Class I Phosphoinositide 3-Kinase PIK3CA/p110α and PIK3CB/p110β Isoforms in Endometrial Cancer

The phosphoinositide 3-kinase (PI3K) signalling pathway is highly dysregulated in cancer, leading to elevated PI3K signalling and altered cellular processes that contribute to tumour development. The pathway is normally orchestrated by class I PI3K enzymes and negatively regulated by the phosphatase and tensin homologue, PTEN. Endometrial carcinomas harbour frequent alterations in components of the pathway, including changes in gene copy number and mutations, in particular in the oncogene PIK3CA, the gene encoding the PI3K catalytic subunit p110, and the tumour suppressor PTEN. PIK3CB, encoding the other ubiquitously expressed class I isoform p110, is less frequently altered but the few mutations identified to date are oncogenic. This isoform has received more research interest in recent years, particularly since PTEN-deficient tumours were found to be reliant on p110 activity to sustain transformation. In this review, we describe the current understanding of the common and distinct biochemical properties of the p110 and p110 isoforms, summarise their mutations and highlight how they are targeted in clinical trials in endometrial cancer.