DLA After Lecture 31 Flashcards
Tc factors as repressors
3 modes
Competition: repressor competes with activator for enhancer
Quenching: repressor binds to and interferes with the DNA-binding domain of activator
Blocking: repressor binds to the activation domain of activator and prevents it from interacting with the basal tc machinery
Hypoxia
Reduction in the normal level of tissue oxygen
Occurs during several pathophysiological process including tumorigenesis
Hypoxia response
HIF1 alpha and HIF1 beta transcription factors dimerize and bind to a DNA sequence called HRE = hypoxia response element 5’-TACGTG-3’
HRE is upstream on many different genes
Require a coordinate response where many genes are switched on or off
HIF 1
Hypoxia-inducible transcription factor
HIF1 alpha: O2 sensitive
HIF1 beta: constitutive
Prolyl hydroxylase
High oxygen: HIF1 alpha is hydroxylated and quickly degraded by the proteosome
Low/no oxygen: HIF1 alpha is stabilized, moves to the nucleus and dimerizes with HIF1 beta, activate HRE
HIF-1 as a therapeutic target to treat 3
Anemia Inflammation Cancer Stroke Solid cancer tumor: make it hypoxic
Glucocorticoids
Anti-inflammatory A major class of steroids, hydrophobic
Binds to GR intracellular: GR is a zinc-finger TF
Actiavted GR complex upregulates the expression o anti-inflammatory genes in the nucleus and represses the expression of pro-inflammatory proteins. In the cytosol
Hormone response elements
Cis element
Inverted repeats
Coordinated gene regulation
Hormone response mechanism
In the absence of glucocorticoid (cortisol), GR is held in the cytoplasm as part of an inactive multi-protein complex
When cortisol binds to GR, it dissociates from the regulatory complex
GR forms a dimer, moves to nucleus, binds to HRE, induce expression o target genes
GR mechanism
GR dimer need coactivators in interact with the basal tc complex
GR dimer may interact with repressors to inhibit interaction with basal tc complex
Myc
Has TRD: transcriptional regulation domain
And DNA binding domain
Will not bind to DNA unless dimerize
Involved in cell cycle progression
Myc/max system
No myc: Max forms a homodimer and represses gene tc by. Binding to enhancer
With Myc: Myc/Max heterodimer is formed to activated gene expression
Myc overexpression
In tumor
Favor Myc/max, impairs differentiation and promotes cell proliferation
Fetal hemoglobin = HbF
Tetramer of 2 alpha chains and 2 gamma chains
Begin at conception with gamma chain expression exponentially decreasing soon after birth
Hemoglobin A - HbA
Tetramer of 2 alpha chains and 2 beta chains
Expression of beta begins at conception with exponential increase to plateau at 6 month
Hemoglobin A2 = HbA2
Tetramer of 2 alpha chains and 2 delta chanis
Expression of delta chain is low after birth
Globin gene famoly- 2 chromosomes
Chromosome 16: alpha-globin, both alpha1 and alpha 2 can provide alpha chains
Chromosome 11: beta globin, for gamma, delta, beta
Locus control regions found 1000 bp upstream of both globin genes
Transcription factor code
The combination of transcription factors expressed by a cell define the cell
2 types os naturally-forming interfering RNAs
Micro RNA = miRNA
Short interfering RNA = siRNA
MiRNA
Derived from specific ds-pre-miRNA
Regulates expression by repressing mRNA translation
Mostly endogenous, from genome
SiRNA
Derived from long dsRNAs and random processing
Regulates expression by mRNA degradation
Often exgenous, from virus or injected
MiRNA processing
Drosha: process pri-miRNAs to pre miRNAs hairpinn structures
Exportin 5: transport pre-miRNA to cytoplasm
Dicer: process them to single stranded RNA and initiates the formation of RISC = RNA-induced silencing complex
RISC binds imperfectly tp 3’-UTR of target mRNA, inhibit ribosome to translate protein, prevent interaction of the translational machinery with the 5’ cap
SiRNA processing
Dicer: process long dsRNA into siRNA
SiRNA has perfect complementarity with 3’UTR of target mRNA, leading to endonuclease AGO2 to cleave mRNA
MiRNA and cancer
Genes encode miRNA are amplified in tumor cells
Cancerous cells lose cell growth regulation and cancer gets larger
MiRNA code
The combination of TF and miRNAs expressed by a cell define the cell
