The serine/threonine kinase Akt family contains several members, including
Akt1 (also designated PKB or RacPK), Akt2 (also designated PKBβ or RacPK-β)
and Akt3 (also designated PKBγ or thyoma viral proto-oncogene 3), which
exhibit sequence homology with the protein kinase A and C families and are
encoded by the c-Akt proto-oncogene. All members of the Akt family have a
Pleckstrin homology domain. Akt1 and Akt2 are activated by PDGF stimulation
that is dependent on PDGFR-β tyrosine residues 740 and 751, which bind the
subunit of the phosphatidylinositol 3-kinase (PI 3-kinase) complex. Akt proteins
become phosphorylated and activated in Insulin/IGF-1-stimulated cells by an
upstream kinase(s), and the activation of Akt1 and Akt2 is inhibited by the PI
kinase inhibitor Wortmannin. Taken together, this data strongly suggests that
the protein signals downstream of the PI kinases.