DLA After Lecture 31

Question 1

Tc factors as repressors

3 modes

Answer 1

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

Question 2

Hypoxia

Answer 2

Reduction in the normal level of tissue oxygen

Occurs during several pathophysiological process including tumorigenesis

Question 3

Hypoxia response

Answer 3

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

Question 4

HIF 1

Answer 4

Hypoxia-inducible transcription factor

HIF1 alpha: O2 sensitive
HIF1 beta: constitutive

Question 5

Prolyl hydroxylase

Answer 5

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

Question 6

HIF-1 as a therapeutic target to treat 3

Answer 6

Anemia
Inflammation
Cancer
Stroke
Solid cancer tumor: make it hypoxic

Question 7

Glucocorticoids

Answer 7

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

Question 8

Hormone response elements

Answer 8

Cis element
Inverted repeats
Coordinated gene regulation

Question 9

Hormone response mechanism

Answer 9

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

Question 10

GR mechanism

Answer 10

GR dimer need coactivators in interact with the basal tc complex

GR dimer may interact with repressors to inhibit interaction with basal tc complex

Question 11

Myc

Answer 11

Has TRD: transcriptional regulation domain

And DNA binding domain

Will not bind to DNA unless dimerize

Involved in cell cycle progression

Question 12

Myc/max system

Answer 12

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

Question 13

Myc overexpression

Answer 13

In tumor

Favor Myc/max, impairs differentiation and promotes cell proliferation

Question 14

Fetal hemoglobin = HbF

Answer 14

Tetramer of 2 alpha chains and 2 gamma chains

Begin at conception with gamma chain expression exponentially decreasing soon after birth

Question 15

Hemoglobin A - HbA

Answer 15

Tetramer of 2 alpha chains and 2 beta chains

Expression of beta begins at conception with exponential increase to plateau at 6 month

Question 16

Hemoglobin A2 = HbA2

Answer 16

Tetramer of 2 alpha chains and 2 delta chanis

Expression of delta chain is low after birth

Question 17

Globin gene famoly- 2 chromosomes

Answer 17

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

Question 18

Transcription factor code

Answer 18

The combination of transcription factors expressed by a cell define the cell

Question 19

2 types os naturally-forming interfering RNAs

Answer 19

Micro RNA = miRNA

Short interfering RNA = siRNA

Question 20

MiRNA

Answer 20

Derived from specific ds-pre-miRNA

Regulates expression by repressing mRNA translation

Mostly endogenous, from genome

Question 21

SiRNA

Answer 21

Derived from long dsRNAs and random processing

Regulates expression by mRNA degradation

Often exgenous, from virus or injected

Question 22

MiRNA processing

Answer 22

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

Question 23

SiRNA processing

Answer 23

Dicer: process long dsRNA into siRNA

SiRNA has perfect complementarity with 3’UTR of target mRNA, leading to endonuclease AGO2 to cleave mRNA

Question 24

MiRNA and cancer

Answer 24

Genes encode miRNA are amplified in tumor cells

Cancerous cells lose cell growth regulation and cancer gets larger

Question 25

MiRNA code

Answer 25

The combination of TF and miRNAs expressed by a cell define the cell