Breast cancer frequently exhibits hyperactivation of the phosphoinositide 3-kinase (PI3K) pathway, commonly driven by mutations in PIK3CA, which encodes the catalytic p110α subunit of PI3K. While PI3K inhibitors initially showed therapeutic promise, their clinical utility has been limited due to pathway reactivation, often arising from rare pre-existing resistance-conferring mutations or adaptive and epigenetic mechanisms.
Although PTEN (phosphatase and tensin homologue) is a canonical negative regulator of PI3K signalling, our studies reveal that PTEN expression alone does not correlate with pathway suppression or therapeutic response. Investigating this disconnect, we identified the deubiquitinase USP10 as a key modulator of PI3K pathway activity and drug resistance. Mechanistically, USP10 stabilises the protein kinase GSK3β, which phosphorylates PTEN at Thr366, a critical residue that negatively regulates PTEN dimerisation and tumour-suppressive activity.
To target USP10, we utilised a rationally engineered ubiquitin-binding variant, UbV10, which phenocopies USP10 knockdown and a catalytically inactive mutant (USP10 C424A). UbV10 expression results in downregulation of both PTEN protein levels and downstream PI3K pathway signalling.
We propose that UbV10-mediated USP10 inhibition disrupts the USP10–GSK3β–PTEN regulatory axis, restoring PTEN dimerisation and tumour suppressor function. To explore its therapeutic potential, we have generated in vitro transcribed (IVT) mRNA encoding UbV10, enabling ectopic expression in resistant breast cancer cells. We are currently investigating whether UbV10 expression can resensitise these cells to PI3K pathway suppression, supporting its potential utility as an RNA-based therapeutic strategy.