Our lab investigates how hypoxia triggers gene expression, impacting metastasis, angiogenesis, senescence, cytoskeleton, and glycolysis. Diverse genes under hypoxia yield unique cell traits: hindered differentiation, reduced senescence, enhanced stemness, and resistance to anticancer therapy. Decades of research have unveiled these intricate mechanisms.
(1) Hypoxia, Cellular Senescence and Histone Demethylases
The intricate relationship between hypoxia, cellular senescence, and histone demethylases has been a central focus of our research since 2008. Our investigations have unveiled intriguing insights into the molecular underpinnings of these interconnected processes.
Members of the Jmj family exhibit diverse histone lysine demethylase (KDM) activities using O2 and 2-oxoglutarate (2OG) as cosubstrates. Each KDM is characterized by unique substrate specificities and Michaelis-Menten constant (Km) values for oxygen (O2) and 2-oxoglutarate (2OG). Consequently, the presence of hypoxic conditions and the limitation of O2 availability converge to elevate the global levels of methylated histones, revealing links hypoxia and histone methylation.
The histone code, a combination of histone tail modifications, influences chromatin processes like replication and transcription. This suggests that hypoxia and metabolic changes swiftly impact chromatin through histone demethylase regulation. Using ChIP-seq and RNA-seq analyses, we identified DNA sequences where histone methylation correlated with gene expression changes in response to hypoxia. These sequences guided the prediction of transcription factors associated with altered histones and gene expression, expanding beyond HIF-1 to multiple factors (Lee et al, 2017).
Considering hypoxia's senescence-reducing effects, we found pre-exposure to 1.5% O2 extended the lifespan and potency of NK cells (Lim et al, 2020).
Building upon these intriguing observations, our inquiries then turned toward understanding whether the sustained elevation of methylated histones under hypoxia contributes to the modulation of cellular senescence. particularly within the framework of Oncogene-Induced Senescence (OIS).
In short, our dedicated efforts to uncover the connections between hypoxia, cellular senescence, and histone demethylases have revealed a complex web of interactions that hold significant importance. By studying these detailed mechanisms, we aim to better understand how cells react to changes in oxygen levels. This could potentially lead us to discover new ways to develop innovative treatments.
Members of the Jmj family exhibit diverse histone lysine demethylase (KDM) activities using O2 and 2-oxoglutarate (2OG) as cosubstrates. Each KDM is characterized by unique substrate specificities and Michaelis-Menten constant (Km) values for oxygen (O2) and 2-oxoglutarate (2OG). Consequently, the presence of hypoxic conditions and the limitation of O2 availability converge to elevate the global levels of methylated histones, revealing links hypoxia and histone methylation.
The histone code, a combination of histone tail modifications, influences chromatin processes like replication and transcription. This suggests that hypoxia and metabolic changes swiftly impact chromatin through histone demethylase regulation. Using ChIP-seq and RNA-seq analyses, we identified DNA sequences where histone methylation correlated with gene expression changes in response to hypoxia. These sequences guided the prediction of transcription factors associated with altered histones and gene expression, expanding beyond HIF-1 to multiple factors (Lee et al, 2017).
Considering hypoxia's senescence-reducing effects, we found pre-exposure to 1.5% O2 extended the lifespan and potency of NK cells (Lim et al, 2020).
Building upon these intriguing observations, our inquiries then turned toward understanding whether the sustained elevation of methylated histones under hypoxia contributes to the modulation of cellular senescence. particularly within the framework of Oncogene-Induced Senescence (OIS).
In short, our dedicated efforts to uncover the connections between hypoxia, cellular senescence, and histone demethylases have revealed a complex web of interactions that hold significant importance. By studying these detailed mechanisms, we aim to better understand how cells react to changes in oxygen levels. This could potentially lead us to discover new ways to develop innovative treatments.
(2) Hypoxia, Adipogenesis, and Lipid Metabolism
Stem cells often reside in hypoxic niches, helping to maintain their stemness and prevent differentiation. Our investigations revealed that hypoxia thwarts the formation of the enhancersome on the enhancer of PPARγ—a pivotal transcription factor in adipogenesis—by blocking C/EBPβ (Park et al, 2010, 2012). Furthermore, we observed that hypoxia suppresses adipogenesis by inducing anti-adipogenic cytokines such as Wnt10b (Park, 2013) and Pref-1 (Moon et al, 2018), in a HIF-2α and HIF-1α-dependent manner, respectively. Another intriguing discovery is that Wnt3a impedes the formation of the enhancersome on the PPARγ enhancer by disrupting TEAD4-GR positive circuits (Park et al, 2019).
In the intricate choreography of hypoxic responses, HIF-1α takes center stage. It triggers the production of STAR13/DEC1, a transcriptional repressor that in turn suppresses a master adipogenic transcription factor, C/EBPs (Choi et al, 2008).
Our exploration also extended to the realm of obesity's impact. We observed that obesity, which enlarges adipocytes, prompts the secretion of Wnt5a into the bloodstream. This effect is orchestrated by the activation of YAZ/TAZ transcription factors, as highlighted in Lee's work in 2022.
In the intricate choreography of hypoxic responses, HIF-1α takes center stage. It triggers the production of STAR13/DEC1, a transcriptional repressor that in turn suppresses a master adipogenic transcription factor, C/EBPs (Choi et al, 2008).
Our exploration also extended to the realm of obesity's impact. We observed that obesity, which enlarges adipocytes, prompts the secretion of Wnt5a into the bloodstream. This effect is orchestrated by the activation of YAZ/TAZ transcription factors, as highlighted in Lee's work in 2022.
(3) Inhibitors of Oxygen-Dependent Dioxygenases
Our research has focused on understanding the relationship between function and structure in oxygen-dependent dioxygenases, specifically PHD2 and FIH-1. The pivotal role of Fe(II) in catalytic activities prompted our investigation into the effects of divalent chelators, such as TPEN and Clioquinol, which deplete this essential element (Choi, 2005; Moon, 2010; Choi, 2006).
To measure the activities of PHD and FIH-1, we pioneered a fluorescence polarization-based interaction assay system (Cho, 2005, 2007). This system enabled us to explore potential regulators among natural compounds (Cho, 2008). Notably, Baicalein emerged as an activator (Cho, 2008), while Icariside (Choi, 2008), β-lapachone (Park et al, 2014), Menadione, and ethacrynic acid (Na et al, 2013) were found to inhibit HIF-1α.
Continuing our investigation, we discovered that Clioquinol occupies the catalytic core of FIH-1, specifically the site where 2OG(α-KG) and O2 are coordinated (Moon et al, 2010). However, the same interaction was not observed with PHD2, reflecting structural differences in their catalytic pockets (Choi et al, 2006). Intriguingly, Clioquinol's inhibitory effect on Ubx, a Zn-containing subunit of VHL-E3 ligase, stabilizes HIF-1α. Consequently, Clioquinol mimics hypoxic conditions, activating HIF-1α and prompting the expression of hypoxic target genes.
Expanding our understanding, we found that Clioquinol also inhibits the jmjC-domains containing 2OGX family, which includes FIH-1 (Moon et al 2022).
In summary, our investigations into oxygen-dependent dioxygenases and their inhibitors provide valuable insights into the intricate mechanisms that govern cellular responses to hypoxia. These findings contribute to a broader comprehension of regulatory pathways and potential avenues for therapeutic interventions.
To measure the activities of PHD and FIH-1, we pioneered a fluorescence polarization-based interaction assay system (Cho, 2005, 2007). This system enabled us to explore potential regulators among natural compounds (Cho, 2008). Notably, Baicalein emerged as an activator (Cho, 2008), while Icariside (Choi, 2008), β-lapachone (Park et al, 2014), Menadione, and ethacrynic acid (Na et al, 2013) were found to inhibit HIF-1α.
Continuing our investigation, we discovered that Clioquinol occupies the catalytic core of FIH-1, specifically the site where 2OG(α-KG) and O2 are coordinated (Moon et al, 2010). However, the same interaction was not observed with PHD2, reflecting structural differences in their catalytic pockets (Choi et al, 2006). Intriguingly, Clioquinol's inhibitory effect on Ubx, a Zn-containing subunit of VHL-E3 ligase, stabilizes HIF-1α. Consequently, Clioquinol mimics hypoxic conditions, activating HIF-1α and prompting the expression of hypoxic target genes.
Expanding our understanding, we found that Clioquinol also inhibits the jmjC-domains containing 2OGX family, which includes FIH-1 (Moon et al 2022).
In summary, our investigations into oxygen-dependent dioxygenases and their inhibitors provide valuable insights into the intricate mechanisms that govern cellular responses to hypoxia. These findings contribute to a broader comprehension of regulatory pathways and potential avenues for therapeutic interventions.
(4) Signals Regulating HIF-1α and Oxygen-Dependent Dioxygenases
Our laboratory has extensively explored endogenous molecules that play pivotal roles in the regulation of HIF-1α activity. Notably, we've investigated how MAPK (p42/p44) enhances transactivity without impacting HIF-1α stability (Hur, 2001; Lee, 2002). Additionally, our research has unveiled the influence of Hsp90 on the DNA binding ability of the HIF-1α/Arnt heterodimer (Hur, 2002). Moreover, we've uncovered a significant role played by the Src kinase pathway. This pathway stabilizes HIF-1α by inducing ROS production, which in turn inhibits two oxygen-dependent dioxygenases, HIF-1α- specific Prolyl hydroxylase 2 (PHD2) and Factor-inhibiting HIF-1a (FIH-1) (Lee, 2011).
Through our research, we're unraveling the intricate network of signals that govern HIF-1α, PHD2 and FIH-1, shedding light on the multifaceted mechanisms that orchestrate cellular responses to changing oxygen levels.
Through our research, we're unraveling the intricate network of signals that govern HIF-1α, PHD2 and FIH-1, shedding light on the multifaceted mechanisms that orchestrate cellular responses to changing oxygen levels.
