Good cop, bad cop: the different faces of NF-kappaB.

Complexes formed from the nuclear factor kappaB (NF-kappaB) family of transcription factors are ubiquitously expressed and are induced by a diverse array of stimuli. This results in their becoming activated in a wide variety of different settings. While the functions of NF-kappaB in many of these contexts have been the subject of intense research and are now well established, it is also clear that there is great diversity in the effects and consequences of NF-kappaB activation. NF-kappaB subunits do not necessarily regulate the same genes, in an identical manner, in all of the different circumstances in which they are induced. This review will discuss the different functions of NF-kappaB, the pathways that modulate NF-kappaB subunit activity and, in contrast to its more commonly thought of role as a promoter of cancer cell growth and survival, the ability of NF-kappaB, under some circumstances, to behave as a tumor suppressor.