Chemotherapy resistance of mouse WAP-SVT/t breast cancer cells is mediated by osteopontin, inhibiting apoptosis downstream of caspase-3.
Impairment of the complex regulatory network of cell death and survival is frequently the reason for therapy resistance of breast cancer cells and a major cause of tumor progression. We established two independent cell lines from a fast growing mouse breast tumor (WAP-SVT/t transgenic animal). Cells from one line (ME-A cells) are sensitive to apoptotic stimuli such as growth factor depletion or treatment with antitumor agents (e.g. doxorubicin). Cells from the second line (ME-C cells), which carry a missense mutation at the p53 codon 242, are very insensitive to apoptotic stimuli. Co-cultivation experiments revealed that the ME-C cells mediate cell death resistance to the ME-A cells. Microarray and Western blot analysis showed that osteopontin (OPN) is selectively overexpressed by the ME-C cells. This glycoprotein is the most abundant protein secreted by the ME-C cells and we obtained strong indications that OPN is the main antiapoptotic factor. However, the OPN containing ME-C cell medium does not alter the expression level of pro- or antiapoptotic genes or known inhibitors of apoptosis (IAPs). Its signaling involves mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK)1/2 as the kinase inhibitor PD98059 restores apoptosis but not the Akt inhibitor. In the ME-A cells, mitochondrial cytochrome c release occurs with and without external apoptotic stimuli. OPN containing ME-C cell medium does not prevent the mitochondrial cytochrome c release and caspase-9 processing. In serum starved ME-A cells, the OPN containing ME-C cell medium prevents caspase-3 activation. However, in doxorubicin-treated cells, although apoptosis is blocked, it does not inhibit caspase-3. This indicates that the ME-A cells distinguish between the initial apoptotic stimuli and that the cells possess a further uncharacterized control element acting downstream from caspase-3.
Graessmann
M
M
Institut für Molekularbiologie und Bioinformatik, Charité Unversitätsmedizin Berlin, Berlin, Germany. monika.graessmann@charite.de
Berg
B
B
Fuchs
B
B
Klein
A
A
Graessmann
A
A
D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics*; D017209:Apoptosis / Q000235:genetics*; D053148:Caspase 3 / Q000502:physiology*; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D015674:Mammary Neoplasms, Animal / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D008894:Milk Proteins / Q000235:genetics*; D008928:Mitochondria / Q000378:metabolism; D008954:Models, Biological; D053495:Osteopontin / Q000378:metabolism / Q000502:physiology*; D014407:Tumor Cells, Cultured
D000903:Antibiotics, Antineoplastic; D000952:Antigens, Polyomavirus Transforming; D016895:Culture Media, Serum-Free; D008894:Milk Proteins; C506896:Spp1 protein, mouse; C024471:whey acidic proteins; D053495:Osteopontin; D004317:Doxorubicin; D045304:Cytochromes c; D048031:JNK Mitogen-Activated Protein Kinases; C505409:Casp3 protein, mouse; D053148:Caspase 3