Control of TH17/Treg Balance by Hypoxia-Inducible Factor 1

The hypoxia-induced increase in IL-17A+ cells is abrogated in HIF-1α−/− T cells.

“This increase was abrogated in HIF-1α −/− T cells (Figure 2D and S2E)”

IL-17A+ cell population is significantly increased upon overexpression of HIF-1α under TH17 skewing conditions.

“The IL-17A+ cell population was also significantly increased upon overexpression of HIF-1α under TH17 skewing conditions (Figure 2C, right panel).”

Increasing amounts of HIF-1α plasmid cause corresponding increases in RORγt promoter activity, particularly upon PMA and ionomycin stimulation.

“Transfection of Jurkat cells with the RORγt promoter-driven reporter construct, together with increasing amounts of HIF-1α plasmid indeed caused corresponding increases in RORγt promoter activity, particularly upon PMA and ionomycin stimulation (Figure S3C).”

mRNA expression of IL-17F and IL-23R is much lower in HIF-1α−/− T cells than WT T cells.

“The mRNA expression of other TH17-related genes such as IL-17F and IL-23R was also much lower in HIF-1α −/− T cells than WT T cells”

Under TH17-skewing, a higher proportion of IL-17A+ cells is observed in hypoxic compared to normoxic culture conditions.

“after TH17-skewing we observed a higher proportion of IL-17A+ cells in hypoxic compared to normoxic culture conditions.”

Stat3-deficient T cells cultured under TH17 skewing conditions for 4 days have very little HIF-1α protein detected by Western blot.

“after isolating CD4+CD62LhighCD25-(naïve) Stat3-deficient T cells from CD4-cre x Stat3flox/flox mice and culturing them under TH17 skewing conditions for 4 days, very little HIF-1α protein was detected by Western blot (Figure 1E).”

No significant differences in IFN-γ or IL-4 are seen between WT and HIF-1α−/− T cells under TH1 or TH2 skewing conditions.

“no significant differences in IFN-γ or IL-4 were seen between WT and HIF-1α−/− T cells under TH1 or TH2 skewing conditions (Figure S2A)”

HIF-1α−/− T cells cultured under TH17 conditions display a marked reduction in IL-17A+ cells.

“these HIF-1 deficient T cells displayed a marked reduction in IL-17A+ cells.”

HIF-1α activates the human RORγt promoter similarly to the mouse.

“Luciferase assays using the human sequence demonstrated that HIF-1α activates this promoter in a similar fashion to that of the mouse (Figure S3D and S3E).”

CD4+ cells from WT and HIF-1α−/− groups show comparable proliferative capacity.

“CD4+ cells from both groups showed comparable proliferative capacity (Figure S2B).”

T-HIF-1−/− mice have normal development of CD4+ and CD8+ T cells, B cells and dendritic cells.

“T-HIF-1−/− mice had normal development of CD4+ and CD8+ T cells, B cells and dendritic cells (Figure S1).”

A HIF-1α mutant lacking the DNA binding domain fails to activate the wild type RORγt promoter.

“the expression of a HIF-1α mutant gene lacking the DNA binding domain failed to activate the wild type RORγt promoter (Figure 3B).”

WT T cells stimulated with TGF-β and IL-6 show significant induction of IL-17A protein.

“We observed significant induction of IL-17A protein by WT T cells stimulated with TGF-β and IL-6 (Figure 2A).”

Ectopic expression of HIF-1α substantially increases the percentage of IL-17A+ cells even in the absence of IL-6 and TGF-β.

“The ectopic expression of HIF-1α substantially increased the percentage of IL-17A+ cells even in the absence of the TH17-driving cytokines IL-6 and TGF-β (Figure 2C).”

HIF-1α overexpression-induced IL-17A is associated with upregulation of RORγt mRNA and protein.

“This induction of IL-17A was associated with the upregulation of both RORγt mRNA and protein (Figure S2).”

Mutated HIF-1α binding sites in the RORγt promoter have much lower luciferase activity compared to wild type RORγt promoter.

“The mutated constructs had much lower luciferase activity compared to that of a wild type RORγt promoter-driven luciferase reporter (Figure 3A).”

HIF-1α−/− T cells show a dramatic increase in proportion of Foxp3+ cells.

“we also noted a dramatic increase in the proportion of Foxp3+ cells in HIF-1α −/− T cells (Figure 2A).”

Recruitment of HIF-1α to these regions is dependent on RORγt since it is abrogated in T cells from RORγt knockout mice.

“This recruitment of HIF-1α was dependent on RORγt since it was abrogated in T cells from RORγt knockout mice (Figure S5A–D).”

GST-HIF-1α (amino acids 1-80), but not GST alone, binds RORγt.

“GST-HIF-1α (amino acids1–80), rather than GST alone, was bound to RORγt (Figure S4F).”

HIF-1α and Foxp3 physically interact in co-transfected 293T cells.

“Immunoprecipitation and Western blot analysis of 293 T cells co-transfected with HIF-1α and Foxp3, in fact, demonstrated a physical interaction between these two molecules (Figure S7A).”

Expression of wild type HIF-1α in the presence of RORγt results in significantly increased IL-17 promoter reporter activity over that induced by RORγt alone.

“The expression of wild type HIF-1α in the presence of RORγt resulted in significantly increased reporter gene activity over that induced by RORγt alone (Figure 4A).”

Foxp3+ cells are significantly decreased under hypoxic conditions relative to normoxia when T cells are cultured with TGF-β and IL-2.

“T cells were thus cultured with TGF-β and IL-2 under hypoxic conditions. Foxp3+ cells were significantly decreased under these hypoxic conditions relative to normoxia (Figure 5D).”

Foxp3 mRNA levels in WT and HIF-1α−/− T cells stimulated under TH17 skewing conditions are essentially identical.

“Foxp3 mRNA levels in WT and HIF-1α −/− T cells stimulated under TH17 skewing conditions were essentially identical (Figure 5A).”

HIF-1α enhances TH17 development.

“HIF-1α enhances TH17 development through direct transcriptional activation of RORvt, and via tertiary complex formation with RORvt and p300 recruitment to the IL17 promoter, thereby regulating TH17 signature genes.”

A HIF-1α mutant with a C-terminal deletion of the p300 binding domain fails to synergize with RORγt and p300 in activation of the IL-17A promoter.

“a HIF-1α mutant with a C-terminal deletion of the p300 binding domain (Arany et al., 1996) failed to synergize with RORγt and p300 in the activation of the IL-17A promoter”

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Mice with HIF-1α deficient T cells are resistant to induction of TH17-dependent experimental autoimmune encephalitis associated with diminished TH17 and increased Treg cells.

“Mice with HIF-1α deficient T cells are resistant to induction of TH17-dependent experimental autoimmune encephalitis associated with diminished TH17 and increased Treg cells.”

The HIF-1α binding domain on Foxp3 maps to the C-terminus of Foxp3.

“The HIF-1α binding domain was further mapped to the C-terminus of Foxp3 (Figure S7B)”

HIF-1α is recruited to several other putative RORγt binding regions, including CNS2.

“ChIP analysis revealed that HIF-1α was recruited to several other putative RORγt binding regions, including CNS2.”

In T-HIF-1−/− mice, steady-state levels of Foxp3+ cells in the lamina propria of the gut are significantly increased compared to controls.

“steady state levels of Foxp3+ cells in the lamina propria of the gut, which, as indicated above (Koch, 2002), is relatively hypoxic, are significantly increased in T-HIF-1−/− mice (Figure S6A–D).”

This binding is specific since no significant signal is detected at a non-RORγt binding region within the IL-17A promoter.

“This binding, as analyzed by ChIP, was specific since no significant signal could be detected at a non-RORγt binding region within the IL-17A promoter.”

In HIF-1α+/+ T cells, retroviral RORγt expression induces a significantly higher proportion of IL-17A+ cells (45.7%) under non-skewing conditions compared to control retrovirus recipients (0.72%).

“In HIF-1α+/+ T cells, retroviral RORγt expression induced a significantly higher proportion of IL-17A+ cells (45.7%) under non-skewing conditions, compared to control retrovirus recipients (0.72%) (Figure 3D and 3E, left panels).”

Ectopic RORγt expression in HIF-1α−/− T cells induces a strikingly diminished population of IL-17A+ cells (1.33%).

“However, ectopic RORγt expression in HIF-1α−/− T cells induced a strikingly diminished population of IL-17A+ cells (1.33%) (Figure 3E, right panel).”

Only GST fusions of the HIF-1α N-terminus (1-80 aa), but not GST alone or other HIF-1α fragments, successfully pull down RORγt.

“Only GST fusions of the HIF-1α N-terminus (1–80 aa), but not GST alone or other HIF-1α fragments, successfully pulled down RORγt (Figure 4C).”

Histones H3 and H4 around the IL-17A promoter region are highly acetylated in WT compared to HIF-1−/− T cells under TH17-inducing conditions.

“ChIP assays revealed that histones H3 and H4 around the IL-17A promoter region were highly acetylated in WT compared to HIF-1−/−T cells under TH17-inducing conditions (Figure 4G).”

A HIF-1α mutant with a characterized DNA binding domain deletion shows no defect in inducing reporter gene activity.

“a HIF-1α mutant with a characterized DNA binding domain deletion (Arany et al., 1996) showed no defect in inducing reporter gene activity”

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Wild type p300, but not Δp300, can synergistically enhance IL-17A promoter activity in the presence of HIF-1α and RORγt.

“Wild type p300, but not Δp300 could synergistically enhance IL-17A promoter activity in the presence of HIF-1α and RORγt (Figure S5E).”

Endogenous HIF-1α and Foxp3 physically interact in iTreg cells.

“This interaction between HIF-1α and Foxp3 was further confirmed by endogenous co-IP in iTreg cells (Figure 5E).”

Under steady state conditions, T-HIF-1−/− mice have reduced proportions of IL-17A+ cells in the lamina propria.

“We found that, under steady state conditions, T-HIF-1−/− mice had reduced proportions of IL-17A+ cells in the lamina propria (Figure S6A–D)”

HIF-1α−/− T cells cultured under Treg skewing conditions (TGF-β plus IL-2) express substantially more Foxp3 than WT T cells.

“HIF-1α −/− T cells cultured under Treg conditions also expressed substantially more Foxp3 than did WT T cells (Figure 5B and 5C).”

This regulation occurs under both normoxic and hypoxic conditions.

“Importantly this regulation occurs under both normoxic and hypoxic conditions.”

Similar co-localized binding of RORγt, HIF-1α and p300 occurs at the promoters of IL-17F and IL-23R.

“we observed similar co-localized binding of RORγt, HIF-1α and p300 at the promoters of the TH17 signature genes IL-17F and IL-23R (Figure 4E).”

A HIF-1α mutant with a deletion in its p300 binding domain fails to activate the IL-17A promoter.

“Furthermore, a HIF-1α mutant with a deletion in its p300 binding domain (Arany et al., 1996) fails to activate the IL-17A promoter.”

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RORγt, HIF-1α and p300 bind to the IL-17A promoter during TH17 differentiation.

“we detected localized binding of RORγt, HIF-1α and p300 to the IL-17A promoter determined using primers flanking the RORγt-binding site located at the IL-17A promoter region (Figure 4D).”

• Also stated in: § Abstract · plain

  “HIF-1α enhances TH17 development through direct transcriptional activation of RORvt, and via tertiary complex formation with RORvt and p300 recruitment to the IL17 promoter, thereby regulating TH17 signature genes.”

HIF-1α co-immunoprecipitates with RORγt when Flag-tagged HIF-1α and Myc-tagged RORγt are co-expressed in Jurkat T cells.

“HIF-1α was found to co-immunoprecipitate (co-IP) with RORγt (Figure S4E).”

Hyper-acetylated histones H3 and H4 are associated with the promoters of TH17 signature genes IL-17F and IL-23R in WT, but not in HIF-1α−/−, TH17 cells.

“Similarly, hyper-acetylated histones H3 and H4 were associated with the promoter of TH17 signature genes IL-17F and IL-23R in WT, but not in HIF-1α −/−, TH17 cells (Figure S6E and S6F).”

IL-17A production in Jurkat T cells co-transfected with RORγt, HIF-1α and p300 is further increased under hypoxic conditions.

“IL-17A production in Jurkat T cells co-transfected with RORγt, HIF-1α and p300 was further increased under hypoxic conditions (Figure 4F).”

Endogenous HIF-1α and RORγt co-immunoprecipitate in T cells cultured under TH17-skewing conditions.

“The association between HIF-1α and RORyt was further confirmed by co-IP of endogenous HIF-1α and RORyt in T cells cultured under TH17-skewing conditions (Figure 4B).”

TH17 differentiation is enhanced under hypoxia in a HIF-1α-dependent manner.

“we found that TH17 differentiation is enhanced under hypoxia in a HIF-1α-dependent manner.”

RORγt protein levels remain unchanged upon co-transfection with HIF-1α in 293T cells.

“RORγt protein levels remained unchanged upon co-transfection with HIF-1α (Figure S7D).”

At peak disease, WT mice have higher proportions of IL-17+ CD4+ T cells in lymph node, spleen, and CNS than T-HIF-1α−/− mice.

“At peak disease, lymph node-, spleen- and central nervous system (CNS)-infiltrating CD4+ T cells from WT mice contained higher proportions of IL-17+ cells compared to those of T-HIF-1α −/− mice (Figure 6B and 6C).”

HIF-1α protein is readily detectable in TH17 cells under normoxia.

“HIF-1α protein is readily detectable in TH17 cells under normoxia”

T-HIF-1α−/− mice are highly resistant to MOG35-55-induced EAE compared to WT mice.

“WT mice immunized with MOG35–55 developed EAE, while T-HIF-1α −/− mice were highly resistant (Figure 6A).”

• Also stated in: § DISCUSSION · boosted

  “Our in vivo findings demonstrate that mice with HIF-1α−/− T cells are resistant to induction of EAE, a TH17-dependent disease whose remission is dependent upon Treg cells (Schraml et al., 2009).”

Under normoxia, TH17 differentiation is significantly impaired without HIF-1α.

“the experiments utilizing HIF-1α−/− T cells confirm that under such conditions TH17 differentiation is significantly impaired without HIF-1α.”

Hypoxic culture significantly enhances Foxp3 degradation in primary iTregs.

“Hypoxic culture significantly enhanced both Foxp3 ubiquitination and degradation in these cells (Figure 5I and 5J).”

HIF-1α-mediated Foxp3 degradation is completely inhibited by a proteasome inhibitor.

“HIF-1α mediated Foxp3 degradation was completely inhibited in the presence of a proteasome inhibitor (Figure S8B).”

Hypoxic culture significantly enhances Foxp3 ubiquitination in primary iTregs.

“Hypoxic culture significantly enhanced both Foxp3 ubiquitination and degradation in these cells (Figure 5I and 5J).”

MG132 prevents ubiquitin-mediated Foxp3 degradation in iTreg cells under hypoxia.

“this ubiquitin-mediated Foxp3 degradation process could be prevented by addition of the proteasomal inhibitor MG132 to iTreg cells under hypoxia.”

During the recovery phase of EAE, T-HIF-1−/− mice show a decrease in the proportion of IL-17+ CD4+ cells.

“T-HIF-1−/− mice showed a significant increase in the percentage of CD4+ Foxp3+ cells during the recovery phase of disease (21 days post-injection), concomitant with a decrease in the proportion of IL-17+ CD4+ cells in T-HIF-1−/−animals (Figure 6D and 6E).”

The Foxp3 binding domain in HIF-1α is within the N-terminal 80 amino acids.

“the Foxp3 binding domain in HIF-1α was found to be within the N-terminal 80 amino acids by GST pull-down experiments (Figure S7C).”

Knockdown of PHD2 with siRNA eliminates the ability of wild-type HIF-1α to mediate Foxp3 degradation.

“Knockdown of PHD2 with siRNA also eliminated the ability of wild type HIF-1α to mediate the degradation of Foxp3 (Figure S8A).”

A non-proline hydroxylatable HIF-1α (CA5-HIF-1α) is incapable of mediating Foxp3 degradation.

“Similar co-transfection assays using a HIF-1α plasmid containing an oxygen dependent domain (ODD) deletion (CA5-HIF-1α) further demonstrated that a non-proline hydroxylatable HIF-1α was incapable of mediating Foxp3 degradation (Figure 5G and 5H).”

A HIF-1α mutant with prolines 402 and 564 mutated to alanines fails to induce Foxp3 degradation.

“The expression of P402A and P564A HIF-1α failed to induce Foxp3 degradation (Figure 5G and 5H).”

During the recovery phase of EAE (21 days post-injection), T-HIF-1−/− mice show a significant increase in the percentage of CD4+ Foxp3+ cells.

“T-HIF-1−/− mice showed a significant increase in the percentage of CD4+ Foxp3+ cells during the recovery phase of disease (21 days post-injection), concomitant with a decrease in the proportion of IL-17+ CD4+ cells in T-HIF-1−/−animals (Figure 6D and 6E).”

Absence of HIF-1 does not significantly affect IFN-γ or IL-4 production in T cells cultured under Th1 or Th2 conditions, respectively.

“We found that neither IFN-y nor IL-4 production was significantly affected by the absence of HIF-1 in T cells cultured under Th1 or Th2 conditions, Respectively.”

Increasing amounts of Flag-tagged HIF-1α progressively decrease Foxp3 protein levels in co-transfected 293T cells.

“upon co-transfection of 293T cells with Foxp3 and increasing amounts of Flag-tagged HIF-1α, Foxp3 protein levels progressively decreased (Figure 5F).”

HIF-1α might facilitate TH17 development through upregulation of RORγt.

“These results support the notion that HIF-1α might facilitate TH17 development through the upregulation of RORγt.”

Hypoxia-induced enhancement of TH17 differentiation is HIF-1α-dependent.

“indicating that the hypoxia-induced enhancement of TH17 differentiation is HIF-1α-dependent.”

HIF-1α regulates multiple genes in the TH17 program.

“indicating that HIF-1α regulates multiple genes in the TH17 program (Figure 2B).”

• Also stated in: § Abstract · plain

  “HIF-1α enhances TH17 development through direct transcriptional activation of RORvt, and via tertiary complex formation with RORvt and p300 recruitment to the IL17 promoter, thereby regulating TH17 signature genes.”

HIF-1α expression is induced in T cells during TH17 differentiation in a Stat3-dependent manner.

“These findings confirm that HIF-1α expression is induced in T cells during TH17 differentiation in a Stat3-dependent manner.”

DNA binding is dispensable for HIF-1α-mediated IL-17A expression.

“which implies that DNA binding is dispensable for HIF-1α-mediated IL-17A expression.”

HIF-1α might be involved in Foxp3 protein modulation in addition to its role in transcriptional activation of the TH17 pathway.

“This implies that HIF-1α might be involved in Foxp3 protein modulation in addition to its role in the transcriptional activation of the TH17 pathway.”

HIF-1 regulates the balance between Treg and TH17 differentiation.

“Here, we show that hypoxia-inducible factor 1 (HIF-1), a key metabolic sensor, regulates the balance between T regulatory (Treg) and TH17 differentiation.”

HIF-1α attenuates Treg development by binding Foxp3 and targeting it for proteasomal degradation.

“Concurrently, HIF-1α attenuates Treg development by binding Foxp3 and targeting it for proteasomal degradation.”

• Also stated in: § INTRODUCTION · plain

  “In addition, HIF-1α inhibits Treg differentiation through an active process that targets Foxp3 protein for degradation.”

Foxp3 can bind to the RORγt protein and antagonize its ability to bind DNA, pushing T cell differentiation away from TH17 and towards Treg.

“Foxp3 can in turn bind to the RORγt protein and antagonize its ability to bind DNA, thus pushing T cell differentiation away from the TH17 transcriptional program and towards the Treg lineage.”

HIF-1α's ability to promote IL-17A production is modulated by oxygen tension.

“These results suggest that, while active under normoxic conditions, HIF-1α’s ability to promote IL-17A production is indeed modulated by oxygen tension.”

p300 is required for the full function of RORγt and HIF-1α in regulation of IL-17A gene expression.

“implying that p300 is required for the full function of RORγt and HIF-1α in the regulation of IL-17A gene expression (Figure S5E).”

p300 possesses histone acetyltransferase (HAT) activity.

“p300 possesses histone acetyltransferase (HAT) activity (Thompson et al., 2004).”

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HIF-1α directly transactivates RORγt gene expression.

“These results collectively indicate that HIF-1α directly transactivates RORγt gene expression.”

• Also stated in: § Abstract · plain

  “HIF-1α enhances TH17 development through direct transcriptional activation of RORvt, and via tertiary complex formation with RORvt and p300 recruitment to the IL17 promoter, thereby regulating TH17 signature genes.”

RORγt and HIF-1α, through recruitment of p300 to the IL-17A promoter, acetylate histones to open chromatin structure and facilitate gene expression.

“These findings indicate that RORγt and HIF-1α, through recruitment of p300 to the IL-17A promoter, acetylate histones to “open” the chromatin structure and facilitate gene expression.”

There is a direct interaction between HIF-1α and RORγt in vitro.

“Taken together, these results suggested a direct interaction between the two proteins in vitro.”

HIF-1α has a potential role in promoting TH17 development in the context of microbial influences.

“indicating a potential role for HIF-1α in promoting TH17 development in the context of microbial influences.”

TH17 and Treg cells share a common requirement for TGF-β in their differentiation despite expressing distinct transcriptional regulators (RORγt vs. Foxp3) and demonstrating opposing functions.

“TH17 and Treg cells share a common requirement for TGF-p in their differentiation requirements despite expressing distinct transcriptional regulators (RORγt vs. Foxp3 respectively) and demonstrating opposing functions (inflammatory vs. anti-inflammatory)(Bettelli et al., 2006; Dong, 2008; Littman and Rudensky, 2010; Mangan et al., 2006; O'Quinn et al., 2008; Veldhoen et al., 2006).”

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• cites Littman and Rudensky, 2010Not checked yet

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Hypoxic culture conditions have opposite effects on IL-17 and Foxp3 induction.

“Thus, hypoxi culture conditions have opposite effects on IL-17 and Foxp3 induction.”

The gut is relatively hypoxic under physiologic conditions.

“the gut, which is known to be relatively hypoxic under physiologic conditions (Koch, 2002)”

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Under both Treg- and TH17-skewing conditions, HIF-1α down-regulates Foxp3 protein levels despite no effect on Foxp3 mRNA levels.

“These findings suggest that under both Treg- and TH17-skewing conditions, HIF-1α down-regulates Foxp3 protein levels despite demonstrating no effect on Foxp3 mRNA levels (Figure 5A).”

HIF-1α can regulate RORγt gene expression.

“These results suggest that HIF-1α can regulate RORγt gene expression.”

In response to TGF-β in vitro as well as in vivo, many T cells co-express RORγt and Foxp3.

“In response to TGF-β in vitro as well as in vivo, many T cells co-express RORγt and Foxp3 (Veldhoen et al., 2006; Yang et al., 2008a).”

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HIF-1α is transcriptionally activated via Stat3 signaling in differentiating T cells.

“Collectively, these in vitro differentiation studies, alongside our transcriptional and biochemical analyses, suggest a model in which HIF-1α is transcriptionally activated via Stat3 signaling in differentiating T cells, resulting in the enhancement of the TH17 genetic program via a RORγt/p300-dependent mechanism and repression of the Treg transcriptional program through induced degradation of Fox”

HIF-1α mediates Foxp3 degradation via PHD-VHL-ubiquitin-mediated proteasomal degradation.

“Collectively, these results are compatible with a scenario in which HIF-1α mediates Foxp3 degradation via PHD-VHL-Ubiquitin-mediated proteasomal degradation, although future studies are needed to delineate precisely how HIF-1α protein turnover dynamics in T cells modulate Foxp3 levels.”

HIF-1α represses the Treg transcriptional program through induced degradation of Foxp3.

“Collectively, these in vitro differentiation studies, alongside our transcriptional and biochemical analyses, suggest a model in which HIF-1α is transcriptionally activated via Stat3 signaling in differentiating T cells, resulting in the enhancement of the TH17 genetic program via a RORγt/p300-dependent mechanism and repression of the Treg transcriptional program through induced degradation of Fox”

HIF-1α enhances the TH17 genetic program via a RORγt/p300-dependent mechanism.

“Collectively, these in vitro differentiation studies, alongside our transcriptional and biochemical analyses, suggest a model in which HIF-1α is transcriptionally activated via Stat3 signaling in differentiating T cells, resulting in the enhancement of the TH17 genetic program via a RORγt/p300-dependent mechanism and repression of the Treg transcriptional program through induced degradation of Fox”

In vivo experiments validate the role of HIF-1α identified by in vitro studies.

“These experiments validate the role of HIF-1α identified by our in vitro studies and further suggest the possibility for metabolic modulation of autoimmune diseases.”

HIF-1α promotes TH17 development through direct transcriptional activation of RORγt.

“Specifically, HIF-1α promotes TH17 development through: a) direct transcriptional activation of RORγt, the major TH17 transcription factor, and b) direct collaboration with RORγt to activate TH17 signature genes, such as IL-17A, through mechanisms involving p300 recruitment and histone acetylation.”

The lamina propria of the gut is relatively hypoxic.

“the lamina propria of the gut, which, as indicated above (Koch, 2002), is relatively hypoxic”

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HIF-1α plays a role in modulating the TH17/Treg balance.

“This altered balance between Treg cells and TH17 cells exactly parallels our in vitro culture studies and suggests that HIF-1α indeed plays a role in modulating the TH17/Treg balance.”

HIF-1α directly collaborates with RORγt to activate TH17 signature genes such as IL-17A through mechanisms involving p300 recruitment and histone acetylation.

“Specifically, HIF-1α promotes TH17 development through: a) direct transcriptional activation of RORγt, the major TH17 transcription factor, and b) direct collaboration with RORγt to activate TH17 signature genes, such as IL-17A, through mechanisms involving p300 recruitment and histone acetylation.”

HIF-1α inhibits differentiation toward the Treg lineage through a distinct, non-transcriptional mechanism.

“HIF-1α inhibits differentiation toward the Treg lineage through a distinct, non-transcriptional mechanism.”

HIF-1 targets Foxp3 for ubiquitination and proteasomal degradation using the same ubiquitin ligase system responsible for degradation of HIF-1α itself.

“We show that HIF-1 targets Foxp3 for ubiquitination and proteasomal degradation, using the same ubiquitin ligase system that is responsible for degradation of HIF-1α itself (Figure 7).”