Cancer Cell
Previews K., Dyer, M.D., Zhang, F., et al. (2011). Cancer Discov. 1, 170–185.
Mino-Kenudson, M., et al. (2013). Proc. Natl. Acad. Sci. USA 110, 21124–21129.
Dang, L., White, D.W., Gross, S., Bennett, B.D., Bittinger, M.A., Driggers, E.M., Fantin, V.R., Jang, H.G., Jin, S., Keenan, M.C., et al. (2009). Nature 462, 739–744.
Engelman, J.A. (2009). Nat. Rev. Cancer 9, 550–562.
Ebi, H., Costa, C., Faber, A.C., Nishtala, M., Kotani, H., Juric, D., Della Pelle, P., Song, Y., Yano, S.,
Jaiswal, B.S., Janakiraman, V., Kljavin, N.M., Chaudhuri, S., Stern, H.M., Wang, W., Kan, Z., Dbouk, H.A., Peters, B.A., Waring, P., et al. (2009). Cancer Cell 16, 463–474.
Sun, M., Hillmann, P., Hofmann, B.T., Hart, J.R., and Vogt, P.K. (2010). Proc. Natl. Acad. Sci. USA 107, 15547–15552. Wu, H., Shekar, S.C., Flinn, R.J., El-Sibai, M., Jaiswal, B.S., Sen, K.I., Janakiraman, V., Seshagiri, S., Gerfen, G.J., Girvin, M.E., and Backer, J.M. (2009). Proc. Natl. Acad. Sci. USA 106, 20258– 20263.
Whipping NF-kB to Submission via GADD45 and MKK7 Michael Karin1,2,* 1Laboratory
of Gene Regulation and Signal Transduction, Departments of Pharmacology and Pathology Cancer Center University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA *Correspondence: [email protected] http://dx.doi.org/10.1016/j.ccell.2014.09.012 2Moores
NF-kB protects malignant cells from death and therefore it was considered as a cancer treatment target. However, systemic NF-kB inhibition resulted in inflammation and other undesired outcomes. In this issue of Cancer Cell, Tornatore and colleagues solve this problem by targeting the GADD45:MKK7 module mediating NF-kB-induced survival of multiple myelomas.
NF-kB transcription factors are activated by numerous inflammatory stimuli and, in turn, induce expression of cytokines, chemokines, secondary inflammatory mediators, and critical immune response genes (Figure 1). Nearly 30 years ago, NF-kB was found to suppress apoptotic cell death and eventually was found to inhibit necrosis as well (Lin and Karin, 2003). Subsequently, it was noted that NF-kB is frequently activated in solid and hematopoietic malignancies (Staudt, 2010), giving rise to the proposal that its protumorigenic function depends on inhibition of malignant cell death, induced by either anticancer therapies or tumor suppressor and surveillance mechanisms (Karin et al., 2002). The logical extension of this hypothesis, which is supported by vast experimental evidence, was that inhibitors of NF-kB activity or activation should be effective either as a standalone treatment or in combination with chemotherapy or radiation therapy in malignancies in which NF-kB is activated by microenvironmental stimuli or genetic changes result in treatment resistance. Not surprisingly, this hypothesis kindled an intense race to develop NF-
kB inhibitors, most often by targeting IkB kinase (IKKb), a protein kinase that is essential for NF-kB activation (DiDonato et al., 2012). However, when such inhibitors were eventually tested either in experimental animals or in human volunteers, they were found to have several undesired side effects, including inflammation, immune deficiencies, and liver damage. Whereas immune deficiencies and liver damage were anticipated from the study of knockout mice and reflect the important role of NF-kB in immunity and tissue maintenance, the inflammatory effect of NF-kB inhibition, observed in both mice and human, was rather surprising. It was found to be due, in part, to a novel function of NF-kB in restraining the activation of caspase 1, the enzyme responsible for secretion of mature IL-1b by activated macrophages (Greten et al., 2007). Such findings brought the clinical development of IKKb/ NF-kB inhibitors to a halt. Approaching NF-kB inhibition from an entirely different direction, Tornatore et al. (2014; this issue of Cancer Cell) seem to have found a clever and practical solution to this problem.
NF-kB mediates its survival function, in part, by preventing the activation of the pro-apoptotic protein kinase JNK (De Smaele et al., 2001; Tang et al., 2001). In certain cell lines, the mediator through which NF-kB curtails JNK activation is the stress-induced protein GADD45b, which interacts with the JNKactivating kinase MKK7 and blocks its catalytic activity (Papa et al., 2004) (Figure 1). However, it was not entirely clear whether GADD45b is used by NFkB to inhibit cell death in all types of cells or only in cancer cells. The finding that GADD45b-deficient mice are relatively healthy and die of old age (Lu et al., 2004), unlike mice lacking IKKb or RelA that die during late embryogenesis due to liver damage (DiDonato et al., 2012; Lin and Karin, 2003), suggested that GADD45b is not essential for the survival of most normal cells. To investigate its importance in the survival of malignant cells, Tornatore et al. (2014) surveyed GADD45b expression in various cancers and found it to be highly elevated in a subset of multiple myelomas (MMs), tumors derived from plasma cells (PCs) that are frequently associated with mutations
Cancer Cell 26, October 13, 2014 ª2014 Elsevier Inc. 447
Cancer Cell
Previews
Figure 1. NF-kB-Dependent Cancer Cell Survival and Its Pharmacological Inhibition NF-kB transcription factors are kept in the cytosol by specific inhibitors (IkB). Upon activation of IkB kinases (IKK), NF-kB proteins enter the nucleus, bind DNA (parallel green lines), and activate transcription of numerous genes encoding chemokines, cytokines, enzymes that produce secondary inflammatory mediators (e.g., Cox2 and iNOS), inhibitors of inflammasome activation (question mark), and inhibitors of apoptosis and GADD45b. The latter binds MKK7 and inhibits its ability to activate the proapoptotic JNK protein kinases. Because IKK and NF-kB activation protect cancer cells from apoptosis, IKK inhibitors were considered for cancer treatment. But their use blocks all NF-kB-dependent functions and can result in inflammation and immune deficiencies. Proteasome inhibitors (bortezomib) also inhibit NF-kB activation, although their therapeutic effect in multiple myeloma (MM) depends on another mechanism. To overcome the complications of general NF-kB inhibition, Tornatore et al. (2014) developed DTP3, which induces the death of multiple myeloma cells that express high amounts of GADD45b by preventing the inhibition of MKK7 and allowing JNK activation to proceed. Inhibitors of NF-kB activation and NF-kBdependent cell survival are marked by the red boxes.
that lead to constitutive NF-kB activation (Staudt, 2010). Because its presence and progression can be easily monitored through blood tests, MM has served as a popular proving ground for the development of anticancer drugs, including the proteasome inhibitor bortezomib (Valcade). Although bortezomib can inhibit NF-kB activity, its therapeutic mode of action in MM is NF-kB independent. Analysis of monoclonal PC isolated from MM patients and MM cell lines demonstrated that GADD45b expression is elevated in at least 50% of them and that the silencing of GADD45b or RelA in six MM cell lines chosen for high GADD45b expression results in spontaneous cell death. Importantly, cell death depends on MKK7-mediated JNK activation, suggesting that a molecule that interferes with the ability of GADD45b to block MKK7 activity would function as a specific inhibitor of GADD45b-mediated
cell survival. To accomplish this goal, Tornatore et al. (2014) followed a road rarely taken by drug developers and chose to develop inhibitors of the GADD45b:MKK7 interaction. By screening a combinatorial library of L-tetrapeptides and lead optimization, they identified two acetylated (Ac) L-tetrapeptides, Ac-LTP1 and Ac-LTP2, that blocked the GADD45b:MKK7 interaction at a very low concentration. Surprisingly, the D-enantiomers of both peptides, Ac-DTP1 and Ac-DTP2, were as active as the parental compounds, with the added advantage of being resistant to serum proteases. Further improvement, mainly geared to increase bioavailability, resulted in development of DTP3, which binds to MKK7 and prevents its inhibition by GADD45b (Figure 1). Although DTP3 is not a rigid molecule, it binds to MKK7 with surprisingly high affinity (Kd = 65 nM) and selectivity, leading to JNK activation and spontaneous killing of
448 Cancer Cell 26, October 13, 2014 ª2014 Elsevier Inc.
high GADD45b-expressing MM cell lines at rather low concentrations. DTP3 also exhibited remarkable potency against primary PCs isolated from MM patients and, unlike bortezomib, hardly exhibited cytotoxicity against normal PC, resulting in a high therapeutic index. Remarkably, the cytotoxic effect of DTP3 was even more pronounced than that of IKKb inhibitors, suggesting that canonical IKKb-dependent NF-kB signaling may not be the only inducer of GADD45b expression. Importantly, DTP3 completely blocked the growth of subcutaneously or orthotopically implanted MM cell lines in mice as long as the treatment was initiated when the tumors were quite small (100–200 mm3). Although mice treated for 8 weeks with a rather high dose of DT3 (29 mg/kg/day) were not found to exhibit any apparent side effects, it may be too early to pop the champagne. First, one would like to see how effective DTP3 is against a high load of advanced tumors that are more reflective of the stage at which MM is detected and treated in patients. Second, one should be aware that not all side effects of NF-kB inhibition are easily apparent. Enhanced inflammasome activation in laboratory mice, which are kept under barrier conditions, is only seen upon challenge with inflammasome activators, and susceptibility to infections is revealed only in the presence of infectious bacteria. Although inhibition of MKK7-mediated JNK activation by GADD45b may have no impact on inflammasome activity, the potentiation of JNK activation in either MM cells or myeloid cells could enhance the production of tumor necrosis factor and other inflammatory cytokines. A third issue that needs to be addressed is the development of drug resistance. The current treatment of MM is plagued by rapid appearance of drug resistance; patients that respond to one treatment regimen often need to be placed on another regimen because of drug resistance. Even a single mutation in the MKK7 gene may disrupt DTP3 binding and upregulation of the JNK-activating kinase MKK4 may have a similar effect. Notwithstanding further evaluation of its safety and therapeutic efficacy, the development of DTP3 is a remarkable achievement in basic cancer biology and its translational application. One would
Cancer Cell
Previews have to eagerly wait for further studies of DTP3 in other NF-kB-dependent hematological malignancies and solid tumors that overexpress GADD45b. Hopefully, these studies will also pave the way for the development of other approaches for curtailing the survival activity of NF-kB in GADD45b-negative cancers. REFERENCES De Smaele, E., Zazzeroni, F., Papa, S., Nguyen, D.U., Jin, R., Jones, J., Cong, R., and Franzoso, G. (2001). Nature 414, 308–313.
DiDonato, J.A., Mercurio, F., and Karin, M. (2012). Immunol. Rev. 246, 379–400. Greten, F.R., Arkan, M.C., Bollrath, J., Hsu, L.C., Goode, J., Miething, C., Go¨ktuna, S.I., Neuenhahn, M., Fierer, J., Paxian, S., et al. (2007). Cell 130, 918–931. Karin, M., Cao, Y., Greten, F.R., and Li, Z.W. (2002). Nat. Rev. Cancer 2, 301–310. Lin, A., and Karin, M. (2003). Semin. Cancer Biol. 13, 107–114. Lu, B., Ferrandino, A.F., and Flavell, R.A. (2004). Nat. Immunol. 5, 38–44.
Papa, S., Zazzeroni, F., Bubici, C., Jayawardena, S., Alvarez, K., Matsuda, S., Nguyen, D.U., Pham, C.G., Nelsbach, A.H., Melis, T., et al. (2004). Nat. Cell Biol. 6, 146–153. Staudt, L.M. (2010). Cold Spring Harb. Perspect. Biol. 2, a000109. Tang, G., Minemoto, Y., Dibling, B., Purcell, N.H., Li, Z., Karin, M., and Lin, A. (2001). Nature 414, 313–317. Tornatore, L., Sandomenico, A., Raimondo, D., Low, C., Rocci, A., Tralau-Stewart, C., Bua, M., Jaxa-Chamiec, A., Thotakura, A., Dyson, J., et al. (2014). Cancer Cell 26, this issue, 495–508.
5-Aza-CdR Delivers a Gene Body Blow Sivakanthan Kasinathan1,2,3 and Steven Henikoff1,4,* 1Basic
Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA Scientist Training Program, University of Washington School of Medicine, Seattle, WA 98195, USA 3Molecular & Cellular Biology Graduate Program, University of Washington, Seattle, WA 98195, USA 4Howard Hughes Medical Institute, Seattle, WA 98109, USA *Correspondence: [email protected] http://dx.doi.org/10.1016/j.ccell.2014.09.004 2Medical
In this issue of Cancer Cell, Yang et al. describe a causal relationship between gene body methylation and gene expression and a role for genic methylation in response to clinical DNA methylation inhibitors, which suggests that the mechanism of action of these inhibitors includes gene body hypomethylation-induced downregulation of cancer-associated genes. DNA cytosine methylation is an ancient regulatory mechanism present in diverse phylogenies, including vertebrates, plants, and some fungi (Jones, 2012). Cytosine methylation of CG dinucleotides by DNA methyltransferases (DNMTs) in promoters is associated with gene silencing, e.g., in X chromosome inactivation and imprinting (Jones, 2012), and promoter hypermethylation is thought to contribute to aberrant regulatory programs in cancer (Shenker and Flanagan, 2012). Within the last decade, so-called ‘‘epigenetic’’ drugs have come to the fore with U.S. Food and Drug Administration approval of cytidine analog DNMT inhibitors such as 5-aza-2-deoxycytidine (5-Aza-CdR) for myelodysplastic syndrome and acute myeloid leukemia. Excitingly, studies have also hinted at the efficacy of this mode of intervention in solid tumors (Shenker and Flanagan, 2012), expanding the utility of these chemotherapeutics beyond hematologic malignancies.
Although promoter methylation, which maintains a ‘‘closed’’ chromatin state that impairs transcriptional initiation (Jones, 2012), has been well studied, less is known about the role of methylation in gene bodies. Intriguingly, unlike at promoters where methylation is associated with gene repression, genic methylation is positively correlated with gene expression (Figure 1A) (Maunakea et al., 2010; Varley et al., 2013). It is thought that DNA methylation inhibitors cause promoter hypomethylation and subsequent gene reactivation (Shenker and Flanagan, 2012). However, the effect of these drugs on gene body methylation has not been extensively studied. In this issue of Cancer Cell, the work of Yang et al. (2014) suggests a causal relationship between gene body methylation and gene expression and expands the understanding of the mechanism of action of cytidine analog
cancer chemotherapeutics. They assayed genome-wide methylation at various time points after short treatment of a dividing colon cancer cell line with 5-Aza-CdR, allowing interrogation of remethylation kinetics and the durability of methylation changes upon drug withdrawal (Figure 1A). A clustering approach used to classify genomic regions into groups with high and low remethylation rates revealed that gene bodies were rapidly remethylated compared to promoters (Figure 1B). Furthermore, gene body remethylation was correlated with gene expression. Exploiting DNMT knockout cell lines, the authors determined that DNMT3B is required for rapid remethylation of gene bodies following 5-Aza-CdR treatment (Figure 1A). Both DNA methylation and gene expression were attenuated in DNMT3B deficient cells following 5-Aza-CdR treatment, suggesting that DNMT inhibitor-induced
Cancer Cell 26, October 13, 2014 ª2014 Elsevier Inc. 449
Previews K., Dyer, M.D., Zhang, F., et al. (2011). Cancer Discov. 1, 170–185.
Mino-Kenudson, M., et al. (2013). Proc. Natl. Acad. Sci. USA 110, 21124–21129.
Dang, L., White, D.W., Gross, S., Bennett, B.D., Bittinger, M.A., Driggers, E.M., Fantin, V.R., Jang, H.G., Jin, S., Keenan, M.C., et al. (2009). Nature 462, 739–744.
Engelman, J.A. (2009). Nat. Rev. Cancer 9, 550–562.
Ebi, H., Costa, C., Faber, A.C., Nishtala, M., Kotani, H., Juric, D., Della Pelle, P., Song, Y., Yano, S.,
Jaiswal, B.S., Janakiraman, V., Kljavin, N.M., Chaudhuri, S., Stern, H.M., Wang, W., Kan, Z., Dbouk, H.A., Peters, B.A., Waring, P., et al. (2009). Cancer Cell 16, 463–474.
Sun, M., Hillmann, P., Hofmann, B.T., Hart, J.R., and Vogt, P.K. (2010). Proc. Natl. Acad. Sci. USA 107, 15547–15552. Wu, H., Shekar, S.C., Flinn, R.J., El-Sibai, M., Jaiswal, B.S., Sen, K.I., Janakiraman, V., Seshagiri, S., Gerfen, G.J., Girvin, M.E., and Backer, J.M. (2009). Proc. Natl. Acad. Sci. USA 106, 20258– 20263.
Whipping NF-kB to Submission via GADD45 and MKK7 Michael Karin1,2,* 1Laboratory
of Gene Regulation and Signal Transduction, Departments of Pharmacology and Pathology Cancer Center University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA *Correspondence: [email protected] http://dx.doi.org/10.1016/j.ccell.2014.09.012 2Moores
NF-kB protects malignant cells from death and therefore it was considered as a cancer treatment target. However, systemic NF-kB inhibition resulted in inflammation and other undesired outcomes. In this issue of Cancer Cell, Tornatore and colleagues solve this problem by targeting the GADD45:MKK7 module mediating NF-kB-induced survival of multiple myelomas.
NF-kB transcription factors are activated by numerous inflammatory stimuli and, in turn, induce expression of cytokines, chemokines, secondary inflammatory mediators, and critical immune response genes (Figure 1). Nearly 30 years ago, NF-kB was found to suppress apoptotic cell death and eventually was found to inhibit necrosis as well (Lin and Karin, 2003). Subsequently, it was noted that NF-kB is frequently activated in solid and hematopoietic malignancies (Staudt, 2010), giving rise to the proposal that its protumorigenic function depends on inhibition of malignant cell death, induced by either anticancer therapies or tumor suppressor and surveillance mechanisms (Karin et al., 2002). The logical extension of this hypothesis, which is supported by vast experimental evidence, was that inhibitors of NF-kB activity or activation should be effective either as a standalone treatment or in combination with chemotherapy or radiation therapy in malignancies in which NF-kB is activated by microenvironmental stimuli or genetic changes result in treatment resistance. Not surprisingly, this hypothesis kindled an intense race to develop NF-
kB inhibitors, most often by targeting IkB kinase (IKKb), a protein kinase that is essential for NF-kB activation (DiDonato et al., 2012). However, when such inhibitors were eventually tested either in experimental animals or in human volunteers, they were found to have several undesired side effects, including inflammation, immune deficiencies, and liver damage. Whereas immune deficiencies and liver damage were anticipated from the study of knockout mice and reflect the important role of NF-kB in immunity and tissue maintenance, the inflammatory effect of NF-kB inhibition, observed in both mice and human, was rather surprising. It was found to be due, in part, to a novel function of NF-kB in restraining the activation of caspase 1, the enzyme responsible for secretion of mature IL-1b by activated macrophages (Greten et al., 2007). Such findings brought the clinical development of IKKb/ NF-kB inhibitors to a halt. Approaching NF-kB inhibition from an entirely different direction, Tornatore et al. (2014; this issue of Cancer Cell) seem to have found a clever and practical solution to this problem.
NF-kB mediates its survival function, in part, by preventing the activation of the pro-apoptotic protein kinase JNK (De Smaele et al., 2001; Tang et al., 2001). In certain cell lines, the mediator through which NF-kB curtails JNK activation is the stress-induced protein GADD45b, which interacts with the JNKactivating kinase MKK7 and blocks its catalytic activity (Papa et al., 2004) (Figure 1). However, it was not entirely clear whether GADD45b is used by NFkB to inhibit cell death in all types of cells or only in cancer cells. The finding that GADD45b-deficient mice are relatively healthy and die of old age (Lu et al., 2004), unlike mice lacking IKKb or RelA that die during late embryogenesis due to liver damage (DiDonato et al., 2012; Lin and Karin, 2003), suggested that GADD45b is not essential for the survival of most normal cells. To investigate its importance in the survival of malignant cells, Tornatore et al. (2014) surveyed GADD45b expression in various cancers and found it to be highly elevated in a subset of multiple myelomas (MMs), tumors derived from plasma cells (PCs) that are frequently associated with mutations
Cancer Cell 26, October 13, 2014 ª2014 Elsevier Inc. 447
Cancer Cell
Previews
Figure 1. NF-kB-Dependent Cancer Cell Survival and Its Pharmacological Inhibition NF-kB transcription factors are kept in the cytosol by specific inhibitors (IkB). Upon activation of IkB kinases (IKK), NF-kB proteins enter the nucleus, bind DNA (parallel green lines), and activate transcription of numerous genes encoding chemokines, cytokines, enzymes that produce secondary inflammatory mediators (e.g., Cox2 and iNOS), inhibitors of inflammasome activation (question mark), and inhibitors of apoptosis and GADD45b. The latter binds MKK7 and inhibits its ability to activate the proapoptotic JNK protein kinases. Because IKK and NF-kB activation protect cancer cells from apoptosis, IKK inhibitors were considered for cancer treatment. But their use blocks all NF-kB-dependent functions and can result in inflammation and immune deficiencies. Proteasome inhibitors (bortezomib) also inhibit NF-kB activation, although their therapeutic effect in multiple myeloma (MM) depends on another mechanism. To overcome the complications of general NF-kB inhibition, Tornatore et al. (2014) developed DTP3, which induces the death of multiple myeloma cells that express high amounts of GADD45b by preventing the inhibition of MKK7 and allowing JNK activation to proceed. Inhibitors of NF-kB activation and NF-kBdependent cell survival are marked by the red boxes.
that lead to constitutive NF-kB activation (Staudt, 2010). Because its presence and progression can be easily monitored through blood tests, MM has served as a popular proving ground for the development of anticancer drugs, including the proteasome inhibitor bortezomib (Valcade). Although bortezomib can inhibit NF-kB activity, its therapeutic mode of action in MM is NF-kB independent. Analysis of monoclonal PC isolated from MM patients and MM cell lines demonstrated that GADD45b expression is elevated in at least 50% of them and that the silencing of GADD45b or RelA in six MM cell lines chosen for high GADD45b expression results in spontaneous cell death. Importantly, cell death depends on MKK7-mediated JNK activation, suggesting that a molecule that interferes with the ability of GADD45b to block MKK7 activity would function as a specific inhibitor of GADD45b-mediated
cell survival. To accomplish this goal, Tornatore et al. (2014) followed a road rarely taken by drug developers and chose to develop inhibitors of the GADD45b:MKK7 interaction. By screening a combinatorial library of L-tetrapeptides and lead optimization, they identified two acetylated (Ac) L-tetrapeptides, Ac-LTP1 and Ac-LTP2, that blocked the GADD45b:MKK7 interaction at a very low concentration. Surprisingly, the D-enantiomers of both peptides, Ac-DTP1 and Ac-DTP2, were as active as the parental compounds, with the added advantage of being resistant to serum proteases. Further improvement, mainly geared to increase bioavailability, resulted in development of DTP3, which binds to MKK7 and prevents its inhibition by GADD45b (Figure 1). Although DTP3 is not a rigid molecule, it binds to MKK7 with surprisingly high affinity (Kd = 65 nM) and selectivity, leading to JNK activation and spontaneous killing of
448 Cancer Cell 26, October 13, 2014 ª2014 Elsevier Inc.
high GADD45b-expressing MM cell lines at rather low concentrations. DTP3 also exhibited remarkable potency against primary PCs isolated from MM patients and, unlike bortezomib, hardly exhibited cytotoxicity against normal PC, resulting in a high therapeutic index. Remarkably, the cytotoxic effect of DTP3 was even more pronounced than that of IKKb inhibitors, suggesting that canonical IKKb-dependent NF-kB signaling may not be the only inducer of GADD45b expression. Importantly, DTP3 completely blocked the growth of subcutaneously or orthotopically implanted MM cell lines in mice as long as the treatment was initiated when the tumors were quite small (100–200 mm3). Although mice treated for 8 weeks with a rather high dose of DT3 (29 mg/kg/day) were not found to exhibit any apparent side effects, it may be too early to pop the champagne. First, one would like to see how effective DTP3 is against a high load of advanced tumors that are more reflective of the stage at which MM is detected and treated in patients. Second, one should be aware that not all side effects of NF-kB inhibition are easily apparent. Enhanced inflammasome activation in laboratory mice, which are kept under barrier conditions, is only seen upon challenge with inflammasome activators, and susceptibility to infections is revealed only in the presence of infectious bacteria. Although inhibition of MKK7-mediated JNK activation by GADD45b may have no impact on inflammasome activity, the potentiation of JNK activation in either MM cells or myeloid cells could enhance the production of tumor necrosis factor and other inflammatory cytokines. A third issue that needs to be addressed is the development of drug resistance. The current treatment of MM is plagued by rapid appearance of drug resistance; patients that respond to one treatment regimen often need to be placed on another regimen because of drug resistance. Even a single mutation in the MKK7 gene may disrupt DTP3 binding and upregulation of the JNK-activating kinase MKK4 may have a similar effect. Notwithstanding further evaluation of its safety and therapeutic efficacy, the development of DTP3 is a remarkable achievement in basic cancer biology and its translational application. One would
Cancer Cell
Previews have to eagerly wait for further studies of DTP3 in other NF-kB-dependent hematological malignancies and solid tumors that overexpress GADD45b. Hopefully, these studies will also pave the way for the development of other approaches for curtailing the survival activity of NF-kB in GADD45b-negative cancers. REFERENCES De Smaele, E., Zazzeroni, F., Papa, S., Nguyen, D.U., Jin, R., Jones, J., Cong, R., and Franzoso, G. (2001). Nature 414, 308–313.
DiDonato, J.A., Mercurio, F., and Karin, M. (2012). Immunol. Rev. 246, 379–400. Greten, F.R., Arkan, M.C., Bollrath, J., Hsu, L.C., Goode, J., Miething, C., Go¨ktuna, S.I., Neuenhahn, M., Fierer, J., Paxian, S., et al. (2007). Cell 130, 918–931. Karin, M., Cao, Y., Greten, F.R., and Li, Z.W. (2002). Nat. Rev. Cancer 2, 301–310. Lin, A., and Karin, M. (2003). Semin. Cancer Biol. 13, 107–114. Lu, B., Ferrandino, A.F., and Flavell, R.A. (2004). Nat. Immunol. 5, 38–44.
Papa, S., Zazzeroni, F., Bubici, C., Jayawardena, S., Alvarez, K., Matsuda, S., Nguyen, D.U., Pham, C.G., Nelsbach, A.H., Melis, T., et al. (2004). Nat. Cell Biol. 6, 146–153. Staudt, L.M. (2010). Cold Spring Harb. Perspect. Biol. 2, a000109. Tang, G., Minemoto, Y., Dibling, B., Purcell, N.H., Li, Z., Karin, M., and Lin, A. (2001). Nature 414, 313–317. Tornatore, L., Sandomenico, A., Raimondo, D., Low, C., Rocci, A., Tralau-Stewart, C., Bua, M., Jaxa-Chamiec, A., Thotakura, A., Dyson, J., et al. (2014). Cancer Cell 26, this issue, 495–508.
5-Aza-CdR Delivers a Gene Body Blow Sivakanthan Kasinathan1,2,3 and Steven Henikoff1,4,* 1Basic
Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA Scientist Training Program, University of Washington School of Medicine, Seattle, WA 98195, USA 3Molecular & Cellular Biology Graduate Program, University of Washington, Seattle, WA 98195, USA 4Howard Hughes Medical Institute, Seattle, WA 98109, USA *Correspondence: [email protected] http://dx.doi.org/10.1016/j.ccell.2014.09.004 2Medical
In this issue of Cancer Cell, Yang et al. describe a causal relationship between gene body methylation and gene expression and a role for genic methylation in response to clinical DNA methylation inhibitors, which suggests that the mechanism of action of these inhibitors includes gene body hypomethylation-induced downregulation of cancer-associated genes. DNA cytosine methylation is an ancient regulatory mechanism present in diverse phylogenies, including vertebrates, plants, and some fungi (Jones, 2012). Cytosine methylation of CG dinucleotides by DNA methyltransferases (DNMTs) in promoters is associated with gene silencing, e.g., in X chromosome inactivation and imprinting (Jones, 2012), and promoter hypermethylation is thought to contribute to aberrant regulatory programs in cancer (Shenker and Flanagan, 2012). Within the last decade, so-called ‘‘epigenetic’’ drugs have come to the fore with U.S. Food and Drug Administration approval of cytidine analog DNMT inhibitors such as 5-aza-2-deoxycytidine (5-Aza-CdR) for myelodysplastic syndrome and acute myeloid leukemia. Excitingly, studies have also hinted at the efficacy of this mode of intervention in solid tumors (Shenker and Flanagan, 2012), expanding the utility of these chemotherapeutics beyond hematologic malignancies.
Although promoter methylation, which maintains a ‘‘closed’’ chromatin state that impairs transcriptional initiation (Jones, 2012), has been well studied, less is known about the role of methylation in gene bodies. Intriguingly, unlike at promoters where methylation is associated with gene repression, genic methylation is positively correlated with gene expression (Figure 1A) (Maunakea et al., 2010; Varley et al., 2013). It is thought that DNA methylation inhibitors cause promoter hypomethylation and subsequent gene reactivation (Shenker and Flanagan, 2012). However, the effect of these drugs on gene body methylation has not been extensively studied. In this issue of Cancer Cell, the work of Yang et al. (2014) suggests a causal relationship between gene body methylation and gene expression and expands the understanding of the mechanism of action of cytidine analog
cancer chemotherapeutics. They assayed genome-wide methylation at various time points after short treatment of a dividing colon cancer cell line with 5-Aza-CdR, allowing interrogation of remethylation kinetics and the durability of methylation changes upon drug withdrawal (Figure 1A). A clustering approach used to classify genomic regions into groups with high and low remethylation rates revealed that gene bodies were rapidly remethylated compared to promoters (Figure 1B). Furthermore, gene body remethylation was correlated with gene expression. Exploiting DNMT knockout cell lines, the authors determined that DNMT3B is required for rapid remethylation of gene bodies following 5-Aza-CdR treatment (Figure 1A). Both DNA methylation and gene expression were attenuated in DNMT3B deficient cells following 5-Aza-CdR treatment, suggesting that DNMT inhibitor-induced
Cancer Cell 26, October 13, 2014 ª2014 Elsevier Inc. 449
