Examples Of Gene Regulation Flashcards
Whaat happens if an activator binds to an enhancer sequence?
It stabilizes the basal transcription apparatus (RNA pol, and the general transcription factors), and transcription levels increase
Many 1000s of bp May separate enhancer region and core promoter
Bind of activator to the enhancer increases efficiency of RNA pol. Transcription initiation
What are the 3 general ways transcription factors may act as repressors ?
- Competition
- Quenching
- Blocking
How May repressors perform competition?
May compete for enhancer sequence: activator vs repressor proteins to bind to the enhancer region which may reduce transcription levels
How May repressor proteins perform quenching?
Occurs when a repressor protein binds to abs interferes with the DNA-binding domain KD an activator protein
This reduces transcription levels.
How do repressor proteins perform blocking?
Occurs when the repressor protein binds to the activation domain of an activator protein and prevents it from interacting with the basal transcriptional machinery
Which species express the hypoxia inducible factor (HIF-1)?
Most, if not all, oxygen breathing species
Explain the hypoxia response
- Hypoxia is a reduction in the normal level of tissue oxygen tension, and it occurs during several patho physiological processes including tumor genesis
- HIF-1 activity leads to the Upregulation of genes that are involved in many aspects of cell survival, glucose metabolism, angiogenesis, cancer progression, and invasion
- Requires a coordinate response where many genes are switched on or switched off to cope with this challenge
- HIF-alpha and HIF-Beta transcription factors must dimerize, then bind to a specific DNA sequence called hypoxia response element (HRE) 5’ -TACGTG-3’
- HRE is found upstream on many different genes to regulate their concerted
What does HIF do?
Regulates gene expression
HIF- alpha inducible oxygen sensitive
HIF-beta (ARNT)-constitutive
Both of the above form two branches of attachment domain
Discuss prolyl hydroxylase relaxation to HIF-1
High oxygen - HIF-1alpha is hydroxylated by prolyl hydroxylase & quickly degraded by the proteosome
Low/no oxygen- HIF-1alpha stabilized, moves to the nucleus & dimerizes with HIF-1B to activate multiple genes that enhance oxygen delivery to tissues and/or energy supply via glycolysis
How does a hypoxia state(HIF-1) ?
Under pathologically low oxygen levels (hypoxia state), HIF-alpha isn’t degraded and will translocate into the cell nucleus
In the nucleus, HIF-alpha will hetero-dimerises with HIF-1B
The final HIF-1alphabeta dimer is able to bind the hypoxia-response element (HRE) Sequence which is found upstream of many genes which are required for the survival 9f cells during hypoxia
Explain HIF- 1 as a therapeutic target
- Anemia
- Inflammation
- Cancer
Stroke, solid cancer tumors, etc
Solid cancers are quick growing and hungry- they are often hypoxic - learning how to inhibit HIF-1alphs/HIF-1beta mediated gene expression may provide a way of selectively killing tumors
Hence the interest in hypoxia
What are glucocorticoids?
These are a major class of steroids
- Steroids are small hydrophobic molecules
- Involved in modulation of a large number of metabolic, cardiovascular, immune and behavioral functions
- Intracellular effects are mediated by the glucocorticoid receptor
Describe the glucocorticoid receptor
The glucocorticoid receptor is a zinc finger type TF
- The activated GR complex up-regulates the expression of anti-inflammatory genes in the nucleus and represses the expression of pro-inflammatory proteins in the cytosol
- Various synthetic glucocorticoids are available; used either as replacement therapy in glucocorticoid deficiency or to suppresses the immune system
- a key anti-inflammatory treatment
Describe the hormone response element (Cis element)
DNA sequence of the glucocorticoid response element:
5’ AGAACAnnnTGTTCT3’
3’TCTTGT nnn. ACAAGA5’
THE “n” represents any nucleotide
-note the inverted repeats
These Hormone Response Elements. (HREs) are DNA sequences found in the promoter and regulatory sequences of many genes
-Another example of how COORDINATED GENE REGULATION at manysites across the genome is accomplished in the eukaryotic cell
In the absence kf glucocorticoid (cortisol)…
The GR is held in the cytoplasm as part of an inactive multi-protein complex