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

Neuroblastoma (NB) cells reportedly accumulate wildtype p53 exclusively in the cytoplasm, However, immunofluorescence assays with five different antib odies 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 co mparison of DO-1 and PAb1801 staining in NB tissue sections confirmed the r esults obtained with NB cells. Nuclear accumulation of p53 was induced in N B cells using substances which disturb p53's tertiary structure at its zinc finger motif, or by treatment with mitomycin C, Constitutive nuclear accum ulation was observed in an SK-N-SH variant, AW-1, which has a point mutatio n in p53 at Cys176>Ser, disturbing the same motif, Even though p53 showed D NA-binding capability after mitomycin C treatment of NB cells, the target g ene products MDM2 and p21(WAF1.CIP1.SDI1) were not synthesized and no p53 t ransactivating activity measured in a reporter gene assay. Therefore we sug gest that p53 in NB cells might be predominantly in a conformation refracto ry to integration into the transcriptional complex, resulting in at Least p artial transcriptional inactivity, hyperactive nuclear export and resistanc e to degradation by exogenously expressed MDM2.