title: Ephrin-A1 inhibits NSCLC tumor growth via induction of Cdx-2 a tumor suppressor gene.
abstract: BACKGROUND
  Tumor formation is a complex process which involves constitutive activation of oncogenes and suppression of tumor suppressor genes. Receptor EphA2 and its ligand ephrin-A1 form an important cell communication system with its functional role in cell-cell interaction and tumor growth. Loss of cell-cell adhesion is central to the cellular transformation and acquisition of metastatic potential. Claudins, the integrated tight junction (TJ) cell-cell adhesion proteins located on the apico-lateral portion of epithelial cells, functions in maintaining cell polarity. There is extensive evidence implicating Eph receptors and ephrins in malignancy, but the mechanisms how these molecular players affect TJ proteins and regulate tumor growth are not clear. In the present study we hypothesized that EphA2 signaling modulates claudin-2 gene expression via induction of cdx-2, a tumor suppressor gene in NSCLC cells.
  
  
  METHODS
  The expression of EphA2, claudin-2 was determined in various NSCLC cell lines by using real-time quantitative polymerase chain reaction and Western blot analysis. The claudin-2 expression was also analyzed by immunofluorescence analysis. EphA2 and erk1/erk2 phosphorylation in ephrin-A1 activated cells was evaluated by Western blot analysis. The cell proliferation and tumor colony formation were determined by WST-1 and 3-D matrigel assays respectively.
  
  
  RESULTS
  NSCLC cells over expressed receptor EphA2 and claudin-2. Ephrin-A1 treatment significantly down regulated the claudin-2 and EphA2 expression in NSCLC cells. The transient transfection of cells with vector containing ephrin-A1 construct (pcDNA-EFNA1) decreased the expression of claudin-2, EphA2 when compared to empty vector. In addition ephrin-A1 activation increased cdx-2 expression in A549 cells. In contrast over-expression of EphA2 with plasmid pcDNA-EphA2 up regulated claudin-2 mRNA expression and decreased cdx-2 expression. The transient transfection of cells with vector containing cdx-2 construct (pcMV-cdx-2) decreased the expression of claudin-2 in A549 cells. Moreover, silencing the expression of receptor EphA2 by siRNA significantly reduced claudin-2 expression and decreased cell proliferation and tumor formation. Furthermore, silencing cdx-2 gene expression before ephrin-A1 treatment increased claudin-2 expression along with increased cell proliferation and tumor growth in A549 cells.
  
  
  CONCLUSIONS
  Our study suggests that EphA2 signaling up-regulates the expression of the TJ-protein claudin-2 that plays an important role in promoting cell proliferation and tumor growth in NSCLC cells. We conclude that receptor EphA2 activation by ephrin-A1 induces tumor suppressor gene cdx-2 expression which attenuates cell proliferation, tumor growth and thus may be a promising therapeutic target against NSCLC.
authors: Division of Pulmonary & Critical Care Medicine, Department of Medicine, University of Florida, Gainesville, FL, USA.
authors: Bhagyalaxmi
authors: B
authors: Sukka-Ganesh
authors: Kamal A
authors: KA
authors: Mohammed
authors: Frederic
authors: F
authors: Kaye
authors: Eugene P
authors: EP
authors: Goldberg
authors: Najmunnisa
authors: N
authors: Nasreen
mesh_terms: D000071616:CDX2 Transcription Factor; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics* / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D036382:Ephrin-A1 / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism*; D036104:Receptor, EphA2 / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D000071616:CDX2 Transcription Factor; C491270:CDX2 protein, human; D036382:Ephrin-A1; D018398:Homeodomain Proteins; D025521:Tumor Suppressor Proteins; D036104:Receptor, EphA2