Evidence that wild-type p53 in neuroblastoma cells is in a conformation refractory to integration into the transcriptional complex.

Neuroblastoma (NB) cells reportedly accumulate wild-type p53 exclusively in the cytoplasm. However, immunofluorescence assays with five different antibodies showed that p53 accumulates in the nucleus of up to 10% of NB cells. PAb1801 detected cytoplasmic 'punctate structures' which were also found in p53-null cells, rendering this antibody unsuitable for p53 detection. A comparison of DO-1 and PAb1801 staining in NB tissue sections confirmed the results obtained with NB cells. Nuclear accumulation of p53 was induced in NB cells using substances which disturb p53's tertiary structure at its zinc finger motif, or by treatment with mitomycin C. Constitutive nuclear accumulation was observed in an SK-N-SH variant, AW-1, which has a point mutation in p53 at Cys176>Ser, disturbing the same motif. Even though p53 showed DNA-binding capability after mitomycin C treatment of NB cells, the target gene products MDM2 and p21(WAF1,CIP1,SDI1) were not synthesized and no p53 transactivating activity measured in a reporter gene assay. Therefore we suggest that p53 in NB cells might be predominantly in a conformation refractory to integration into the transcriptional complex, resulting in at least partial transcriptional inactivity, hyperactive nuclear export and resistance to degradation by exogenously expressed MDM2.