Characterization of human NSCLC cell line with innate etoposide‐resistance mediated by cytoplasmic localization of topoisomerase II alpha

Abstract

(1) This enzyme is essential for the viability of cells because it is involved in chromosome segregation and is the major component of the nuclear matrix and mitotic and meiotic chromosomes.(2) Topo II alpha is a major target for a variety of antineoplastic agents. Epipodophyllotoxins (etoposide [VP16] ), teniposide (VM-26), aminocridines (m-AMSA), anthracyclines, anthracenediones, doxorubicin, daunorubicin, mitoxantrone and actinomycin D, are examples of such agents and are collectively referred to as topo II poisons.(3) These agents allow topo II to cleave DNA, and slow the religation steps catalyzed by the enzyme. As a consequence, covalent topo II breaks accumulate in the cell and produce cell death. (4) Resistance to topo II-targeting drugs in drug-selected cell lines has been associated with reduced expression of the topo II alpha enzyme. In addition, a number of point mutations or deletions in topo II alpha have been described in resistant cell lines. These mutations tend to be clustered in either the NH 2 -proximal ATP-binding domain (5)(6)(7)(8) or near to the active site of tyrosine residue in the central DNA binding and religation domain.(9 -12) More recently, a third cluster of mutations and deletions has been described in the COOH-terminal region of the enzyme, all of which result in the aberrant localization of topo II alpha in the cytoplasm. (13 -25) The presence of a cytoplasmic enzyme provides a plausible explanation for the resistance of topo II poisons, as it would result in the formation of fewer topo II/DNA complexes that could be stabilized by topo II-targeting drugs and, hence, reduce drug sensibility.The first description of topo II poison resistance and topo II alpha cytoplasmic localization was found in the small-cell lung cancer (SCLC) cell line H69 / VP with resistance to etoposide, (13,14) and later to several other topo II poison-resistant cell lines representative from different tissues. (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) In all these cell lines, deletions in the TOP2A gene around the nucleotide 4267 conduce to an alternative splicing that is translated into a truncated 160 kDa topo II alpha with cytoplasmic localization. A remarkable finding of these studies is that the truncation affected at least one of the two bipartite nuclear localization signals (NLS) present in the COOHterminal region of topo II alpha. (26) In these cells, topo II alpha retains most of its catalytic activity intact, but a significant reduction in the nuclear enzyme concentration has been used to explain the increase in topo II poison resistance.In the present report, we characterized a non-small-cell lung cancer (NSCLC) cell line with innate resistance to etoposide. This resistance could be associated with the expression of topo II alpha mainly in the cytoplasmic region. INER-37 cells transcribe two topo II alpha mRNAs: 4.8 kb and 2.0 kb. The large transcript appears to be translated into a truncated protein product of 160 kDa, where the more proximal COOH-terminal NLS 1454 −1497 has been lost. ...

Mouse Mammary Tumor Virus-Like Gene Sequences in Breast Cancer Samples of Mexican Women

“…This report is the first to find a virus related to MMTV in the northeastern Mestiza Mexican population (78.5% Spanish, 21.5% native Mexicans) [25] . Our results confirm the presence of a MMTV-like sequence in breast cancer patients and other populations as the INER-51 cell line which was established and obtained from the Instituto Nacional de Enfermedades Respiratorias-SSA, Mexico City, from the pleural effusion of a patient diagnosed with primary lung cancer [26] . A MMTV-like sequence has been found in breast cancer, lymphocyte, and other cell lines.…”

Overexpression of MEOX2 and TWIST1 Is Associated with H3K27me3 Levels and Determines Lung Cancer Chemoresistance and Prognosis

“…A total of 55 lung tumors (LT), 15 adjacent non-involved lung matched tissues (LNAT) and 20 lung precursor lesions (LP) from Fresh Frozen (FF) and Formalin-Fixed and Paraffin Embedded (FFPE) tissues processing methods, were collected from the Thoracic Surgical Service and Pathology Service at the National Institute of Respiratory Diseases (INER). Additionally, the NSCLC cell lines SK-MES-1, A-549, A-427, were obtained from the American Type Culture Collection (ATCC, Manassas, VA, USA) and INER-37, INER-51 were obtained from Mexican Mestizo patients, as previously reported [18] , [19] .…”

Tumor and host factors that may limit efficacy of chemotherapy in non-small cell and small cell lung cancer

“…Still other etoposide-resistant SCLC169, 236, 298–301 or NSCLC299, 302 cell lines with cross-resistance to doxorubicin299, 301 or teniposide236, 299 (but not to cisplatin298 or vinca alkaloids236, 298) had mutated topo II-α236, 298, 299, 302 (in some cases with relocalization of topo II-α to cytoplasm from the nucleus302) and reduced levels of topo II-α protein and/or mRNA236, 298, 299, 301, or reduced topo II activity169, 300, compared to their sensitive parent lines. Some also had decreased cleaved complex formation in the presence of etoposide298, 300, 301 or decreased expression of topo II- β301.…”