piperidines and triciribine

DNA damage is a double-edged sword for cancer cells. On the one hand, DNA damage-induced genomic instability contributes to cancer development; on the other hand, accumulating damage compromises proliferation and survival of cancer cells. Understanding the key regulators of DNA damage repair machinery would benefit the development of cancer therapies that induce DNA damage and apoptosis. In this study, we found that isoprenylcysteine carboxylmethyltransferase (ICMT), a posttranslational modification enzyme, plays an important role in DNA damage repair. We found that ICMT suppression consistently reduces the activity of MAPK signaling, which compromises the expression of key proteins in the DNA damage repair machinery. The ensuing accumulation of DNA damage leads to cell cycle arrest and apoptosis in multiple breast cancer cells. Interestingly, these observations are more pronounced in cells grown under anchorage-independent conditions or grown in vivo. Consistent with the negative impact on DNA repair, ICMT inhibition transforms the cancer cells into a "BRCA-like" state, hence sensitizing cancer cells to the treatment of PARP inhibitor and other DNA damage-inducing agents.

Topics: Animals; Apoptosis; Benzamides; Breast Neoplasms; Cell Cycle Checkpoints; Cell Line, Tumor; Cell Proliferation; DNA Damage; DNA Repair; Female; Genetic Vectors; HEK293 Cells; Humans; Indazoles; MAP Kinase Signaling System; Mice; Mice, SCID; Piperidines; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Protein Methyltransferases; Ribonucleosides; RNA, Small Interfering; Tumor Burden; Xenograft Model Antitumor Assays

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