Biomedical subjects

Jianguo Gu

Publications and source records attributed to Jianguo Gu.

40 records · Page 3Linked to original sources

PubMed2003

Involvement of oligosaccharide changes in alpha5beta1 integrin in a cisplatin-resistant human squamous cell carcinoma cell line.

Multiple mechanisms are involved in the resistance of cancer cells to cisplatin, including the expression of multidrug resistance-associated protein (MRP) and enhanced DNA repair. Here, we report findings to show that oligosaccharide changes in alpha5beta1 integrin are associated with cisplatin resistance in a head and neck squamous cell carcinoma cell line, HSC-2. Cisplatin-resistant HSC-2 (HSC-2/CR) cells were established by stepwise treatment with various concentrations of cisplatin. The oligosaccharides containing beta1, 6-N-acetylglucosamine (beta1-6GlcNAc) branching, detected by leukoagglutinating phytohemagglutinin (L(4)-PHA) lectin blot, were found to be dramatically decreased in alpha5beta1 integrin immunoprecipitated from HSC-2/CR cells. To better understand the mechanisms underlying cisplatin resistance and oligosaccharide alteration, we analyzed the downstream signaling of alpha5beta1 integrin, one of the target glycoproteins of beta1-6GlcNAc transferase [UDP-GlcNAc:alpha-D-mannoside beta1, 6-N-acetylglucosaminyltransferase (GnT-V)]. Cell adhesion to fibronectin and phosphorylation of focal adhesion kinase (FAK), which are associated with alpha5beta1 integrin and involved in a cell survival signaling, were found to be increased in the cisplatin-resistant cells. Enhancement of the inhibition of cell adhesion and FAK phosphorylation also support the above data in GnT-V transfectants of HSC-2 cells. Interestingly, the differences in sensitivity to cisplatin and FAK phosphorylation between cisplatin-sensitive and -resistant cells were completely abolished by treatment with a neutral antibody of alpha5beta1 integrin. These results suggest that modification of oligosaccharides of alpha5beta1 integrin represents one of the possible mechanisms of drug resistance in head and neck cancer cells.

Carcinoma, Squamous Cell↗

PubMed2002

Laminin-10/11 and fibronectin differentially prevent apoptosis induced by serum removal via phosphatidylinositol 3-kinase/Akt- and MEK1/ERK-dependent pathways.

Cell adhesion to the extracellular matrix inhibits apoptosis, but the molecular mechanisms underlying the signals transduced by different matrix components are not well understood. Here, we examined integrin-mediated antiapoptotic signals from laminin-10/11 in comparison with those from fibronectin, the best characterized extracellular adhesive ligand. We found that the activation of protein kinase B/Akt in cells adhering to laminin-10/11 can rescue cell apoptosis induced by serum removal. Consistent with this, wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase, or ectopic expression of a dominant-negative mutant of Akt selectively accelerated cell death upon serum removal. In contrast to laminin-10/11, fibronectin rescued cells from serum depletion-induced apoptosis mainly through the extracellular signal-regulated kinase pathway. Cell survival on fibronectin but not laminin was significantly reduced by treatment with PD98059, a specific inhibitor of mitogen- or extracellular signal-regulated kinase kinase-1 (MEK1) and by expression of a dominant-negative mutant of MEK1. Laminin-10/11 was more potent than fibronectin in preventing apoptosis induced by serum depletion. These results, taken together, demonstrate laminin-10/11 potency as a survival factor and demonstrate that different extracellular matrix components can transduce distinct survival signals through preferential activation of subsets of multiple integrin-mediated signaling pathways.

Apoptosis↗

PubMed2002

Expression of adenosine triphosphate P2X3 receptors in rat molar pulp and trigeminal ganglia.

OBJECTIVE: The objective of this study was to investigate the expression of adenosine triphosphate P2X3 receptor subunits in rat molar pulp and trigeminal ganglia and their relationship to substance P. STUDY DESIGN: Rat molar pulp and trigeminal ganglia were fixed and sectioned. Double immunostaining with anti-P2X3 and anti-substance P were used to localize P2X3 and substance P expression simultaneously with different stains. RESULTS: P2X3 immunoreactivity (IR) fibers were present in root and coronal pulp. P2X3-IR fibers formed subodontoblastic plexus and advanced into the predentin and dentin. P2X3-IR neurons were localized in small and medium-sized cells in trigeminal ganglia. Colocalization of P2X3 and substance P was not found in either molar pulp or trigeminal ganglia. CONCLUSION: The results of this study indicated that adenosine triphosphate in pulp tissues may stimulate a subpopulation of non-substance P trigeminal afferent fibers through activation of P2X3 receptors.

Adenosine Triphosphate↗

PubMedDate not supplied

Differential regulation of focal adhesion kinase and paxillin phosphorylation by the small GTP-binding protein Rho in human corneal epithelial cells.

PURPOSE: Lysophosphatidic acid (LPA), which activates the small guanosine triphosphate (GTP)-binding protein Rho, was previously shown to promote migration of the rabbit corneal epithelium in culture. The signaling pathway responsible for this effect of LPA was examined in this study with a human corneal epithelial (HCE) cell line. METHODS: The activation of Rho was detected with a pull-down assay. Tyrosine phosphorylation of paxillin and of focal adhesion kinase (FAK) were examined both by immunofluorescence staining and by immunoprecipitation and immunoblot analyses. Expression of integrins alpha5 and beta1 was evaluated by immunoblot analysis. RESULTS: Incubation of cells with LPA (10 micro M) for 2 min resulted in marked activation of Rho, and this effect was blocked by pretreatment with the Rho inhibitor exoenzyme C3 (2 micro g/ml) for 24 h. Tyrosine phosphorylation of both paxillin and FAK was detected in HCE cells under basal conditions by immunofluorescence staining, immunoprecipitation, and immunoblot analyses. LPA induced a concentration- and time-dependent increase in the tyrosine phosphorylation of paxillin, which was maximal at a concentration of 10 micro M and a time of 2 min. Exoenzyme C3 inhibited LPA-induced paxillin phosphorylation. Neither LPA nor exoenzyme C3 affected tyrosine phosphorylation of FAK or expression of integrins alpha5 and beta1. CONCLUSIONS: LPA induces Rho activation and the consequent tyrosine phosphorylation of paxillin in HCE cells, and these effects likely contribute to the promotion of corneal epithelial migration by this agent.

Cell Line↗