Phosphatidylinositide-3-kinases (PI3K) PI3Ka, is a lipid kinase frequently mutated in several cancer
types. Under normal physiological conditions it initiates a number of signaling pathways by recruiting
other kinases, such as Akt, to the plasma membrane. The mutations observed in tumors increase PI3K
kinase activity, leading to increased cell survival, cell motility, cell metabolism, and cell cycle
progression. The structure of the complex between the catalytic subunit of PI3Ka, p110a, and a portion
of its regulatory subunit, p85a reveals that many of the oncogenic mutations occur at the interfaces
between p110a domains and between p110a and p85a domains. At these positions, mutations may
disrupt interactions that result in changes in the kinase domain that may increase enzymatic activity.
Other mutations may dislodge the nSH2 domain from its inhibitory position in the complex. The
structure also suggests that interaction with the membrane is mediated by a region of the heterodimer
that includes one of the p85a domains (iSH2). The structure of the most common oncogenic mutation,
H1047R, shows differences in p110a with the wild-type that indicates that this mutation may increase
its interaction with the cellular membrane resulting in activation by increasing accessibility to the
substrate. These findings may provide novel structural loci for the design of new isoform-specific,
mutant-specific anti-cancer drugs