Intracellular translocation in Aktion: small molecule inhibitor effects on AKT localization

Abstract

Upregulation of the AKT pathway leads to a variety of human cancers. Phosphatidylinositol ether analogs, or PIAs, are small molecules designed to inhibit the Ser/Thr kinase AKT, by binding to its pleckstrin homology (PH) domain and preventing translocation from the cytoplasm to the nucleus. D‐3′‐deoxy‐diC8‐phosphatidylinositol is a soluble PIA that has an IC50 of 40 µM in U937 human lymphoma cells, which predominantly express Akt1. This compound (and not related further deoxygenated inositol lipids or L‐inositol species) does not appear to affect activation and growth of cells that have other Akt isoforms as well as Akt1 (e.g., B cells). We have shown that D‐3′‐deoxy‐diC8PI inhibits phosphorylation of proteins downstream of Akt1. However, near normal levels of phosphorylation of Akt1 strongly indicate that plasma membrane translocation of Akt1 has not been significantly inhibited. A GFP‐Akt1 fusion protein was expressed in U937 and MCF‐7 cell lines, and the movement of Akt1 when treated with D‐3′‐deoxy‐diC8PI was tracked using confocal microscopy. Treatment with D‐3′‐deoxy‐diC8PI did not inhibit plasma membrane or nuclear translocation, indicating cytotoxicity occurs by a different mechanism. Binding of the Akt1 PH domain in the absence and presence of the short‐chain PIA has also been examined to confirm the in vivo results.(This work is supported by N.I.H. GM60418).