The p65 subunit of nuclear factor-kappaB is a molecular target for radiation sensitization of human squamous carcinoma cells.

The transcription factor nuclear factor-kappaB (NF-kappaB) is activated in response to various stimuli including ionizing radiation. Disruption of NF-kappaB activation by mutant forms of the NF-kappaB inhibitor IkappaB-alpha or by proteasome inhibitors enhances both sensitivity to radiation and radiation-induced apoptosis. Human squamous carcinoma SCC-35 cells stably expressing a fragment (residues 1 to 84) of human p65 have been shown to exhibit down-regulation of both endogenous p65 mRNA and its protein. The mutant protein also inhibited radiation-induced NF-kappaB activation by preventing the proteolysis of IkappaB-alpha. This resulted in enhancement of cellular radiosensitivity and radiation-induced apoptosis. The NH(2)-terminal region of p65 is thus a potential molecular target for disruption of NF-kappaB activation and sensitization of tumors to radiotherapy.