Oncogenic Alterations in PI3K Signaling Emulated Optogenetically Recapitulate Some Phenotypic Changes in Mammary Epithelia

Cancer is known to be a disease of altered cellular signaling; however, the relationship between mutation-specific changes to signal transduction and the phenotypic consequences produced remains poorly understood. Here, we investigate two common breast cancer driver mutations, the <i>PIK3CA</i>^{<i>H1047R</i>} mutation and the <i>ErbB2</i> amplification, both of which activate the PI3K-Akt pathway but paradoxically drive distinct cellular outcomes. Indeed, in nontransformed mammary epithelial cells, PI3K^{<i>H1047R</i>} expression induced features of epithelial-mesenchymal transition (EMT), while ErbB2^<i>amp</i> cells exhibited a hyperproliferative phenotype. Characterization of PI3K axis signaling revealed that ErbB2^<i>amp</i> cells display prolonged, stimulus-dependent PI3K activation, whereas PI3K^{<i>H1047R</i>} cells show constitutive, ligand-independent signaling. To test whether these distinct dynamics contribute to the phenotypic responses, we employed an iLID-based optogenetic system that enables precise, tunable control of endogenous PI3K activity. Using this tool to mimic the mutation-specific dynamics in MCF10A mammary epithelial cells, we found that PI3K signaling patterns alone were sufficient to reproduce key features of the <i>PIK3CA H1047R</i>-associated EMT phenotype but not the <i>ErbB2</i>-associated proliferative phenotype. These findings suggest that the temporal encoding of pathway activity, not merely its magnitude, can drive some phenotypic changes in oncogenic progression, explain how distinct mutations within a common signaling pathway can produce divergent cellular phenotypes, and provide a workflow for interrogating the functional consequences of changes in signaling dynamics.