The regulatory subunit of PI3K, p85α (encoded by PIK3R1), binds, stabilizes and inhibits the PI3K p110 catalytic subunit. Functional characterization of PIK3R1 mutations has identified not only hypomorphs with reduced inhibition of p110, but also hypomorphs and dominant negative mutants that disrupt a novel regulatory role of p85α on PTEN or neomorphs that activate unexpected signaling pathways. The diverse phenotypic spectrum of these PIK3R1 driver mutations underscores the need for different treatment strategies targeting tumors harboring these mutations. This article describes the functional consequences of the spectrum of PIK3R1 driver mutations and therapeutic liabilities they may engender.
Keywords: MAPK; PI3K; PIK3R1; mutation; p85; targeted therapy.