Nrf2 Flashcards
- What is Nrf2, how is it regulated, and why does it promote cell survival - What are cyanoenone triterpenoids - How do cyanoenone triterpenoids activate Nrf2 - What is the evidence that Nrf2 protects against inflammation - What is itaconate and how does it activate Nrf2 - That Nrf2 is inactivated in certain viral infections - The effect of pharmacological Nrf2 acrtivators in viral infections
Nrf2
- normally bound to Keap1, which targets Nrf2 for ubiquitination and degradation by the proteasome
What is Nrf2
- TF
- regulates the cellular defense against toxic and oxidative insults
- regulates redox homeostasis
- involved in cellular processes e.g. metabolism and inflammation
- binds to ARE
How is Nrf2 regulated?
- complex transcriptional and post-translational network
- adaptation to various pathological stressors to maintain homeostasis
How does Nrf2 promote cell survival?
1) Antioxidant effects
2) Detoxification
3) Inflammation suppression
4) Proteostasis
How does Nrf2 exhibit antioxidant effects
activates SOD, catalase, glutathione peroxidase, and heme oxygenase-1 (HO-1); scavenge ROS and other free radicals that cause oxidative damage to cellular macromolecules
How does Nrf2 exhibit detoxification effects
regulates expression of phase II detoxification enzymes (e.g. GSTs, UGTs, NQO1); which conjugate and eliminate electrophilic xenobiotics and endogenous metabolites that can damage DNA
How does Nrf2 suppress inflammation
inhibits expression of pro-inflammatory cytokines and chemokines (IL-1B, IL-6, TNF-a, COX-2); reduces tissue damage and promotes tissue repair
Role of Nrf2 in proteostasis
regulates expression of molecular chaperones (HSPs) and proteasomal subunits that maintain protein folding and degradation; Nrf2 protects cells from apoptosis
Role of Nrf2 in redox homeostasis
Glutathione and thioredoxin biosynthesis and utilisation via positive regulation of:
- Glutathione S-transferases
- y-Glutamylcysteine synthestase
- Glutathione reductase 1
- Thioredoxin
- Thioredoxin reductase
NADPH regeneration and utilisation via positive regulation of:
- Malic enzyme 1
- Isocitrate dehydrogenase 1
- 6-Phosphogluconate dehydrogenase
- Glucose-6-phosphate dehydrogenase
Keap1 sensor
- cystine based
- suppresses Nrf2 transcriptional activity
- specifically binds Nrf2 to the amino-terminal regulatory domain
- antagonised by electrophilic agents
How do electrophilic inducers affect the Keap1 cycle
- disrupt the cycle by modifying sensor cysteines of Keap1, preventing Nrf2 ubiquitination and Keap1 regeneration
NQO1
- two-electron reductase responsible for detoxification of quinones and also bioactivation of certain quinones
- abnormally overexpressed in tumours
- intimately linked with carcinogenic processes
- selective anticancer therapy
What are cyanoenone triterpenoids
- potent users of NQO1 and Nrf2
- semi-synthetic derivatives
- abundant in plants
- used in wound dressing due to weak anti-inflammatory activity
Explain the linear correlation between suppression in the iNOS and the induction of NQO1
by activating Nrf2, we can suppress inflammation
Persistent activation of Nrf2
- promotes the progression of cancer
- promotes treatment resistance
- triggered by Keap1-inactivating mutations
- triggered by mutations in ETGE and DLG motifs
- triggered by epigenetic silencing of Keap1/disruption of Nrf2-Keap1 interaction
Transient activation of Nrf2
protect against cancer development
Nrf2 activators
- oltipraz (OPZ)
- curcumin (CUR)
- promote functions of antioxidants, phase II detoxification factors, and transducers
Nrf2 inhibitors
- luteolin
- ascorbic acid (AScA)
- trigonelline (Trg)
- downregulate drug detoxification/elimination enzymes
- sensitize cancer cells to chemotherapy
How do cyanoenone triterpenoids activate Nrf2
1) Keap1/Nrf2 dissociation: cyanoenone triterpenoids can covalently modify cysteine residues in Keap1, causing a conformational change disrupting the KEap1/Nrf2 interaction; preventing Nrf2 degradation
2) Nuclear translocation of Nrf2: once Nrf2 has dissociated from Keap1, it is transported to the nucleus; cyanoenone triterpenoids enhance Nrf2 nuclear accumulation by activating PKC pathway, phosphorylating Nrf2 and promoting nuclear translocation
3) Co-activator recruitment: in the nucleus, Nrf2 recruits CBP and p200 (co-activators), facilitating transcription of ARE-containing genes. Cyanoneone triterpenoids can enhance co-activator recruitment by increasing the acetylation of histones, promoting chromatin remodelling and facilitating transcription
What is the evidence that Nrf2 protects against inflammation
- genetic activation of Nrf2 protects against SSUV radiation-mediated inflammation
What is itaconate
- acid that is transported to cytoplasm using citrate transporter
- produced by activation of Irg1
- promotes anti-inflammatory
- can inhibit bacterial invastion as it can inhibit activity in bacteria
- weakly electrophilic
- involved in LPS-mediated stabilisation of nrf2
How does itaconate activate Nrf2
- via alkylation of Keap1
- 4-octyl itaconate activates nrf2 by causing 2,3-dicarboxypropylation of Keap1
- C151 is a sensor for 4-octyl itaconate
- Nrf2 activation potentiates macrophage response to LPS, favouring pathogen inactivation whilst attenuating IL1beta pro-inflammatory signalling
Nrf2 in viral infections
- Nrf2 is suppressed by COVID-19
- at later stage of infection strongly infected cells have high nrf2 activity as cells are using nrf2 to survive
What is the pharmacological effect of Nrf2 activators in viral infections
measure release of viral DNA
Nrf2 in glutathione and thioredoxin biosynthesis and utilization
positively regulates:
- glutathione S-transferases
- y-Glutamylcysteine synthetase
- Glutathione reductase 1
- Thioredoxin
- Thioredoxin reductase
Nrf2 in NADPH regeneration and utilisation
positively regulates:
- malic enzyme 1
- isocitrate dehydrogenase 1
- 6-phosphogluconate dehydrogenase
- glucose-6-phosphate dehydrogenas
Nrf2 in carbohydrate metabolism
positively regulates:
- UDP-glucose dehydrogenase
suppresses:
- pyruvate kinase
- glycerol phosphate dehydrogenase 2
Nrf2 in lipid metabolism
suppresses:
- ATP citrate lyase
- acteyl-coenzyme A carboxylase
- fatty acid synthase
- stearoyl-coenzyme A desaturase
- lipase
Nrf2 in amino acid metabolism
positively regulates:
- serine/glycine biosynthesis enzymes (PHGDH, PSAT1, SHMT2 via ATF4)
Nrf2 in pentose phosphate pathway / nucleotide metabolism
positively regulates:
- glucose-6-phosphate dehydrogenase
- 6-phosphogluconate dehydrogenase
- transaldolase
- transketolase
