Targeting the NF-κB pathway in estrogen receptor negative MDA-MB-231 breast cancer cells using small inhibitory RNAs

✍ Scribed by Noel R. Monks; Arthur B. Pardee

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 246 KB
• Volume: 98
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.20789

✦ Synopsis

Cancer cells in order to survive are often mutated to block apoptosis. One chemotherapeutic option is the re-establishment of apoptosis. An example of such a therapy is the PKC inhibitor Go ¨6976, which activates apoptosis and shrinks in vivo tumors in estrogen receptor-negative breast cancers. We proposed as a mechanism blockage of activation of the transcription factor NF-kB, which is anti-apoptotic and often elevated in cancers. Over recent years, questions have arisen regarding the specificity of these ''small-molecule inhibitors.'' We have therefore explored the role of NF-kB inhibition in MDA-MB-231 breast cancer cells using small inhibitory RNAs (siRNA). siRNAs designed against NF-kB protein p65 (RelA) and IKKa, IKKb, and IKKg, strongly decreased the target proteins. But, unlike Go ¨6976, they did not decrease basal NF-kB or cause apoptosis. In particular, the decrease in p65 protein had no effects on apoptosis or cell proliferation, thus questioning the importance of NF-kB alone in the maintenance of these cells. Furthermore, the proteasome inhibitor MG-132 caused loss of IkBa, and an increase of it is phosphorylated form, but basal NF-kB was unchanged, whilst activation of NF-kB by TNFa was completely inhibited, suggesting that MG-132 activity is independent of constitutive NF-kB activation. We ascribe these differences to the specificity of inhibition by siRNAs as compared to the well-known non-specificity of small-molecule inhibitors. We conclude that the mutations in these cancer cells made them resistant to apoptosis, by elevating their NF-kB and activating other basal pathways that are blocked by Go ¨6976 but not by IKK and p65 siRNAs.