Expression of the potential therapeutic target CXXC5 in primary acute myeloid leukemia cells-high expression is associated with adverse prognosis as well as altered intracellular signaling and transcriptional regulation

Oncotarget

Volumn 6, Issue 5, 2015, Pages 2794-2811

  Bruserud, Øystein ^a,b   Reikvam, Håkon ^a,b   Fredly, Hanne ^a,b   Skavland, Jørn ^b   Hagen, Karen Marie ^a   Van Hoang, Tuyen Thy ^a   Brenner, Annette K ^a   Kadi, Amir ^c,d,e   Astori, Audrey ^c,d,e   Gjertsen, Bjørn Tore ^a,b   Pendino, Frederic ^a,c,d,e  

^a UNIVERSITY OF BERGEN   (Norway)

^b HAUKELAND UNIVERSITY HOSPITAL   (Norway)

^c INSTITUT COCHIN   (France)

^d CNRS   (France)

^e UNIVERSITÉ PARIS DESCARTES   (France)

Author keywords

Acute myeloid leukemia; All trans retinoic acid; CXXC5; Cytokines; Transcription

Indexed keywords

CELL PROTEIN; CYCLIC AMP RESPONSIVE ELEMENT BINDING PROTEIN; DNA METHYLTRANSFERASE; DNA METHYLTRANSFERASE 3; MESSENGER RNA; MITOGEN ACTIVATED PROTEIN KINASE P38; PHOSPHOINOSITIDE DEPENDENT PROTEIN KINASE 1; PROTEIN C MYB; PROTEIN RPS6; STAT1 PROTEIN; STAT3 PROTEIN; STEROID RECEPTOR COACTIVATOR 1; TRANSCRIPTION FACTOR; TRANSCRIPTION FACTOR GATA 2; TRANSCRIPTION FACTOR RUNX1; TRANSCRIPTION FACTOR SPI1; UNCLASSIFIED DRUG; WT1 PROTEIN; CARRIER PROTEIN; CXXC5 PROTEIN, HUMAN; TUMOR MARKER;

ACUTE GRANULOCYTIC LEUKEMIA; ARTICLE; AUTOPHAGY; CANCER PROGNOSIS; CELL MIGRATION; CELL PROLIFERATION; CELL SHAPE; CELL VIABILITY; CONTROLLED STUDY; CXXC5 GENE; CYTOKINE PRODUCTION; CYTOKINE RELEASE; GENE EXPRESSION; HEMATOPOIESIS; HEMATOPOIETIC STEM CELL; HUMAN; HUMAN CELL; LEUKEMIA CELL; PROTEIN EXPRESSION; PROTEIN FUNCTION; PROTEIN PHOSPHORYLATION; TRANSCRIPTION REGULATION; TSC22 GENE; TUMOR SUPPRESSOR GENE; ACUTE MYELOBLASTIC LEUKEMIA; ADULT; AGED; FEMALE; GENE EXPRESSION PROFILING; GENE EXPRESSION REGULATION; GENETIC TRANSCRIPTION; GENETIC TRANSFECTION; GENETICS; MALE; METABOLISM; MIDDLE AGED; PHOSPHORYLATION; PRIMARY CELL CULTURE; PROGNOSIS; RNA INTERFERENCE; SIGNAL TRANSDUCTION; TUMOR CELL CULTURE; TUMOR CELL LINE; UPREGULATION; VERY ELDERLY;

ADULT; AGED; AGED, 80 AND OVER; BIOMARKERS, TUMOR; CARRIER PROTEINS; CELL LINE, TUMOR; FEMALE; GENE EXPRESSION PROFILING; GENE EXPRESSION REGULATION, LEUKEMIC; HUMANS; LEUKEMIA, MYELOID, ACUTE; MALE; MIDDLE AGED; PHOSPHORYLATION; PRIMARY CELL CULTURE; PROGNOSIS; RNA INTERFERENCE; RNA, MESSENGER; SIGNAL TRANSDUCTION; TRANSCRIPTION, GENETIC; TRANSFECTION; TUMOR CELLS, CULTURED; UP-REGULATION;

EID: 84923287164     PISSN: None     EISSN: 19492553     Source Type: Journal    
DOI: 10.18632/oncotarget.3056     Document Type: Article

References (80)

1. Boultwood J, Pellagatti A, McKenzie AN and Wainscoat JS. Advances in the 5q-syndrome. Blood. 2010; 116(26):5803-5811.
2. Pendino F, Nguyen E, Jonassen I, Dysvik B, Azouz A, Lanotte M, Segal-Bendirdjian E and Lillehaug JR. Functional involvement of RINF, retinoid-inducible nuclear factor (CXXC5), in normal and tumoral human myelopoiesis. Blood. 2009; 113(14):3172-3181.
3. Kim HY, Yang DH, Shin SW, Kim MY, Yoon JH, Kim S, Park HC, Kang DW, Min D, Hur MW and Choi KY. CXXC5 is a transcriptional activator of Flk-1 and mediates bone morphogenic protein-induced endothelial cell differentiation and vessel formation. FASEB J. 2014; 28(2):615-626.
4. Astori A, Fredly H, Aloysius TA, Bullinger L, Mansat-De Mas V, de la Grange P, Delhommeau F, Hagen KM, Recher C, Dusanter-Fourt I, Knappskog S, Lillehaug JR, Pendino F and Bruserud O. CXXC5 (retinoid-inducible nuclear factor, RINF) is a potential therapeutic target in high-risk human acute myeloid leukemia. Oncotarget. 2013; 4(9):1438-1448.
5. Kühnl A, Valk PJM, Sanders MA, Hills RK, Mills KI, Gale RE, Kaiser M, Dillon R, Joannides M, Ivey A, Gilkes AF, Haferlach T, Schnittger S, Duprez E, Linch D, Delwel R, et al. Downregulation Of The Wnt Inhibitor CXXC5 Predicts a Better Prognosis In Acute Myeloid Leukemia. Blood. 2013; 122(21):52.
6. Bruserud O, Hovland R, Wergeland L, Huang TS and Gjertsen BT. Flt3-mediated signaling in human acute myelogenous leukemia (AML) blasts: a functional characterization of Flt3-ligand effects in AML cell populations with and without genetic Flt3 abnormalities. Haematologica. 2003; 88(4):416-428.
7. Hatfield KJ, Hovland R, Oyan AM, Kalland KH, Ryningen A, Gjertsen BT and Bruserud O. Release of angiopoietin-1 by primary human acute myelogenous leukemia cells is associated with mutations of nucleophosmin, increased by bone marrow stromal cells and possibly antagonized by high systemic angiopoietin-2 levels. Leukemia. 2008; 22(2):287-293.
8. Bruserud O, Gjertsen BT and von Volkman HL. In vitro culture of human acute myelogenous leukemia (AML) cells in serum-free media: studies of native AML blasts and AML cell lines. J Hematother Stem Cell Res. 2000; 9(6):923-932.
9. Stapnes C, Ryningen A, Hatfield K, Oyan AM, Eide GE, Corbascio M, Kalland KH, Gjertsen BT and Bruserud O. Functional characteristics and gene expression profiles of primary acute myeloid leukaemia cells identify patient subgroups that differ in susceptibility to histone deacetylase inhibitors. Int J Oncol. 2007; 31(6):1529-1538.
10. Fredly H, Ersvaer E, Gjertsen BT and Bruserud O. Immunogenic apoptosis in human acute myeloid leukemia (AML): primary human AML cells expose calreticulin and release heat shock protein (HSP) 70 and HSP90 during apoptosis. Oncol Rep. 2011; 25(6):1549-1556.
11. Stapnes C, Doskeland AP, Hatfield K, Ersvaer E, Ryningen A, Lorens JB, Gjertsen BT and Bruserud O. The proteasome inhibitors bortezomib and PR-171 have antiproliferative and proapoptotic effects on primary human acute myeloid leukaemia cells. Br J Haematol. 2007; 136(6):814-828.
12. Irish JM, Hovland R, Krutzik PO, Perez OD, Bruserud O, Gjertsen BT and Nolan GP. Single cell profiling of potentiated phospho-protein networks in cancer cells. Cell. 2004; 118(2):217-228.
13. Skavland J, Jorgensen KM, Hadziavdic K, Hovland R, Jonassen I, Bruserud O and Gjertsen BT. Specific cellular signal-transduction responses to in vivo combination therapy with ATRA, valproic acid and theophylline in acute myeloid leukemia. Blood Cancer J. 2011; 1:e4.
14. Skavland J, Reikvam H and Bruserud Ø. Survival Stratification In Acute Myeloid Leukemia By Single Cell Signal Profiling. Blood. 2013; 122(21):2625.
15. Gandoura S, Weiss E, Rautou PE, Fasseu M, Gustot T, Lemoine F, Hurtado-Nedelec M, Hego C, Vadrot N, Elkrief L, Letteron P, Tellier Z, Pocidalo MA, Valla D, Lebrec D, Groyer A, et al. Gene-and exon-expression profiling reveals an extensive LPS-induced response in immune cells in patients with cirrhosis. J Hepatol. 2013; 58(5):936-948.
16. Wang E, Aslanzadeh V, Papa F, Zhu H, de la Grange P and Cambi F. Global profiling of alternative splicing events and gene expression regulated by hnRNPH/F. PLoS One. 2012; 7(12):e51266.
17. de la Grange P, Dutertre M, Martin N and Auboeuf D. FAST DB: a website resource for the study of the expression regulation of human gene products. Nucleic Acids Res. 2005; 33(13):4276-4284.
18. de la Grange P, Dutertre M, Correa M and Auboeuf D. A new advance in alternative splicing databases: from catalogue to detailed analysis of regulation of expression and function of human alternative splicing variants. BMC Bioinformatics. 2007; 8:180.
19. Cassidy SA, Cheent KS and Khakoo SI. Effects of Peptide on NK cell-mediated MHC I recognition. Front Immunol. 2014; 5:133.
20. Lichterfeld M and Yu XG. The emerging role of leukocyte immunoglobulin-like receptors (LILRs) in HIV-1 infection. J Leukoc Biol. 2012; 91(1):27-33.
21. Gondi CS and Rao JS. Cathepsin B as a cancer target. Expert Opin Ther Targets. 2013; 17(3):281-291.
22. Repnik U, Stoka V, Turk V and Turk B. Lysosomes and lysosomal cathepsins in cell death. Biochim Biophys Acta. 2012; 1824(1):22-33.
23. Hatfield KJ, Reikvam H and Bruserud O. The crosstalk between the matrix metalloprotease system and the chemokine network in acute myeloid leukemia. Curr Med Chem. 2010; 17(36):4448-4461.
24. Lee EJ, Min HY, Chung HJ, Park EJ, Shin DH, Jeong LS and Lee SK. A novel adenosine analog, thio-Cl-IB-MECA, induces G0/G1 cell cycle arrest and apoptosis in human promyelocytic leukemia HL-60 cells. Biochem Pharmacol. 2005; 70(6):918-924.
25. Schneider C, Wiendl H and Ogilvie A. Biphasic cytotoxic mechanism of extracellular ATP on U-937 human histiocytic leukemia cells: involvement of adenosine generation. Biochim Biophys Acta. 2001; 1538(2-3):190-205.
26. Elton TS, Selemon H, Elton SM and Parinandi NL. Regulation of the MIR155 host gene in physiological and pathological processes. Gene. 2013; 532(1):1-12.
27. Zhang Y and Derynck R. Transcriptional regulation of the transforming growth factor-beta -inducible mouse germ line Ig alpha constant region gene by functional cooperation of Smad, CREB, and AML family members. J Biol Chem. 2000; 275(22):16979-16985.
28. Lan Y and Yang X. The role of Smad signaling in vascular and hematopoietic development revealed by studies using genetic mouse models. Science China Life sciences. 2010; 53(4):485-489.
29. Blank U and Karlsson S. The role of Smad signaling in hematopoiesis and translational hematology. Leukemia. 2011; 25(9):1379-1388.
30. Larsson J and Karlsson S. The role of Smad signaling in hematopoiesis. Oncogene. 2005; 24(37):5676-5692.
31. Ruscetti FW, Akel S and Bartelmez SH. Autocrine transforming growth factor-beta regulation of hematopoiesis: many outcomes that depend on the context. Oncogene. 2005; 24(37):5751-5763.
32. Liu B and Mao N. Smad5: signaling roles in hematopoiesis and osteogenesis. Int J Biochem Cell Biol. 2004; 36(5):766-770.
33. Eppert K, Takenaka K, Lechman ER, Waldron L, Nilsson B, van Galen P, Metzeler KH, Poeppl A, Ling V, Beyene J, Canty AJ, Danska JS, Bohlander SK, Buske C, Minden MD, Golub TR, et al. Stem cell gene expression programs influence clinical outcome in human leukemia. Nat Med. 2011; 17(9):1086-1093.
34. Diffner E, Beck D, Gudgin E, Thoms JA, Knezevic K, Pridans C, Foster S, Goode D, Lim WK, Boelen L, Metzeler KH, Micklem G, Bohlander SK, Buske C, Burnett A, Ottersbach K, et al. Activity of a heptad of transcription factors is associated with stem cell programs and clinical outcome in acute myeloid leukemia. Blood. 2013; 121(12):2289-2300.
35. Wilson NK, Foster SD, Wang X, Knezevic K, Schutte J, Kaimakis P, Chilarska PM, Kinston S, Ouwehand WH, Dzierzak E, Pimanda JE, de Bruijn MF and Gottgens B. Combinatorial transcriptional control in blood stem/ progenitor cells: genome-wide analysis of ten major transcriptional regulators. Cell Stem Cell. 2010; 7(4):532-544.
36. Curtis DJ, Salmon JM and Pimanda JE. Concise review: Blood relatives: formation and regulation of hematopoietic stem cells by the basic helix-loop-helix transcription factors stem cell leukemia and lymphoblastic leukemia-derived sequence 1. Stem Cells. 2012; 30(6):1053-1058.
37. Baer R. TAL1, TAL2 and LYL1: a family of basic helixloop-helix proteins implicated in T cell acute leukaemia. Semi Cancer Biol. 1993; 4(6):341-347.
38. Bruserud O and Ulvestad E. Effects of gamma-irradiation on acute myelogenous leukemia blasts: in vitro studies of proliferation, constitutive cytokine secretion, and accessory cell function during T cell activation. J Hematother Stem Cell Res. 1999; 8(4):431-441.
39. Bruserud O, Gjertsen BT, Foss B and Huang TS. New strategies in the treatment of acute myelogenous leukemia (AML): in vitro culture of aml cells--the present use in experimental studies and the possible importance for future therapeutic approaches. Stem Cells. 2001; 19(1):1-11.
40. Reikvam H, Oyan AM, Kalland KH, Hovland R, Hatfield KJ and Bruserud O. Differences in proliferative capacity of primary human acute myelogenous leukaemia cells are associated with altered gene expression profiles and can be used for subclassification of patients. Cell Prolif. 2013; 46(5):554-562.
41. Ersvaer E, Skavland J, Ulvestad E, Gjertsen BT and Bruserud O. Effects of interferon gamma on native human acute myelogenous leukaemia cells. Cancer Immunol Immunother. 2007; 56(1):13-24.
42. Irish JM, Anensen N, Hovland R, Skavland J, Borresen-Dale AL, Bruserud O, Nolan GP and Gjertsen BT. Flt3 Y591 duplication and Bcl-2 overexpression are detected in acute myeloid leukemia cells with high levels of phosphorylated wild-type p53. Blood. 2007; 109(6):2589-2596.
43. Salem M, Delwel R, Touw I, Mahmoud L and Lowenberg B. Human AML colony growth in serum-free culture. Leuk Res. 1988; 12(2):157-165.
44. Bruserud O, Frostad S and Foss B. In vitro culture of acute myelogenous leukemia blasts: a comparison of four different culture media. J Hematother. 1999; 8(1):63-73.
45. Bayascas JR. PDK1: the major transducer of PI 3-kinase actions. Cur Topic Microbiol Immunol. 2010; 346:9-29.
46. Byeon SE, Yi YS, Oh J, Yoo BC, Hong S and Cho JY. The role of Src kinase in macrophage-mediated inflammatory responses. Med Inflam. 2012; 2012:512926.
47. Magnuson B, Ekim B and Fingar DC. Regulation and function of ribosomal protein S6 kinase (S6K) within mTOR signalling networks. Biochem J. 2012; 441(1):1-21.
48. Cho EC, Mitton B and Sakamoto KM. CREB and leukemogenesis. Crit Rev Oncog. 2011; 16(1-2):37-46.
49. Fagard R, Metelev V, Souissi I and Baran-Marszak F. STAT3 inhibitors for cancer therapy: Have all roads been explored? Jak-Stat. 2013; 2(1):e22882.
50. Oeztuerk-Winder F and Ventura JJ. The many faces of p38 mitogen-activated protein kinase in progenitor/stem cell differentiation. Biochem J. 2012; 445(1):1-10.
51. Bruserud Ø. IL-4, IL-10 and IL-13 in acute myelogenous leukemia. Cytokines Cell Mol Ther. 1998; 4(3): 187-198.
52. Bruserud O. Effects of interleukin-13 on cytokine secretion by human acute myelogenous leukemia blasts. Leukemia. 1996; 10(9):1497-1503.
53. Bruns HA and Kaplan MH. The role of constitutively active Stat6 in leukemia and lymphoma. Crit Rev Oncol/Hematol. 2006; 57(3):245-253.
54. Hebenstreit D, Wirnsberger G, Horejs-Hoeck J and Duschl A. Signaling mechanisms, interaction partners, and target genes of STAT6. Cytokine & Growth Fact Rev. 2006; 17(3):173-188.
55. De Luca A, Maiello MR, D'Alessio A, Pergameno M and Normanno N. The RAS/RAF/MEK/ERK and the PI3K/ AKT signalling pathways: role in cancer pathogenesis and implications for therapeutic approaches. Exp Opini Ther Targ. 2012; 16 Suppl 2:S17-27.
56. Kawamata H, Fujimori T and Imai Y. TSC-22 (TGFbeta stimulated clone-22): a novel molecular target for differentiation-inducing therapy in salivary gland cancer. Curr Cancer Drug Targets. 2004; 4(6):521-529.
57. Lu Y, Kitaura J, Oki T, Komeno Y, Ozaki K, Kiyono M, Kumagai H, Nakajima H, Nosaka T, Aburatani H and Kitamura T. Identification of TSC-22 as a potential tumor suppressor that is upregulated by Flt3-D835V but not Flt3-ITD. Leukemia. 2007; 21(11):2246-2257.
58. Hino S, Kawamata H, Omotehara F, Uchida D, Miwa Y, Begum NM, Yoshida H, Sato M and Fujimori T. Cytoplasmic TSC-22 (transforming growth factor-betastimulated clone-22) markedly enhances the radiation sensitivity of salivary gland cancer cells. Biochem Biophys Res Commun. 2002; 292(4):957-963.
59. Burk RF and Hill KE. Selenoprotein P-expression, functions, and roles in mammals. Biochim Biophys Acta. 2009; 1790(11):1441-1447.
60. Zeng H. Selenium as an essential micronutrient: roles in cell cycle and apoptosis. Molecules. 2009; 14(3):1263-1278.
61. Schwartz S, Heinecke A, Zimmermann M, Creutzig U, Schoch C, Harbott J, Fonatsch C, Loffler H, Buchner T, Ludwig WD and Thiel E. Expression of the C-kit receptor (CD117) is a feature of almost all subtypes of de novo acute myeloblastic leukemia (AML), including cytogenetically good-risk AML, and lacks prognostic significance. Leuk Lymphoma. 1999; 34(1-2):85-94.
62. Kümpers P, Koenecke C, Hecker H, Hellpap J, Horn R, Verhagen W, Buchholz S, Hertenstein B, Krauter J, Eder M, David S, Gohring G, Haller H and Ganser A. Angiopoietin-2 predicts disease-free survival after allogeneic stem cell transplantation in patients with highrisk myeloid malignancies. Blood. 2008; 112(5):2139-2148.
63. Lee CY, Tien HF, Hu CY, Chou WC and Lin LI. Marrow angiogenesis-associated factors as prognostic biomarkers in patients with acute myelogenous leukaemia. Br J Cancer. 2007; 97(7):877-882.
64. Schliemann C, Bieker R, Thoennissen N, Gerss J, Liersch R, Kessler T, Buchner T, Berdel WE and Mesters RM. Circulating angiopoietin-2 is a strong prognostic factor in acute myeloid leukemia. Leukemia. 2007; 21(9):1901-1906.
65. Radich JP, Dai H, Mao M, Oehler V, Schelter J, Druker B, Sawyers C, Shah N, Stock W, Willman CL, Friend S and Linsley PS. Gene expression changes associated with progression and response in chronic myeloid leukemia. PNAS. 2006; 103(8):2794-2799.
66. WHO. World Health Organization Classification of Tumors of Haematopoietic and Lymphoid Tissues, 4th Edition. (Lyon: international Agency for Cancer). 2008.
67. Steelman LS, Abrams SL, Whelan J, Bertrand FE, Ludwig DE, Basecke J, Libra M, Stivala F, Milella M, Tafuri A, Lunghi P, Bonati A, Martelli AM and McCubrey JA. Contributions of the Raf/MEK/ERK, PI3K/PTEN/Akt/ mTOR and Jak/STAT pathways to leukemia. Leukemia. 2008; 22(4):686-707.
68. Hers I, Vincent EE and Tavare JM. Akt signalling in health and disease. Cell Signal. 2011; 23(10):1515-1527.
69. Benekli M, Xia Z, Donohue KA, Ford LA, Pixley LA, Baer MR, Baumann H and Wetzler M. Constitutive activity of signal transducer and activator of transcription 3 protein in acute myeloid leukemia blasts is associated with short disease-free survival. Blood. 2002; 99(1):252-257.
70. Reikvam H, Tamburini J, Skrede S, Holdhus R, Poulain L, Ersvaer E, Hatfield KJ and Bruserud O. Antileukaemic effect of PI3K-mTOR inhibitors in acute myeloid leukaemia-gene expression profiles reveal CDC25B expression as determinate of pharmacological effect. Br J Haematol. 2014; 164(2):200-211.
71. Hutchins AP, Diez D and Miranda-Saavedra D. Genomic and computational approaches to dissect the mechanisms of STAT3's universal and cell type-specific functions. Jak-Stat. 2013; 2(4):e25097.
72. Bruserud O, Nepstad I, Hauge M, Hatfield K and Reikvam H. STAT3 as a possible therapeutic target in human malignancies: Lessions from acute myeloid leukemia. Exp Rev Hematol. 2014; 6:1-13.
73. Marvin J, Swaminathan S, Kraker G, Chadburn A, Jacobberger J and Goolsby C. Normal bone marrow signaltransduction profiles: a requisite for enhanced detection of signaling dysregulations in AML. Blood. 2011; 117(15):e120-130.
74. Redell MS, Ruiz MJ, Alonzo TA, Gerbing RB and Tweardy DJ. Stat3 signaling in acute myeloid leukemia: liganddependent and -independent activation and induction of apoptosis by a novel small-molecule Stat3 inhibitor. Blood. 2011; 117(21):5701-5709.
75. Mandal T, Bhowmik A, Chatterjee A, Chatterjee U, Chatterjee S and Ghosh MK. Reduced phosphorylation of Stat3 at Ser-727 mediated by casein kinase 2-Protein phosphatase 2A enhances Stat3 Tyr-705 induced tumorigenic potential of glioma cells. Cell Signal. 2014; 26(8):1725-1734.
76. Huang G, Yan H, Ye S, Tong C and Ying QL. STAT3 phosphorylation at tyrosine 705 and serine 727 differentially regulates mouse ESC fates. Stem Cells. 2014; 32(5):1149-1160.
77. Miyakoshi M, Yamamoto M, Tanaka H and Ogawa K. Serine 727 phosphorylation of STAT3: an early change in mouse hepatocarcinogenesis induced by neonatal treatment with diethylnitrosamine. Molec Carcinogen. 2014; 53(1):67-76.
78. Wakahara R, Kunimoto H, Tanino K, Kojima H, Inoue A, Shintaku H and Nakajima K. Phospho-Ser727 of STAT3 regulates STAT3 activity by enhancing dephosphorylation of phospho-Tyr705 largely through TC45. Genes Cells. 2012; 17(2):132-145.
79. Nosaka T, Kawashima T, Misawa K, Ikuta K, Mui AL and Kitamura T. STAT5 as a molecular regulator of proliferation, differentiation and apoptosis in hematopoietic cells. EMBO J. 1999; 18(17):4754-4765.
80. McCubrey JA, Steelman LS, Chappell WH, Abrams SL, Franklin RA, Montalto G, Cervello M, Libra M, Candido S, Malaponte G, Mazzarino MC, Fagone P, Nicoletti F, Basecke J, Mijatovic S, Maksimovic-Ivanic D, et al. Ras/ Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR cascade inhibitors: how mutations can result in therapy resistance and how to overcome resistance. Oncotarget. 2012; 3(10):1068-1111.