Oncogenic PIK3CA induces centrosome amplification and tolerance to genome doubling

Abstract

Mutations in PIK3CA are very frequent in cancer and lead to sustained PI3K pathway activation. The impact of acute expression of mutant PIK3CA during early stages of malignancy is unknown. Using a mouse model to activate the Pik3ca H1047R hotspot mutation in the heterozygous state from its endogenous locus, we here report that mutant Pik3ca induces centrosome amplification in cultured cells (through a pathway involving AKT, ROCK and CDK2/Cyclin E-nucleophosmin) and in mouse tissues, and increased in vitro cellular tolerance to spontaneous genome doubling. We also present evidence that the majority of PIK3CA H1047R mutations in the TCGA breast cancer cohort precede genome doubling. These previously unappreciated roles of PIK3CA mutation show that PI3K signalling can contribute to the generation of irreversible genomic changes in cancer. While this can limit the impact of PI3K-targeted therapies, these findings also open the opportunity for therapeutic approaches aimed at limiting tumour heterogeneity and evolution.

NODAL/TGFβ signalling mediates the self-sustained stemness induced by PIK3CAH1047R homozygosity in pluripotent stem cells

“…High-depth transcriptomics confirmed that heterozygosity for PIK3CA H1047R fails to induce widespread substantial transcriptional remodeling, whether chronically modelled in CRISPR-edited iPSCs or acutely induced in mouse embryonic fibroblasts (MEFs) by Cre expression, despite induction of canonical PI3K pathway activation in both cases (current study and Ref. ( 5, 28, 48 )). Similarly, iPSCs with heterozygous expression of PIK3CA E418K , a “non-hotspot” mutation, were transcriptionally indistinguishable from their isogenic wild-type controls.…”

Perspective: Potential Impact and Therapeutic Implications of Oncogenic PI3K Activation on Chromosomal Instability

“…At present, it is not clear whether the observed defects in cell cycle progression are an artefact of forced overexpression of supra-physiologically active PI3K constructs, or whether this would also occur upon endogenous oncogenic PIK3CA activation. In this regard, we did not find evidence for cell cycle blockade in MEFs expressing an endogenous heterozygous PIK3CA H1047R allele [72]. Oncogenic activation of PI3K signaling has also been shown to elicit senescence in some cellular contexts [91,95,96] but not in others [72,97].…”

“…Our demonstration that physiological induction of PIK3CA H1047R (i.e. in the heterozygous state and expressed from the endogenous promotor) can induce centrosome amplification and aneuploidy [72] more firmly establishes this biological role of mutant PI3K. In fact, PI3K also controls tetraploidization under physiological conditions: in rodents, modulation of insulin concentration, and consequently Akt/PKB activity, orients hepatocytes into a specific cell cycle program, leading to the generation of binucleated tetraploid cells [80].…”

“…We recently reported that expression of the PIK3CA H1047R mutant can lead to centrosome amplification (in mouse embryonic fibroblasts (MEFs), the MCF10A immortalised breast cell line and in mouse tissues) and increased in vitro tolerance to WGD (in MEFs) [72], indicating that PI3K activation might be involved in CIN. Signalling pathways involved in PIK3CA H1047R -driven centrosome amplification include AKT, ROCK and CDK2/Cyclin E-nucleophosmin [72]. Overexpression of Akt/PKB has been shown to induce supernumerary centrosomes/aneuploidy in cell lines [73,74].…”

“…PIK3CA mutation is very common in breast cancer, where it appears to be an early, clonal event [72]. Moreover, in genome-doubled breast cancers, the majority of PIK3CA mutations precede the genome duplication event, with PIK3CA mutations showing a tendency to be mutually exclusive with mutations in TP53 [72], a known tolerance mechanism towards genome doubling [41][42][43]. These data indicate a potential role of PIK3CA mutation as a tolerance mechanism for genome doubling in breast cancer, independent of the p53 pathway.…”