Involvement of Fyn tyrosine kinase in actin stress fiber formation in fibroblasts

Lysophosphatidic acid (LPA) and sphingosylphosphorylcholine (SPC) activated Fyn tyrosine kinase and induced stress fiber formation, which was blocked by pharmacological inhibition of Fyn, gene silencing of Fyn, or dominant negative Fyn. Overexpressed constitutively active Fyn localized at both ends of F-actin bundles and triggered stress fiber formation, only the latter of which was abolished by Rho-kinase (ROCK) inhibition. SPC, but not LPA, induced filopodia-like protrusion formation, which was not mediated by Fyn and ROCK. Thus, Fyn appears to act downstream of LPA and SPC to specifically stimulate stress fiber formation mediated by ROCK in fibroblasts.     

Palladin is a novel binding partner of ILKAP in eukaryotic cells

Palladin was a novel binding partner of ILKAP in eukaryotic cells. Palladin’s C-terminal fragment including only its last three Ig domains (residues 710–1106) and the PP2C domain of ILKAP (residues 108–392) were necessary and sufficient for their interaction. The biological significance of the interaction between palladin and ILKAP was that palladin recruited the cytoplasmic ILKAP to initiate ILKAP-induced apoptosis. Our results suggested that palladin played a specific role in modulating the subcellular localization of the cytoplasmic ILKAP and promoting the ILKAP-induced apoptosis.     

Methylcobalamin promotes proliferation and migration and inhibits apoptosis of C2C12 cells via the Erk1/2 signaling pathway

Methylcobalamin (MeCbl) is a vitamin B12 analog that has some positive effects on peripheral nervous disorders. Although some previous studies revealed the effects of MeCbl on neurons, its effect on the muscle, which is the final target of motoneuron axons, remains to be elucidated. This study aimed to determine the effect of MeCbl on the muscle. We found that MeCbl promoted the proliferation and migration of C2C12 myoblasts in vitro and that these effects are mediated by the Erk1/2 signaling pathway without affecting the activity of the Akt signaling pathway. We also demonstrated that MeCbl inhibits C2C12 cell apoptosis during differentiation. Our results suggest that MeCbl has beneficial effects on the muscle in vitro. MeCbl administration may provide a novel therapeutic approach for muscle injury or degenerating muscle after denervation.     

Wisp2/CCN5 up-regulated in the central nervous system of GM3-only mice facilitates neurite formation in Neuro2a cells via integrin-Akt signaling

Wisp2/CCN5 belongs to CCN family proteins which are involved in cell proliferation, angiogenesis, tumorigenesis and wound healing. Although a number of studies on the roles of Wisp2/CCN5 in cancers have been reported, no study on the expression and function of Wisp2/CCN5 in the central nervous system has been reported. In this study, we focused on Wisp2/CCN5 that was up-regulated in nervous tissues in GM3-only mice. Over-expression of Wisp2/CCN5 enhanced neurite outgrowth potently after serum withdrawal with increased phosphorylation levels of Akt and ERKs. When cells were cultured with recombinant Wisp2/CCN5 proteins, more and longer neurites were formed than in the controls. Thus, we demonstrated for the first time that Wisp2/CCN5 facilitates neurite formation in a mouse neuroblastoma cell line, Neuro2a. Akt phosphorylation induced by recombinant Wisp2/CCN5 was suppressed after knockdown of integrin β1. Moreover, Wisp2/CCN5-over-expressing cells were resistant to apoptosis induced by H₂O₂. These results suggested that secreted Wisp2/CCN5 induces Akt and ERK phosphorylation via integrins, and consequently facilitates neurite formation and conferred resistance to apoptosis. Up-regulation of Wisp2/CCN5 in GM3-only mice should be, therefore, a reaction to protect nervous tissues from neurodegeneration caused by ganglioside deficiency.     

S1P(2) receptors mediate inhibition of glioma cell migration through Rho signaling pathways independent of PTEN

Sphingosine 1-phosphate (S1P) induced the inhibition of glioma cell migration. Here, we characterized the signaling mechanisms involved in the inhibitory action by S1P. In human GNS-3314 glioblastoma cells, the S1P-induced inhibition of cell migration was associated with activation of RhoA and suppression of Rac1. The inhibitory action of S1P was recovered by a small interference RNA specific to S1P₂ receptor, a carboxyl-terminal region of Gα12 or Gα13, an RGS domain of p115RhoGEF, and a dominant-negative mutant of RhoA. The inhibitory action of S1P through S1P₂ receptors was also observed in both U87MG glioblastoma and 1321N1 astrocytoma cells, which have no protein expression of a phosphatase and tensin homolog deleted on chromosome 10 (PTEN). These results suggest that S1P₂ receptors/G_12/13-proteins/Rho signaling pathways mediate S1P-induced inhibition of glioma cell migration. However, PTEN, recently postulated as an indispensable molecule for the inhibition of cell migration, may not be critical for the S1P₂ receptor-mediated action in glioma cells.     

Platycodin D inhibits migration,invasion, and growth of MDA-MB-231 human breast cancer cells via suppression of EGFR-mediated Akt and MAPK pathways

Platycodin D (PD), an active triterpenoid saponin from Platycodon grandiflorum, has been known to inhibit the proliferation of a variety of cancer cells, but the effect of PD on the invasiveness of cancer cells is largely unknown. In this study, we first determined the molecular mechanism by which PD inhibits the migratory and invasive abilities of the highly metastatic MDA-MB-231 breast cancer cell line. We demonstrated that a non-cytotoxic concentration of PD markedly suppressed wound healing migration, invasion through the matrigel, and adhesion to an ECM-coated substrate in a dose-dependent manner. Moreover, PD inhibited cell invasion by reducing matrix metalloproteinase (MMP)-9 enzyme activity and mRNA expression. Western blot analysis indicated that PD potently suppressed the phosphorylation of extracellular signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK) as well as blocked the phosphatidylinositol-3-kinase (PI3K)/Akt/mTOR signaling pathway. Furthermore, PD treatment inhibited the DNA binding activity of NF-κB, which is known to mediate the expression of epidermal growth factor receptor (EGFR), as observed by electrophoretic mobility shift assay. Specific mechanisms of action exerted by PD involved the downregulation of EGFR and the inhibition of EGF-induced activation of the EGFR, MAPK, and PI3K/Akt pathways. The in vivo studies showed that PD significantly inhibited the growth of MDA-MB-231 xenograft tumors in BALB/c nude mice. These results suggest that PD might be a potential therapeutic candidate for the treatment of breast cancer metastasis.     

Bm-TFF2, a toad trefoil factor, promotes cell migration, survival and wound healing

Toad skin is naked and continually confronted by various injurious factors. Constant skin renewal and repairs occur frequently. However, the mechanisms of the renewal and repair have not clearly elucidated. In our previous work, a trefoil factor (TFF), Bm-TFF2, has been purified from the Bombina maxima skin and characterized as a platelet agonist. The mRNA of TFFs in toad skin was up-regulated greatly during the metamorphosis, indicating a pivotal role of TFFs in amphibian skin. Here, we presented the effects of Bm-TFF2 on the cell migration, apoptosis and proliferation. Bm-TFF2 bound to epithelial cells and showed strong cell motility activity. At the concentrations of 1-100 nM, Bm-TFF2-induced migration of human epithelial AGS and HT-29 cells, and rat intestinal epithelial IEC-6 cell lines. The in vitro wound healing assay also verified the activity of Bm-TFF2. Bm-TFF2 could also inhibit cell apoptosis induced by ceramide and sodium butyrate. The cell migration-promoting activity was abolished by MEK1 inhibitors, U0126 and PD98059, suggesting that ERK1/2 activation is crucial for Bm-TFF2 to stimulate cell migration. Taken together, Bm-TFF2 promoted wound healing by stimulating cell migration via MAPK pathway and preventing cell apoptosis. The potent biological activity of Bm-TFF2 makes it a useful molecular tool for further studies of structure-function relationship of the related human TFFs.     

Determination of cathepsin V activity and intracellular trafficking by N-glycosylation

Cathepsin V (L2), a lysosomal cysteine protease, is a member of cathepsin family, relating to cancer invasion and metastasis. Cathepsin V contains two predicted N-glycosylation sites, but it has not been reported whether cathepsin V is glycosylated or not. In this study, we clarified the role of N-glycosylation of cathepsin V for its functions. We demonstrated that cathepsin V is N-glycosylated at both Asn²²¹ and Asn²⁹² using mass spectrometry and site-directed mutagenesis. N-glycosylation of cathepsin V was important for transportation to lysosome, secretion, and activity in HT1080 cells. These data demonstrated that functions of cathepsin V are controlled by N-glycosylation.     

Selection of DNA aptamers against epidermal growth factor receptor with high affinity and specificity

Epidermal growth factor receptor (EGFR/HER1/c-ErbB1), is overexpressed in many solid cancers, such as epidermoid carcinomas, malignant gliomas, etc. EGFR plays roles in proliferation, invasion, angiogenesis and metastasis of malignant cancer cells and is the ideal antigen for clinical applications in cancer detection, imaging and therapy. Aptamers, the output of the systematic evolution of ligands by exponential enrichment (SELEX), are DNA/RNA oligonucleotides which can bind protein and other substances with specificity. RNA aptamers are undesirable due to their instability and high cost of production. Conversely, DNA aptamers have aroused researcher’s attention because they are easily synthesized, stable, selective, have high binding affinity and are cost-effective to produce. In this study, we have successfully identified DNA aptamers with high binding affinity and selectivity to EGFR. The aptamer named TuTu22 with K_d 56 ± 7.3 nM was chosen from the identified DNA aptamers for further study. Flow cytometry analysis results indicated that the TuTu22 aptamer was able to specifically recognize a variety of cancer cells expressing EGFR but did not bind to the EGFR-negative cells. With all of the aforementioned advantages, the DNA aptamers reported here against cancer biomarker EGFR will facilitate the development of novel targeted cancer detection, imaging and therapy.     

Implication of protein tyrosine phosphatase 1B in MCF-7 cell proliferation and resistance to 4-OH tamoxifen

The protein tyrosine phosphatase 1B (PTP1B) and the T-cell protein tyrosine phosphatase (TC-PTP) were initially thought to be mainly anti-oncogenic. However, overexpression of PTP1B and TC-PTP has been observed in human tumors, and recent studies have demonstrated that PTP1B contributes to the appearance of breast tumors by modulating ERK pathway. In the present work, we observed that decreasing the expression of TC-PTP or PTP1B in MCF-7 cells using siRNA reduced cell proliferation without affecting cell death. This reduction in proliferation was associated with decreased ERK phosphorylation. Moreover, selection of tamoxifen-resistant MCF-7 cells, by long-term culture in presence of 4-OH tamoxifen, resulted in cells that display overexpression of PTP1B and TC-PTP, and concomitant increase in ERK and STAT3 phosphorylation. siRNA experiments showed that PTP1B, but not TC-PTP, is necessary for resistance to 4-OH tamoxifen. Therefore, our work indicates that PTP1B could be a relevant therapeutic target for treatment of tamoxifen-resistant breast cancers.     

Rapamycin decreases tau phosphorylation at Ser214 through regulation of cAMP-dependent kinase

Preventing or reducing tau hyperphosphorylation is considered to be a therapeutic strategy in the treatment of Alzheimer’s disease (AD). Rapamycin may be a potential therapeutic agent for AD, because the rapamycin-induced autophagy may enhance the clearance of the hyperphosphorylated tau. However, recent rodent studies show that the protective effect of rapamycin may not be limited in the autophagic clearance of the hyperphosphorylated tau. Because some tau-related kinases are targets of the mammalian target of rapamycin (mTOR), we assume that rapamycin may regulate tau phosphorylation by regulating these kinases. Our results showed that in human neuroblastoma SH-SY5Y cells, treatment with rapamycin induced phosphorylation of the type IIα regulatory (RIIα) subunit of cAMP-dependent kinase (PKA). Rapamycin also induced nuclear translocation of the catalytic subunits (Cat) of PKA and decreases in tau phosphorylation at Ser214 (pS214). The above effects of rapamycin were prevented by pretreatment with the mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) inhibitor U0126. In addition, these effects of rapamycin might not depend on the level of tau expression, because similar results were obtained in both the non-tau-expressing wild type human embryonic kidney 293 (HEK293) cells and HEK293 cells stably transfected with the longest isoform of recombinant human tau (tau441; HEK293/tau441). These findings suggest that rapamycin decreases pS214 via regulation of PKA. Because tau phosphorylation at Ser214 may prime tau for further phosphorylation by other kinases, our findings provide a novel possible mechanism by which rapamycin reduces or prevents tau hyperphosphorylation.     

A novel mutation of ALK2, L196P, found in the most benign case of fibrodysplasia ossificans progressiva activates BMP-specific intracellular signaling equivalent to a typical mutation, R206H

Naphthoquinone derivatives have been reported to possess various pharmacological activities, such as antiplatelet, anticancer, antifungal, and antiviral properties. In this study, we investigated the effects of a newly-synthesized naphthoquinone derivative, 2-decylamino-5,8-dimethoxy-1,4-naphthoquinone (2-decylamino-DMNQ), on VSMC proliferation and examined the molecular basis of the underlying mechanism. In a dose-dependent manner, 2-decylamino-DMNQ inhibited PDGF-stimulated VSMC proliferation with no apparent cytotoxic effect. While 2-decylamino-DMNQ did not affect PDGF-Rβ or Akt, it did inhibit the phosphorylation of Erk1/2 and PLCγ1 induced by PDGF. Moreover, 2-decylamino-DMNQ suppressed DNA synthesis through the arrest of cell cycle progression at the G₀/G₁ phase, including the suppression of pRb phosphorylation and a decrease in PCNA expression, which was related to the downregulation of cell cycle regulatory factors, such as cyclin D1/E and CDK 2/4. It was demonstrated that both U0126, an Erk1/2 inhibitor, and U73122, a PLCγ inhibitor, increased the proportion of cells in the G₀/G₁ phase of the cell cycle. Thus, these results suggest that 2-decylamino DMNQ has an inhibitory effect on PDGF-induced VSMC proliferation and the mechanism of this action is through cell cycle arrest at the G₀/G₁ phase. This may be a useful tool for studying interventions for vascular restenosis in coronary revascularization procedures and stent implantation.     

Carnosic acid and carnosol inhibit adipocyte differentiation in mouse 3T3-L1 cells through induction of phase2 enzymes and activation of glutathione metabolism

In the previous studies, we reported that carnosic acid (CA) and carnosol (CS) originating from rosemary protected cortical neurons by activating the Keap1/Nrf2 pathway, which activation was initiated by S-alkylation of the critical cysteine thiol of the Keap1 protein by the “electrophilic” quinone-type of CA or CS. Here, we found that CA and CS inhibited the in vitro differentiation of mouse preadipocytes, 3T3-L1 cells, into adipocytes. In contrast, other physiologically-active and rosemary-originated compounds were completely negative. These actions seemed to be mediated by activation of the antioxidant-response element (ARE) and induction of phase2 enzymes. This estimation is justified by our present findings that only CA and CS among rosemary-originated compounds significantly activated the ARE and induced the phase2 enzymes. Next, we performed cDNA microarray analysis in order to identify the gene(s) responsible for these biological actions and found that phase2 enzymes (Gsta2, Gclc, Abcc4, and Abcc1), all of which are involved in the metabolism of glutathione (GSH), constituted 4 of the top 5 CA-induced genes. Furthermore, CA and CS, but not the other compounds tested, significantly increased the intracellular level of total GSH. Thus, we propose that the stimulation of GSH metabolism may be a critical step for the inhibition of adipocyte differentiation in 3T3-L1 cells and suggest that pro-electrophilic compounds such as CA and CS may be potential drugs against obesity-related diseases.     

The unfolded protein response to endoplasmic reticulum stress in cultured astrocytes and rat brain during experimental diabetes

Oxidative-nitrosative stress and inflammatory responses are associated with endoplasmic reticulum (ER) stress in diabetic retinopathy, raising the possibility that disturbances in ER protein processing may contribute to CNS dysfunction in diabetics. Upregulation of the unfolded protein response (UPR) is a homeostatic response to accumulation of abnormal proteins in the ER, and the present study tested the hypothesis that the UPR is upregulated in two models for diabetes, cultured astrocytes grown in 25 mmol/L glucose for up to 4 weeks and brain of streptozotocin (STZ)-treated rats with diabetes for 1–7 months. Markers associated with translational blockade (phospho-eIF2α and apoptosis (CHOP), inflammatory response (inducible nitric oxide synthase, iNOS), and nitrosative stress (nuclear translocation of glyceraldehyde-3-phosphate dehydrogenase, GAPDH) were not detected in either model. Nrf2 was present in nuclei of low- and high-glucose cultures, consistent with oxidative stress. Astrocytic ATF4 expression was not altered by culture glucose concentration, whereas phospho-IRE and ATF6 levels were higher in low- compared with high-glucose cultures. The glucose-regulated chaperones, GRP78 and GRP94, were also expressed at higher levels in low- than high-glucose cultures, probably due to recurrent glucose depletion between feeding cycles. In STZ-rat cerebral cortex, ATF4 level was transiently reduced at 4 months, and p-IRE levels were transiently elevated at 3 months. However, GRP78 and GRP94 expression was not upregulated, and iNOS, amyloid-β, and nuclear accumulation of GAPDH were not evident in STZ-diabetic brain. High-glucose cultured astrocytes and STZ-diabetic brain are relatively resistant to diabetes-induced ER stress, in sharp contrast with cultured retinal Müller cells and diabetic rodent retina.     

Activation of nuclear receptor NR5A2 increases Glut4 expression and glucose metabolism in muscle cells

NR5A2 is a nuclear receptor which regulates the expression of genes involved in cholesterol metabolism, pluripotency maintenance and cell differentiation. It has been recently shown that DLPC, a NR5A2 ligand, prevents liver steatosis and improves insulin sensitivity in mouse models of insulin resistance, an effect that has been associated with changes in glucose and fatty acids metabolism in liver. Because skeletal muscle is a major tissue in clearing glucose from blood, we studied the effect of the activation of NR5A2 on muscle metabolism by using cultures of C2C12, a mouse-derived cell line widely used as a model of skeletal muscle. Treatment of C2C12 with DLPC resulted in increased levels of expression of GLUT4 and also of several genes related to glycolysis and glycogen metabolism. These changes were accompanied by an increased glucose uptake. In addition, the activation of NR5A2 produced a reduction in the oxidation of fatty acids, an effect which disappeared in low-glucose conditions. Our results suggest that NR5A2, mostly by enhancing glucose uptake, switches muscle cells into a state of glucose preference. The increased use of glucose by muscle might constitute another mechanism by which NR5A2 improves blood glucose levels and restores insulin sensitivity.     

Inhibition of protein synthesis and JNK activation are not required for cell death induced by anisomycin and anisomycin analogues

Anisomycin was identified in a screen of clinical compounds as a drug that kills breast cancer cells (MDA16 cells, derived from the triple negative breast cancer cell line, MDA-MB-468) that express high levels of an efflux pump, ABCB1. We show the MDA16 cells died by a caspase-independent mechanism, while MDA-MB-468 cells died by apoptosis. There was no correlation between cell death and either protein synthesis or JNK activation, which had previously been implicated in anisomycin-induced cell death. In addition, anisomycin analogues that did not inhibit protein synthesis or activate JNK retained the ability to induce cell death. These data suggest that either a ribosome-ANS complex is a death signal in the absence of JNK activation or ANS kills cells by binding to an as yet unidentified target.