Effect of CD40 activation on p53 transactivation in RPMI 8226 and HS Sultan MM cell lines.

RPMI 8226 (A) and HS Sultan (B) cells (10 × 10⁶/sample) were transfected with either PG13-luc, a plasmid containing 13 copies of normal p53-binding site, or with MG15-luc, a plasmid containing 15 copies of mutated p53-binding site, using electroporation. Tumor cells were incubated at 37°C for 14 to 16 hours and cultured in media and with formalin-fixed NIH3T3/CD40LT at 37°C or 30°C for up to 40 hours. Cells were harvested, and luciferase activity was normalized to total cellular protein content. Experiments were performed in triplicate, and results are expressed as mean ± SEM normalized luciferase activity.