PI3-Kinases (PI3-Ks) are a family of lipid kinases that are implicated in signal transduction. PI3-K consists of two subunits; p85 and p110. The p85 subunit localize PI3-K activity to the plasma membrane while the p110 subunit contains the catalytic domain of PI3-K. Four isoforms of p110 has been found; the alpha, beta, gamma, and the delta subunit. The delta isoform is predominantly expressed in leukocytes and has been shown to interact with p85 and GTP-bound Ras via its SH2/SH3 domain.