Regulation Of Akt Signaling Research Articles

PI3K/AKT and Mdm2 activation are associated with inhibitory effect of cAMP increasing agents on DNA damage-induced cell death in human pre-B NALM-6 cells

DNA damage response (DDR) consists of both proapoptotic and prosurvival signaling branches. Superiority of each signaling branch determines the outcome of DNA damage: death or allowing the repair. The present authors have previously shown that an increased intracellular level of cAMP disrupts p53-mediated apoptosis in human pre-B NALM-6 cells and inhibition of NF-κB prevents prosurvival effect of cAMP during DNA damage. AKT/PKB (protein kinase B) is a general mediator of survival signaling. AKT signaling inhibits p53-mediated transcription and apoptosis. The results of present study showed that cAMP disrupted DNA damage/p53-mediated apoptosis through AKT and subsequent NF-κB activation. These results suggested that AKT may be found as part of a complex with scaffolding proteins, beta-arrestins and PDE4D. cAMP disarticulated the complex through binding to PDE4D compartment. It seems that release of AKT protein potentiated DDR activated pro-survival AKT in NALM-6 cells.Taken together, the present data indicated that regulation of AKT signaling may determine the fate of cells exposed to genotoxic stress.

Receptor-type protein tyrosine phosphatase κ directly dephosphorylates CD133 and regulates downstream AKT activation.

Although CD133 has been considered to be a molecular marker for cancer stem cells, its functional roles in tumorigenesis remain unclear. We here examined the molecular basis behind CD133-mediated signaling. Knockdown of CD133 resulted in the retardation of xenograft tumor growth of colon cancer-derived HT-29 and LoVo cells accompanied by hypophosphorylation of AKT, which diminished β-catenin/T-cell factor-mediated CD44 expression. As tyrosine residues of CD133 at positions 828 and 852 were phosphorylated in HT-29 and SW480 cells, we further addressed the significance of this phosphorylation in the tumorigenesis of SW480 cells expressing mutant CD133, with substitution of these tyrosine residues by glutamate (CD133-EE) or phenylalanine (CD133-FF). Forced expression of CD133-EE promoted much more aggressive xenograft tumor growth relative to wild-type CD133-expressing cells accompanied by hyperphosphorylation of AKT; however, CD133-FF expression had negligible effects on AKT phosphorylation and xenograft tumor formation. Intriguingly, the tyrosine phosphorylation status of CD133 was closely linked to the growth of SW480-derived spheroids. Using yeast two-hybrid screening, we finally identified receptor-type protein tyrosine phosphatase κ (PTPRK) as a binding partner of CD133. In vitro studies demonstrated that PTPRK associates with the carboxyl-terminal region of CD133 through its intracellular phosphatase domains and also catalyzes dephosphorylation of CD133 at tyrosine-828/tyrosine-852. Silencing of PTPRK elevated the tyrosine phosphorylation of CD133, whereas forced expression of PTPRK reduced its phosphorylation level markedly and abrogated CD133-mediated AKT phosphorylation. Endogenous CD133 expression was also closely associated with higher AKT phosphorylation in primary colon cancer cells, and ectopic expression of CD133 enhanced AKT phosphorylation. Furthermore, lower PTPRK expression significantly correlated with the poor prognosis of colon cancer patients with high expression of CD133. Thus, our present findings strongly indicate that the tyrosine phosphorylation of CD133, which is dephosphorylated by PTPRK, regulates AKT signaling and has a critical role in colon cancer progression.

Abstract 524: Deletion of Methionine Sulfoxide Reductase A in Mice Increases Vascular Smooth Muscle Cell Proliferation and Neointimal Hyperplasia

Introduction: Neointima formation is the leading cause of restenosis after balloon angioplasty and surgical endarterectomy. ROS production promotes neointimal hyperplasia and causes methionine oxidation. Recent data suggest that oxidation of methionines can alter specific protein activity and induce cell signaling. Methionine Sulfoxide Reductase A (MsrA) reverses methionine oxidation. In humans, two independent genome-wide association studies have found MsrA polymorphisms to correlate with increased ischemic cardiovascular disease. Hypothesis: MsrA protects against neointimal formation. Methods: Immunofluorescence for MsrA was performed in autopsy specimen of arteries with and without neointimal hyperplasia. 12-week old WT and MsrA-/- mice underwent ligation of the left common carotid artery and received two injections of BrdU prior to sacrifice. Fourteen days after ligation, the neointimal area was determined using Image J. Cell proliferation and apoptosis in the neointima were quantified by BrdU and TUNEL staining. Proliferation of vascular smooth muscle cells (VSMC) from MsrA-/- and WT mice was determined by cell counts and FACS analysis. Levels of cell cycle proteins, pAkt, pGSK3β were analyzed by immunoblot in MsrA-/- and WT VSMC, mRNA levels by qrtPCR. Results: MsrA was detected in all layers of the vascular wall and in neointima in humans. Neointimal area was significantly increased in MsrA-/- compared to WT mice 14 days post-ligation (n=5-9, p<0.05). Additionally, neointimas from MsrA-/- mice contained a higher percentage of proliferating cells (0.92±1.42% vs 8.89±8.89%, p=0.007). MsrA-/- VSMC displayed significantly increased proliferation compared to WT VSMC (p<0.05). Moreover, the progression to S phase was accelerated and protein levels of the cell cycle regulators Cyclin D and CDK4 were upregulated in MsrA-/- VSMC. However, cyclin D mRNA levels are not increased (p=0.24). This implies that MsrA post-translationally regulates cyclin D. GSK3β, which is inhibited by Akt, promotes cyclin D degradation. An increase in pAkt and pGSK3β was identified in MsrA-/- VSMC. Conclusion: These data indicate that MsrA regulates neointima formation after vascular injury and support a role for MsrA in the regulation of Akt signaling.

The WD40-repeat Proteins WDR-20 and WDR-48 Bind and Activate the Deubiquitinating Enzyme USP-46 to Promote the Abundance of the Glutamate Receptor GLR-1 in the Ventral Nerve Cord of Caenorhabditis elegans

Ubiquitin-mediated endocytosis and degradation of glutamate receptors controls their synaptic abundance and is implicated in modulating synaptic strength. The deubiquitinating enzymes (DUBs) that function in the nervous system are beginning to be defined, but the mechanisms that control DUB activity in vivo are understood poorly. We found previously that the DUB USP-46 deubiquitinates the Caenorhabditis elegans glutamate receptor GLR-1 and prevents its degradation in the lysosome. The WD40-repeat (WDR) proteins WDR20 and WDR48/UAF1 have been shown to bind to USP46 and stimulate its catalytic activity in other systems. Here we identify the C. elegans homologs of these WDR proteins and show that C. elegans WDR-20 and WDR-48 can bind and stimulate USP-46 catalytic activity in vitro. Overexpression of these activator proteins in vivo increases the abundance of GLR-1 in the ventral nerve cord, and this effect is further enhanced by coexpression of USP-46. Biochemical characterization indicates that this increase in GLR-1 abundance correlates with decreased levels of ubiquitin-GLR-1 conjugates, suggesting that WDR-20, WDR-48, and USP-46 function together to deubiquitinate and stabilize GLR-1 in neurons. Overexpression of WDR-20 and WDR-48 results in alterations in locomotion behavior consistent with increased glutamatergic signaling, and this effect is blocked in usp-46 loss-of-function mutants. Conversely, wdr-20 and wdr-48 loss-of-function mutants exhibit changes in locomotion behavior that are consistent with decreased glutamatergic signaling. We propose that WDR-20 and WDR-48 form a complex with USP-46 and stimulate the DUB to deubiquitinate and stabilize GLR-1 in vivo.

Macrophage Migration Inhibitory Factor Regulates AKT Signaling in Hypoxic Culture to Modulate Senescence of Human Mesenchymal Stem Cells

Hypoxic culture has been shown to delay premature senescence occurring during in vitro culture. Human mesenchymal stem cells (hMSCs) cultured under hypoxia have been reported to maintain their stemness properties and delay senescence compared to the cells cultured under normoxia. However, the molecular mechanism by which hypoxia regulates premature senescence has not been fully revealed. In this study, hMSCs were cultured under the conditions of 21% (normoxia) and 1% O2 (hypoxia) tension and analyzed for cell growth, expression of MSC surface markers, multilineage differentiation, and cellular senescence. Our results showed that more cells retained MSC surface markers in hypoxic culture than those in normoxic culture, and hypoxia was able to enhance multilineage differentiation of hMSCs. The hypoxic condition also delayed cellular senescence of hMSCs, increased activation of AKT signaling, and upregulated both intra- and extracellular levels of macrophage migration inhibitory factor (MIF) compared to the normoxic condition. Inhibition of AKT activity in hypoxic culture increased the number of cells with positive staining for senescence-associated β-galactosidase activity, upregulated expression levels of senescence-associated markers p16 and p21 mRNA transcripts, and decreased expression levels of potency-associated markers, including NANOG, OCT3/4, and SOX2. On the other hand, upregulated intra- and extracellular levels of MIF by stable MIF overexpression in normoxic culture increased the activation of AKT while decreasing mRNA expression of senescence-associated markers and increasing expression of potency-associated markers. Taken together, our findings suggest that hMSCs in hypoxic culture produce endogenous MIF to activate AKT signaling to delay the progression of cellular senescence.

MicroRNA-409-3p Functions as a Tumor Suppressor in Human Lung Adenocarcinoma by Targeting c-Met

Background/Aims: Dysregulation of microRNAs is correlated with tumor development. The aim of this study is to investigate the clinicopathologic and prognostic significance of microRNA (miR)-409-3p and its tumor suppressor roles in lung adenocarcinoma (LAD). Methods: Quantitative real-time PCR (qRT-PCR) was performed to detect miR-409-3p expression in LAD tissues and corresponding noncancerous tissues. Additionally, the correlations of miR-409-3p expression with clinicopathologic factors and prognosis of patients were statistically analyzed. Next, we investigated whether miR-409-3p could function as a tumor suppressor in LAD cells via regulation of Akt signaling by targeting receptor tyrosine kinase (c-Met). Results: MiR-409-3p was significantly downregulated in LAD tissues compared with corresponding noncancerous tissues. Low miR-409-3p expression was observed to be significantly correlated with poorer tumor differentiation, advanced pTNM stage and higher incidence of lymph node metastasis. Multivariate Cox regression analyses showed that miR-409-3p expression was an independent prognostic factor for LAD patients. Functional analyses indicated that miR-409-3p could inhibit growth, induce apoptosis, reduce migration and invasion in LAD cells via inactivation of Akt signaling by targeting c-Met. Conclusions: MiR-409-3p was an independent prognostic factor and functioned as a tumor suppressor in LAD via regulation of Akt signaling by targeting c-Met.

Akt modes of stem cell regulation: more than meets the eye?

Akt signaling regulates many cellular functions that are essential for the proper balance between self-renewal and differentiation of tissue-specific and embryonic stem cells (SCs). However, the roles of Akt and its downstream signaling in SC regulation are rather complex, as Akt activation can either promote SC self-renewal or depletion in a context-dependent manner. In this review we have evidenced three "modes" of Akt-dependent SC regulation, which can be exemplified by three different SC types. In particular, we will discuss: 1) the integration of Akt signaling within the "core" SC signaling circuitry in the maintenance of SC self-renewal and pluripotency (embryonic SCs); 2) quantitative changes in Akt signaling in SC metabolic activity and exit from quiescence (hematopoietic SCs); 3) qualitative changes of Akt signaling in SC regulation: signaling compartment-talization and isoform-specific functions of Akt proteins in SC self-renewal and differentiation (limbal-corneal keratinocyte SCs). These diverse modes of action are not to be intended as mutually exclusive. Rather, it is likely that Akt proteins participate with multiple parallel mechanisms to regulation of the same SC type. We propose that under specific circumstances dictated by distinct developmental stages, differentiation programs or tissue culture conditions, one mode of Akt action prevails over the others in determining SC fates.

DHHC17 Palmitoylates ClipR-59 and Modulates ClipR-59 Association with the Plasma Membrane

ClipR-59 interacts with Akt and regulates Akt compartmentalization and Glut4 membrane trafficking in a plasma membrane association-dependent manner. The association of ClipR-59 with plasma membrane is mediated by ClipR-59 palmitoylation at Cys534 and Cys535. To understand the regulation of ClipR-59 palmitoylation, we have examined all known mammalian DHHC palmitoyltransferases with respect to their ability to promote ClipR-59 palmitoylation. We found that, among 23 mammalian DHHC palmitoyltransferases, DHHC17 is the major ClipR-59 palmitoyltransferase, as evidenced by the fact that DHHC17 interacted with ClipR-59 and palmitoylated ClipR-59 at Cys534 and Cys535. By palmitoylating ClipR-59, DHHC17 directly regulates ClipR-59 plasma membrane association, as ectopic expression of DHHC17 increased whereas silencing of DHHC17 reduced the levels of ClipR-59 associated with plasma membrane. We have also examined the role of DHHC17 in Akt signaling and found that silencing of DHHC17 in 3T3-L1 adipocytes decreased the levels of Akt as well as ClipR-59 on the plasma membrane and impaired insulin-dependent Glut4 membrane translocation. We suggest that DHHC17 is a ClipR-59 palmitoyltransferase that modulates ClipR-59 plasma membrane binding, thereby regulating Akt signaling and Glut4 membrane translocation in adipocytes.

Abstract A10: Withaferin-A, a natural compound inhibits AKT-induced metastatic colorectal cancer

Abstract The survival rate of metastatic colorectal carcinoma (CRC) is less than 5%. Use of 5-fluorouracil (5-FU), radiation, and surgery are the primary treatments; however, most metastatic cancers eventually cause death. Developing approaches to prevent progression to metastasis could therefore be part of an important therapeutic strategy, especially for high-risk patients, including those patients already diagnosed with high grade polyps or localized colon cancer. In our preclinical and clinical data, we hypothesized that accumulation of AKT (protein kinase-B) is a critical step in the aggressive phenotype of disease. The metastatic cascade of CRC involves the crucial process of the epithelial–mesenchymal transition (EMT), which endows cancer cells with migratory and invasive capabilities via acquisition of a mesenchymal phenotype. These characteristics also contribute to cellular resistance to chemotherapeutic drugs. Withaferin-A (WA) is a potent herbal molecule from withania sominefera herbal plant, inhibited CRC growth by down regulating AKT signaling. Furthermore, over expression of AKT significantly increased cell proliferation, aggressiveness and angiogenesis of colon tumors in xenograft models. However, WA overcomes AKT mediated growth in both cell culture and animal models by transcriptionally down regulating Epithelial Mesenchymal Transition (EMT) related transcription factors and genes such as Snail, Slug and β-catenin. We also found AKT expression is steadily increased in CRC patients in a stage specific manner, suggesting accumulation of AKT could be a critical step for CRC metastasis. We found that WA binds to AKT with a predicted affinity of -10.6 kcal/mol and inhibited its activation. We have identified several novel WA–derived analogs which may be more potent than the parental compound with high AKT binding affinity. We have identified a potent analog which inhibited AKT kinase activity and induced growth arrest (~30 times potent) more significantly than WA. Currently, we are testing the invivo efficacy of the potent analog of WA, which could be a used as a novel agent for chemoprevention and/or chemotherapy of colon cancer. Citation Format: Suman Suman, Trinath P. Das, Chendil Damodaran. Withaferin-A, a natural compound inhibits AKT-induced metastatic colorectal cancer. [abstract]. In: Proceedings of the Twelfth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2013 Oct 27-30; National Harbor, MD. Philadelphia (PA): AACR; Can Prev Res 2013;6(11 Suppl): Abstract nr A10.

Regulation of Cell Proliferation and Migration by Keratin19-Induced Nuclear Import of Early Growth Response-1 in Breast Cancer Cells

Keratin19 (KRT19) is the smallest known type I intermediate filament and is used as a marker for reverse transcriptase PCR-mediated detection of disseminated tumors. In this study, we investigated the functional analysis of KRT19 in human breast cancer. Using a short hairpin RNA system, we silenced KRT19 in breast cancer cells. KRT19 silencing was verified by Western blot analysis and immunocytochemistry. We further examined the effect of KRT19 silencing on breast cancer cells by cell proliferation, migration, invasion, colony formation assay, cell-cycle analysis, immunocytochemistry, immunohistochemistry, and mouse xenograft assay. Silencing of KRT19 resulted in increased cell proliferation, migration, invasion, and survival. These effects were mediated by upregulation of Akt signaling as a result of reduced PTEN mRNA expression. Silencing of KRT19 decreased the nuclear import of early growth response-1 (Egr1), a transcriptional factor for PTEN transcription, through reduced association between Egr1 and importin-7. We also confirmed that silencing of KRT19 increased tumor formation in a xenograft model. KRT19 is a potential tumor suppressor that negatively regulates Akt signaling through modulation of Egr1 nuclear localization.

Oct4 Interaction with Hmgb2 Regulates Akt Signaling and Pluripotency

In pluripotent stem cells, bivalent domains mark the promoters of developmentally regulated loci. Histones in these chromatin regions contain coincident epigenetic modifications of gene activation and repression. How these marks are transmitted to maintain the pluripotent state in daughter progeny remains poorly understood. Our study demonstrates that Oct4 post-translational modifications (PTMs) form a positive feedback loop, which promotes Akt activation and interaction with Hmgb2 and the SET complex. This preserves H3K27me3 modifications in daughter progeny and maintains the pluripotent gene expression signature in murine embryonic stem cells. However, if Oct4 is not phosphorylated, a negative feedback loop is formed that inactivates Akt and initiates the DNA damage response. Oct4 sumoylation then is required for G1/S progression and transmission of the repressive H3K27me3 mark. Therefore, PTMs regulate the ability of Oct4 to direct the spatio-temporal formation of activating and repressing complexes to orchestrate chromatin plasticity and pluripotency. Our work highlights a previously unappreciated role for Oct4 PTM-dependent interactions in maintaining restrained Akt signaling and promoting a primitive epigenetic state.

Loss of T-cadherin (CDH-13) regulates AKT signaling and desensitizes cells to apoptosis in melanoma

An understanding of signaling pathways is a basic requirement for the treatment of melanoma. Currently, kinases are at the center of melanoma therapies. According to our research, additional alternative molecules are equally important for development of melanoma. In this regard, cancer progression is, among other factors, driven by an altered adhesion via cadherins. For instance, the de-regulated expression of the adhesion molecule T-cadherin is found in various cancer types, including melanoma, and influences migration and invasion. T-cadherin is thought to affect cellular function largely through its signaling and not its adhesion properties because the molecule is anchored into the cell membrane by a glycosylphosphatidylinositol (GPI) moiety. However, detailed knowledge about the consequences of the loss of T-cadherin in melanoma is currently lacking. For this reason, we were interested in assessing which signaling pathways are initiated by T-cadherin. The tumor growth of subcutaneously injected T-cadherin-positive melanoma cells was diminished compared with T-cadherin-negative cells in nude mice. The difference in tumor volume was not due to decreased proliferation but rather due to increased apoptosis. After the expression of T-cadherin was induced, we detected V-AKT murine thymoma viral oncogene homolog (AKT) and FoxO3a hypophosphorylation accompanied by the downregulation of the antiapoptotic molecules BCL-2, BCL-x and Clusterin. Furthermore, we detected a diminished transcriptional activity of CREB and AP-1. We demonstrated that T-cadherin functions as a pro-apoptotic tumor suppressor that antagonizes AKT/CREB/AP-1/FoxO3a signaling, whereas NFκB, TCF/LEF and mTOR are not part of the T-cadherin signaling pathway. Notably, we found that the restoration of T-cadherin in melanoma cells causes sensitization to apoptosis induced by CD95/Fas antibody CH-11.

Abstract 2583: Regulation of AKT-FoxO signaling by PKG2 inhibits colon cancer cell growth.

Abstract Signaling through cGMP has emerged as a potentially important suppressor of tumorigenesis in the colon, but the mechanism is poorly defined. Studies of guanylyl-cyclase (GCC) knockout mice indicate that cGMP signaling suppresses proliferation in the colon epithelium, and more recently that inhibition of AKT has an important role. Type-2 cGMP-dependent protein kinase (PKG2) is a central effector of cGMP in the colon epithelium and is a likely mediator of the homeostatic effects of cGMP signaling. The present study sought to determine whether PKG2 can regulate AKT signaling in colon cancer cells and in the colon mucosa. Activation of PKG2 in LS174T and HT29 colon cancer cells inhibited cell proliferation and increased G1 arrest. PKG2 activation also inhibited AKT activity in these cells as determined by immunoblotting for phospho-AKT and downstream phospho-S6. Suggestive of a mechanism, analysis of upstream components revealed that PKG2 increased the levels of phosphatase and tensin homolog (PTEN). Central to the growth-promoting role of AKT signaling is the inactivation of forkhead transcription factors (FoxO), which regulate growth-inhibitory and pro-apoptotic target gene expression. Consistent with the inhibition of AKT signaling, activation of PKG2 significantly increased luciferase reporter activity driven by FoxO-responsive elements in colon cancer cells. This activation was associated with increased levels of several FoxO target genes, including catalase, p27kip. The regulation of AKT/FoxO pathway by PKG2 in vivo was supported by increased phospho-AKT levels, and reduced FoxO target gene expression in the colon mucosa of Prkg2-/- mice compared to wild type siblings. Moreover, activation of cGMP signaling in the colon mucosa led to increased expression of FoxO targets, and suppression of both proliferation and redox stress. Taken together these data define a novel signaling pathway in the colon epithelium, where of PKG2 leads to activation of FoxO. The established tumor suppressor role of the FoxO proteins highlights the potential therapeutic role for cGMP signaling in the prevention of colon cancer. Citation Format: Rui Wang, In-Kiu Kwon, Muhan Hu, Darren D. Browning. Regulation of AKT-FoxO signaling by PKG2 inhibits colon cancer cell growth. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2583. doi:10.1158/1538-7445.AM2013-2583

Abstract 846: ROS-mediated activation of AKT induces apoptosis via pVHL in prostate cancer cells .

Abstract Reactive oxygen species (ROS) play a central role in oxidative stress, which leads to the onset of diseases, such as cancer. Furthermore, ROS contributes to the delicate balance between tumor cell survival and death. However, the mechanisms by which tumor cells decide to elicit survival or death signals during oxidative stress are not completely understood. We have previously reported that ROS enhanced tumorigenic functions in prostate cancer cells, such as cell migration and invasion, which depended on CXCR4 and AKT signaling. Here, we report a novel mechanism by which ROS facilitated cell death through activation of AKT. We initially observed that ROS increased expression of phosphorylated AKT (p-AKT) in 22Rv1 human prostate cancer cells. The tumor suppressor PTEN, a negative regulator of AKT signaling, was rendered catalytically inactive through oxidation by ROS, although the expression levels remained consistent. Despite these events, cells still underwent apoptosis. Further investigation into apoptosis revealed that expression of the tumor suppressor pVHL increased, with concomitant decreased expression of HIF1α. Further investigation into pVHL during apoptosis revealed that the tumor suppressor becomes phosphorylated at S111 prior to activity; S111 is within a target motif (RXXS) forphosphorylation by AKT kinase. We then determined that pVHL and p-AKT associated in vitro via co-immunoprecipitation assay. Moreover, knockdown of pVHL by siRNA rescued HIF1α protein expression and rescued cells from apoptosis, which was determined by Annexin-V and cleaved-PARP. Collectively, our study suggests that in the context of oxidative stress, activatedAKT facilitated apoptosis by inducing pVHL function. Moreover, our studies suggest a novel paradigm for AKT-that it may participate in tumor suppressor rather than oncogenesis. Citation Format: Mahandranauth A. Chetram, Kia J. Jones, Christopher Coke, Ayesha Don-Salu-Hewage, Danaya A. Bethea, Cimona V. Hinton. ROS-mediated activation of AKT induces apoptosis via pVHL in prostate cancer cells . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 846. doi:10.1158/1538-7445.AM2013-846

Abstract 5204: Downregulation of PHLLP expression contributes to hypoxia-induced resistance to chemotherapy in colon cancer cells.

Abstract Hypoxia is a feature of solid tumors. Most tumors are at least partially hypoxic. This hypoxic environment plays a critical role in promoting resistance to anticancer drugs. PHLPP, a novel family of Ser/Thr protein phosphatases, functions as a tumor suppressor by negatively regulating Akt signaling in colon cancer. Here, we show that the expression of both PHLPP isoforms is negatively regulated by hypoxia in colon cancer cells. Hypoxia-induced decrease of PHLPP expression is attenuated by silencing HIF-1α but not HIF-2α, indicating that PHLPP downregulation is HIF-1α-dependent. Whereas the mRNA levels of PHLPP are not significantly altered in hypoxia, the reduction of PHLPP expression is caused by decreased protein translation downstream of mTOR and increased protein degradation. Specifically, hypoxia-induced downregulation of PHLPP is partially rescued in TSC2 or 4E-BP1 knockdown cells as the result of elevated levels of mTOR activity and protein synthesis. In addition, we show that hypoxia promotes PHLPP degradation by increasing the mRNA expression of USP46, a PHLPP-specific deubiquitinase, and resulting in upregulation of PHLPP ubiquitination. Functionally, downregulation of PHLPP plays an important role in hypoxia-induced chemoresistance in colon cancer cells. Taken together, we have identified hypoxia as a novel mechanism by which PHLPP is downregulated in colon cancer, and the expression of PHLPP may serve as a biomarker for better understand the drug resistance in cancer treatment. Citation Format: Yang-an Wen, Tianyan Gao. Downregulation of PHLLP expression contributes to hypoxia-induced resistance to chemotherapy in colon cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5204. doi:10.1158/1538-7445.AM2013-5204

Abstract 3239: Discovery and biological characterization of ON108600, a small molecule inhibitor of protein kinase CK2.

Abstract Protein kinase CK2 (Casein kinase 2) is a highly conserved, constitutively active Ser/Thr protein kinase implicated in cellular transformation and tumorigenesis. CK2 regulates multiple oncogenic pathways involved in cell cycle progression, suppression of apoptosis, hypoxia, angiogenesis, inflammation and DNA repair. Unlike other signaling molecules such as PI3K, RAF, RAS, where genetic alterations lead to deregulated signaling pathways, in the case of CK2, only its high expression levels have been associated with a disease state and no mutations have been found to date. Here we describe the mechanism of action of ON108600 a potent small molecule inhibitor of both catalytic subunits of protein kinase CK2. ON108600 showed broad-spectrum anti-proliferative and cytotoxic activity in multiple cancer cell lines while having little or no effect on normal cells. CK2 regulates Akt signaling through phosphorylation and inactivation of PTEN and via direct and specific phosphorylation of Akt at S129. Treatment with ON108600 resulted in dramatic reductions of phosphorylation of PTEN and Akt S129 and downstream targets of Akt in multiple cancer cell lines. Further, phosphorylation of p21Cip1/Waf1 at Thr145 and its cytoplasmic localization has been shown to be a poor prognostic marker in breast cancer. ON108600 showed a dose and time dependant dephosphorylation of p21 at Thr145 and induced a potent mitotic cell cycle arrest in most cancer cell lines. CK2 has also been implicated in regulating Caspase signaling via phosphorylation of caspase cleavage sites and thus exerting its pro-survival effects. ON108600 treatment induced potent apoptosis by activating the Caspase 3/7 signaling cascade. To understand the structural basis of CK2 inhibition by ON108600 we performed x-ray crystallographic studies of ON108600-CK2. The co-crystal structure of ON108600-CK2 revealed that ON108600 binds in the active site pocket of CK2α wherein it mimics the binding of GTP in the CK2 active site. Structural studies also revealed that ON108600 induces a conformational change in the β4-β5 loop of the catalytic subunit which is known to interact with the β-regulatory subunit of CK2 and critical for substrate recognition and activation. CK2α has been reported to be a structural microtubule associated protein and the CK2 holoenzyme has been shown to regulate microtubule dynamics. Interestingly, ON108600 was found to inhibit CK2 holoenzyme mediated polymerization of β-tubulins in in-vitro assays. CK2 has emerged as novel druggable target and selective inhibitors of CK2 such as ON108600 may prove as a potential anti-cancer therapy. Our ongoing studies are focused towards identifying novel combinations of ON108600 with existing chemotherapeutic agents in multiple myeloma, prostate and breast cancer. Citation Format: Amol Padgaonkar, Olga Rechkoblit, Stephen Cosenza, Venkat R. Pallela, Venkata Subbaiah DRC, MV Ramana Reddy, Aneel Aggarwal, E Premkumar Reddy. Discovery and biological characterization of ON108600, a small molecule inhibitor of protein kinase CK2. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3239. doi:10.1158/1538-7445.AM2013-3239 Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.

Abstract 5436: Oct4 interaction with Hmgb2 regulates Akt signaling and the pluripotent gene expression signature.

Abstract Akt signaling impacts multiple cellular functions associated with the hallmark characteristics of pluripotency such as cell cycle progression, cell growth, and enhanced cellular survival. Constitutive Akt activation promotes the pluripotent state and has also been implicated in several forms of cancer. Recent studies have suggested that while Akt activation may be a positive factor, the active nuclear form of Akt is associated with poor prognosis for many cancers, including lung cancer. Here, we describe a novel transcriptional regulatory feedback loop between Oct4, Hmgb2, and Akt. We show that Akt signaling promotes Oct4 phosphorylation and stability. This maintains interaction with Akt, Hmbg2 and other members of the SET complex such as Nme1 and Set. Upon differentiation, when Akt is inactive, their decreased interaction is observed. A functional genomics approach was therefore employed to determine the relevance of Oct4 interaction with Hmgb2 in maintaining the pluripotent state. Despite its previously described role in Polycomb group recruitment and transcriptional repression in Drosophila, we find that Hmgb2 knockdown results in decreased Akt signaling and decreased expression of many Oct4 transcriptional targets including genes implicated in cell cycle regulation, DNA repair, chromatin structure, as well as the pluripotency regulators Oct4, Sox2, and Nanog. Taken together, our results suggest that Oct4, Hmgb2, and the SET complex participate in a PTM-dependent feed forward regulatory loop that promotes active Akt signaling and the pluripotent gene expression signature. Future work will be focused upon dissecting the role of this network in maintaining constitutive nuclear Akt activation and promoting the primitive epigenetic state found in cancer. These findings may provide insight into the role of Akt in lung cancer chemoresistance and suggest alternate targets for more efficacious treatment. Citation Format: Pearl A. Campbell, David J. Stewart, Michael A. Rudnicki. Oct4 interaction with Hmgb2 regulates Akt signaling and the pluripotent gene expression signature. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5436. doi:10.1158/1538-7445.AM2013-5436

Icotinib, a potent and specific EGFR tyrosine kinase inhibitor, inhibits growth of squamous cell carcinoma cell line A431 through negatively regulating AKT signaling

Icotinib is a potent and specific epidermal growth factor receptor tyrosine kinase inhibitor. In this study, we reported that icotinib had the antitumor activity on human squamous cell carcinoma cell line A431 in vitro. Meanwhile, adhesion to fibronectin and expression of integrin α3 and β1 were significantly reduced in a dose-dependent manner after the treatment of icotinib. Moreover, icotinib induced cell cycle arrested and affected expression of various cell cycle related proteins in squamous cancer cell line A431, whereas it did not cause apoptosis. Furthermore, icotinib remarkably down-regulated phosphorylation of protein kinase B (AKT) though blocking the interaction between 3-phosphoinositide-dependent protein kinase-1 (PDK1) and AKT in A431 cells. Taken together, it is shown that the small molecular compound, icotinib, has an anti-squamous cell carcinoma activity in vitro and its antitumor mechanism is associated with the blockage of the interaction between PDK1 and AKT. These results provide a novel strategy for anti-squamous cell carcinoma therapy.

Carboxyl terminus of Hsp70‐interacting protein (CHIP) is required to modulate cardiac hypertrophy and attenuate autophagy during exercise

The carboxyl terminus of HSP70‐interacting protein (CHIP) is a ubiquitin ligase/co‐chaperone critical for the maintenance of cardiac function. Mice lacking CHIP (CHIP −/−) suffer decreased survival, enhanced myocardial injury, and increased arrhythmias compared to wild type controls following challenge with cardiac ischemia reperfusion injury. Recent evidence implicates a role for CHIP in chaperone‐assisted selective autophagy, a process that is associated with exercise‐induced cardioprotection. To determine whether CHIP is involved in cardiac autophagy, we challenged CHIP −/− mice with voluntary exercise. CHIP −/− mice respond to exercise with an enhanced autophagic response that is associated with an exaggerated cardiac hypertrophy phenotype. No impairment of function was identified in the CHIP −/− mice by serial echocardiography over the five weeks of running, indicating that the cardiac hypertrophy was physiologic not pathologic in nature. It was further determined that CHIP plays a role in inhibiting Akt signaling and autophagy determined by autophagic flux in cardiomyocytes and in the intact heart. Taken together, cardiac CHIP appears to play a role in regulating autophagy during the development of cardiac hypertrophy, possibly by its role in regulating Akt signaling, induced by voluntary running in vivo.

The ESCRT machinery regulates Akt signaling mediated by the G protein‐coupled receptor CXCR4

The chemokine receptor CXCR4/stromal cell‐derived factor (SDF)‐1 alpha signaling axis is important in health and disease. Dysregulated CXCR4 signaling has been linked to cardiovascular disease, WHIM syndrome and cancer. However, despite the role of aberrant CXCR4 signaling in disease, the molecular mechanisms that govern CXCR4 signaling are poorly understood. The objective of this study is to elucidate the molecular mechanisms that govern CXCR4 signaling. Activated CXCR4 is rapidly ubiquitinated and sorted for lysosomal degradation via the endosomal sorting complex required for transport (ESCRT) machinery. The ESCRT machinery (ESCRT‐0, I, II and III) act in a coordinated manner to target ubiquitinated membrane proteins into intraluminal vesicles of multivesicular bodies for subsequent lysosomal degradation. While the ESCRT machinery mediates downregulation of CXCR4, our data indicate that it also has a novel positive role in CXCR4 signaling. Here, we provide evidence that the ESCRT machinery mediates CXCR4‐induced activation of Akt. Our data indicate that depletion of ESCRT‐0, I and II by siRNA inhibits CXCR4‐induced phosphorylation of Akt on serine 473, which corresponds to a decrease in Akt activity as phosphorylation of Tsc2, an Akt substrate, is also reduced. We show that Tsg101 (an ESCRT‐I subunit) interacts directly with Akt and under basal conditions Tsg101 and Akt are constitutively associated, as assessed by co‐immunoprecipitation; CXCR4 activation disrupts this interaction. Our data also reveal that CXCR4 internalization is required for Akt activation. Therefore CXCR4‐induced Akt activation is mediated by CXCR4 internalization onto endosomes and by the ESCRT machinery. This work was supported by grants from the AHA and the NIGMS.