TNF-α mediated transport of NF-κB to the nucleus is independent of the cytoskeleton-based transport system in non-neuronal cells

In unstimulated cells, proteins of the nuclear factor κB (NF-κB) transcription factor family are sequestered in the cytoplasm through interactions with IκB inhibitor proteins. Tumor necrosis factor alpha (TNF-α) activates the degradation of IκB-α and the nuclear import of cytoplasmic NF-κB. Nuclear localization of numerous cellular proteins is mediated by the ability of the cytoskeleton, usually microtubules, to direct their perinuclear accumulation. In a former study we have shown that activated NF-κB rapidly moves from distal processes in neurons towards the nucleus. The fast transport rate suggests the involvement of motor proteins in the transport of NF-κB. Here we address the question how NF-κB arrives at the nuclear membrane before import in non-neuronal cells, i.e., by diffusion alone or with the help of active transport mechanisms. Using confocal microscopy imaging and analysis of nuclear protein extracts, we show that NF-κB movement through the cytoplasm to the nucleus is independent of the cytoskeleton, in the three cell lines investigated here. Additionally we demonstrate that NF-κB p65 is not associated with the dynein/dynactin molecular motor complex. We propose that cells utilize two distinct mechanisms of NF-κB transport: (1) signaling via diffusion over short distances in non-neuronal cells and (2) transport via motor proteins that move along the cytoskeleton in neuronal processes where the distances between sites of NF-κB activation and nucleus can be vast.