Hypoxia inducible factor (hif)

HIF-1 -expressed uniquely in response to hypoxia & it promote or repress the transcription.

1. ©[email protected]
Biology of Hypoxia Biology of Hypoxia Biology of Hypoxia Biology of Hypoxia Inducible Inducible Inducible Inducible Factors (HIFs) Factors (HIFs) Factors (HIFs) Factors (HIFs)
DrDharmendra
Deptof Physiology
AFMC

2. EEEE
Scope Scope Scope Scope
•Introduction
•History
•Structure
•Isoformsof HIF
•Regulation of synthesis
•Functions
•Applied
•Recent Advances
•Conclusion

3. 3
Introduction Introduction Introduction Introduction
•Hypoxia is an essential developmental and physiolog ical stimulus
•Cellular response to changes in oxygen tension
•Regulated by an oxygen-regulated transcription factor-h ypoxia-inducible
factor (HIF)
•Essential roles in a diverse range of biological pr ocesses
•HIF becomes active under specific conditions, inclu ding low oxygen
(hypoxic) stress.

4. 4
Introduction Introduction Introduction Introduction
•HIF-1 -expressed uniquely in response to hypoxia
•Promote or repress the transcription
•Complete deficiency of HIF-1α resulted in developmental arrest and
lethality of embryos (mice)
•Neural tube defects, cardiovascular malformations
•Master regulator of cellular O
2homeostasis

5. HHHH
History History History History
•1992: Semenzaand Wang discovered HIF1

6. IIII
Structure Structure Structure Structure
•Heterodimericcomplex
•Basic Helix-loop-helix-PAS
domain (bHLH-PAS)
transcription factor
•One α-subunit and one β-
subunit
•Ubiquitous Expression
HIF-1αααα
hypoxia
Pol II
complex
CBP/p300
HIF-1ββββ
HIF-1

7. 7
Isoforms of HIF Isoforms of HIF Isoforms of HIF Isoforms of HIF
•HIF 1= HIF 1α-subunit + HIF 1β-subunit
•HIF 2= HIF 2α-subunit + HIF 1β-subunit
•HIF 3= HIF 3α-subunit + HIF 1β-subunit
•HIF-1β or ARNT (aryl hydrocarbon receptor nuclear t ranslocator
protein)
•HIF-1 and HIF-2 have different physiological roles.

8. 8
Genes Genes Genes Genes
encoding distinct encoding distinct encoding distinct encoding distinct
HIFHIFHIF HIF
αααα
isoforms isoforms isoforms isoforms
•Three genes encoding distinct
HIFαisoforms exist in humans:
•HIF1A, encoding HIF 1α;
•EPAS1, encoding HIF2α;
•and HIF3A, which is expressed as
multiple HIF3α variants.

9. LLLL
HIF 1 HIF 1 HIF 1 HIF 1αααα----subunit subunit subunit subunit
DNA binding
for
heterodimerization
Oxygen dependant
degradable domain
Pj
p300
/CBP
Pj
Pj
PHD FIH-1
•HIF 2α-subunit: Endothelial PAS protein/HIF like factor (HLF)/ HIF related
factor (HRF)
•HIF 3α-subunit: Opposite action from HIF 1α-subunit & HIF2α-subuni t.

10. 10
•HIF-αsubunits may mediate different adaptive responses t o hypoxia

11. 11
HIF hydroxylase Pathway HIF hydroxylase Pathway HIF hydroxylase Pathway HIF hydroxylase Pathway
•Hydroxylation •Interact with
VHL
•Ubiquitination
•Proteasomal
Degradation
Normoxia
Hypoxia

12. 12
HIF hydroxylase Pathway HIF hydroxylase Pathway HIF hydroxylase Pathway HIF hydroxylase Pathway
•Hydroxylation •Interact with
VHL
•Ubiquitination
•Proteasomal
Degradation
Normoxia
Hypoxia

13. 13
Regulation of HIF Regulation of HIF Regulation of HIF Regulation of HIF
•Thus, stability and activity of The HIFs are modula ted by
hydroxylation (by both PHDs & FIH-1)
•Other mechanism: HIF-1α-upregulatedby the mammalian
target of rapamycin(mTOR) via an mTORsignalingpathw ay.
Pj
Pj

14. DGDGDGDG
Functions of HIF system Functions of HIF system Functions of HIF system Functions of HIF system
1. Two major categories of proteins that are encoded
•That increase O2 delivery and decrease O2 consumption
2. “Turns on” genes needed for survival under hypoxi c conditions
3. Involves in functionally diverse responses
•Cell motility and differentiation
•Glucose metabolism
•Angiogenesis etc
4. In synthesis of proteins with opposing effects
•Growth factors and Pro-apoptotic mediation

15. 15
HIFHIFHIF HIF
----
1 Target Genes 1 Target Genes 1 Target Genes 1 Target Genes
These HIF-1 Target Genes can be classified into 3 ma in groups: •Group 1: O
2Delivery
•EPO, NOS2, VEGF
•Group 2: Glucose /Energy Metabolism
•LDH-A, PFK-L, Hexokinase
•Group 3: Cell Proliferation/Viability
•IGF-2

16. 16
RRRR
oles oles oles oles
of HIF in cell biology of HIF in cell biology of HIF in cell biology of HIF in cell biology
•Role of HIF-1αin cell biology.
1. Glucose metabolism
2. Embryonic development
3. Immunity

17. DJDJDJDJ
Role of HIF in Glucose metabolism Role of HIF in Glucose metabolism Role of HIF in Glucose metabolism Role of HIF in Glucose metabolism
•Mediates transition from oxidative
to glycolytic pathways
•Activates transcriptions of genes
encoding
•GLUT
•Glycolyticenzyme
•Pyruvatedehydrogenasekinase1
•LDHA
•The purpose: To prevent excess ROS
formation

18. 18
Hypoxia
Mitochondrial ROS
HIF-1αstabilization
Gene expression for LDHA & PDK1
Mitochondrial ROS

19. DLDLDLDL
Role in Role in Role in Role in EEEEmbryonic mbryonic mbryonic mbryonic Development Development Development Development
•Embrogenesis: <40 mmHg
•Metabolic shift to glycolysis during ESC–EpiSC
transition
•Zhou et al (2012) ESCs also undergo a metabolic
shift, regulated by HIF1a
•Mice lacking HIF1α-subunit died by embryonic
10.5 days
•However, severe hypoxia ………….. dysregulate
development.

20. 20
Role of HIF in immunity Role of HIF in immunity Role of HIF in immunity Role of HIF in immunity
•HIF-1α: promotes differentiation of TH17 cells
•B and T cell differentiation
•Similarly, mTOR-mediated upregulationof HIF1a -indu ce
differentiation of naive T cells to proinflammatory TH17 cells,

21. 21
Role in control of EPO Role in control of EPO Role in control of EPO Role in control of EPO
systhesis systhesis systhesis systhesis
•In mice: renal and liver EPO systhesisis HIF 2 depe ndent
•In high altitude: genetic variant of HIF2A gene
•Congenital polycyathemia:
•HIF1α& HIF2β
•Mutations in PHD2 and VHL gene

22. 22
Role As a therapeutic target
1. Anemia:
•Roxadustat, Vadadustat
•Iron chelatorssuch as desferrioxamine
(DFO)
2. Inflammation and cancer:
•HIF inhibitors
•Acriflavine

23. EFEFEFEF
Applied Applied Applied Applied
•Diseases in which HIF1 mediates protective response
•CAD
•Carotid body
•PAD
•Wound Healing
•Organ Transplantation rejection
•Diseases in which HIF1 activities contributes to pat hogenesis
•Cancer
•Pulmonary HTN

24. EGEGEGEG
Recent Advances Recent Advances Recent Advances Recent Advances
•PHD & FIH1 inhibitors
like DMOG
induces HIF activity and under trial
for CAD and PAD
•HIF inhibitors
are being
considered for cancer therapy
(4-OH-2-quinolone derivatives )
•ML-228 :
•HIF-1α-p300/CBP Inhibitors as
Anti-Cancer Agents
@ Mini Reviews in Medicinal Chemistry:Recent Advances in the Discovery of HIF-1α-p300/CBP Inhibitors as Anti-Cancer Agents, 2018

25. 25
Summary Summary Summary Summary
α
HIF-1 is a transcription factor that is composed of HIF-1ααααand HIF-1ββββ
subunits.
α
HIF-1ααααis degraded by proteasome viaVHL.
α
More than 100 target genes have been found to be r egulated by
HIF-1.
α
HIF-1 expression is positively correlated with tumor vascularity,
indicating HIF-1 plays a crucial role in tumor angi ogenesis
progression.

26. EIEIEIEI
Conclusion Conclusion Conclusion Conclusion
B
Essential for prenatal development and postnatal physiology.
B
Protective and pathogenic roles .
B
Central role in oxygen sensing and is therefore vital for survival of the
organism and rapid adaptation of cells to hypoxia B
The molecular blockade of HIF activity involves a cascade of enzyme-
mediated events B
Can induce gene transcription that might or might not be beneficial
B
The development of pharmacological approaches- therapeutic
benefit

27. 27
References References References References
•Guyton, 13
th
Ed
•Ganong’sReview of Medical physiology, 24
th
Ed
•The updated biology of hypoxia-inducible factor, Wa ng et all, 2012
•Journal of Cell Science; HIF at a glance, M. Christ iane Brahimi-Horn
•Annual reviews: Oxygen Sensing, Hypoxia-Inducible F actors, and
Disease Pathophysiology by Semenza2014