IKBKE inhibits TSC1 to activate the mTOR/S6K pathway for oncogenic transformation

IKBKE (IKKε) has emerged as a key modulator of multiple substrates, controlling oncogenic pathways in various malignancies.mTOR signaling, required for cellular growth, proliferation, and vascular angiogenesis in cancer, is potentially one of the pathwaysregulated by IKKε. Upon activation by various stimuli, PI3K/AKT or similar effectors can relieve the inhibitory effect of the TSC1/TSC2complex through their phosphorylation to favor mTOR/S6K activation in the downstream. Therefore, any activity that interferes withPI3K/AKT or their downstream targets, such as TSC1/2 or GSK3α/β, may activate the mTOR/S6K pathway for oncogenic transformationin normal cells. Previous studies have shown that PI3K/AKT can be directly phosphoregulated by IKKε. Here, we propose a newregulatory function for IKKε in the mTOR/S6K pathway through its direct interaction with TSC1, leading to TSC1 phosphorylation,which is vital to suppress its inhibitory role in mTOR activation. Experimentally, upon IKKε deficiency in colorectal cancer cells, weobserved that S6K activity was diminished while TSC1 levels were found to be stabilized. We hypothesized that these observations mayresult from direct interaction between IKKε and TSC1. Indeed, the interaction of these two proteins involves the phosphoregulation ofTSC1 in various cell lines. Therefore, we propose a mechanism where IKKε, through regulating TSC1 stability in cancer cells, may createan alternative regulatory loop for the activation of mTOR signaling. These results can potentially be important for the development ofnovel therapeutic strategies targeting mTOR signaling.

PDF

___

AlQurashi N, Hashimi SM, Wei MQ (2013). Chemical inhibitors and microRNAs (miRNA) targeting the mammalian target of rapamycin (mTOR) pathway: potential for novel anticancer therapeutics. Int J Mol Sci 14: 3874-3900.
Barbie TU, Alexe G, Aref AR, Li S, Zhu Z, Zhang X, Imamura Y, Thai TC, Huang Y, Boyden M et al. (2014). Targeting an IKBKE cytokine network impairs triple-negative breast cancer growth. J Clin Invest 124: 5411-5423.
Bianchini A, Loiarro M, Bielli P, Busà R, Paronetto MP, Loreni F, Geremia R, Sette C (2008). Phosphorylation of eIF4E by MNKs supports protein synthesis, cell cycle progression and proliferation in prostate cancer cells. Carcinogenesis 29: 2279- 2288.
Bodur C, Kazyken D, Huang K, Ekim Ustunel B, Siroky KA, Tooley AS, Gonzalez IR, Foley DH, Acosta-Jaquez HA, Barnes TM et al. (2018). The IKK-related kinase TBK1 activates mTORC1 directly in response to growth factors and innate immune agonists. EMBO J 37: 19-38.
Challa S, Guo JP, Ding X, Xu CX, Li Y, Kim D, Smith MA, Cress DW, Coppola D, Haura EB, et al. (2016). IKBKE is a substrate of EGFR and a therapeutic target in non-small cell lung cancer with activating mutations of EGFR. Cancer Res 76: 4418-4429.
Chau TL, Gioia R, Gatot JS, Patrascu F, Carpentier I, Chapelle JP, O’Neill L, Beyaert R, Piette J, Chariot A (2008). Are the IKKs and IKK-related kinases TBK1 and IKK-epsilon similarly activated? Trends Biochem Sci 33: 171-180.
Cooper JM, Ou YH, McMillan EA, Vaden RM, Zaman A, Bodemann BO, Makkar G, Posner BA, White MA (2017). TBK1 provides context-selective support of the activated Akt/mTOR pathway in lung cancer. Cancer Res 77: 5077-5094.
Dowling RJ, Topisirovic I, Fonseca BD, Sonenberg N (2010). Dissecting the role of mTOR: lessons from mTOR inhibitors. Biochim Biophys Acta 1804: 433-439.
Feng Z, Zhang H, Levine AJ, Jin S (2005). The coordinate regulation of the p53 and mTOR pathways in cells. P Natl Acad Sci USA 102: 8204-8209.
Göktuna SI, Canli O, Bollrath J, Fingerle AA, Horst D, Diamanti MA, Pallangyo C, Bennecke M, Nebelsiek T, Mankan AK et al. (2014). IKKα promotes intestinal tumorigenesis by limiting recruitment of M1-like polarized myeloid cells. Cell Rep 7: 1914-1925.
Göktuna SI, Shostak K, Chau TL, Heukamp LC, Hennuy B, Duong HQ, Ladang A, Close P, Klevernic I, Olivier F et al. (2016). The prosurvival IKK-related kinase IKKε integrates LPS and IL17A signaling cascades to promote Wnt-dependent tumor development in the intestine. Cancer Res 76: 2587-2599.
Guo JP, Coppola D, Cheng JQ (2011). IKBKE protein activates Akt independent of phosphatidylinositol 3-kinase/PDK1/ mTORC2 and the Pleckstrin homology domain to sustain malignant transformation. J Biol Chem 286: 37389-37398.
Hsieh AC, Costa M, Zollo O, Davis C, Feldman ME, Testa JR, Meyuhas O, Shokat KM, Ruggero D (2010). Genetic dissection of the oncogenic mTOR pathway reveals druggable addiction to translational control via 4EBP-eIF4E. Cancer Cell 17: 249- 261.
Hsu S, Kim M, Hernandez L, Grajales V, Noonan A, Anver M, Davidson B, Annunziata CM (2012). IKKε coordinates invasion and metastasis of ovarian cancer. Cancer Res 72: 5494-5504.
Huang J, Manning BD (2008). The TSC1–TSC2 complex: a molecular switchboard controlling cell growth. Biochem J 412: 179-190.
Huang J, Manning BD (2009). A complex interplay between Akt, TSC2, and the two mTOR complexes. Biochem Soc Trans 37: 217-222.
Huang K, Fingar DC (2014). Growing knowledge of the mTOR signaling network. Semin Cell Dev Biol 36: 79-90.
Inoki K, Corradetti MN, Guan KL (2005). Dysregulation of the TSCmTOR pathway in human disease. Nat Genet 37: 19-24.
Inoki K, Li Y, Xu T, Guan KL (2003a). Rheb GTPase is a direct target of TSC2 GAP activity and regulates mTOR signaling. Genes Dev 17: 1829-1834.
Inoki K, Li Y, Zhu T, Wu J, Guan KL (2002). TSC2 is phosphorylated and inhibited by Akt and suppresses mTOR signalling. Nat Cell Biol 4: 648-657.
Inoki K, Ouyang H, Zhu T, Lindvall C, Wang Y, Zhang X, Yang Q, Bennett C, Harada Y, Stankunas K et al. (2006). TSC2 integrates Wnt and energy signals via a coordinated phosphorylation by AMPK and GSK3 to regulate cell growth. Cell 126: 955-968.
Inoki K, Zhu T, Guan KL (2003b). TSC2 mediates cellular energy response to control cell growth and survival. Cell 115: 577-590.
Jastrzebski K, Hannan KM, Tchoubrieva EB, Hannan RD, Pearson RB (2007). Coordinate regulation of ribosome biogenesis and function by the ribosomal protein S6 kinase, a key mediator of mTOR function. Growth Factors 25: 209-226.
Kim JY, Beg AA, Haura EB (2013). Non-canonical IKKs, IKKε and TBK1, as novel therapeutic targets in the treatment of nonsmall cell lung cancer. Expert Opin Ther Tar 17: 1109-1112.
Laplante M, Sabatini DM (2012). mTOR signaling in growth control and disease. Cell 149: 274-293.
Lee DF, Kuo HP, Chen CT, Hsu JM, Chou CK, Wei Y, Sun HL, Li LY, Ping B, Huang WC et al. (2007). IKKβ suppression of TSC1 links inflammation and tumor angiogenesis via the mTOR pathway. Cell 130: 440-455.
Lu J, Yang Y, Guo G, Liu Y, Zhang Z, Dong S, Nan Y, Zhao Z, Zhong Y, Huang Q (2017). IKBKE regulates cell proliferation and epithelial–mesenchymal transition of human malignant glioma via the Hippo pathway. Oncotarget 8: 49502-49514.
Ma L, Chen Z, Erdjument-Bromage H, Tempst P, Pandolfi PP (2005). Phosphorylation and functional inactivation of TSC2 by Erk implications for tuberous sclerosis and cancer pathogenesis. Cell 121: 179-193.
Manning BD, Tee AR, Logsdon MN, Blenis J, Cantley LC (2002). Identification of the tuberous sclerosis complex-2 tumor suppressor gene product tuberin as a target of the phosphoinositide 3-kinase/akt pathway. Mol Cell 10: 151-162.
Niederberger E, Moser CV, Kynast KL, Geisslinger G (2013). The non-canonical IκB kinases IKKε and TBK1 as potential targets for the development of novel therapeutic drugs. Curr Mol Med 13: 1089-1097.
Péant B, Gilbert S, Le Page C, Poisson A, L’Ecuyer E, Boudhraa Z, Bienz MN, Delvoye N, Saad F, Mes-Masson AM (2017). IκBKinase-epsilon (IKKε) over-expression promotes the growth of prostate cancer through the C/EBP-β dependent activation of IL-6 gene expression. Oncotarget 8: 14487-14501.
Potter CJ, Pedraza LG, Xu T (2002). Akt regulates growth by directly phosphorylating Tsc2. Nat Cell Biol 4: 658-665.
Rajurkar M, Dang K, Fernandez-Barrena MG, Liu X, FernandezZapico ME, Lewis BC, Mao J (2017). IKBKE is required during KRAS-induced pancreatic tumorigenesis. Cancer Res 77: 320- 329.
Roux PP, Ballif BA, Anjum R, Gygi SP, Blenis J (2004). Tumorpromoting phorbol esters and activated Ras inactivate the tuberous sclerosis tumor suppressor complex via p90 ribosomal S6 kinase. P Natl Acad Sci USA 101: 13489-13494.
Saitoh M, Pullen N, Brennan P, Cantrell D, Dennis PB, Thomas G (2002). Regulation of an activated S6 kinase 1 variant reveals a novel mammalian target of rapamycin phosphorylation site. J Biol Chem 277: 20104-20112.
Saxton RA, Sabatini DM (2017). mTOR signaling in growth, metabolism, and disease. Cell 168: 960-976.
She QB, Halilovic E, Ye Q, Zhen W, Shirasawa S, Sasazuki T, Solit DB, Rosen N (2010). 4E-BP1 is a key effector of the oncogenic activation of the AKT and ERK signaling pathways that integrates their function in tumors. Cancer Cell 18: 39-51.
Shen RR, Hahn WC (2011). Emerging roles for the non-canonical IKKs in cancer. Oncogene 30: 631-641.
Sommese RF, Sivaramakrishnan S (2016). Substrate affinity differentially influences protein kinase C regulation and inhibitor potency. J Biol Chem 291: 21963-21970.
Sun Z, Wang Z, Liu X, Wang D (2015). New development of inhibitors targeting the PI3K/AKT/mTOR pathway in personalized treatment of non-small-cell lung cancer. Colloq Inse 26: 1-14.
Xie X, Zhang D, Zhao B, Lu MK, You M, Condorelli G, Wang CY, Guan KL (2011). IκB kinase ε and TANK-binding kinase 1 activate AKT by direct phosphorylation. P Natl Acad Sci USA 108: 6474-6479.
Zhao P, Wong KI, Sun X, Reilly SM, Uhm M, Liao Z, Skorobogatko Y, Saltiel AR (2018). TBK1 at the crossroads of inflammation and energy homeostasis in adipose tissue. Cell 172: 731-743.
Zoncu R, Sabatini DM, Efeyan A (2011). mTOR: From growth signal integration to cancer, diabetes and ageing. Nat Revs Mol Cell Biol 12: 21-35.
Zubair H, Azim S, Srivastava SK, Ahmad A, Bhardwaj A, Khan MA, Patel GK, Arora S, Carter JE, Singh S et al. (2016). Glucose metabolism reprogrammed by overexpression of IKKε promotes pancreatic tumor growth. Cancer Res 76: 7254-7264.