The expression of the ΔNp73β isoform of p73 leads to tetraploidy

The p73 locus gene has a complex structure encoding a plethora of isoforms. The different ΔN truncated isoforms of p73 may exert different activities depending on the cellular context. The β isoform of ΔNp73 seems to have a particular pattern of action even if its role in cell cycle and mitosis is still under investigation. To gain further knowledge of ΔNp73β's function, we investigated the effects of its over-expression in tumour cellular models, using the tetracycline-inducible expression system. In the human lung carcinoma cell line H1299, ΔNp73β over-expression resulted in suppression of cell growth and in cell death. Surprisingly stable over-expression of ΔNp73β impaired the genomic stability of tumour cells, leading to the formation of tetraploid cells. The cells become enlarged and multinucleate, with incorrect mitotic figures, and died by apoptotic-independent pathways. Our data suggest that ΔNp73β-induced aberrant mitosis evades the control of the mitotic spindle assay checkpoint, leading to tetraploidy and cell death through mitotic catastrophe rather than apoptosis. The various C-terminal regions of ΔNp73 may influence the final cellular phenotype and we assume that the β one in particular could be important in both cell growth control and regulation of mitosis.