Inhibition of Akt Kinase Activity by a Peptide Spanning the βA Strand of the Proto-oncogene TCL1

Abstract

Akt plays a central role in the regulation of cellular anti-apoptosis underlying various human neoplastic diseases. We have demonstrated previously that TCL1 (a proto-oncogene underlying human T cell prolymphocytic leukemia) interacts with Akt and functions as an Akt kinase co-activator. With the aim to develop an Akt kinase inhibitor, we hypothesized that a peptide, which spans the Akt-binding site, binds to Akt and modulates Akt kinase activity and its downstream biological responses. Indeed, we demonstrated that a peptide, named "Akt-in" (Akt inhibitor, NH 2 -AVTDHPDRLWAWEKF-COOH, encompassing the ␤A strand of human TCL1), interacted with Akt and specifically inhibited its kinase activity. Nuclear magnetic resonance studies suggested that interaction of Akt-in with the pleckstrin homology domain (PH) of Akt caused conformational changes on the variable loop 1 of Akt, the locus mediating phosphoinositide binding. Consistently, interaction of Akt-in with the Akt PH domain prevented phosphoinositide binding and hence inhibited membrane translocation and activation of Akt. Moreover, Akt-in inhibited not only cellular proliferation and anti-apoptosis in vitro but also in vivo tumor growth without any adverse effect. The roles of Akt, which possesses a PH domain, in intracellular signaling were well established. Hence, Akt inhibitors create an attractive target for anticancer therapy. However, no effective inhibitors specific for Akt have been developed. Akt-in, which inhibits association of phosphatidylinositol with Akt, is the first molecule to demonstrate specific Akt kinase inhibition potency. This observation will facilitate the design of specific inhibitors for Akt, a core intracellular survival factor underlying various human neoplastic diseases.

Expression of TCL-1 as a potential prognostic factor for treatment outcome in B-cell chronic lymphocytic leukemia

“…If validated in larger studies, especially by using rigorous protein quantification techniques on carefully obtained samples, TCL-1 expression may serve as a novel prognostic factor with relevance at the point when therapy is needed. Additionally, efforts to target TCL-1, through down-regulation or interference with TCL-1/AKT interactions [7] might represent a novel therapeutic approach. …”

Potent synergy of dual antitumor peptides for growth suppression of human glioblastoma cell lines

“…injection protocol at 48-h intervals, whereas the most comparable work elsewhere entailed peptide injections in numerous stages (>10 times; refs. 34 -37), at closer intervals (34), or in a more localized and invasive manner (36,37). Another significant advantage we showed is that in vivo the Wr-T transportermediated system offers long-range delivery far from the site of introduction, suggesting locational versatility; this is especially advantageous for malignant tumors including glioblastomas in view of the functional impairment of tumor-generated blood vessels as shown in the bloodbrain barrier at tumor site.…”

Insulin-like growth factor-binding protein-1 (IGFBP-1) regulates human schwannoma proliferation, adhesion and survival

“…Staining specificity was determined using FAK shRNA (left panel control mock shRNA and right panel shRNA FAK). (c) AKT pathway is pro-survival in schwannoma cells as shown by AKT-in inhibitory peptide (NH2-AVTDHPDRLWAWEKFCOOH encompassing the A strand of human TCL1 interacting and specifically inhibiting AKT kinase activity) and PI3 K inhibitor LY294002 (Hiromura et al, 2004). The cells were cultured in serum-free medium (DMEM) in the presence of AKT-in peptide, mock (amino acid positions 29-40 of human TCL1 not binding to AKT) or LY294002 for 48 h. Cell viability was monitored by propidium iodide (PI) (2.5 mg/ml).…”