Regulation of Soluble E-Cadherin Signaling in Non-Small-Cell Lung Cancer Cells by Nicotine, BDNF, and β-Adrenergic Receptor Ligands

The ectodomain of the transmembrane protein E-cadherin can be cleaved and released in a soluble form referred to as soluble E-cadherin, or sE-cad, accounting for decreased E-cadherin levels at the cell surface. Among the proteases implicated in this cleavage are matrix metalloproteases (MMP), including MMP9. Opposite functions have been reported for full-length E-cadherin and sE-cad. In this study, we found increased MMP9 levels in the media of two non-small cell lung cancer (NSCLC) cell lines, A549 and H1299, treated with BDNF, nicotine, or epinephrine that were decreased upon cell treatment with the β-adrenergic receptor blocker propranolol. Increased MMP9 levels correlated with increased sE-cad levels in A549 cell media, and knockdown of MMP9 in A549 cells led to downregulation of sE-cad levels in the media. Previously, we reported that A549 and H1299 cell viability increased with nicotine and/or BDNF treatment and decreased upon treatment with propranolol. In investigating the function of sE-cad, we found that immunodepletion of sE-cad from the media of A549 cells untreated or treated with BDNF, nicotine, or epinephrine reduced activation of EGFR and IGF-1R, decreased PI3K and ERK1/2 activities, increased p53 activation, decreased cell viability, and increased apoptosis, while no effects were found using H1299 cells under all conditions tested.