title: Enhanced sensitivity to tumor necrosis factor-alpha in doxorubicin-resistant tumor cell lines due to down-regulated c-erbB2.
abstract: We have studied the relationship between tumor necrosis factor (TNF)-sensitivity and doxorubicin-resistance in our doxorubicin-resistant cell line panel consisting of the parental cell line GLC4 plus GLC4-Adr2x and GLC4-Adr350x with respective resistance factors of 2 and 350 compared with GLC4. At the highest dose of 1000 ng/ml TNF, GLC4 was almost completely resistant to TNF, whereas 37% and 68% growth inhibition was observed in GLC4-Adr2x and GLC4-Adr350x, respectively. Sensitivity to TNF appeared to correlate inversely with the expression and gene copies of topoisomerase IIalpha in these cell lines. The gene encoding for c-erbB2 is in the proximity of the topoisomerase IIalpha gene and its product is a known cause for TNF-resistance. We found that our doxorubicin-resistant cell lines with decreased topoisomerase IIalpha gene copies have a simultaneous decrease in c-erbB2 gene copies, probably due to linkage between these 2 genes. This reduced number of c-erbB2 gene copies resulted in decreased c-erbB2 expression and subsequently in increased sensitivity to TNF. Additionally, we tried to establish some of the mechanisms associated with TNF-resistance in GLC4 related to c-erbB2 overexpression. There was no difference in TNF-receptor-1 expression between the cell lines. Compared with the TNF-sensitive GLC4-Adr350x, GLC4 appeared to have a decreased activation of NF-kappaB after exposure to TNF that might indicate a reduced TNF-receptor function. In GLC4, increased Bcl-2 expression was found, a protein described to confer TNF-resistance. Moreover, it was demonstrated that combining TNF with the poly-ADP-ribose polymerase (PARP) inhibitors 6-aminonicotinamide and 3-aminobenzamide did not affect TNF-sensitivity in GLC4 and GLC4-Adr350x, excluding a pivotal role of PARP in TNF-resistance in these cell lines. In conclusion, our data show that doxorubicin-resistant tumor cell lines with decreased topoisomerase IIalpha gene copies can become sensitive to TNF due to loss of c-erbB2 gene copies. We also found that several mechanisms associated with c-erbB2 overexpressing contribute to TNF-resistance in GLC4.
authors.affiliation: Department of Internal Medicine, University Hospital Groningen, The Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Sleijfer
authors.forename: J G
authors.initials: JG
authors.lastname: Asschert
authors.forename: H
authors.initials: H
authors.lastname: Timmer-Bosscha
authors.forename: N H
authors.initials: NH
authors.lastname: Mulder
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D018288:Carcinoma, Small Cell / Q000188:drug therapy / Q000235:genetics*; D015536:Down-Regulation; D004317:Doxorubicin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D018734:Genes, erbB-2; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000235:genetics*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D000903:Antibiotics, Antineoplastic; D004317:Doxorubicin; D018719:Erb-b2 Receptor Tyrosine Kinases; D014409:Tumor Necrosis Factor-alpha