mk-2206 and triciribine

Protein kinase B (AKT) is a serine/threonine kinase that functions as an important downstream effector of phosphoinositide 3-kinase. We have recently shown that MK-2206 and triciribine, two highly selective AKT inhibitors increase the level of low density lipoprotein receptor (LDLR) mRNA which leads to increased amount of cell-surface LDLRs. However, whereas MK-2206 induces transcription of the LDLR gene, triciribine stabilizes LDLR mRNA, raising the possibility that the two inhibitors may actually affect other kinases than AKT. In this study, we aimed to ascertain the role of AKT in regulation of LDLR mRNA expression by examining the effect of five additional AKT inhibitors on LDLR mRNA levels. Here we show that in cultured HepG2 cells, AKT inhibitors ARQ-092, AKT inhibitor VIII, perifosine, AT7867 and CCT128930 increase LDLR mRNA levels by inducing the activity of LDLR promoter. CCT128930 also increased the stability of LDLR mRNA. To study the role of AKT isoforms on LDLR mRNA levels, we examined the effect of siRNA-mediated knockdown of AKT1 or AKT2 on LDLR promoter activity and LDLR mRNA stability. Whereas knockdown of either AKT1 or AKT2 led to upregulation of LDLR promoter activity, only knockdown of AKT2 had a stabilizing effect on LDLR mRNA. Taken together, these results provide strong evidence for involvement of AKT in regulation of LDLR mRNA expression, and point towards the AKT isoform specificity for upregulation of LDLR mRNA expression.

Topics: Aminopyridines; Animals; Benzimidazoles; CHO Cells; Cricetinae; Cricetulus; Hep G2 Cells; Heterocyclic Compounds, 3-Ring; Humans; Imidazoles; Phosphorylcholine; Piperidines; Protein Kinase Inhibitors; Proto-Oncogene Proteins c-akt; Pyrazoles; Pyrimidines; Pyrroles; Quinoxalines; Receptors, LDL; Ribonucleosides; RNA Stability; RNA, Messenger; Transcriptional Activation

Serine/threonine kinase Akt regulates key cellular processes such as cell growth, proliferation, and survival. Activation of Akt by mitogenic factor depends on phosphatidylinositol 3-kinase (PI3K). Here, we report that IKBKE (also known as IKKε and IKKi) activates Akt through a PI3K-independent pathway. IKBKE directly phosphorylates Akt-Thr308 and Ser473 independent of the pleckstrin homology (PH) domain. IKBKE activation of Akt was not affected by inhibition of PI3K, knockdown of PDK1 or mTORC2 complex. Further, this activation could be inhibited by Akt inhibitors MK-2206 and GSK690693 but not the compounds (perifosine and triciribine) targeting the PH domain of Akt. Expression of IKBKE largely correlates with activation of Akt in breast cancer. Moreover, inhibition of Akt suppresses IKBKE oncogenic transformation. These findings indicate that IKBKE is an Akt-Thr308 and -Ser473 kinase and directly activates Akt independent of PI3K, PDK1, and mTORC2 as well as PH domain. Our data also suggest that Akt inhibitors targeting the PH domain have no effect on the tumors in which hyperactive Akt resulted from elevated IKBKE.

Topics: 3-Phosphoinositide-Dependent Protein Kinases; Animals; Breast Neoplasms; Cell Line, Tumor; Cell Transformation, Neoplastic; Enzyme Activation; Female; Gene Deletion; HEK293 Cells; Heterocyclic Compounds, 3-Ring; Humans; I-kappa B Kinase; Mammary Neoplasms, Animal; Mice; Mice, Knockout; NIH 3T3 Cells; Oxadiazoles; Phosphatidylinositol 3-Kinases; Phosphorylation; Phosphorylcholine; Protein Serine-Threonine Kinases; Protein Structure, Tertiary; Proto-Oncogene Proteins c-akt; Ribonucleosides; Trans-Activators; Transcription Factors