A hyper-dynamic equilibrium between promoter-bound and nucleoplasmic dimers controls NF-kappaB-dependent gene activity.
Because of its very high affinity for DNA, NF-kappaB is believed to make long-lasting contacts with cognate sites and to be essential for the nucleation of very stable enhanceosomes. However, the kinetic properties of NF-kappaB interaction with cognate sites in vivo are unknown. Here, we show that in living cells NF-kappaB is immobilized onto high-affinity binding sites only transiently, and that complete NF-kappaB turnover on active chromatin occurs in less than 30 s. Therefore, promoter-bound NF-kappaB is in dynamic equilibrium with nucleoplasmic dimers; promoter occupancy and transcriptional activity oscillate synchronously with nucleoplasmic NF-kappaB and independently of promoter occupancy by other sequence-specific transcription factors. These data indicate that changes in the nuclear concentration of NF-kappaB directly impact on promoter function and that promoters sample nucleoplasmic levels of NF-kappaB over a timescale of seconds, thus rapidly re-tuning their activity. We propose a revision of the enhanceosome concept in this dynamic framework.
Institute for Research in Biomedicine, Bellinzona, Switzerland.
Daniela
D
Bosisio
Ivan
I
Marazzi
Alessandra
A
Agresti
Noriaki
N
Shimizu
Marco E
ME
Bianchi
Gioacchino
G
Natoli
D001683:Biological Clocks / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism*; D002843:Chromatin / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D016328:NF-kappa B / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000502:physiology*; D011485:Protein Binding / Q000502:physiology; D013997:Time Factors; D014158:Transcription, Genetic / Q000502:physiology*
D002843:Chromatin; D016328:NF-kappa B; D004247:DNA