p53 deficiency exacerbates pleiotropic mitotic defects, changes in nuclearity and polyploidy in transdifferentiating pancreatic acinar cells

Abstract

In a primary culture model for pancreatic acinar-ductal transdifferentiation, cells exhibited increased proliferation, changes in nuclearity and polyploidy. We identify the 'nucleus to centrosome' ratio of the progenitor cell, the dissemination of centrosomes at spindle poles and cytokinesis failure as critical determinants of mitosis outcome and centrosome inheritance. Abortive cytokinesis of mononuclear cells contributes to the binuclear cell pool, whereas enclosure of entire mitotic formations, within a single nuclear envelope, perpetuates polyploidization. Binuclear cell nuclei combine their genomes on a single metaphase plate, doubling descendant ploidy. Moreover, B42% of binuclear and tetraploid cells assemble aberrant spindles with up to 8 centrosomes/poles. These phenotypes were exacerbated in p53-deficient cultures exhibiting increased S-phase entry, giant nuclei, multinucleation, multipolar mitoses and centrosome hyperamplification. The tendency of p53-proficient cells to spontaneously evade the tetraploidy checkpoint degenerates to uncontrolled polyploid progression in p53-deficient cultures, explaining why p53 abrogation alone rapidly descends to aneuploidy in this system. We detected constitutively nuclear mdm2, which may circumvent endogenous cellcycle checkpoints, and pronounced accumulation of p21 and p27 in multinuclear cells and giant nuclei, consistent with roles in polyploidization. This in vitro model may recapitulate the processes underlying genomic instability in pancreatic tumours in vivo, and attests to the existence of a p53-dependent polyploidy checkpoint acting to limit the degree of polyploidization.

Essential Dosage-Dependent Functions of the Transcription Factor Yin Yang 1 in Late Embryonic Development and Cell Cycle Progression

“…Inactivation of survivin was shown to induce p53 up-regulation and subsequent activation of a p53-and p21-dependent checkpoint, resulting in cell cycle arrest in G 1 phase (78). Despite contradictory reports, other studies support the hypothesis that cytokinesis failure activates a tetraploidy checkpoint response blocking cell cycle progression in G 1 phase (1,63,69,70,75).…”

Ribosomal Protein S27-like, a p53-Inducible Modulator of Cell Fate in Response to Genotoxic Stress

“…In addition, RPS27L induction by p53 seemed to be required to prevent tetraploidy upon DNA damage. Loss of the tetraploidy checkpoint due to a missing cell cycle arrest has been believed to contribute to the genomic instability induced by p53 inactivation (42,43). Thus, it raises the possibility that RPS27L might also have a role in maintaining genome stability upon DNA damage.…”

The involvement of MCT-1 oncoprotein in inducing mitotic catastrophe and nuclear abnormalities

“…Although p53 loss or mutation impairs centrosomal structure and mitotic spindle checkpoint, 2,4,[9][10][11] it is completely unknown whether MCT-1 oncoprotein can synergistically affect mitotic development in circumstances of p53 deficiency. ATR kinase is implicated in centrosomal function and spindle assembly.…”

“…For example, BRCA1, p53, Chk1, Chk2, TopBP1, Aurora A, Plk1, cyclin B1 and Cdk1 all function as centrosome integrators, which positively or negatively engage in mitotic entry or exit. 8 Loss or mutation of p53 abnormally amplifies number of centrosomes through the impairment of the centrosome duplication cycle, which is connected with mitotic spindle abnormality and cytokinesis failure 4,[9][10][11] and also results in chromosomal instability. 2,[12][13][14] Moreover, p53 regulates…”