3416400801

NF-kB and radiosensilivity • C. Didelot et al. 1357

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NF-kB

NFkB

Fig. 3. Modulation of the DNA-binding activity of NF-kB in (A) KB and (B) KB3 cells by cxposurc to (2) TNFa or (4) l)EX and comparcd with (l) untreated cells. Nuclcar extracts (5 /xg) from KB and KB3 cells exposcd to 10 pM DEX or 2.5 ng/mL TNFa wcre incubated with the radiolabeled NF-kB binding site. The DNA/NF-kB complex was analyzcd in nativc polyacrylamide gcls. A competition was carried out with 100-fold molar excess of unlabeled NF-kB binding site, which was also shown (3) using samplc with TNFa treatment. These pictures were rcpresentativc of three independent expcriments.

nuclear activity was higher in the KB celi linę than in the KB3 linę. For both celi lines, NF-kB protein complex was ;haracteri/.ed as P50/P65 heterodimer by supershift assay Fig. 2).

KB and KB3 cells were exposed to DEX or TNFa at lifferent concentrations (respectively, 1-10 /xM for 12-24 h and 2.5-10 ng/mL for 10 min to l h). Nuclear ;xtracts were then prepared and assayed for NF-kB DNA-binding activity. Only the most effective condi-ions using the lowest drug concentrations in each celi ine were selectcd and subsecjuently used. Exposure of <B and KB3 cells to 10^-6 M DEX for 24 h resulted in an dmost complcte inhibition of NF-kB binding activity. ixposure to 2.5 ng/mL TNFa for 10 min led to signifi-ant incrcasc in NF-kB DNA-binding activity in KB and CB3 celi lines (Fig. 3).

Zonseąuences of NF-kB DNA-binding activity modulation <n apoptosis level

In untreated celi lines, KB displayed a significantly ower apoptosis ratę than KB3, with, respectively, 5% nd 16% (p < 0.05). In the KB celi linę (Fig. 4A), DEX xposure led to 1.6-fold apoptosis induction, and TNFa xposure did not lead to a significant effect on apoptosis ratę. In the KB3 celi linę (Fig. 4B), DEX exposure led to a weak apoptosis induction, and TNFa exposure resulted in a significant decrease in apoptosis, reaching 50% for the KB3 celi linę as compared to the untreated control.

Conseąuetices of NF-kB DNA-binding activity modulation on radiosensitmty parameters

To decrease the high constitutive NF-kB DNA-binding activity, KB cells were exposed for 24 h to 10~° M DEX. Conversely, KB3 cells were exposed to 2.5 ng/mL TNFa for 10 min, to inerease the Iow constitutivc NF-kB binding activity. After modulation of constitutive NF-kB DNA binding activity in each celi linę, radiosensitivity parameters were calculated and compared to untreated Controls. In the KB celi linę (Fig. 5A), DEX exposure significantly decreased radioresistance at Iow doses from 0.5 to 2 Gy, with the a parameter decreasing from 0.114 to 0.052 (Table 1). At higher doses (greater than 3 Gy), DEX exposure induced an inerease in radioresistance, with the /3 parameter inereasing from 0.012 to 0.030 (Table I). In the KB3 celi linę (Fig. 5B), whatevcr the irradiation dose, TNFa exposure led to an inerease in radioresistance. The SF₂ value inereased 1.32-fold with TNFa pretreatment (Table 1).