Genetic inactivation of AKT1 , AKT2 , and PDPK1 in human colorectal cancer cells clarifies their roles in tumor growth regulation

Abstract

Phosphotidylinositol-3-kinase (PI3K) signaling is altered in the majority of human cancers. To gain insight into the roles of members of this pathway in growth regulation, we inactivated AKT1 , AKT2 , or PDPK1 genes by targeted homologous recombination in human colon cancer cell lines. Knockout of either AKT1 or AKT2 had minimum effects on cell growth or downstream signaling. In contrast, knockout of both AKT1 and AKT2 resulted in markedly reduced proliferation in vitro when growth factors were limiting and severely affected experimental metastasis in mice. Unexpectedly, AKT1 and AKT2 appeared to regulate growth through FOXO proteins, but not through either GSK3β or mTOR. In contrast, inactivation of PDPK1 affected GSK3β and mTOR activation. These findings show that the PI3K signaling pathway is wired differently in human cancer cells than in other cell types or organisms, which has important implications for the design and testing of drugs that target this pathway.

A nanoparticle formulation that selectively transfects metastatic tumors in mice

“…One of the most effective formulations, in vivo-jetPEI (Polyplus Transfection), has been evaluated for gene delivery in a number of cancer models in vivo (20)(21)(22)(23)(24)(25)(26), although rarely via systemic injection (27)(28)(29), as well as in several clinical trials for heart disease (30), HIV (31), and cancer (32). Because s.c. tumor models might not faithfully reflect the architecture of internal tumors, we elected to use a model established by intrasplenic injection of the HCT116 line of human colorectal cancer cells in NOD-SCID-IL-2Rγ-deficient mice (NOG mice) (33). In addition to primary tumors that formed in the spleen in this model, multiple metastases developed in the lungs and liver within 4 wk of tumor cell injection.…”

MRE11 promotes AKT phosphorylation in direct response to DNA double-strand breaks

“…However, we cannot exclude the possibility that masking of the T308 epitope by other DSB-associated proteins prevents detection of pAKT-T308 at DSB. While AKT S473 phosphorylation is independent of PDK1, 43,44 T308 phosphorylation appears to occur more efficiently when S473 is phosphorylated. 45 Thus, it is possible that DSB-induced S473 phosphorylation promotes subsequent T308 phosphorylation throughout the nucleus, and our laboratory is currently evaluating this hypothesis.…”

Akt2 interacts with Snail1 in the E-cadherin promoter

“…In most cells, Akt1 seems to have a role in the maintenance of the epithelial phenotype (Irie et al, 2005;Iliopoulos et al, 2009). However, in some cells its downregulation decreases the formation of metastasis (Ericson et al, 2010). On the other hand, Akt2 is required for EMT as it is activated during this transition and its downregulation prevents the acquisition of the mesenchymal phenotype or the formation of metastasis (Irie et al, 2005;Cheng et al, 2007;Rychahou et al, 2008;Dillon et al, 2009;Iliopoulos et al, 2009;Ericson et al, 2010).…”

“…However, in some cells its downregulation decreases the formation of metastasis (Ericson et al, 2010). On the other hand, Akt2 is required for EMT as it is activated during this transition and its downregulation prevents the acquisition of the mesenchymal phenotype or the formation of metastasis (Irie et al, 2005;Cheng et al, 2007;Rychahou et al, 2008;Dillon et al, 2009;Iliopoulos et al, 2009;Ericson et al, 2010). However, these effects are cell-dependent as in some cells Akt2 depletion by itself does not promote any effect but prevents the EMT induced by Akt1 depletion.…”