Mol. Cells 2020; 43(2): 176-181
Published online January 23, 2020
https://doi.org/10.14348/molcells.2019.0285
© The Korean Society for Molecular and Cellular Biology
Correspondence to : itok@nagasaki-u.ac.jp
This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/.
The RUNX transcription factors serve as master regulators of development and are frequently dysregulated in human cancers. Among the three family members, RUNX3 is the least studied, and has long been considered to be a tumor-suppressor gene in human cancers. This idea is mainly based on the observation that RUNX3 is inactivated by genetic/epigenetic alterations or protein mislocalization during the initiation of tumorigenesis. Recently, this paradigm has been challenged, as several lines of evidence have shown that RUNX3 is upregulated over the course of tumor development. Resolving this paradox and understanding how a single gene can exhibit both oncogenic and tumor-suppressive properties is essential for successful drug targeting of RUNX. We propose a simple explanation for the duality of RUNX3: p53 status. In this model, p53 deficiency causes RUNX3 to become an oncogene, resulting in aberrant upregulation of MYC.
Keywords c-Myc, p53, RUNX3
The Runt-related transcription factor (RUNX) family consists of three members, which share the highly conserved ‘Runt’ DNA-binding domain that associates with their co-factor, core binding factor β (CBFβ). All three RUNX proteins and CBFβ exert tumor-related functions in context-dependent manners. RUNX3 is the least studied member of the family, as it has been reported to act as both a tumor-suppressor and oncogene in human cancers. Initially, its broad tumor-suppressive function attracted attention, originating from observations of gastric phenotypes in
The past two decades of RUNX3 research have further clarified its original tumor-suppressive functions, but have also elaborated its opposing roles as an oncogene, provoking an essential question: how is the dual nature of RUNX3 determined by cellular context? Given the potential medical value of targeting the RUNX transcription factors, the demand for an answer to this question continues to grow (Bushweller, 2019; Cunningham et al., 2012; Morita et al., 2017). As we will show below, RUNX3 acts as a tumor-suppressor when interacting with p53, but as a tumor promoter when associating with MYC. These observations led us to focus on p53 and MYC, two central figures in tumor development, as contextual determinants of the duality of RUNX3.
RUNX3 acts as a positive regulator for p53, the quintessential gatekeeper and guardian of the genome, under two circumstances: upon DNA damage or upon oncogene activation (Bae et al., 2019; Lee et al., 2017). In the former case, RUNX3 is induced by DNA damage, forms a complex with p53, and facilitates its modifications (i.e., phosphorylation at Ser-15), thereby stabilizing p53 activity and promoting apoptosis (Ozaki et al., 2013; Yamada et al., 2010). On the other hand, RUNX3 is also activated by oncogenic KRAS and indirectly stabilizes p53 by transcriptionally upregulating
Another oncogenic stress that invokes the ARF–p53 pathway is MYC (Eischen et al., 1999; Murphy et al., 2008; Phesse et al., 2014; Schmitt et al., 1999; Zindy et al., 1998), a master regulator of cell proliferation broadly involved in the pathogenesis of human cancer. Indeed, MYC transcriptionally activates RUNX3 in NKTL (natural killer/T-cell lymphoma) cells (Selvarajan et al., 2017), suggesting that MYC, as well as KRAS, is one of the oncogenes that trigger the RUNX3–ARF–p53 pathway. p53 protects against MYC either directly, by transcriptional repression (Ho et al., 2005; Porter et al., 2017), or indirectly, via miR-145 induction (Sachdeva et al., 2009). Moreover,
Once activated by RUNX3, p53 seems to repress RUNX3 function. Aberrant upregulation of Runx3 coincides with the apparent loss of heterozygosity (LOH) of
If the tumor-suppressive functions of RUNX3 are governed by p53 in this manner, p53 inactivation might be the very event that triggers Runx3 dysregulation and its conversion to an oncogene. In fact, upregulation of Runx3 in
p53 hotspot mutations might also contribute to the oncogenic conversion of Runx3. p53 hotspot mutants, exemplified by p53R175H (p53R172H in mice), possess oncogenic (gain-of-function) properties in addition to defects in tumor suppression (Donehower and Lozano, 2009). As mentioned above, wild-type p53 promotes its own tumor-suppressive activities by directly interacting with RUNX3, whereas p53 hotspot mutants do not follow suit. On the contrary, it is suggested that p53R175H is also capable of directly interacting with RUNX3, and that the p53R175H–RUNX3 complex is aberrantly stable and exerts its oncogenic activities by altering the transcriptional targets of each of its components (Whittle and Hingorani, 2017; Whittle et al., 2015). In fact, p53R175H is involved in the switching of transforming growth factor β (TGF-β) signaling from a tumor-suppressor to a tumor-promoter (Adorno et al., 2009); TGF-β requires tumor-suppressive RUNX3 to exert some of its anti-tumor effects (Chang et al., 2010; Chi et al., 2005; Ikushima and Miyazono, 2010; Yano et al., 2006). In line with this series of evidence,
As listed in Table 1, several lines of evidence have revealed the oncogenic behavior of RUNX3 in multiple types of cancer. Unfortunately, most of these studies have not been able to identify the precise molecular mechanisms underlying the oncogenic phenotypes observed, although these phenotypes can be attributed to aberrant RUNX3 upregulation. We propose that the association of RUNX3 with MYC under p53 deficiency can resolve this enigma.
By retrovirus insertional mutagenesis, all
In bone-related cells, RUNX3 is highly upregulated across several Ewing’s sarcoma cell lines and facilitates their cell growth (Bledsoe et al., 2014). Notably in this regard, RUNX2 binds and epigenetically activates the
Taken together, these observations suggest the following model: in a cell governed by the tumor-suppressor p53, RUNX3 is invoked by either DNA damage or oncogenic stress, and positively regulates p53, which protects against MYC. Upon p53 inactivation, however, RUNX3 is unable to properly associate with p53, and therefore begins to act as an oncogene by aberrantly activating MYC (Fig. 1).
Previously, we reported that RUNX3 prevents tumorigenesis of the gastrointestinal tract, possibly by repressing MYC. This may appear to contradict our proposal that MYC is activated by RUNX3. In mechanistic terms, RUNX3 attenuates the DNA-binding activity of the TCF4/β-catenin complex that induces MYC, the principal oncogene for gastrointestinal cancer (Ito et al., 2008; Ito et al., 2011). It should be noted, however, that this tumor-suppressive role of RUNX3 was demonstrated in precancerous states using systemic
We proposed p53 status as a contextual determinant of the dual nature of RUNX3. In this model, p53 inactivation is the crucial event responsible for causing RUNX3 to contribute to cancer development. If that is the case, p53 deficiency and MYC dysregulation, two major phenomena related to most cancer initiation and progression in humans, may be connected by RUNX3, providing a rationale for targeting RUNX3 in malignancies (Fig. 2).
Indeed, Runx3 evidently does help to repress tumorigenesis in mouse models of gastrointestinal and lung cancers, but the
In fact, several other transcription factors play dual roles in cancer development: NF-κB in TNF-α signaling (Perkins, 2004); SMADs in TGF-β signaling (David and Massagué, 2018); AP-1 in MAPK signaling (Eferl and Wagner, 2003); YAP/TAZ in Hippo signaling (Moroishi et al., 2015); and RBPJ in Notch signaling (Lobry et al., 2014). Many of these signal-driven transcription factors (SDTFs) (Zhang and Glass, 2013) interact with RUNX3 (Chuang et al., 2013). RUNX family members are thought to be lineage-determining transcription factors (LDTFs) that specify cell identity and determine the genome-wide binding pattern of SDTFs over the course of normal development (Link et al., 2018; Zhang and Glass, 2013). Thus, a contextual determinant of the dual nature of RUNX3 might be shared by other transcription factors.
The authors have no potential conflicts of interest to disclose.
Oncogenic functions of RUNX3 reported so far
Cancer type | Oncogenic RUNX3 functions | References |
---|---|---|
AML | Drug resistance acquisition | (Damdinsuren et al., 2015) |
T-ALL | Apoptosis inhibition | (Choi et al., 2017) |
Basal cell carcinoma | Cell growth stimulation | (Lee et al., 2011a) |
Head and neck cancer | Cell growth stimulation | (Tsunematsu et al., 2009) |
Ovarian cancer | Tumorigenicity enhancement | (Barghout et al., 2015; Chen et al., 2019; Lee et al., 2011b; Nevadunsky et al., 2009) |
Drug resistance acquisition | ||
Cell growth stimulation | ||
Pancreatic cancer | Metastasis promotion | (Whittle et al., 2015) |
Ewing’s sarcoma | Tumorigenicity enhancement | (Bledsoe et al., 2014) |
Mol. Cells 2020; 43(2): 176-181
Published online February 29, 2020 https://doi.org/10.14348/molcells.2019.0285
Copyright © The Korean Society for Molecular and Cellular Biology.
1Department of Molecular Bone Biology, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki 852-8588, Japan, 2Japan Society for the Promotion of Science, Tokyo 102-0083, Japan
Correspondence to:itok@nagasaki-u.ac.jp
This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/.
The RUNX transcription factors serve as master regulators of development and are frequently dysregulated in human cancers. Among the three family members, RUNX3 is the least studied, and has long been considered to be a tumor-suppressor gene in human cancers. This idea is mainly based on the observation that RUNX3 is inactivated by genetic/epigenetic alterations or protein mislocalization during the initiation of tumorigenesis. Recently, this paradigm has been challenged, as several lines of evidence have shown that RUNX3 is upregulated over the course of tumor development. Resolving this paradox and understanding how a single gene can exhibit both oncogenic and tumor-suppressive properties is essential for successful drug targeting of RUNX. We propose a simple explanation for the duality of RUNX3: p53 status. In this model, p53 deficiency causes RUNX3 to become an oncogene, resulting in aberrant upregulation of MYC.
Keywords: c-Myc, p53, RUNX3
The Runt-related transcription factor (RUNX) family consists of three members, which share the highly conserved ‘Runt’ DNA-binding domain that associates with their co-factor, core binding factor β (CBFβ). All three RUNX proteins and CBFβ exert tumor-related functions in context-dependent manners. RUNX3 is the least studied member of the family, as it has been reported to act as both a tumor-suppressor and oncogene in human cancers. Initially, its broad tumor-suppressive function attracted attention, originating from observations of gastric phenotypes in
The past two decades of RUNX3 research have further clarified its original tumor-suppressive functions, but have also elaborated its opposing roles as an oncogene, provoking an essential question: how is the dual nature of RUNX3 determined by cellular context? Given the potential medical value of targeting the RUNX transcription factors, the demand for an answer to this question continues to grow (Bushweller, 2019; Cunningham et al., 2012; Morita et al., 2017). As we will show below, RUNX3 acts as a tumor-suppressor when interacting with p53, but as a tumor promoter when associating with MYC. These observations led us to focus on p53 and MYC, two central figures in tumor development, as contextual determinants of the duality of RUNX3.
RUNX3 acts as a positive regulator for p53, the quintessential gatekeeper and guardian of the genome, under two circumstances: upon DNA damage or upon oncogene activation (Bae et al., 2019; Lee et al., 2017). In the former case, RUNX3 is induced by DNA damage, forms a complex with p53, and facilitates its modifications (i.e., phosphorylation at Ser-15), thereby stabilizing p53 activity and promoting apoptosis (Ozaki et al., 2013; Yamada et al., 2010). On the other hand, RUNX3 is also activated by oncogenic KRAS and indirectly stabilizes p53 by transcriptionally upregulating
Another oncogenic stress that invokes the ARF–p53 pathway is MYC (Eischen et al., 1999; Murphy et al., 2008; Phesse et al., 2014; Schmitt et al., 1999; Zindy et al., 1998), a master regulator of cell proliferation broadly involved in the pathogenesis of human cancer. Indeed, MYC transcriptionally activates RUNX3 in NKTL (natural killer/T-cell lymphoma) cells (Selvarajan et al., 2017), suggesting that MYC, as well as KRAS, is one of the oncogenes that trigger the RUNX3–ARF–p53 pathway. p53 protects against MYC either directly, by transcriptional repression (Ho et al., 2005; Porter et al., 2017), or indirectly, via miR-145 induction (Sachdeva et al., 2009). Moreover,
Once activated by RUNX3, p53 seems to repress RUNX3 function. Aberrant upregulation of Runx3 coincides with the apparent loss of heterozygosity (LOH) of
If the tumor-suppressive functions of RUNX3 are governed by p53 in this manner, p53 inactivation might be the very event that triggers Runx3 dysregulation and its conversion to an oncogene. In fact, upregulation of Runx3 in
p53 hotspot mutations might also contribute to the oncogenic conversion of Runx3. p53 hotspot mutants, exemplified by p53R175H (p53R172H in mice), possess oncogenic (gain-of-function) properties in addition to defects in tumor suppression (Donehower and Lozano, 2009). As mentioned above, wild-type p53 promotes its own tumor-suppressive activities by directly interacting with RUNX3, whereas p53 hotspot mutants do not follow suit. On the contrary, it is suggested that p53R175H is also capable of directly interacting with RUNX3, and that the p53R175H–RUNX3 complex is aberrantly stable and exerts its oncogenic activities by altering the transcriptional targets of each of its components (Whittle and Hingorani, 2017; Whittle et al., 2015). In fact, p53R175H is involved in the switching of transforming growth factor β (TGF-β) signaling from a tumor-suppressor to a tumor-promoter (Adorno et al., 2009); TGF-β requires tumor-suppressive RUNX3 to exert some of its anti-tumor effects (Chang et al., 2010; Chi et al., 2005; Ikushima and Miyazono, 2010; Yano et al., 2006). In line with this series of evidence,
As listed in Table 1, several lines of evidence have revealed the oncogenic behavior of RUNX3 in multiple types of cancer. Unfortunately, most of these studies have not been able to identify the precise molecular mechanisms underlying the oncogenic phenotypes observed, although these phenotypes can be attributed to aberrant RUNX3 upregulation. We propose that the association of RUNX3 with MYC under p53 deficiency can resolve this enigma.
By retrovirus insertional mutagenesis, all
In bone-related cells, RUNX3 is highly upregulated across several Ewing’s sarcoma cell lines and facilitates their cell growth (Bledsoe et al., 2014). Notably in this regard, RUNX2 binds and epigenetically activates the
Taken together, these observations suggest the following model: in a cell governed by the tumor-suppressor p53, RUNX3 is invoked by either DNA damage or oncogenic stress, and positively regulates p53, which protects against MYC. Upon p53 inactivation, however, RUNX3 is unable to properly associate with p53, and therefore begins to act as an oncogene by aberrantly activating MYC (Fig. 1).
Previously, we reported that RUNX3 prevents tumorigenesis of the gastrointestinal tract, possibly by repressing MYC. This may appear to contradict our proposal that MYC is activated by RUNX3. In mechanistic terms, RUNX3 attenuates the DNA-binding activity of the TCF4/β-catenin complex that induces MYC, the principal oncogene for gastrointestinal cancer (Ito et al., 2008; Ito et al., 2011). It should be noted, however, that this tumor-suppressive role of RUNX3 was demonstrated in precancerous states using systemic
We proposed p53 status as a contextual determinant of the dual nature of RUNX3. In this model, p53 inactivation is the crucial event responsible for causing RUNX3 to contribute to cancer development. If that is the case, p53 deficiency and MYC dysregulation, two major phenomena related to most cancer initiation and progression in humans, may be connected by RUNX3, providing a rationale for targeting RUNX3 in malignancies (Fig. 2).
Indeed, Runx3 evidently does help to repress tumorigenesis in mouse models of gastrointestinal and lung cancers, but the
In fact, several other transcription factors play dual roles in cancer development: NF-κB in TNF-α signaling (Perkins, 2004); SMADs in TGF-β signaling (David and Massagué, 2018); AP-1 in MAPK signaling (Eferl and Wagner, 2003); YAP/TAZ in Hippo signaling (Moroishi et al., 2015); and RBPJ in Notch signaling (Lobry et al., 2014). Many of these signal-driven transcription factors (SDTFs) (Zhang and Glass, 2013) interact with RUNX3 (Chuang et al., 2013). RUNX family members are thought to be lineage-determining transcription factors (LDTFs) that specify cell identity and determine the genome-wide binding pattern of SDTFs over the course of normal development (Link et al., 2018; Zhang and Glass, 2013). Thus, a contextual determinant of the dual nature of RUNX3 might be shared by other transcription factors.
The authors have no potential conflicts of interest to disclose.
Oncogenic functions of RUNX3 reported so far
Cancer type | Oncogenic RUNX3 functions | References |
---|---|---|
AML | Drug resistance acquisition | (Damdinsuren et al., 2015) |
T-ALL | Apoptosis inhibition | (Choi et al., 2017) |
Basal cell carcinoma | Cell growth stimulation | (Lee et al., 2011a) |
Head and neck cancer | Cell growth stimulation | (Tsunematsu et al., 2009) |
Ovarian cancer | Tumorigenicity enhancement | (Barghout et al., 2015; Chen et al., 2019; Lee et al., 2011b; Nevadunsky et al., 2009) |
Drug resistance acquisition | ||
Cell growth stimulation | ||
Pancreatic cancer | Metastasis promotion |
(Whittle et al., 2015) |
Ewing’s sarcoma | Tumorigenicity enhancement | (Bledsoe et al., 2014) |
. Oncogenic functions of RUNX3 reported so far.
Cancer type | Oncogenic RUNX3 functions | References |
---|---|---|
AML | Drug resistance acquisition | (Damdinsuren et al., 2015) |
T-ALL | Apoptosis inhibition | (Choi et al., 2017) |
Basal cell carcinoma | Cell growth stimulation | (Lee et al., 2011a) |
Head and neck cancer | Cell growth stimulation | (Tsunematsu et al., 2009) |
Ovarian cancer | Tumorigenicity enhancement | (Barghout et al., 2015; Chen et al., 2019; Lee et al., 2011b; Nevadunsky et al., 2009) |
Drug resistance acquisition | ||
Cell growth stimulation | ||
Pancreatic cancer | Metastasis promotion | (Whittle et al., 2015) |
Ewing’s sarcoma | Tumorigenicity enhancement | (Bledsoe et al., 2014) |
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