Direct Inhibition Of Akt Research Articles

FGF1 protects FGFR1-overexpressing cancer cells against drugs targeting tubulin polymerization by activating AKT via two independent mechanisms.

Cancer drug resistance is a common, unpredictable phenomenon that develops in many types of tumors, resulting in the poor efficacy of current anticancer therapies. One of the most common, and yet the most complex causes of drug resistance is a mechanism related to dysregulation of tumor cell signaling. Abnormal signal transduction in a cancer cell is often stimulated by growth factors and their receptors, including fibroblast growth factors (FGFs) and FGF receptors (FGFRs). Here, we investigated the effect of FGF1 and FGFR1 activity on the action of drugs that disrupt tubulin polymerization (taltobulin, paclitaxel, vincristine) in FGFR1-positive cell lines, U2OS stably transfected with FGFR1 (U2OSR1) and DMS114 cells. We observed that U2OSR1 cells exhibited reduced sensitivity to the tubulin-targeting drugs, compared to U2OS cells expressing a negligible level of FGFRs. This effect was dependent on receptor activation, as inhibition of FGFR1 by a specific small-molecule inhibitor (PD173074) increased the cells’ sensitivity to these drugs. Expression of functional FGFR1 in U2OS cells resulted in increased AKT phosphorylation, with no change in total AKT level. U2OSR1 cells also exhibited an elevated MDR1 and blocking MDR1 activity with cyclosporin A increased the toxicity of paclitaxel and vincristine, but not taltobulin. Analysis of tubulin polymerization pattern using fluorescence microscopy revealed that FGF1 in U2OSR1 cells partially reverses the drug-altered phenotype in paclitaxel- and vincristine-treated cells, but not in taltobulin-treated cells. Furthermore, we showed that FGF1, through activation of FGFR1, reduces caspase 3/7 activity and PARP cleavage, preventing apoptosis induced by tubulin-targeting drugs. Next, using specific kinase inhibitors, we investigated which signaling pathways are responsible for the FGF1-mediated reduction of taltobulin cytotoxicity. We found that AKT kinase is a key factor in FGF1-induced cell protection against taltobulin in U2OSR1 and DMS114 cells. Interestingly, only direct inhibition of AKT or dual-inhibition of PI3K and mTOR abolished this effect for cells treated with taltobulin. This suggests that both canonical (PI3K-dependent) and alternative (PI3K-independent) AKT-activating pathways may regulate FGF1/FGFR1-driven cancer cell survival. Our findings may contribute to the development of more effective therapies and may facilitate the prevention of drug resistance in FGFR1-positive cancer cells.

Abstract 3547: B cell receptor signaling regulates cellular metabolism in Chronic Lymphocytic Leukemia

Abstract Peripheral blood B cells in chronic lymphocytic leukemia (CLL) are quiescent, yet have an active RNA transcription and protein translation processes, suggesting that these malignant lymphocytes may be metabolically active. However, CLL metabolism and its relationship to disease biology has not been well-explored. In our previous investigation, we reported that compared with proliferative B-cell lines, metabolic fluxes of oxygen and lactate were low in quiescent peripheral blood B lymphocytes from CLL patients (Vangapandu, H.V. et al, AACR 2014). In 45 patient samples tested, glycolysis (extracellular acidification rate, ECAR) was consistently low (1 to 15 mpH/min/5 x 105 lymphocytes), whereas, oxygen consumption rate (OCR) varied considerably (5 to 190 pMoles/min/5 x 105 lymphocytes). Among the prognostic factors, high OCR correlated strongly with ZAP 70 positivity, unmutated IGHV status, greater β2M levels and higher Rai stage. In contrast, glycolytic flux (ECAR) from same patient samples did not associate with prognostic factors. Further, OCR did not vary on the basis of frequently occurring cytogenetic abnormalities, 13q14, 17p, and 11q deletions or trisomy 12. Since, ZAP 70 and IGHV unmutated status are associated with augmented B-cell receptor (BCR) pathway signaling, we tested the impact on OCR after genetic ablation of B-cell receptor (CH2 region of IgM). A CRISPR-Cas9-mediated BCR knockout mitigated OCR in a malignant B cell line without impacting the rate of proliferation. A critical node in the BCR pathway is PI3 Kinase and PI3K isoforms, δ and γ are involved in B-cell malignancies. Consistent with BCR ablation results, knocking out PIK3CD (codes for catalytic subunit δ), dramatically reduced OCR and ECAR. Pharmacological inhibitors of the PI3K pathway, duvelisib (a PI3K δ/γ inhibitor in phase III clinical trials) or idelalisib (FDA approved PI3K δ inhibitor) also decreased OCR. Direct inhibition of AKT with MK-2206 showed similar results. Collectively, these data suggest that CLL cellular metabolism is associated with prognostic factors and linked to BCR signaling pathway. Since, the PI3K inhibitors used in our study are being tested clinically for patients with CLL, investigations on the impact on metabolomics during therapy and translation of results to combination strategies need to be explored. Note: This abstract was not presented at the meeting. Citation Format: Hima V. Vangapandu, Ondrej Havranek, William G. Wierda, Michael J. Keating, Richard Eric Davis, Christine M. Stellrecht, Varsha Gandhi. B cell receptor signaling regulates cellular metabolism in Chronic Lymphocytic Leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3547. doi:10.1158/1538-7445.AM2017-3547

Protein mediated regulation of the NHE1 isoform of the Na+/H+ exchanger in renal cells. A regulatory role of Hsp90 and AKT kinase

Na+/H+ exchanger isoform one (NHE1) is a pH regulatory protein that is present in renal tissues and serves to remove protons from within cells and protect against intracellular acidification. NHE1 has a large 315 amino acid cytosolic regulatory domain that regulates the catalytic membrane domain. We examined protein-mediated regulation of NHE1 through the cytosolic domain. Affinity chromatography with the C-terminus of NHE1 yielded a number of NHE1 binding proteins including 14-3-3 protein, heat shock proteins (Hsp90 and Hsp70) and Na+/K+ ATPase. We confirmed that 14-3-3 and heat shock proteins bind to or regulate NHE1 but could not confirm that Na+/K+ ATPase binds to the intact protein. The Hsp90 inhibitor 17-AAG decreased NHE1 activity and NHE1 phosphorylation in MDCK cells but did not decrease protein levels. Additionally, 17-AAG decreased phospho-AKT levels. Direct inhibition of AKT with MK2206 decreased NHE1 activity, though this effect was not additive with the effect of 17-AAG. The results demonstrate that in renal cells, NHE1 is associated with several regulatory proteins including Hsp90, and that Hsp90 affects its function possibly through altered phosphorylation of the protein via the AKT kinase.

Inhibition of PKCδ Protects Against Cisplatin-induced Renal Tubular Cell Apoptosis by Activation of Autophagy Through Direct Inhibition of AKT/ mTOR Signalling

Inhibition of PKCδ Protects Against Cisplatin-induced Renal Tubular Cell Apoptosis by Activation of Autophagy Through Direct Inhibition of AKT/ mTOR Signalling

Using Small Molecules To Identify Critical Signaling Pathways Of Mutant N-RAS In Acute Leukemia Cells

Activating point mutations in NRAS are detected in more than 10% of AML patients, making NRAS an important therapeutic target. Using small molecules to directly target NRAS or inhibit post-translational modification, such as farnesylation, have been extensively investigated. The potential of strategies focused on targeting downstream effectors of RAS, such as RAF or MEK, has been limited by the complexity of RAS signaling, including redundancy and feedback loops. Large-scale RNAi screens have been used to identify genes (TBK1, STK33 and GATA2, for example) that are synthetically lethal with RAS mutations and these are being explored as therapeutic targets. Recognizing the complexity of RAS signaling, we tested the notion that small molecule screens designed to simultaneously inhibit multiple signaling pathways might identify combinations of pathways that are critical for NRAS signaling in leukemic cells. Initially, we created an experimental Ba/F3 cell line model that was completely dependent on oncogenic N-RAS-G12D for growth and survival. Knockdown of NRAS suppressed growth >95%, but could be rescued by interleukin-3 (IL-3). A chemical screen using panels of multi-targeted small molecule kinase inhibitors against BaF3-NRAS-G12D cells revealed a lead compound, NRAS1 (N-(4-methyl-3-(1-methyl-7-(6-methylpyridin-3-ylamino)-2-oxo-1,2-dihydropyrimido[4,5-d]pyrimidin-3(4H)-yl)phenyl)-3-(trifluoromethyl)benzamide), with high selectivity and sensitivity toward leukemia cell lines with NRAS mutations in vitro. A number of studies were then performed to investigate the targets of this compound. Transcriptional profiling before and after treatment of two AML cell lines with NRAS mutation (OCI-AML3 and KO52 cells, respectively) showed profiles similar to that obtained by knocking down NRAS, supporting the hypothesis that this compound suppressed NRAS signaling. Biochemical studies demonstrated that NRAS1 did not inhibit several classical targets of RAS signaling, including, RAF, MEK and ERK. In contrast, NRAS1 was found to substantially reduce AKT and RPS6 phosphorylation. Over-expression of a constitutively active allele of AKT, myrAKT, in Ba/F3-NRAS G12D cells conferred strong resistance to NRAS1, confirming that suppression of phospho-AKT may be important for the function of NRAS1. However, direct inhibition of AKT only partially recapitulated the effects of NRAS1. Kinase selectivity profiling of NRAS1 (1μM) in OCI-AML3 cells (EC50: 0.3μM) identified 13 major binding partners with more than 85% efficacy. The targets consisted mainly of SRC family proteins (ie SRC, FGR, and LYN) and MAPK family proteins (ie GCK, KSH, and p38), but not MEK1/2, ERK1/2 or AKT1-3. A series of analogs of NRAS1 was synthesized and structure/function studies were carried out. One compound, (LKB-0304601, 1% EC50 of original compound) lost the ability to bind to the MAP4K family of proteins, especially GCK (MAPK4K2). A combination effect was observed between a known GCK inhibitor, NG25, and a known allosteric AKT inhibitor, MK-2206, against mutant NRAS-expressing cells. This finding supports the hypothesis that simultaneous inhibition of GCK and AKT has suppressive activity against leukemia cells transformed by NRAS. Furthermore, a putative gate-keeper mutation introduced into GCK (GCK G96S) resulted in partial resistance to growth suppression by NG25 or NRAS1. Growth suppression of NRAS-transformed leukemic cells was further induced by knock-down of GCK by shRNAs in cells with mutant NRAS, THP-1 cells and MOLT-3, and this effect could be rescued by over-expression of GCK. Finally, in a xenotransplant model using NRAS-mutant-expressing OCI-AML3 cells and MOLT-3 cells, NRAS1 significantly reduced tumor burden and prolonged survival compared to controls. Overall, by using a chemical screen designed to inhibit multiple signaling pathways simultaneously in oncogene-addicted cells, followed by signaling studies, cell biological studies and kinase selectivity profiling, we found that simultaneous inhibition of AKT and GCK, by either NRAS1 or selective inhibitors, exhibits activity against NRAS-transformed leukemia cells. Disclosures:Griffin:Novartis Pharmaceuticals: Research Funding.

Emerging treatment options for the treatment of neuroblastoma: potential role of perifosine

Achieving a cure for high-risk neuroblastoma, the most common extracranial solid tumor in children, remains a formidable task despite the recent addition of antibody-mediated anti-GD2 immunotherapy to established multimodality therapy. The PI3K/Akt pathway is a pivotal signaling pathway utilized by a plethora of receptor tyrosine kinases that contribute to the aggressive phenotype of high-risk neuroblastoma. Akt is aberrantly activated in high-risk neuroblastoma and is therefore an attractive therapeutic target. Perifosine is the best-characterized Akt inhibitor in preclinical studies and in clinical trials in adults, although safety in children is not yet confirmed. It is a synthetic third-generation alkylphospholipid with good oral bioavailability and modest side effects. Perifosine targets the lipid-binding PH domain of Akt and inhibits the translocation of Akt to the cell membrane, an essential step for Akt activation. It decreases Akt phosphorylation and increases caspase-dependent apoptosis in neuroblastoma cell lines, inhibits growth of neuroblastoma xenografts, and overcomes RTK/ligand-mediated chemoresistance. It is currently being studied in two Phase I clinical trials in children with recurrent or refractory solid tumors including neuroblastoma. In the single agent trial (ClinicalTrials.gov identifier NCT00776867), maximum tolerated dose has not yet been reached and pharmacokinetic data has been accrued. In the second study (ClinicalTrials.gov identifier NCT01049841), patients are treated with a combination of perifosine and the mTOR-inhibitor temsirolimus based on preclinical data showing synergy of the two agents, and the premise that direct Akt inhibition may overcome Akt activation secondary to mTOR inhibition. Based on results from adult trials, it is unlikely that perifosine alone will produce dramatic therapeutic effects against high-risk neuroblastoma. However, given the recent encouraging early-phase combination therapy results in adults with multiple myeloma and colorectal carcinoma, rational perifosine-containing combination regimens hold promise for neuroblastoma therapy. These will be explored after safety in children is established in Phase I studies.

Radiation-induced Akt activation modulates radioresistance in human glioblastoma cells.

BackgroundIonizing radiation (IR) therapy is a primary treatment for glioblastoma multiforme (GBM), a common and devastating brain tumor in humans. IR has been shown to induce PI3K-Akt activation in many cell types, and activation of the PI3K-Akt signaling pathway has been correlated with radioresistance.MethodsInitially, the effects of IR on Akt activation were assessed in multiple human GBM cell lines. Next, to evaluate a potential causative role of IR-induced Akt activation on radiosensitivity, Akt activation was inhibited during IR with several complementary genetic and pharmacological approaches, and radiosensitivity measured using clonogenic survival assays.ResultsThree of the eight cell lines tested demonstrated IR-induced Akt activation. Further studies revealed that IR-induced Akt activation was dependent upon the presence of a serum factor, and could be inhibited by the EGFR inhibitor AG1478. Inhibition of PI3K activation with LY294002, or with inducible wild-type PTEN, inhibition of EGFR, as well as direct inhibition of Akt with two Akt inhibitors during irradiation increased the radiosensitivity of U87MG cells.ConclusionThese results suggest that Akt may be a central player in a feedback loop whereby activation of Akt induced by IR increases radioresistance of GBM cells. Targeting the Akt signaling pathway may have important therapeutic implications when used in combination with IR in the treatment of a subset of brain tumor patients.

Breast tumor cells with PI3K mutation or HER2 amplification are selectively addicted to Akt signaling.

Abstract Abstract #3061 Background: Activation of the PI3K/Akt pathway is a common event in human cancers and is responsible for key aspects of the transformed phenotype. This pathway is activated in most breast cancers, but by different mechanisms including HER2 amplification, PI3K mutation and PTEN inactivation. Inhibition of this pathway is thus thought to be clinically useful, but the functional output of PI3K/Akt signaling and the corresponding clinical effects of its inhibition may be due to the mechanisms by which it is activated. The objective of this study was to determine the role of Akt activation in breast cancer as a function of mechanism of activation and whether inhibition of Akt signaling is a feasible approach to therapy.
 Methodology/Principal Findings: Using a panel of human breast cancer cell lines that harbor HER2 amplification, PI3K or PTEN mutations, or wild-type of PI3K and PTEN, and a selective, PH-domain dependent, allosteric inhibitor of Akt1 and Akt2 (AKTi-1/2), and a variety of biochemical, molecular, and cellular techniques as well as in vivo xenograft models, we show that AKTi-1/2 resulted in the selective inhibition of breast tumor cell lines with either mutant PI3K or amplified HER2, but not those in which PI3K/Akt signaling is not mutationally activated. Cellular sensitivity was due to induction of G1 arrest and of apoptosis and associated with inhibition of Akt signaling, loss of D-cyclin expression, and dephosphorylation of Rb. Most importantly, AKTi-1/2 effectively inhibited Akt kinase and its downstream effectors in vivo and caused complete suppression of the growth of breast cancer xenografts with PI3K mutation or HER2 amplification, including models of the latter selected for resistance to Herceptin. Furthermore, chronic administration of the drug was well-tolerated, causing only transient hyperglycemia without gross toxicity to the host despite the pleiotropic normal functions of Akt.
 Conclusions/Significance: Our data demonstrate the exquisite dependence of PI3K-mutated or HER2-amplified breast cancer cells on Akt signaling, and that effective inhibition of Akt in tumors is feasible and effective in vivo. These findings suggest that direct inhibition of Akt may represent a therapeutic strategy for breast cancers that are addicted to the pathway and in patients with clinical resistance to Herceptin. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3061.

Breast Tumor Cells with PI3K Mutation or HER2 Amplification Are Selectively Addicted to Akt Signaling

BackgroundDysregulated PI3K/Akt signaling occurs commonly in breast cancers and is due to HER2 amplification, PI3K mutation or PTEN inactivation. The objective of this study was to determine the role of Akt activation in breast cancer as a function of mechanism of activation and whether inhibition of Akt signaling is a feasible approach to therapy.Methodology/Principal FindingsA selective allosteric inhibitor of Akt kinase was used to interrogate a panel of breast cancer cell lines characterized for genetic lesions that activate PI3K/Akt signaling: HER2 amplification or PI3K or PTEN mutations in order to determine the biochemical and biologic consequences of inhibition of this pathway. A variety of molecular techniques and tissue culture and in vivo xenograft models revealed that tumors with mutational activation of Akt signaling were selectively dependent on the pathway. In sensitive cells, pathway inhibition resulted in D-cyclin loss, G1 arrest and induction of apoptosis, whereas cells without pathway activation were unaffected. Most importantly, the drug effectively inhibited Akt kinase and its downstream effectors in vivo and caused complete suppression of the growth of breast cancer xenografts with PI3K mutation or HER2 amplification, including models of the latter selected for resistance to Herceptin. Furthermore, chronic administration of the drug was well-tolerated, causing only transient hyperglycemia without gross toxicity to the host despite the pleiotropic normal functions of Akt.Conclusions/SignificanceThese data demonstrate that breast cancers with PI3K mutation or HER2 amplification are selectively dependent on Akt signaling, and that effective inhibition of Akt in tumors is feasible and effective in vivo. These findings suggest that direct inhibition of Akt may represent a therapeutic strategy for breast and other cancers that are addicted to the pathway including tumors with resistant to Herceptin.

Molecular imaging of Akt kinase activity.

The serine/threonine kinase Akt mediates mitogenic and anti-apoptotic responses that result from activation of multiple signaling cascades. It is considered a key determinant of tumor aggressiveness and is a major target for anticancer drug development. Here, we describe a new reporter molecule whose bioluminescence activity within live cells and in mice can be used to measure Akt activity. Akt activity in cultured cells and tumor xenografts was monitored quantitatively and dynamically in response to activation or inhibition of receptor tyrosine kinase, inhibition of phosphoinositide 3-kinase, or direct inhibition of Akt. The results provide unique insights into the pharmacokinetics and pharmacodynamics of agents that modulate Akt activity, revealing the usefulness of this reporter for rapid dose and schedule optimization in the drug development process.

Epidermal Growth Factor Receptor Expression and Activation in Neuroendocrine Tumours

Epidermal growth factor receptor (EGFR) is expressed in many cancers and is associated with poor prognosis. EGFR activation pathways have been well characterised using tumour cell lines and are known to involve EGFR activation through autophosphorylation. Phosphorylation of downstream signalling molecules, such as ERK1/2 (extra-cellular regulated kinase 1 and 2) and PKB/Akt (protein kinase B), leads to enhanced tumour cell survival and proliferation. Although EGFR expression has been determined in neuroendocrine tumour tissue, its activation and subsequent effects on the downstream signalling molecules, ERK1/2 and Akt, have not been studied. We therefore planned to determine the role of EGFR in neuroendocrine tumours (NETs) by determining its pattern of expression and activation, and the subsequent activation of downstream signalling molecules ERK1/2 and Akt. Paraffin-embedded tumour tissue was available from 98 patients with NETs (39 foregut, 42 midgut, four hindgut, five paragangliomas, and four of unknown origin). Immunohistochemical evaluation was performed for the expression of EGFR, p-EGFR, p-Akt, and p-ERK1/2. Ninety-six percent of tumour samples were positive for EGFR expression; 63% were positive for activated EGFR; 76% were positive for activated Akt; and 96% were positive for activated ERK1/2. Importantly, the histological score for the activation of Akt and ERK1/2 correlated with the histological score for activated EGFR. These data provide a rationale for considering EGFR inhibitors in the treatment of NETs. Additionally, direct inhibition of Akt and ERK1/2 may provide further therapeutic options in the treatment of NETs in the future.

Potent and selective inhibitors of Akt kinases slow the progress of tumors in vivo

The Akt kinases are central nodes in signal transduction pathways that are important for cellular transformation and tumor progression. We report the development of a series of potent and selective indazole-pyridine based Akt inhibitors. These compounds, exemplified by A-443654 (K(i) = 160 pmol/L versus Akt1), inhibit Akt-dependent signal transduction in cells and in vivo in a dose-responsive manner. In vivo, the Akt inhibitors slow the progression of tumors when used as monotherapy or in combination with paclitaxel or rapamycin. Tumor growth inhibition was observed during the dosing interval, and the tumors regrew when compound administration was ceased. The therapeutic window for these compounds is narrow. Efficacy is achieved at doses approximately 2-fold lower than the maximally tolerated doses. Consistent with data from knockout animals, the Akt inhibitors induce an increase in insulin secretion. They also induce a reactive increase in Akt phosphorylation. Other toxicities observed, including malaise and weight loss, are consistent with abnormalities in glucose metabolism. These data show that direct Akt inhibition may be useful in cancer therapy, but significant metabolic toxicities are likely dose limiting.

Urokinase-Induced Smooth Muscle Cell Migration Requires PI3-K and Akt Activation 1,2

To examine the role of the phospho-inositol-3'-kinase (PI3-K)-akt signaling axis during smooth muscle cell (SMC) migration in response to the aminoterminal fragment of urokinase (ATF). Urokinase (uPA) is involved in vessel remodeling and mediates smooth muscle cell migration. Migration in response to urokinase is dependent on ATF. The role of PI3-K/akt signaling during migration in response to the uPA fragments is not understood. Murine arterial SMCs were cultured in vitro. Linear wound and Boyden microchemotaxis assays of migration were performed in the presence of ATF with and without the PI3-K inhibitors (Wortmannin, Wn [10 nm] and LY294002, LY [10 microm]) and an akt inhibitor (aktI, [10 microm]). Western blotting was performed for akt, ERK1/2, and GSK3beta phosphorylation after cells were stimulated with ATF in the presence and absence of the inhibitors. Statistics were analyzed by one-way ANOVA. Both PI3-K and akt inhibitors blocked the migratory response to ATF in both assays. ATF induced time-dependent increases in akt phosphorylation at both S472 and T308 sites and ERK1/2 phosphorylation. Activation of akt and ERK1/2 was inhibited by Wn and LY. Manumycin A, a ras inhibitor, did not inhibit activation of akt but did inhibit ERK1/2 activation. Activation of akt and the dephosphorylation of its downstream kinase GSK3beta were inhibited by the akt inhibitor. Direct inhibition of akt did not influence ERK1/2 activation and inhibition of ERK1/2 did not influence akt activation. ATF mediated migration is PI3-K dependent and activates two separate pathways: ERK1/2 and akt. ATF induces akt phosphorylation through a PI3K-mediated but ras-independent mechanism while both ras and PI3K are required for ERK1/2 activation. Defining key signaling pathways is vital to regulate vessel remodeling.

Urokinase-induced smooth muscle cell migration requires both PI3K/akt and PI3K/ERK1/2 activation

Background. Urokinase is involved in vessel remodeling and mediates smooth muscle cell migration. Migration in response to urokinase is dependent on the amino terminal fragment (ATF). The role of PI3-K/akt signaling in ATF-mediated cell migration is not understood. Methods. Rat arterial smooth muscle cells were cultured in vitro. Linear wound and Boyden microchemotaxis assays of migration were performed in the presence of ATF with and without the Gαi inhibitor (Pertussis toxin, PTx), the PI3-K inhibitors (Wortmannin, Wn [10 nM] and LY294002, LY [10 μM]), and akt inhibitor (aktI [10 μM]). Western blotting was performed for akt, ERK1/2, and GSK3β phosphorylation after stimulation with ATF in the presence and absence of the inhibitors. Results. PI3-K and akt inhibitors blocked the migratory response to ATF in both assays. ATF induced time-dependent increases in akt and ERK1/2 phosphorylation, which was PTx sensitive. Activation of akt and ERK1/2 was inhibited by PI3-K inhibition with WN and LY. Manumycin A, a ras inhibitor, did not inhibit activation of akt but did inhibit ERK1/2 activation. Activation of akt and its effects on its downstream kinase GSK3β were inhibited by the akt inhibitor only. Direct inhibition of akt did not influence ERK1/2 activation and inhibition of ERK1/2 with PD98098 did not influence akt activation. Conclusion. ATF-mediated migration is Gαi dependent and PI3K dependent and involves two separate pathways: ERK1/2 and akt. ATF induces akt phosphorylation through a PI3K-mediated but ras-independent mechanism, while both ras and PI3K are required for ERK1/2 activation. Defining key signaling pathways is vital in order to regulate vessel remodeling.