Expression of the major vault protein LRP in human non-small-cell lung cancer cells: Activation by short-term exposure to antineoplastic drugs

Abstract

Non-small-cell lung cancer (NSCLC) cells are characterised by resistance to the toxic impact of antineoplastic drugs both in vivo and in vitro. The lung resistance-related protein (LRP), identical with the human major vault protein, is over-expressed in a variety of tumour cells characterised by intrinsic or acquired chemoresistance. We investigated the expression and cellular localisation of LRP in 16 unselected NSCLC cell lines, immortalised bronchial epithelial cells and embryonic lung fibroblasts. All cell lines analysed expressed LRP mRNA, while protein expression ranged from undetectable up to high levels. Cell fractionation and immunofluorescence staining in selected cell lines localised LRP almost exclusively to the cytoplasm. LRP was contained in the 100, 000 g pellet and absent in the soluble, cytosolic fraction and nuclei. A small proportion of LRP, however, was shown to be loosely associated with the outside of the nuclei. Sucrose gradient equilibrium centrifugation revealed presence of LRP exclusively in the fraction known to accumulate purified vault particles. Short-term exposure (16 hr) to subtoxic daunomycin (DM)-, and bleomycin (BM)-concentrations significantly (up to 4-fold) enhanced LRP expression in 2/4 cell lines tested. Cisplatin (CDDP) had a minor effect while vinblastine (VBL) was ineffective. At cytotoxic conditions all drugs rather decreased than increased LRP expression. When basic LRP expression was compared with chemosensitivity, a significant correlation was detected for resistance to CDDP but not DM, doxorubicin (DOX), etoposide (VP-16), VBL and BM. Summing up, our data suggest a role of vaults both in basic CDDP resistance and, additionally, in an short-term defensive response of NSCLC cells against several other drugs.