Activation of the p53 pathway in myeloma cells without del(17p) represses CD46 expression and MV-GFP infection. (A) Total mononuclear cells from 13 patients with or without del(17)p were incubated for 24 hours with or without nutlin3a (10 μM) prior to DR5 and CD46 staining. After washing to remove nutlin3a, cells were subjected to infection as described in the Figure 5A legend. GFP expression was assessed 2 days later. Expression of DR5 or CD46 (MFIR) in CD138⁺ cells was assessed in double staining with anti-CD138 mAb before incubation with MV-GFP. GFP expression in CD138⁺ cells is reported as the percentage of positive cells and the MFIR, which was the FL1 expression level in infected GFP-positive CD138⁺ cells over paired control samples (without and with nutlin3a). Statistical analyses were performed using the Wilcoxon matched-paired sign rank test. (B) Nutlin3a-induced regulation of DR5, CD46, and GFP expression occurred in samples without del(17)p. The DR5, CD46, and GFP fold-changes (nutlin3a/cont) represent the MFIR ratio in nutlin3a-treated over control paired samples (see supplemental Table 4). Statistical analyses were performed using the Mann-Whitney U test. (C) Nutlin3a induced a correlated regulation of DR5, CD46, and GFP. Fold changes of DR5, CD46, and GFP expression were plotted against each other, and correlations were calculated using the Spearman test. **P < .01.