Abstract. The discoidin domain receptor (DDR) is a class of receptor tyrosine kinases that binds to several collagens. DDR1 is widely expressed in fast-growing invasive tumors of the breast, ovary, esophagus, brain and lung. However, there is little information on the expression of DDR1 in hepatocellular carcinoma (HCC) or its function in migration and invasion. Western blot analysis was performed to determine if four HCC cell lines (HLE, Huh-7, HepG2 and SH-J1) express DDR1. The HLE and Huh-7 cell lines were transfected with two isoforms of DDR1, DDR1a and DDR1b. Immunoprecipitation for DDR1 was then performed. Migration and invasion assays were carried out and the number of migrating cells was counted in 6 randomly selected fields per well under an optical microscope. Zymography was used to determine the level of the matrix metalloproteinase (MMP)-2 and -9 expression. DDR1 was expressed in all four cell lines. In the migration assay, the number of migrating cells was significantly higher in the DDR1a-or DDR1b-overexpressing HLE and Huh-7 cells, particularly after collagen type I stimulation (P<0.001). Collagen type I stimulation activated DDR1. In the invasion assay, there was a significantly higher number of invading cells in the DDR1a-or DDR1b-overexpressing HLE cells and DDR1a-overexpressing Huh-7 cells than in the control (P<0.01). The DDR1a-and DDR1b-overexpressing HLE cells showed a remarkable increase in the MMP-9 and -2 expression, particularly the active MMP-2. The DDR1a-and DDR1b-overexpressing Huh-7 cells showed a slight increase in the MMP-9 and -2 expression. The increased invasiveness of the HCC may be associated with the overexpression of either DDR1a or DDR1b mediated by MMP-2 and -9. Although this study provided one possible mechanism for the invasion of HCC cells, more studies are needed to understand the signal through which DDR1a and DDR1b act in invasion.
Background :Hypersecretion of mucin due to goblet cell hyperplasia is frequently encountered in many chronic airway diseases, such as chronic bronchitis, bronchiectasis, bronchial asthma and cystic fibrosis. Even in normal individuals, viral infection or bacterial pneumonia frequently provoke huge amounts of bronchial secretions which may cause airway obstruction. The production of mucin was regulated by epidermal growth factor (EGF) in vitro2). To know whether this EGF system regulates mucin secretion in vivo and Pseudomonas also stimulates the mucin secretion by the same pathway, we studied these relationships in the cultured rat tracheal epithelial cells.Methods :Rat tracheal epithelial cells were obtained by pronase dissociation from the male Fisher 344 rats. When cells became confluent, they were divided into 6 groups and stimulated with either EGF for 24 hours or Pseudomonas extracts for 12 hours with or without selective EGF-R tyrosine kinase inhibitor tyrphostin AG 1478.Results :We found that both EGF and Pseudomonas extracts phosphorylated the tyrosine residue in the EGF receptor from the rat tracheal epithelial cells and this tyrosine phosphorylation was nearly completely blocked by selective EGF-R tyrosine kinase inhibitor tyrphostin AG 1478. The mucin secretion was also stimulated by either EGF or Pseudomonas extracts but more strong secretion of mucin and MUC5AC gene expression in the rat tracheal epithelial cell was done by Pseudomonas extracts.Conclusion :These data suggest that Pseudomonas secretes the mucin by way of the EGF receptor and MUC5AC gene expression and the inhibitors of EGF receptor tyrosine phosphorylation would be useful to prevent the huge production of mucin due to Pseudomonas aeruginosa lung infection.
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