Mechanisms underlying lung resistance-related protein (LRP)-mediated doxorubicin resistance of non-small cell lung cancer cells

Lung resistance-related protein (LRP) is a human major vault protein (MVP) implicated in drug resistance of cancer cells in a cell-type dependent manner. The primary goal of the study was to understand the role(s) of LRP in doxorubicin (DOX) resistance of non-small cell lung cancer (NSCLC) cells and the underlying working mechanisms. In the study, the roles of LRP in the regulation of DOX dynamics, nuclear import of minor vault proteins (vault poly (ADP-ribose) polymerase, vPARP and telomerase associated protein-1, TEP-1) and DOX-mediated cytotoxicity were examined in CH27 and H460 cells. Our results were the first to show that the CH27 cells with higher LRP expression levels were more resistant to DOX-induced cytotoxicity as shown in apoptosis experiments. LRP at the nuclear membrane could regulate DOX efflux from the nucleus to the cytosol, and also the reverse vPARP/TEP1 influx from the cytosol, to protect NSCLC cells from DOX-induced apoptosis. Cytosolic LRP could bind to DOX, vPARP and TEP1 to clear DOX away from the nucleus and promote the assembly of vaults for cell protection again. Based on the data obtained, the molecular mechanisms responsible for DOX resistance of NSCLC were delineated to demonstrate that LRP, vPARP and TEP1 were potential targets for NSCLC therapy. Inhibitors of these proteins, including small interfering LRP (siLRP), wheat-germ agglutenin (WGA), 3-aminobenzamide (3-AB) and 3,6,9-trisubstituted acridine 9-[4-(N,N-dimethylamino) phenylamino]-3,6-bis(3-pyrrolodinopropionamido) acridine (BRACO-19), break down the DOX resistance of NSCLC cells, particularly in CH27 cells, and may have therapeutic values in the control of NSCLC.