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TAp73 mediated transcriptional activity and apoptosis are influenced by diverse p53 isoforms

Introduction. The p53 activities are due, at least in part, to its ability to form oligomers that bind to specific DNA sequences and activate transcription. Since some mutant p53 proteins, as well as ΔNp73 isoforms form heterocomplex with TAp73, we asked whether p53 isoforms can do the same and potentially act as dominant-negative inhibitors of TAp73. Moreover, it was already found that some isoforms form complex with wtp53 and some of them inhibit p53 tumor suppressor functions. Material and method. The p53 null human cell line H1299 cells were used as a model. Proteins were extracted and western blot was preformed by standard methods. The complex formation was determined by coimmunoprecipitation assay. Transcriptional and apoptotic activity TAp73β were measured by Dual-Glo Luciferase Assay or Annexin- V-FLUOS staining kit, respectively. The half lives of different p53 isoforms have been determined using pulse chase method with cyclohexamide. Results and discussion. Coimmunoprecipitation assay has shown that all six p53 isoforms examined can form complexes with TAp73β, while only D133p53 isoforms (α, β and γ) with TAp73α. All p53 isoforms counteracts TAp73 transactivation function but with different efficiency and in a promoter- dependent manner. Furthermore, apoptotic activity of TAp73β was augmented by coexpression of p53, while Δ133p53α and Δ133p53β inhibit its apoptotic activity most efficiently. The half lives of different p53 isoforms have shown that p53γ isoform has the shortest while Δ133p53γ has the longest half life. Inhibitory interactions of two proteins in complex often lead to their stabilization. However, only three isoforms (Δ133p53α, Δ133p53β and Δ40p53α) stabilize TAp73β. Conclusion. p53 isoforms can modulate p53 family tumor suppressor activities, and the expression ratio between members of the family is probably the most important factor in determining the cell fate and outcome.

isoforms p53; p73; apoptosis; transcriptional activity

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