The Novel Phosphatase Domain Mutations Q171R and Y65S Switch PTEN from Tumor Suppressor to Oncogene

Phosphatase and tensin homolog deleted on chromosome 10, or PTEN, is a well-characterized tumor suppressor with both lipid and protein phosphatase activities. PTEN is often downregulated by epigenetic mechanisms such as hypermethylation, which leads to constitutive activation of the PI3K–Akt pathway. Large datasets from next-generation sequencing, however, revealed that mutations in PTEN may not only hamper protein function but may also affect interactions with downstream effectors, leading to variable oncogenic readouts. Here, two novel PTEN mutations, Q171R and Y65S, identified in Filipino colorectal cancer patients, were phenotypically characterized in NIH3T3 and HCT116 cells, alongside the C124S canonical mutant and wild-type controls. The novel mutants increased cellular proliferation, resistance to apoptosis and migratory capacity. They induced gross morphological changes including cytoplasmic shrinkage, increased cellular protrusions and extensive cytoskeletal reorganization. The mutants also induced a modest increase in Akt phosphorylation. Further mechanistic studies will help determine the differential oncogenic potencies of these mutants, and resolve whether the structural constraints imposed by the mutations may have altered associations with downstream effectors.