fluid homeostasis and undergo anatomical and physiological changes during inflammation and aging. While lymphatic endothelial cells (LECs) undergo mesenchymal transition in response to transforming growth factor-ß (TGF-ß), the molecular mechanisms underlying endothelial-to-mesenchymal transition (EndMT) of LECs remain largely unknown. In this study, we examined the effect of TGF-ß2 and tumor necrosis factor-α (TNF-α), an inflammatory cytokine, on EndMT using human skin-derived lymphatic endothelial cells (HDLECs). TGF-ß2-treated HDLECs showed increased expression of SM22α, a mesenchymal cell marker accompanied by increased cell motility and vascular permeability, suggesting HDLECs to undergo EndMT. Our data also revealed that TNF-α could enhance TGF-ß2-induced EndMT of HDLECs. Furthermore, both cytokines induced the production of Activin A while decreasing the expression of its inhibitory molecule Follistatin, and thus enhancing EndMT. Finally, we demonstrated that human dermal lymphatic vessels underwent EndMT during aging, characterized by double immunostaining for LYVE1 and SM22α. These results suggest that both TGF-ß and TNF-α signals play a central role in EndMT of LECs and could be potential targets for senile edema.

KIF11 as a Potential Marker of Spermatogenesis Within Mouse Seminiferous Tubule Cross-sections.

The arrangement of immature germ cells changes regularly and periodically along the axis of the seminiferous tubule, and is used to describe the progression of spermatogenesis. This description is based primarily on the changes in the acrosome and the nuclear morphology of haploid spermatids. However, such criteria cannot be applied under pathological conditions with arrested spermatid differentiation. In such settings, the changes associated with the differentiation of premeiotic germ cells must be analyzed. Here, we found that the unique bipolar motor protein, KIF11 (kinesin-5/Eg5), which functions in spindle formation during mitosis and meiosis in oocytes and early embryos, is expressed in premeiotic germ cells (spermatogonia and spermatocytes). Thus, we aimed to investigate whether KIF11 could be used to describe the progression of incomplete spermatogenesis. Interestingly, KIF11 expression was barely observed in haploid spermatids and Sertoli cells. The KIF11 staining allowed us to evaluate the progression of meiotic processes, by providing the time axis of spindle formation in both normal and spermatogenesis-arrested mutant mice. Accordingly, KIF11 has the potential to serve as an excellent marker to describe spermatogenesis, even in the absence of spermatid development.

Interleukin-13 receptor α2 is a novel marker and potential therapeutic target for human melanoma.

Malignant melanoma is one of the untreatable cancers in which conventional therapeutic strategies, including chemotherapy, are hardly effective. Therefore, identification of novel therapeutic targets involved in melanoma progression is urgently needed for developing effective therapeutic methods. Overexpression of interleukin-13 receptor α2 (IL13Rα2) is observed in several cancer types including glioma and pancreatic cancer. Although IL13Rα2 is implicated in the progression of various types of cancer, its expression and roles in the malignant melanoma have not yet been elucidated. In the present study, we showed that IL13Rα2 was expressed in approximately 7.5% melanoma patients. While IL13Rα2 expression in human melanoma cells decreased their proliferation in vitro, it promoted in vivo tumour growth and angiogenesis in melanoma xenograft mouse model. We also found that the expression of amphiregulin, a member of the epidermal growth factor (EGF) family, was correlated with IL13Rα2 expression in cultured melanoma cells, xenograft tumour tissues and melanoma clinical samples. Furthermore, expression of amphiregulin promoted tumour growth, implicating causal relationship between the expression of IL13Rα2 and amphiregulin. These results suggest that IL13Rα2 enhances tumorigenicity by inducing angiogenesis in malignant melanoma, and serves as a potential therapeutic target of malignant melanoma.

Vasohibin-2 is required for epithelial-mesenchymal transition of ovarian cancer cells by modulating transforming growth factor-ß signaling.

Vasohibin-2 (VASH2) is a homolog of VASH1, an endothelium-derived angiogenesis inhibitor. Vasohibin-2 is mainly expressed in cancer cells, and has been implicated in the progression of cancer by inducing angiogenesis and tumor growth. Although VASH2 has been recently reported to be involved in epithelial-mesenchymal transition (EMT), its precise roles are obscure. The aim of the present study was to clarify the role of VASH2 in the EMT of cancer cells in relation to transforming growth factor-ß (TGF-ß) signaling, which is a major stimulator of EMT. Decreased expression of VASH2 in ovarian cancer cells significantly repressed the expression of TGF-ß type I receptor, namely activin receptor-like kinase 5. Transforming growth factor-ß1-induced phosphorylation of Smad2 and Smad3 was markedly decreased in VASH2 knockdown cells while the expression of Smad2 and Smad3 was unchanged. Accordingly, the responses to TGF-ß1 shown by promoter assay and plasminogen activator inhibitor type 1 expression were significantly attenuated in VASH2 knockdown cells. Furthermore, knockdown of VASH2 in cancer cells abrogated the TGF-ß1-induced reduced expression of epithelial markers including E-cadherin, and the elevated expression of mesenchymal markers including fibronectin, ZEB2, and Snail2, suggesting that endogenous VASH2 is required for TGF-ß1-induced EMT. In accordance with these results, the effects of TGF-ß1 on cell morphology, migration, invasion, and MMP2 expression were also abrogated when VASH2 was knocked down. These results indicate that VASH2 played a significant role in the EMT by modulating the TGF-ß signaling. We propose that VASH2 would be a novel molecular target for the prevention of EMT in cancers.

PDMP, a ceramide analogue, acts as an inhibitor of mTORC1 by inducing its translocation from lysosome to endoplasmic reticulum.

Mammalian or mechanistic target of rapamycin complex 1 (mTORC1) is a master regulator of cell growth, metabolism, and cell differentiation. Recent studies have revealed that the recruitment of mTORC1 to lysosomes is essential for its activation. The ceramide analogue 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), a well known glycosphingolipid synthesis inhibitor, also affects the structures and functions of various organelles, including lysosomes and endoplasmic reticulum (ER). We investigated whether PDMP regulates the mTORC1 activity through its effects on organellar behavior. PDMP induced the translocation of mTORC1 from late endosomes/lysosomes, leading to the dissociation of mTORC1 from its activator Rheb in MC3T3-E1 cells. Surprisingly, we found mTORC1 translocation to the ER upon PDMP treatment. This effect of PDMP was independent of its action as the inhibitor, since two stereoisomers of PDMP, with and without the inhibitor activity, showed essentially the same effect. We confirmed that PDMP inhibits the mTORC1 activity based on the decrease in the phosphorylation of ribosomal S6 kinase, a downstream target of mTORC1, and the increase in LC3 puncta, reflecting autophagosome formation. Furthermore, PDMP inhibited the mTORC1-dependent osteoblastic cell proliferation and differentiation of MC3T3-E1 cells. Accordingly, the present results reveal a novel mechanism of PDMP, which inhibits the mTORC1 activity by inducing the translocation of mTOR from lysosomes to the ER.

Characterization of Heparan Sulfate Proteoglycan-positive Recycling Endosomes Isolated from Glioma Cells.

BACKGROUND: Heparan sulfate proteoglycans (HSPGs)-dependent endocytic events have been involved in glioma progression. Thus, comprehensive understanding of the intracellular trafficking complexes formed in presence of HSPGs would be important for development of glioma treatments. MATERIALS AND METHODS: Subcellular fractionation was used to separate vesicles containing HSPGs from the rat C6 glioma cell line. Isolated HSPG-positive vesicles were further characterized with liquid chromatography-mass spectrometry. RESULTS: The HSPG-positive vesicular fractions, distinct from plasma membrane-derived material, were enriched in endocytic marker, Rab11. Proteomic analysis identified more than two hundred proteins to be associated with vesicular membrane, among them, over eighty were related to endosomal uptake, recycling or vesicular transport. CONCLUSION: Part of HSPGs in glioma cells is internalized through clathrin-dependent endocytosis and undergo recycling. The development of compounds regulating HSPG-mediated trafficking will likely enable design of effective glioma treatment.

Lysosome-associated membrane proteins-1 and -2 (LAMP-1 and LAMP-2) assemble via distinct modes.

Lysosome-associated membrane proteins 1 and 2 (LAMP-1 and LAMP-2) have a large, heavily glycosylated luminal domain composed of two subdomains, and are the most abundant protein components in lysosome membranes. LAMP-1 and LAMP-2 have distinct functions, and the presence of both proteins together is required for the essential regulation of autophagy to avoid embryonic lethality. However, the structural aspects of LAMP-1 and LAMP-2 have not been elucidated. In the present study, we demonstrated that the subdomains of LAMP-1 and LAMP-2 adopt the unique ß-prism fold, similar to the domain structure of the dendritic cell-specific-LAMP (DC-LAMP, LAMP-3), confirming the conserved aspect of this family of lysosome-associated membrane proteins. Furthermore, we evaluated the effects of the N-domain truncation of LAMP-1 or LAMP-2 on the assembly of LAMPs, based on immunoprecipitation experiments. We found that the N-domain of LAMP-1 is necessary, whereas that of LAMP-2 is repressive, for the organization of a multimeric assembly of LAMPs. Accordingly, the present study suggests for the first time that the assembly modes of LAMP-1 and LAMP-2 are different, which may underlie their distinct functions.

Preferential recognition of isocitrate dehydrogenase by a rabbit monoclonal antibody (ab124797) against the C-terminal peptide of RANKL.

A rabbit monoclonal antibody (Abcam ab124797), with high affinity for a synthetic peptide corresponding to the C-terminal region of the receptor activator of nuclear factor (NF)-κB ligand (RANKL), specifically recognizes a 37 kDa protein by immunoblotting, in good agreement with the molecular mass of RANKL. However, our mass spectroscopy analysis revealed that the protein recognized by the antibody is the α-subunit of NAD(+)-dependent isocitrate dehydrogenase (ICDH), a key Krebs cycle enzyme in mitochondria. Consistently, immunocytochemical staining with the antibody revealed a network organization characteristic of mitochondria, which overlapped with staining by MitoTracker and was lost after the siRNA-mediated downregulation of ICDH. The C-terminal peptide of ICDH contains similar chemical characteristics to that of the RANKL peptide and interacts with the antibody, although the affinity is a hundred times weaker. The present study provides an example of the preferential recognition of a surrogate protein by a rabbit monoclonal antibody.

Lysosome-associated membrane proteins (LAMPs) regulate intracellular positioning of mitochondria in MC3T3-E1 cells.

The intracellular positioning of both lysosomes and mitochondria meets the requirements of degradation and energy supply, which are respectively the two major functions for cellular maintenance. The positioning of both lysosomes and mitochondria is apparently affected by the nutrient status of the cells. However, the mechanism coordinating the positioning of the organelles has not been sufficiently elucidated. Lysosome-associated membrane proteins-1 and -2 (LAMP-1 and LAMP-2) are highly glycosylated proteins that are abundant in lysosomal membranes. In the present study, we demonstrated that the siRNA-mediated downregulation of LAMP-1, LAMP-2 or their combination enhanced the perinuclear localization of mitochondria, in the pre-osteoblastic cell line MC3T3-E1. On the other hand, in the osteocytic cell line MLO-Y4, in which both the lysosomes and mitochondria originally accumulate in the perinuclear region and mitochondria also fill dendrites, the effect of siRNA of LAMP-1 or LAMP-2 was barely observed. LAMPs are not directly associated with mitochondria, and there do not seem to be any accessory molecules commonly required to recruit the motor proteins to lysosomes and mitochondria. Our results suggest that LAMPs may regulate the positioning of lysosomes and mitochondria. A possible mechanism involving the indirect and context-dependent action of LAMPs is discussed.

Sphingosine kinase 2 inhibitor SG-12 induces apoptosis via phosphorylation by sphingosine kinase 2.

Sphingosine kinase (SPHK), which catalyzes the phosphorylation of sphingosine to generate sphingosine 1-phosphate, has two mammalian isotypes, SPHK1 and SPHK2. Both isozymes are promising anti-cancer therapeutic targets. In this report, we found that SG-12, a synthetic analogue of sphingosine that acts as a SPHK2 inhibitor, induces apoptosis via phosphorylation by SPHK2. The present results revealed the novel anti-cancer potential of a sphingosine analogue in the pathological setting where SPHK2 is upregulated.

Tetrameric interaction of the ectoenzyme CD38 on the cell surface enables its catalytic and raft-association activities.

The leukocyte cell-surface antigen CD38 is the major nicotinamide adenide dinucleotide glycohydrolase in mammals, and its ectoenzyme activity is involved in calcium mobilization. CD38 is also a raft-dependent signaling molecule. CD38 forms a tetramer on the cell surface, but the structural basis and the functional significance of tetramerization have remained unexplored. We identified the interfaces contributing to the homophilic interaction of mouse CD38 by site-specific crosslinking on the cell surface with an expanded genetic code, based on a crystallographic analysis. A combination of the three interfaces enables CD38 to tetramerize: one interface involving the juxtamembrane α-helix is responsible for the formation of the core dimer, which is further dimerized via the other two interfaces. This dimerization of dimers is required for the catalytic activity and the localization of CD38 in membrane rafts. The glycosylation prevents further self-association of the tetramer. Accordingly, the tetrameric interaction underlies the multifaceted actions of CD38.

Syndecans reside in sphingomyelin-enriched low-density fractions of the plasma membrane isolated from a parathyroid cell line.

BACKGROUND: Heparan sulfate proteoglycans (HSPGs) are one of the basic constituents of plasma membranes. Specific molecular interactions between HSPGs and a number of extracellular ligands have been reported. Mechanisms involved in controlling the localization and abundance of HSPG on specific domains on the cell surface, such as membrane rafts, could play important regulatory roles in signal transduction. METHODOLOGY/PRINCIPAL FINDINGS: Using metabolic radiolabeling and sucrose-density gradient ultracentrifugation techniques, we identified [(35)S]sulfate-labeled macromolecules associated with detergent-resistant membranes (DRMs) isolated from a rat parathyroid cell line. DRM fractions showed high specific radioactivity ([(35)S]sulfate/mg protein), implying the specific recruitment of HSPGs to the membrane rafts. Identity of DRM-associated [(35)S]sulfate-labeled molecules as HSPGs was confirmed by Western blotting with antibodies that recognize heparan sulfate (HS)-derived epitope. Analyses of core proteins by SDS-PAGE revealed bands with an apparent MW of syndecan-4 (30-33 kDa) and syndecan-1 (70 kDa) suggesting the presence of rafts with various HSPG species. DRM fractions enriched with HSPGs were characterized by high sphingomyelin content and found to only partially overlap with the fractions enriched in ganglioside GM1. HSPGs could be also detected in DRMs even after prior treatment of cells with heparitinase. CONCLUSIONS/SIGNIFICANCE: Both syndecan-1 and syndecan-4 have been found to specifically associate with membrane rafts and their association seemed independent of intact HS chains. Membrane rafts in which HSPGs reside were also enriched with sphingomyelin, suggesting their possible involvement in FGF signaling. Further studies, involving proteomic characterization of membrane domains containing HSPGs might improve our knowledge on the nature of HSPG-ligand interactions and their role in different signaling platforms.