tokens: Similar to the p53 beta isoform in SK - N - AS , the p53 in IGR - NB8 that lacks 67 amino acids at C - terminus was , alone , unable to induce p21 / WAF1 promoter activation except with endogenous wt - p53 on SH - SY5Y cells where transfection with IGR - NB8 significantly augmented the transcriptional activation of the p21 / Waf - 1 promoter ( Figure 5A ) .