Translation initiation and activity of eukaryotic initiation factor-alpha (eIF2α), the rate-limiting step of translation initiation, is often overactivated in malignant cells. Here, we investigated the regulation and role of eIF2α in acute promyelocytic (APL) and acute myeloid leukemia (AML) cells in response to all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), the front-line therapies in APL. ATRA and ATO induce Ser-51 phosphorylation (inactivation) of eIF2α, through the induction of protein kinase C delta (PKCδ) and PKR, but not other eIF2α kinases, such as GCN2 and PERK in APL (NB4) and AML cells (HL60, U937, and THP-1). Inhibition of eIF2α reduced the expression of cellular proteins that are involved in apoptosis (DAP5/p97), cell cycle (p21Waf1/Cip1), differentiation (TG2) and induced those regulating proliferation (c-myc) and survival (p70S6K). PI3K/Akt/mTOR pathway is involved in regulation of eIF2α through PKCδ/PKR axis. PKCδ and p-eIF2α protein expression levels revealed a significant association between the reduced levels of PKCδ ( ？？ = 0 . 0 3 7 8 ) and peIF2 ( ？？ = 0 . 0 0 4 1 ) and relapses in AML patients ( ？？ = 4 7 ). In conclusion, our study provides the first evidence that PKCδ regulates/inhibits eIF2α through induction of PKR in AML cells and reveals a novel signaling mechanism regulating translation initiation. 1. Introduction Differentiation block or arrest is one of the major characteristics of acute myeloid leukemia (AML) [1]. All-trans retinoic acid (ATRA), an active metabolite of vitamin A, is a potent inducer of cellular differentiation and growth arrest in various tumor cell lines and has been successfully used in the treatment of acute promyelocytic leukemia (APL) [1–5]. The success of ATRA in the treatment of APL introduced the concept of differentiation therapy in treating malignant diseases [1]. Arsenic trioxide (ATO), an FDA approved drug, induces both differentiation and apoptosis in APL and AML cells [5]. The molecular events that are involved in underlying mechanism of these drugs are not completely elucidated. Understanding the pathways regulating cell proliferation and differentiation may help designing new molecularly targeted therapies in AML. Translation initiation is a highly regulated process of translation in response to cellular stress and mitogenic stimulation [6–11]. Increased translation and protein synthesis are associated with cell proliferation and malignant disease [6, 7]. Translational regulation plays a vital role in the expression of oncogenic, and growth-regulatory, differentiation, and
References
[1]
L. Altucci and H. Gronemeyer, “The promise of retinoids to fight against cancer,” Nature Reviews Cancer, vol. 1, no. 3, pp. 181–193, 2001.
[2]
M. Lanotte, V. Martin-Thouvenin, S. Najman, P. Balerini, F. Valensi, and R. Berger, “NB4, a maturation inducible cell line with t(15;17) marker isolated from a human acute promyelocytic leukemia (M3),” Blood, vol. 77, no. 5, pp. 1080–1086, 1991.
[3]
T. R. Breitman, S. J. Collins, and B. R. Keene, “Terminal differentiation of human promyelocytic leukemic cells in primary culture in response to retinoic acid,” Blood, vol. 57, no. 6, pp. 1000–1004, 1981.
[4]
C. Chomienne, P. Fenaux, and L. Degos, “Retinoid differentiation therapy in promyelocytic leukemia,” FASEB Journal, vol. 10, no. 9, pp. 1025–1030, 1996.
[5]
Z. X. Shen, G. Q. Chen, J. H. Ni et al., “Use of arsenic trioxide (As2O3) in the treatment of acute promyelocytic leukemia (AFL): II. Clinical efficacy and pharmacokinetics in relapsed patients,” Blood, vol. 89, no. 9, pp. 3354–3360, 1997.
[6]
M. J. Clemens and U. A. Bommer, “Translational control: the cancer connection,” International Journal of Biochemistry and Cell Biology, vol. 31, no. 1, pp. 1–23, 1999.
[7]
A. E. Willis, “Translational control of growth factor and proto-oncogene expression,” International Journal of Biochemistry and Cell Biology, vol. 31, no. 1, pp. 73–86, 1999.
[8]
C. O. Brostrom and M. A. Brostrom, “Regulation of translational initiation during cellular responses to stress,” Progress in Nucleic Acid Research and Molecular Biology, vol. 58, pp. 79–125, 1998.
[9]
M. J. Clemens, “Initiation factor eIF2α phosphorylation in stress responses and apoptosis,” Progress in Molecular and Subcellular Biology, vol. 27, pp. 57–89, 2001.
[10]
M. J. Clemens, “Targets and mechanisms for the regulation of translation in malignant transformation,” Oncogene, vol. 23, no. 18, pp. 3180–3188, 2004.
[11]
O. Donze, R. Jagus, A. E. Koromilas, J. W. B. Hershey, and N. Sonenberg, “Abrogation of translation initiation factor eIF-2 phosphorylation causes malignant transformation of NIH 3T3 cells,” The EMBO Journal, vol. 14, no. 15, pp. 3828–3834, 1995.
[12]
V. M. Pain, “Initiation of protein synthesis in eukaryotic cells,” European Journal of Biochemistry, vol. 236, no. 3, pp. 747–771, 1996.
[13]
T. E. Dever, “Gene-specific regulation by general translation factors,” Cell, vol. 108, no. 4, pp. 545–556, 2002.
[14]
A. Sudhakar, A. Ramachandran, S. Ghosh, S. E. Hasnain, R. J. Kaufman, and K. V. A. Ramaiah, “Phosphorylation of serine 51 in initiation factor 2α (eIF2α) promotes complex formation between eIF2α(P) and eIF2B and causes inhibition in the guanine nucleotide exchange activity of eIF2B,” Biochemistry, vol. 39, no. 42, pp. 12929–12938, 2000.
[15]
B. Datta, R. Datta, S. Mukherjee, and Z. Zhang, “Increased phosphorylation of eukaryotic initiation factor 2α at the G2/M boundary in human osteosarcoma cells correlates with deglycosylation of p67 and a decreased rate of protein synthesis,” Experimental Cell Research, vol. 250, no. 1, pp. 223–230, 1999.
[16]
A. Leroux and I. M. London, “Regulation of protein synthesis by phosphorylation of eukaryotic initiation factor 2α in intact reticulocytes and reticulocyte lysates,” Proceedings of the National Academy of Sciences of the United States of America, vol. 79, no. 7 I, pp. 2147–2151, 1982.
[17]
A. Lazaris-Karatzas, K. S. Montine, and N. Sonenberg, “Malignant transformation by a eukaryotic initiation factor subunit that binds to mRNA 5′ cap,” Nature, vol. 345, no. 6275, pp. 544–547, 1990.
[18]
A. DeBenedetti and R. E. Rhoads, “Overexpression of eukaryotic protein synthesis initiation factor 4E in HeLa cells results in aberrant growth and morphology,” Proceedings of the National Academy of Sciences of the United States of America, vol. 87, no. 21, pp. 8212–8216, 1990.
[19]
A. DeBenedetti and A. L. Harris, “EIF4E expression in tumors: its possible role in progression of malignancies,” International Journal of Biochemistry and Cell Biology, vol. 31, no. 1, pp. 59–72, 1999.
[20]
T. Fukuchi-Shimogori, I. Ishii, K. Kashiwagi, H. Mashiba, H. Ekimoto, and K. Igarashi, “Malignant transformation by overproduction of translation initiation factor eIF4G,” Cancer Research, vol. 57, no. 22, pp. 5041–5044, 1997.
[21]
C. Bauer, I. Diesinger, N. Brass, H. Steinhart, H. Iro, and E. U. Meese, “Translation initiation factor eIF-4G is immunogenic, overexpressed, and amplified in patients with squamous cell lung carcinoma,” Cancer, vol. 92, no. 4, pp. 822–829, 2001.
[22]
M. B？hm, K. Sawicka, J. P. Siebrasse, A. Brehmer-Fastnacht, R. Peters, and K. H. Klempnauer, “The transformation suppressor protein Pdcd4 shuttles between nucleus and cytoplasm and binds RNA,” Oncogene, vol. 22, no. 31, pp. 4905–4910, 2003.
[23]
I. B. Rosenwald, D. B. Rhoads, L. D. Callanan, K. J. Isselbacher, and E. V. Schmidt, “Increased expression of eukaryotic translation initiation factors eIF-4E and eIF-2α in response to growth induction by c-myc,” Proceedings of the National Academy of Sciences of the United States of America, vol. 90, no. 13, pp. 6175–6178, 1993.
[24]
I. B. Rosenwald, “Upregulated expression of the genes encoding translation initiation factors eIF-4E and eIF-2α in transformed cells,” Cancer Letters, vol. 102, no. 1-2, pp. 113–123, 1996.
[25]
R. C. Wek, H. Y. Jiang, and T. G. Anthony, “Coping with stress: EIF2 kinases and translational control,” Biochemical Society Transactions, vol. 34, no. 1, pp. 7–11, 2006.
[26]
I. Topisirovic, M. L. Guzman, M. J. McConnell et al., “Aberrant eukaryotic translation initiation factor 4E-dependent mRNA transport impedes hematopoietic differentiation and contributes to leukemogenesis,” Molecular and Cellular Biology, vol. 23, no. 24, pp. 8992–9002, 2003.
[27]
J. Eberle, K. Krasagakis, and C. E. Orfanos, “Translation initiation factor eIF-4A1 mRNA is consistently overexpressed in human melanoma cells in vitro,” International Journal of Cancer, vol. 71, no. 3, pp. 396–401, 1997.
[28]
A. M. Krichevsky, E. Metzer, and H. Rosen, “Translational control of specific genes during differentiation of HL-60 cells,” The Journal of Biological Chemistry, vol. 274, no. 20, pp. 14295–14305, 1999.
[29]
N. Meani, S. Minardi, S. Licciulli et al., “Molecular signature of retinoic acid treatment in acute promyelocytic leukemia,” Oncogene, vol. 24, no. 20, pp. 3358–3368, 2005.
[30]
D. N. Jackson and D. A. Foster, “The enigmatic protein kinase Cδ: complex roles in cell proliferation and survival,” FASEB Journal, vol. 18, no. 6, pp. 627–636, 2004.
[31]
J. E. Coligan, A. M. Kruisbeck, D. H. Margulies, E. M. Shevach, and W. Strober, Current Protocols in Immunology, vol. 1, Wiley-Interscience, New York, NY, USA, 1995.
[32]
M. N. Harris, B. Ozpolat, F. Abdi et al., “Comparative proteomic analysis of all-trans-retinoic acid treatment reveals systematic posttranscriptional control mechanisms in acute promyelocytic leukemia,” Blood, vol. 104, no. 5, pp. 1314–1323, 2004.
[33]
B. Ozpolat, U. Akar, M. Steiner et al., “Programmed cell death-4 tumor suppressor protein contributes to retinoic acid-induced terminal granulocytic differentiation of human myeloid leukemia cells,” Molecular Cancer Research, vol. 5, no. 1, pp. 95–108, 2007.
[34]
B. Ozpolat, U. Akar, M. Harris et al., “All-trans-retinoic acid and arsenic trioxide (ATO)-induced supression of translational initiation involves death associated protein 5 (DAP5/p97/NAT1) in leukemia cell differentiation and apoptosis,” Apoptosis, vol. 4, pp. 1–11, 2008.
[35]
C. N. Landen Jr., A. Chavez-Reyes, C. Bucana et al., “Therapeutic EphA2 gene targeting in vivo using neutral liposomal small interfering RNA delivery,” Cancer Research, vol. 65, no. 15, pp. 6910–6918, 2005.
[36]
S. M. Kornblau, Y. Qiu, W. Chen et al., “Proteomic profiling of 150 proteins in 511 acute myelogenous leukemia (AML) patient samples using reverse phase proteins arrays (RPPA) reveals recurrent proteins expression signatures with prognostic implications,” Blood, vol. 112, no. 11, pp. 281–282, 2008.
[37]
S. M. Kornblau, N. Singh, Y. Qiu, W. Chen, N. Zhang, and K. R. Coombes, “Highly phosphorylated FOXO3A is an adverse prognostic factor in acute myeloid leukemia,” Clinical Cancer Research, vol. 16, no. 6, pp. 1865–1874, 2010.
[38]
M. Giannì, M. H. M. Koken, M. K. Chelbi-Alix et al., “Combined arsenic and retinoic acid treatment enhances differentiation and apoptosis in arsenic-resistant NB4 cells,” Blood, vol. 91, no. 11, pp. 4300–4310, 1998.
[39]
A. Grolleau, N. Sonenberg, J. Wietzerbin, and L. Beretta, “Differential regulation of 4E-BP1 and 4E-BP2, two repressors of translation initiation, during human myeloid cell differentiation,” Journal of Immunology, vol. 162, no. 6, pp. 3491–3497, 1999.
[40]
A. Kentsis, E. C. Dwyer, J. M. Perez et al., “The RING domains of the promyelocytic leukemia protein PML and the arenaviral protein Z repress translation by directly inhibiting translation initiation factor eIF4E,” Journal of Molecular Biology, vol. 312, no. 4, pp. 609–623, 2001.
[41]
M. S. Sheikh and A. J. Fornace, “Regulation of translation initiation following stress,” Oncogene, vol. 18, no. 45, pp. 6121–6128, 1999.
[42]
R. J. Kaufman, “Stress signaling from the lumen of the endoplasmic reticulum: coordination of gene transcriptional and translational controls,” Genes and Development, vol. 13, pp. 1211–1233, 1999.
[43]
R. C. Wek, “EIF-2 kinases: regulators of general and gene-specific translation initiation,” Trends in Biochemical Sciences, vol. 19, no. 11, pp. 491–496, 1994.
[44]
E. A. Kohlhepp, M. E. Condon, and A. W. Hamburger, “Recombinant human interferon α enhancement of retinoic-acid-induced differentiation of HL-60 cells,” Experimental Hematology, vol. 15, no. 4, pp. 414–418, 1987.
[45]
Y. Atsumi, R. C. Dodd, F. W. Maddux, S. J. Citron, and T. K. Gray, “Retinoids induce U937 cells to express macrophage phenotype,” American Journal of the Medical Sciences, vol. 292, no. 3, pp. 152–156, 1986.
[46]
J. Drach, G. Lopez-Berestein, T. McQueen, M. Andreeff, and K. Mehta, “Induction of differentiation in myeloid leukemia cell lines and acute promyelocytic leukemia cells by liposomal all-trans-retinoic acid,” Cancer Research, vol. 53, no. 9, pp. 2100–2104, 1993.
[47]
Z. Balajthy, K. Csomós, G. Vámosi, A. Szántó, M. Lanotte, and L. Fésüs, “Tissue-transglutaminase contributes to neutrophil granulocyte differentiation and functions,” Blood, vol. 108, no. 6, pp. 2045–2054, 2006.
[48]
S. Kambhampati, Y. Li, A. Verma et al., “Activation of protein kinase Cδ by all-trans-retinoic acid,” The Journal of Biological Chemistry, vol. 278, no. 35, pp. 32544–32551, 2003.
[49]
M. Gschwendt, H. J. Muller, K. Kielbassa et al., “Rottlerin, a novel protein kinase inhibitor,” Biochemical and Biophysical Research Communications, vol. 199, no. 1, pp. 93–98, 1994.
[50]
A. M. Martelli, M. Ny？kern, G. Tabellini et al., “Phosphoinositide 3-kinase/Akt signaling pathway and its therapeutical implications for human acute myeloid leukemia,” Leukemia, vol. 20, no. 6, pp. 911–928, 2006.
[51]
C. Nishioka, T. Ikezoe, J. Yang, S. Gery, H. P. Koeffler, and A. Yokoyama, “Inhibition of mammalian target of rapamycin signaling potentiates the effects of all-trans retinoic acid to induce growth arrest and differentiation of human acute myelogenous leukemia cells,” International Journal of Cancer, vol. 125, no. 7, pp. 1710–1720, 2009.
[52]
G. Tabellini, P. L. Tazzari, R. Bortul et al., “Phosphoinositide 3-kinase/Akt inhibition increases arsenic trioxide-induced apoptosis of acute promyelocytic and T-cell leukaemias,” British Journal of Haematology, vol. 130, no. 5, pp. 716–725, 2005.
[53]
X. M. Ma and J. Blenis, “Molecular mechanisms of mTOR-mediated translational control,” Nature Reviews Molecular Cell Biology, vol. 10, no. 5, pp. 307–318, 2009.
[54]
T. Casini and P. G. Pelicci, “A function of p21 during promyelocytic leukemia cell differentiation independent of CDK inhibition and cell cycle arrest,” Oncogene, vol. 18, no. 21, pp. 3235–3243, 1999.
[55]
S. Yamanaka, X. Y. Zhang, M. Maeda et al., “Essential role of NAT1/p97/DAP5 in embryonic differentiation and the retinoic acid pathway,” The EMBO Journal, vol. 19, no. 20, pp. 5533–5541, 2000.
[56]
H. Imataka, H. S. Olsen, and N. Sonenberg, “A new translational regulator with homology to eukaryotic translation initiation factor 4G,” The EMBO Journal, vol. 16, no. 4, pp. 817–825, 1997.
[57]
A. Melnick and J. D. Licht, “Deconstructing a disease: RARα, its fusion partners, and their roles in the pathogenesis of acute promyelocytic leukemia,” Blood, vol. 93, no. 10, pp. 3167–3215, 1999.
[58]
J. Chung, C. J. Kuo, G. R. Crabtree, and J. Blenis, “Rapamycin-FKBP specifically blocks growth-dependent activation of and signaling by the 70 kd S6 protein kinases,” Cell, vol. 69, no. 7, pp. 1227–1236, 1992.
[59]
E. A. Chiocca, P. J. A. Davies, and J. P. Stein, “Regulation of tissue transglutaminase gene expression as a molecular model for retinoid effects on proliferation and differentiation,” Journal of Cellular Biochemistry, vol. 39, no. 3, pp. 293–304, 1989.
[60]
T. Suzuki, Y. Koyama, H. Ichikawa et al., “1,25-Dihydroxyvitamin D3 suppresses gene expression of eukaryotic translation initiation factor 2 in human promyelocytic leukemia HL-60 cells,” Cell Structure and Function, vol. 30, no. 1, pp. 1–6, 2005.
[61]
C. Billottet, L. Banerjee, B. Vanhaesebroeck, and A. Khwaja, “Inhibition of class I phosphoinositide 3-kinase activity impairs proliferation and triggers apoptosis in acute promyelocytic leukemia without affecting ATRA-induced differentiation,” Cancer Research, vol. 69, no. 3, pp. 1027–1034, 2009.
[62]
T. A. Lin, X. Kong, T. A. J. Haystead et al., “PHAS-I as a link between mitogen-activated protein kinase and translation initiation,” Science, vol. 266, no. 5185, pp. 653–656, 1994.
[63]
A. Pause, G. J. Belsham, A. C. Gingras et al., “Insulin-dependent stimulation of protein synthesis by phosphorylation of a regulator of 5′-cap function,” Nature, vol. 371, no. 6500, pp. 762–767, 1994.
[64]
H. S. Yang, A. P. Jansen, A. A. Komar et al., “The transformation suppressor Pdcd4 is a novel eukaryotic translation initiation factor 4A binding protein that inhibits translation,” Molecular and Cellular Biology, vol. 23, no. 1, pp. 26–37, 2003.
[65]
X. Wang and D. Ron, “Stress-induced phosphorylation and activation of the transcription factor CHOP (GADD153) by p38 MAP kinase,” Science, vol. 272, no. 5266, pp. 1347–1349, 1996.
