Requirement for NF-κB signalling in a mouse model of lung adenocarcinoma

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Abstract
Mutations in genes of the RAS family are preset on about 20% of human cancers, making RAS proteins prime potential targets for cancer therapy. Direct targeting of RAS proteins has not so far been productive, but two papers published in this issue offer the prospect of alternative targets in a signalling pathway downstream of RAS. Using a synthetic lethality RNAi screen, Barbie et al. identify TBK1 as a kinase in the NF-κB signalling pathway that is essential for the survival of KRAS-transformed cells. TBK1 induces anti-apoptotic signals and may be a therapeutic cancer target. And in an elegant mouse model for lung cancer driven by Kras mutation and loss of p53, Meylan et al. show that NF-κB signalling is activated by the concerted actions of these two alterations and required for tumour initiation and tumour maintenance. NF-κB transcription factors have been implicated in cellular transformation and tumorigenesis, but despite extensive biochemical characterization of NF-κB signalling, its requirement in tumour development is not completely understood. Here, the NF-κB pathway is shown to be required for the development of tumours in a mouse model of lung adenocarcinoma in a p53-status-dependent manner, providing support for the development of NF-κB inhibitory drugs as targeted therapies. NF-κB transcription factors function as crucial regulators of inflammatory and immune responses as well as of cell survival1. They have also been implicated in cellular transformation and tumorigenesis2,3,4,5,6. However, despite extensive biochemical characterization of NF-κB signalling during the past twenty years, the requirement for NF-κB in tumour development in vivo, particularly in solid tumours, is not completely understood. Here we show that the NF-κB pathway is required for the development of tumours in a mouse model of lung adenocarcinoma. Concomitant loss of p53 (also known as Trp53) and expression of oncogenic Kras(G12D) resulted in NF-κB activation in primary mouse embryonic fibroblasts. Conversely, in lung tumour cell lines expressing Kras(G12D) and lacking p53, p53 restoration led to NF-κB inhibition. Furthermore, the inhibition of NF-κB signalling induced apoptosis in p53-null lung cancer cell lines. Inhibition of the pathway in lung tumours in vivo, from the time of tumour initiation or after tumour progression, resulted in significantly reduced tumour development. Together, these results indicate a critical function for NF-κB signalling in lung tumour development and, further, that this requirement depends on p53 status. These findings also provide support for the development of NF-κB inhibitory drugs as targeted therapies for the treatment of patients with defined mutations in Kras and p53.