Retinoic acid protects human breast cancer cells against etoposide-induced apoptosis by NF-kappaB-dependent but cIAP2-independent mechanisms.
BACKGROUND
Retinoids, through their cognate nuclear receptors, exert potent effects on cell growth, differentiation and apoptosis, and have significant promise for cancer therapy and chemoprevention. These ligands can determine the ultimate fate of target cells by stimulating or repressing gene expression directly, or indirectly through crosstalking with other signal transducers.


RESULTS
Using different breast cancer cell models, we show here that depending on the cellular context retinoids can signal either towards cell death or cell survival. Indeed, retinoids can induce the expression of pro-apoptotic (i.e. TRAIL, TNF-Related Apoptosis-Inducing Ligand, Apo2L/TNFSF10) and anti-apoptotic (i.e. cIAP2, inhibitor of apoptosis protein-2) genes. Promoter mapping, gel retardation and chromatin immunoprecipitation assays revealed that retinoids induce the expression of this gene mainly through crosstalk with NF-kappaB. Supporting this crosstalk, the activation of NF-kappaB by retinoids in T47D cells antagonizes the apoptosis triggered by the chemotherapeutic drugs etoposide, camptothecin or doxorubicin. Notably apoptosis induced by death ligands (i.e. TRAIL or antiFAS) is not antagonized by retinoids. That knockdown of cIAP2 expression by small interfering RNA does not alter the inhibition of etoposide-induced apoptosis by retinoids in T47D cells reveals that stimulation of cIAP2 expression is not the cause of their anti-apoptotic action. However, ectopic overexpression of a NF-kappaB repressor increases apoptosis by retinoids moderately and abrogates almost completely the retinoid-dependent inhibition of etoposide-induced apoptosis. Our data exclude cIAP2 and suggest that retinoids target other regulator(s) of the NF-kappaB signaling pathway to induce resistance to etoposide on certain breast cancer cells.


CONCLUSIONS
This study shows an important role for the NF-kappaB pathway in retinoic acid signaling and retinoic acid-mediated resistance to cancer therapy-mediated apoptosis in breast cancer cells, independently of cIAP2. Our data support the use of NF-kappaB pathway activation as a marker for screening that will help to develop novel retinoids, or retinoid-based combination therapies with improved efficacy.
Jiménez-Lara
Ana M
AM
Instituto de Investigaciones Biomédicas de Madrid Alberto Sols, CSIC/UAM, Madrid, Spain. amjimenez@iib.uam.es
Aranda
Ana
A
Gronemeyer
Hinrich
H
D000077556:Alitretinoin; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D000075747:Baculoviral IAP Repeat-Containing 3 Protein; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D002454:Cell Differentiation / Q000187:drug effects; D045744:Cell Line, Tumor; D019610:Cytoprotection / Q000187:drug effects*; D005047:Etoposide / Q000494:pharmacology*; D005260:Female; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D051034:Inhibitor of Apoptosis Proteins / Q000235:genetics / Q000378:metabolism; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051996:Transcription Factor RelA / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014212:Tretinoin / Q000494:pharmacology*; D044767:Ubiquitin-Protein Ligases
D000970:Antineoplastic Agents; D020672:I-kappa B Proteins; D051034:Inhibitor of Apoptosis Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D018168:Receptors, Retinoic Acid; D051996:Transcription Factor RelA; D000072000:NF-KappaB Inhibitor alpha; D000077556:Alitretinoin; D014212:Tretinoin; D005047:Etoposide; C494832:BIRC3 protein, human; D000075747:Baculoviral IAP Repeat-Containing 3 Protein; D044767:Ubiquitin-Protein Ligases