NF-κB Activation by Ultraviolet Light Not Dependent on a Nuclear Signal

Exposure of mammalian cells to radiation triggers the ultraviolet (UV) response, which includes activation of activator protein-1 (AP-1) and nuclear factor kappa B (NF-κ B). This was postulated to occur by induction of a nuclear signaling cascade by damaged DNA. Recently, induction of AP-1 by UV was shown to be mediated by a pathway involving Src tyrosine kinases and the Ha-Ras small guanosine triphosphate-binding protein, proteins located at the plasma membrane. It is demonstrated here that the same pathway mediates induction of NF-κ B by UV. Because inactive NF-κ B is stored in the cytosol, analysis of its activation directly tests the involvement of a nuclear-initiated signaling cascade. Enucleated cells are fully responsive to UV both in NF-κ B induction and in activation of another key signaling event. Therefore, the UV response does not require a signal generated in the nucleus and is likely to be initiated at or near the plasma membrane.