Epidermal growth factor down-regulates the expression of neutrophil gelatinase-associated lipocalin (NGAL) through E-cadherin in pancreatic cancer cells

BACKGROUND: The authors previously reported that neutrophil gelatinase-associated lipocalin (NGAL) overexpression significantly blocked invasion and angiogenesis of pancreatic ductal adenocarcinoma (PDAC). They also demonstrated a loss of NGAL expression in the advanced stages of PDAC. However, little is known regarding the mechanisms of NGAL regulation in PDAC. Because the epidermal growth factor (EGF)-EGF receptor (EGFR) axis is up-regulated significantly in PDAC, they examined EGF-mediated NGAL regulation in these cells. METHODS: The NGAL-positive cell lines AsPC-1 and BxPC-3 were used as a model system. Quantitative real-time polymerase chain reaction (RT-PCR), Western blot analysis, and immunofluorescence studies were used to investigate EGF-mediated effects on NGAL expression. E-cadherin expression was manipulated using lentiviral overexpression or small hairpin RNA constructs. NGAL promoter activity was assessed by luciferase-reporter assay and electrophoretic mobility shift assay. RESULTS: NGAL expression was positively associated with tumor differentiation and was down-regulated significantly after EGF treatment along with a concomitant reduction of E-cadherin expression in PDAC cells. E-cadherin down-regulation was partly through the EGFR-dependent mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) (MEK-ERK) signaling pathway. In addition, E-cadherin down-regulation reduced NGAL expression in PDAC cells, whereas overexpression of E-cadherin led to increased NGAL expression and partly rescued the inhibition of NGAL expression by EGF. Furthermore, EGF, in part through E-cadherin, reduced NGAL promoter activity by blocking nuclear factor κB (NF-κB) activation. CONCLUSIONS: The current study demonstrated for the first time that EGF potently blocked NGAL expression in PDAC cells. This effect was mediated in part through activation of the EGFR-MEK-ERK signaling pathway, which, in turn, down-regulated E-cadherin with a subsequent reduction in NF-κB activation. These findings illustrate a novel mechanism by which EGF regulates NGAL expression in PDAC.