ß1,6 GlcNAc branches-modified protein tyrosine phosphatase Mu attenuates its tyrosine phosphatase activity and promotes glioma cell migration through PLCγ-PKC pathways.

The metastatic potential of malignant tumor has been shown to be correlated with the increased expression of tri- and tetra-antennary ß1,6-N-acetylglucosamine (ß1,6-GlcNAc) N-glycans. In this study, We found that GnT-V expression was negatively correlated with receptor protein tyrosine phosphatase type µ(RPTPµ) in human glioma tissues. To study whether RPTPµ is a novel substance of GnT-V which further affect RPTPµ's downstream dephosphorylation function, we preform lentiviral infection with GnT-V gene to construct stably transfected GnT-V glial cell lines. We found RPTPµ undergone severer cleavage in GnT-V transfected glioma cells compare to Mock cells. RPTPµ intracellular domain fragments increased while ß1,6-GlcNAc-branched N-glycans increased, in consistent with the decrease of RPTPµ's catalytic activity. The results showed that abnormal glycosylation could decrease the phosphorylation activity of PTP µ, and affect PLCγ-PKC pathways. Both protease inhibitor Furin and N-glycan biosynthesis inhibitor swainsonine could decrease cell mobility in GnT-V-U87 transfectants and other glioma cell lines. All results above suggest increased post-translational modification of RPTPµ N-glycans by GnT-V attenuates its tyrosine phosphatase activity and promotes glioma cell migration through PLCγ-PKC pathways, and that the ß1,6-GlcNAc-branched N-glycans of RPTPµ play a crucial role in glioma invasivity.

N-Glycosylation at Asn 402 Stabilizes N-Cadherin and Promotes Cell-Cell Adhesion of Glioma Cells.

Cadherin is crucial for cell-cell adhesion and N-glycosylation of N-cadherin has been implicated in the process of mammary, renal, and ovarian carcinogenesis. However, whether N-glycosylation of N-cadherin plays a role in glioma remains unknown. Previous studies had indicated that N-glycosylation could occur at three asparagine residues of N-cadherin. By generating and over-expressing N-glycosylation-deficient N-cadherin mutants in the human glioma cell lines SHG66 and U87, we found that mutation of N402 but not of the other potentially N-glycosylated residues destabilized N-cadherin and led to its ubiquitylation and subsequent proteasomal degradation. Furthermore, destabilized N-cadherin inhibited cadherin-mediated cell-cell adhesion and promoted cell migration. Our findings reveal that N-glycosylation controls N-cadherin stability and plays a role in glioma migration. J. Cell. Biochem. 118: 1423-1431, 2017. © 2016 Wiley Periodicals, Inc.

ß1,6 GlcNAc branches-modified protein tyrosine phosphatase alpha enhances its stability and promotes focal adhesion formation in MCF-7 cells.

Receptor-like protein tyrosine phosphatase alpha (RPTPα or PTPα), a type I transmembrane glycoprotein with complex N-glycans, executes multifunction roles on cell behaviors. However, its effect on tumorigenesis and metastasis remains controversial. In this study, PTPα is identified as a novel substrate of N-Acetylglucosaminyltransferase V (GnT-V). Immunofluorescence results showed that addition of ß1,6 GlcNAc branches on PTPα enhanced PTPα's cytomembrane assemble in GnT-V-MCF-7 compared with Mock-MCF-7 (MCF7 cells transfected with the vector pcDNA3). Then we found the alleviating degradation of PTPα was observed in GnT-V-MCF-7 while PTPα in Mock-MCF-7 was prone to quick degradation. Increased cell-surface retention subsequently enhanced PTPα's catalytic activity on the dephosphorylation of Src kinase at Tyr529 and promoted focal adhesion formation and mature. Therefore, our findings could provide an insight into the molecular mechanism of how GnT-V promoted cell migration, suggesting that PTPα could be one of factors regulating promote migration of breast cancer cell.

Maternal protein restriction reduces perlecan at mid-metanephrogenesis in rats.

AIM: Maternal dietary protein restriction reduces nephron number in offspring and increases the risk of cardiovascular and chronic kidney diseases. Perlecan is the major basement membrane/extracellular matrix heparan sulfate proteoglycan (HSPG) that plays a crucial role in nephron formation. This study was to determine whether maternal dietary protein restriction during pregnancy leads to an abnormal perlecan expression pattern during kidney development and a correlation with aberrant cell proliferation and apoptosis. METHODS: Pregnant Sprague-Dawley rats were divided into two groups, maintained on either a low-protein diet (MLP group) or a normal-protein diet (MNP group). Kidneys were dissected from embryos of different kidney development stages. Real-time PCR and immunohistochemistry were performed to detect the transcript level of rHSPG2, the coding gene of perlecan, and its protein expression pattern. Apoptosis and proliferation cell were detected by TUNEL system and Ki67 marker. RESULTS: Embryonic weights and nephron number were significantly affected by maternal low protein diets. The transcript level of rHSPG2 in the MLP group was significantly lower at embryonic day 18 and the neonatal period. Immunohistochemistry study was consistent with the RT-PCR results. The proliferation level of the MLP group was significantly lower than the MNP group at E18 and more apoptotic cells was detected in MLP newborn. CONCLUSION: Maternal protein restriction reduced the expression of perlecan and lead aberrant cell proliferation and apoptosis during mid-metanephrogenesis in offspring. This data may provide new evidence to understand the mechanism of reduced nephron number due to maternal protein restriction and enlighten solution.

A novel role of angiopoietin-like-3 associated with podocyte injury.

BACKGROUND: Angiopoietin-like-3 (ANGPTL3) expression is increased in glomerular podocytes of nephrotic syndrome. We hypothesize whether ANGPTL3 plays an important role in podocyte injury and promoting proteinuria. METHODS: Angptl3(+/+) and Angptl3(-/-) female mice on B6;129S5 gene background were injected with adriamycin by tail vein at the dose of 25 mg/Kg to produce nephropathy. Proteinuira was measured and podocytes ultrastructure was observed by electron microscopy. The interaction between ANGPTL3 and intergrin ß3 was analyzed by CO-IP and confocal immunofluorescence. The relative gene and protein expression were analyzed by RT-PCR and western blot. RESULTS: The deletion of ANGPTL3 tremendously attenuates proteinuria (more than a fivefold decrease in albuminuria) and protects podocytes from injury in a mouse model of adriamycin-induced nephropathy. We further demonstrate that ANGPTL3 interacts with and activates podocyte-expressed integrin ß3 and regulate expression of α-actinin-4, which may result in the cytoskeletal rearrangement of podocytes. Additionally, we identify the activation of the ANGPTL3-integrin ß3 signaling pathway in patients with nephrotic syndrome. CONCLUSION: ANGPTL3 might play a crucial role in podocyte injury. Either decreasing ANGPTL3 expression or interfering with the ANGPTL3-integrin ß3 interaction might be benefit for podocyte protection and decrease proteinuira.

A vital role for Angptl3 in the PAN-induced podocyte loss by affecting detachment and apoptosis in vitro.

BACKGROUND: Podocyte detachment and apoptosis are two risk factors causing podocyte loss, F-actin rearrangement is involved in detachment and apoptosis. However, the nature of events that promote detachment and apoptosis of podocytes and whether detachment occurred simultaneously with apoptosis are still unclear. Previously, it was found that angiopoietin-like3 (Angptl3) induces F-actin rearrangement in podocytes. In this study we investigate whether Angptl3 influences podocyte loss (detachment and apoptosis) and the process through which Angptl3 exactly influenced the podocyte loss. METHODS: In conditionally immortalized mice podocytes, recombinant mice Angptl3 protein (rm-Angptl3) was used to mimic Angptl3 overexpression model and transfection with small interfering RNA (siRNA) to knockdown the expression of Angptl3. Both flow cytometry analysis and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay were used to detect apoptosis. Rearrangement of F-actin was assessed using confocal microscopy. Western blot assay was used to measure levels of Angptl3, integrin α3ß1, integrin-linked kinase (ILK), p53, caspase 3, and phosphorylation of integrin ß1. RESULTS: In a puromycin aminonucleoside (PAN)-induced podocyte injury model, rm-Angptl3 accelerated the loss of podocytes, both detachment and apoptosis occurred, and F-actin rearrangement is involved in the process. However, knockdown of Angptl3 by siRNA markedly ameliorated these injuries. Observed effects were partially correlated with the altered integrin α3ß1, ILK and p53, rather than caspase 3. CONCLUSIONS: Angptl3 is a novel factor involved in the PAN-induced podocyte loss by affecting detachment and apoptosis in vitro. This study helps to deepen the understanding of the mechanisms of podocyte loss and lays the foundation for developing a new successful therapy for podocyte injury via lower expression of Angptl3.

Altered ß1,6-GlcNAc branched N-glycans impair TGF-ß-mediated epithelial-to-mesenchymal transition through Smad signalling pathway in human lung cancer.

The change of oligosaccharide structure has been revealed to be crucial for glycoproteins' biological functions and cell biological characteristics. N-acetylglucosaminy transferase V (GnT-V), a key enzyme catalysing the reaction of adding ß1, 6-N-acetylglucosamine (GlcNAc) on asparagine-linked oligosaccharides of cell proteins, has been implicated to a metastastic-promoting oncoprotein in some carcinomas. However, this correlation might not be subjected to all types of cancers, for example, in non-small cell lung cancers, low level of GnT-V expression is associated with relatively short survival time and poor prognosis. To explain the role of GnT-V in lung cancer progression, we studied the association of GnT-V expression with lung cancer EMT behaviour. We found that GnT-V expression was correlated with epithelial marker positively and mesenchymal marker negatively. GnT-V levels, as well as ß1,6-GlcNAc branched N-glycans, were strongly reduced in TGF-ß1-induced EMT of human lung adenocarcinoma A549 cells. Further studies showed that suppression of ß1,6-GlcNAc branched N-glycans by inhibitor or GnT-V silencing in A549 cells could promote TGF-ß1-induced EMT-like changes, cell migration and invasion. Meanwhile, overexpression of GnT-V impaired TGF-ß1-induced EMT, migration and invasion. It suggests that GnT-V suppresses the EMT process of lung cancer cells through inhibiting the TGF-ß/Smad signalling and its downstream transcription factors in a GnT-V catalytic activity-dependent manner. Taken together, the present study reveals a novel mechanism of GnT-V as a suppressor of both EMT and invasion in human lung cancer cells, which may be useful for fully understanding N-glycan's biological roles in lung cancer progression.

Down-regulation of DNA methyltransferase 3B in staurosporine-induced apoptosis and its mechanism in human hepatocarcinoma cell lines.

Abnormal DNA methylation is one of the important characteristics in tumor cells. Apoptosis plays an essential role in cell survival and processing. It is not clear whether DNA methyltransferases (DNMTs) change in apoptosis and how DNMTs are regulated in apoptosis. In this study, we found that SMMC-7721 or BEL-7404 cells were induced to apoptosis by STS, meanwhile the DNMT3B protein and mRNA level were decreased. To explore the mechanism of DNMT3B down-regulation, we found that the mRNA decay was not changed and core promoter activity of DNMT3B gene was decreased in STS-induced apoptosis. In order to figure out the signal molecule involved in transcriptional regulation of DNMT3B gene by STS, p-JNK, p-ERK, and p-p38 were examined. In STS-induced apoptosis p-JNK level was increased, and p-ERK and p-p38 were decreased. Furthermore, the inhibitor of p-JNK significantly alleviated the decline of DNMT3B protein. We also found that the siRNA of DNMT3B strengthened the cleavage of PARP and pro-caspase-3 as well as up-regulated the p16 gene expression in STS-treated cells. We concluded here that STS-regulated DNMT3B gene expression via p-JNK and down-regulation of DNMT3B-mediated STS-induced apoptosis through the up-regulation p16 expression.

254C>G: a TRPC6 promoter variation associated with enhanced transcription and steroid-resistant nephrotic syndrome in Chinese children.

BACKGROUND: Mutations in canonical transient receptor potential channel 6 (TRPC6) have been identified as responsible for the development of focal segmental glomerulosclerosis, a proteinuric disease with steroid resistance and poor prognosis. This study explores the prevalence of TRPC6 variants in Chinese children with idiopathic nephrotic syndrome (INS), the genotype/phenotype correlation of TRPC6 variants, the therapeutic response, and the underlying molecular mechanism. METHODS: Fifty-one children with sporadic INS were enrolled: 23 steroid-sensitive cases and 28 steroid-resistant cases Polymerase chain reaction was used to amplify 13 exons and the promoter sequences of TRPC6 before sequencing. The expression of TRPC6 in renal tissues was illustrated by immunohistochemistry staining. The transcriptional activity of variants in TRPC6 promoter was measured by the luciferase assay. RESULTS: Three variants (-254C>G, rs3824934; +43C/T, rs3802829; and 240 G>A, rs17096918) were identified. The allele frequency of the -254C>G single-nucleotide polymorphism (SNP) in the steroid-resistant nephrotic syndrome (SRNS) patients (40.5%) was higher than that in the steroid-sensitive nephrotic syndrome subjects (27.1%; P = 0.046). The -254C>G SNP enhanced transcription from TRPC6 promoter in vitro and was associated with increased TRPC6 expression in renal tissues of SRNS patients. CONCLUSION: -254C>G, a SNP underlying enhanced TRPC6 transcription and expression, may be correlated with the development of steroid resistance in Chinese children with INS.

Profilin1 facilitates staurosporine-triggered apoptosis by stabilizing the integrin ß1-actin complex in breast cancer cells.

Profilin1 (Pfn1) functions as a tumour suppressor against malignant phenotypes of cancer cells. A minimum level of Pfn1 is critical for the differentiation of human epithelial cells, and its lower expression correlates with the tumourigenesis of breast cancer cells and tissues. However, the molecular mechanisms underlying its anti-tumour action remain largely unknown. In this study, we found that stable expression of ectopic Pfn1 sensitized the breast cancer cell line MDA-MB-468 to apoptosis induced by staurosporine, a widely used natural apoptosis-inducing agent. Pfn1 overexpression could also up-regulate the expression of integrin α5ß1, which has been shown to inhibit the transformed phenotype of cancer cells. Furthermore, the Pfn1-facilitated apoptosis induced by staurosporine was blocked in cells attached to a supplementary fibronectin substrate, which serves as a ligand of integrin α5ß1. These results suggest that the insufficient fibronectin caused by the integrin α5ß1 up-regulation might activate a signalling pathway leading to an increase of cellular apoptosis. Moreover, Pfn1 that primarily functions to promote local superstructure formation involving actin filaments and integrin ß1 may contribute to its promotion on apoptosis. Our study indicated a previously uncharacterized role of Pfn1 in mediating staurosporine-inducing apoptosis in breast cancer cells via up-regulating integrin α5ß1, and suggested a new target for breast cancer therapy.

Osteopontin and integrin are involved in cholesterol gallstone formation.

BACKGROUND: This study aimed to investigate the role of osteopontin and its receptor, integrin αv, in gallstone formation using human tissue specimens and a guinea pig lithogenic model. MATERIAL/METHODS: The nucleation role of osteopontin was determined in patients' and normal gallbladder bile samples in vitro. Normal gallbladder was the control, and gallstone gallbladders were divided into group I (with normal epithelia) and group II (with degenerated epithelia) based on pathology change. Immunostaining, mRNA and protein expressions of osteopontin and integrin αv were analyzed. The animals were randomly divided into a lithogenic diet group and a normal diet group; the osteopontin mRNA expression in gallbladder and liver and osteopontin concentrations were determined. RESULTS: Osteopontin prolonged nucleation time and inhibited the pro-nucleating role induced by calcium in human bile in vitro. Immunostaining for osteopontin and integrin αv in human gallbladder tissues showed a higher reactivity in Group I than control group and Group II. The immunostaining in Group II was weaker than control group; similar results were observed for mRNA and protein expression of osteopontin and integrin αv. In the animal assay, the mRNA expression and concentration of osteopontin in gallbladder and liver gradually increased at initial stages and decreased in later stages. The concentrations of osteopontin in bile and serum of guinea pig showed similar trends. CONCLUSIONS: Our results suggest that osteopontin is involved in cholesterol gallstone formation, and the role of osteopontin might correlate with integrin αv and calcium.

α-Actinin-4 is involved in the process by which dexamethasone protects actin cytoskeleton stabilization from adriamycin-induced podocyte injury.

AIM: Glucocorticoid therapy has been used in childhood nephrotic syndrome since the 1950s, where the characteristic change is effacement of the actin-rich foot process of glomerular podocytes. Recent studies have shown that glucocorticoids, in addition to their general immunosuppressive and anti-inflammatory effects, have a direct effect on podocytes, regulate some apoptotic factors, and increase the stability of actin filaments. However, the precise mechanism(s) underlying the protective effects of glucocorticoids on podocytes remain unclear. It is known that adriamycin (ADR) can induce podocyte foot process effacement and trigger massive proteinuria in rodent models. However, few reports have examined the direct role of ADR in podocyte actin rearrangement in vitro. In this study, we investigated how ADR directly induced podocyte actin cytoskeleton rearrangement and further analyzed how dexamethasone prevented such injury. METHODS: We used confocal microscopy to assess podocyte actin rearrangement. Western blot analysis and real-time polymerase chain reaction were performed to measure the protein and mRNA levels of α-actinin-4. RESULTS: We demonstrated that there was a time-dependent ADR-induced podocyte actin rearrangement with less than 12 h of ADR treatment in cultured podocytes. Dexamethasone could protect podocytes from ADR-induced injury and also stabilize the expression of α-actinin-4. CONCLUSION: This study showed that dexamethasone had direct effects on podocytes: α-actinin-4 may be one of the potential target molecules.

Ghrelin inhibits 5-fluorouracil-induced apoptosis in colonic cancer cells.

BACKGROUND AND AIM: The aim of the present study was to investigate if ghrelin inhibits apoptosis in colonic cancer cells. METHODS: Cell viability in HT-29 cells was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Apoptosis was measured using 4',6-diamidino-2-phenylindole staining and flow cytometry. The protein expression of Bcl-2, Bax, and caspase-3 activation was examined using Western blotting. RESULTS: Ghrelin dose dependently decreased the growth inhibition of HT-29 cells induced by 5-fluorouracil (5-FU). Cells treated with 5-FU displayed chromatin condensation and nuclear fragmentation, which are typical changes of apoptosis. However, co-treatment with ghrelin reduced these changes. Flow cytometry after staining with Annexin V and propidium iodide showed that ghrelin decreased the apoptotic rate of HT-29 cells induced by 5-FU. Caspase-3 activation was significantly lower in the co-treated group than in the group treated with 5-FU alone. In addition, ghrelin reversed the 5-FU-induced Bcl-2/Bax protein ratio. CONCLUSION: Ghrelin inhibits 5-FU-induced apoptosis in colon cancer cells through the regulation of the Bcl-2/Bax protein ratio.

Increased integrin alpha5beta1 heterodimer formation and reduced c-Jun expression are involved in integrin beta1 overexpression-mediated cell growth arrest.

Integrins, heterodimers of alpha and beta subunits, are a family of cell surface molecules mediating cell-cell and cell-extracellular matrix interaction. The largest subgroup is formed by the beta(1) subunit containing integrins which consist of 12 members with different ligand-binding properties. We previously reported that overexpressed integrin beta(1) subunit in the hepatocellular carcinoma cell line SMMC-7721 imposed a growth inhibitory effect through the upregulation of p21(cip1) and p27(kip1). In this study, we confirmed the growth inhibitory effect of beta(1) subunit overexpression in different cancer cell lines. The upregulated CDK inhibitors induced by beta(1) integrin overexpression were essential for this integrin-mediated growth arrest. Reduced c-Jun level after integrin beta(1) overexpression plays an important role in the transcriptional activation of p21 through the Sp1 sites. Solely overexpressed beta(1) subunit could induce the expression of diverse alpha subunit in different cell lines, among which alpha(5) subunit was found to be correlated with integrin beta(1)-mediated growth arrest. Relative lack of ECM-integrin interaction might be a reason for integrin beta(1) overexpression-mediated growth arrest. These results helped us understand more about the mechanisms that integrins regulate cell growth.

Transcriptional and post-transcriptional control of DNA methyltransferase 3B is regulated by phosphatidylinositol 3 kinase/Akt pathway in human hepatocellular carcinoma cell lines.

DNA methyltransferases (DNMTs) are essential for maintenance of aberrant methylation in cancer cells and play important roles in the development of cancers. Unregulated activation of PI3K/Akt pathway is a prominent feature of many human cancers including human hepatocellular carcinoma (HCC). In present study, we found that DNMT3B mRNA and protein levels were decreased in a dose- and time-dependent manner in HCC cell lines with LY294002 treatment. However, we detected that LY294002 treatment did not induce increase of the degradation of DNMT3B protein using protein decay assay. Moreover we found that Akt induced alteration of the expression of DNMT3B in cells transfected with myristylated variants of Akt2 or cells transfected with small interfering RNA respectively. Based on DNMT3B promoter dual-luciferase reporter assay, we found PI3K pathway regulates DNMT3B expression at transcriptional level. And DNMT3B mRNA decay analysis suggested that down-regulation of DNMT3B by LY294002 is also post-transcriptional control. Furthermore, we demonstrated that LY294002 down-regulated HuR expression in a time-dependent manner in BEL-7404. In summary, we have, for the first time, demonstrate that PI3K/Akt pathway regulates the expression of DNMT3B at transcriptional and post-transcriptional levels, which is particularly important to understand the effects of PI3K/Akt and DNMT3B on hepatocarcinogenesis.

The effect of receptor protein tyrosine phosphatase kappa on the change of cell adhesion and proliferation induced by N-acetylglucosaminyltransferase V.

N-acetylglucosaminyltransferase V (GnT-V) has been reported to be positively associated with tumor progression, but its mechanism still remains unknown. In the present study, we found that GnT-V overexpression not only changed the glycosylation of receptor protein tyrosine phosphatase kappa (RPTPkappa) but also decreased its protein level. Moreover, GnT-V overexpression decreased cell calcium-independent adhesion and increased the tyrosine phosphorylation level of beta-catenin, in which RPTPkappa played an important role. Since RPTPkappa has an RXKR motif, which is a favored cleavage site for furin, we used furin inhibitor to further explore the effect of RPTPkappa on the change of cell adhesion and beta-catenin signaling induced by GnT-V. Our results showed that preventing RPTPkappa cleavage rescued the above effects of GnT-V, suggesting that furin cleavage could be one of the factors for RPTPkappa to regulate cell adhesion and beta-catenin signaling in GnT-V overexpression cell lines. In addition, the increased tyrosine phosphorylation level of beta-catenin was associated with the increased nuclear level of beta-catenin and downstream signaling molecules such as c-myc and cyclin D1 that were associated with cell proliferation. Our results suggest that GnT-V could decrease human hepatoma SMMC-7721 cell adhesion and promote cell proliferation partially through RPTPkappa.

Angiopoietin-like protein 3 regulates the motility and permeability of podocytes by altering nephrin expression in vitro.

It is well known that podocyte injury plays a vital role in massive proteinuria. The increase of podocyte motility results in podocyte foot process (FP) effacement, a typical form of podocyte injury. Our previous studies demonstrated that glomerular podocytes can express angiopoietin-like protein 3 (ANGPTL3) and that the increase of ANGPTL3 in dysfunctional glomerulus is correlated with podocyte FP effacement. Little is known, however, about the role of ANGPTL3 in podocyte injury. In this study, we investigated ANGPTL3's effect on the motility and permeability of podocytes and on the expression of nephrin, a key molecule in podocytes. By scrape-wound and transwell migration assay, we found that ANGPTL3 over-expression significantly increased podocyte motility, whereas after ANGPTL3 knockdown by RNA interference, motility remained the same as that of the control group. Adriamycin (ADR) treatment significantly promoted podocyte motility. However, the same dose of ADR treatment could not promote motility after the knockdown of ANGPTL3. In addition, we assayed the diffusion of FITC-BSA across the podocytes' monolayer to investigate whether ANGPTL3 could promote protein loss by means of an increase in podocyte motility. The results showed that the changes in the FITC-BSA permeability of the podocytes corresponded to changes in motility. Furthermore, we found that ANGPTL3 over-expression dramatically increased the expression of nephrin but that the up-regulation of nephrin induced by ADR was significantly inhibited when ANGPTL3 was diminished by RNAi. In conclusion, we found ANGPTL3 to be capable of regulating the motility and permeability of podocytes and that the mechanism of ANGPTL3's regulation could be associated with the altered expression of nephrin.

The effect of epidermal growth factor receptor variant III on glioma cell migration by stimulating ERK phosphorylation through the focal adhesion kinase signaling pathway.

Epidermal growth factor receptor variant III (EGFRvIII), the most common EGFR mutation, is associated with cell migration of glioblastoma multiforme (GBM) cases; however, the mechanism has not been elucidated. In this study, we found that the EGFRvIII-promoted glioma cell migration was closely linked to high levels of tyrosine phosphorylation in focal adhesion kinase (FAK) Y397. We also demonstrated that EGFRvIII formed a complex with FAK, resulting in enhanced tyrosine phosphorylation levels of FAK Y397 and EGFR Y1068. After knockdown of FAK expression via anti-FAK shRNA, the U87ΔEGFR cell migration was significantly inhibited, accompanying with the reduced phosphorylation levels of extracellular signal-regulated kinase (ERK1/2). Furthermore, the role of ERK1/2 in FAK-regulated cell migration was confirmed. Taken together, our results suggest that FAK and its downstream molecule ERK were involved in EGFRvIII-promoted glioma cell migration in U87ΔEGFR cells.

Post-transcriptional and post-translational regulation of PTEN by transforming growth factor-beta1.

PTEN is a critical tumor suppressor gene mutated frequently in various human cancers. Previous studies have showed that PTEN mRNA expression is down-regulated by TGF-beta1 in various cell lines. In present study, we have found that TGF-beta1 down-regulates PTEN mRNA and protein expression in a dose- and time-dependent manner in hepatocarcinoma cell line SMMC-7721. Based on the PTEN promoter dual-luciferase report assay, we have found that PTEN transcription is not affected by TGF-beta1. By using transcriptional inhibitor actinomycin D (Act D), the turnover rate of PTEN transcripts appeared to be accelerated during TGF-beta1 stimulation, which indicated that down-regulation of PTEN by TGF-beta1 was post-transcriptional. What interested us was that transfection of PTEN coding sequence increased TGF-beta1-induced degradation of PTEN mRNA, suggesting that PTEN coding region was account for TGF-beta1-mediated down-regulation of PTEN. In addition, TGF-beta1 down-regulated PTEN expression was blocked by the TbetaIR inhibitor SB431542 and the p38 inhibitor SB203580, suggesting Smad and p38 MAPK signal pathways played crucial roles in PTEN down-regulation via TGF-beta1 stimulation. In this study, we also found TGF-beta1 accelerated down-regulation of PTEN through the ubiquitin-proteasome pathway. Collectively, our data clearly demonstrated that TGF-beta1-mediated down-regulation of PTEN was post-transcriptional and post-translational, depending on its coding sequence, Smad and p38-MAPK signal pathways were involved in this down-regulation.

E-cadherin decreased human breast cancer cells sensitivity to staurosporine by up-regulating Bcl-2 expression.

E-cadherin, a well-characterized cell-cell adhesion molecule, executes multifunction roles on cell behaviors. However, its effect on chemo-resistance remains controversial. In this study, we found that E-cadherin positive breast cell lines were less sensitive to staurosporine compared to E-cadherin negative ones. Next, we substantiated that the expression of E-cadherin in MDA-MB-435 cells could partly counteract the cytotoxic effect induced by staurosporine through a series of apoptosis assay. The resistance of E-cadherin over-expressing cells to staurosporine may due to the up-regulation of Bcl-2/Bax ratio. When E-cadherin interference plasmids were transfected into MCF-7 cells, Bcl-2 expression was down-regulated. Moreover, perturbation of E-cadherin function by blocking the cell-cell contact resulted in decreased cellular levels of Bcl-2 protein expression. All these results demonstrated the chemo-resistance function of E-cadherin in the condition of staurosporine treatment, therefore, might contribute effective therapeutic strategies in breast carcinoma.