Lec2/3HumanGeneTranscription Flashcards
Why are transactivators important in development?
Expression and asymmetric distribution of transactivators to daughter cells is KEY in cell linage determination
(Also can be viewed as a circuit)
Examples of Transactivators in development
-Globin switching (Biochemical)
-Heart morphology (Morphological)
What is the path of globin switching from fetus to adult?
-Start with Epsilon globin gene cluster
-Switch to gamma with higher O2 affinity (5-6 weeks, expressed in liver)
-End with beta (+delta) with lower O2 affinity (just before birth, in bone marrow)
What is the region that allows for transcription for fetal or adult goblin genes?
Locus Control Region (LCR)
LCR: Locus Control Region
An enhancer that allows for the transactivators to express fetal or adult hemoglobin (also a regulatory element)
What happens to the cells and transactivator that express fetal hemoglobin after birth?
They will die after birth
The fetal hemoglobin system is an example of what?
Example of”synthesis” as a mechanism for regulating transactivator function
What do adult transactivator bind?
They bind the adult globin gene regulatory elements
What is the basis for hereditary persistence of fetal hemoglobin?
-Fetal cells express different transactivators in development.
-The cells expressing the transactivator would be early stage stem cells.
What does HBAC (histone deac contribute too in globin switching?
-Contributes to silencing the fetal promoters at the adult stage
-Keeps fetal globin genes from getting transcribed
How do we switch form Fetal to adult globin?
- Missing fetal globin transactivator
- HDAC keeps fetal genes condensed
What is the AA mutation in sickle cell anemia?
Glutamate —> Valine
What happens to hemoglobin because of valine?
-Causes it to become a polymer because it wants to exclude H2O due to its hydrophobicity
-these polymers cause a deformity making the sickle shape which leads to a decrease in O2 transfer (can cause pain)
Vorinostat (______ inhibitor)
- Treatment for sickle cell anemia
-HDAC
Lack of HDAC allows for
-Allow for a PIC to form a little and some fetal genes will be transcribed (still no fetal transactivator)
-Then fetal hemoglobin can insert itself into the polymers of the globin in the sickle cell and allow for better O2 transfer
Tbox article:
What are TBXs?
TBX: Transactivators (ex; TBX1 & TBX2)
Tbox article:
Mutation/Removal of TBX transactivator cause what?
Morphological changes in the heart (cardiac congenital anomaly syndromes)
What is an inducible regulation of transcription?
Signal Transduction Pathway
(leading to the activation of a transactivator and transcription)
Definition of a Signal Transduction Pathway
-An extracellular signal (eg. peptide hormone in the blood) can lead to a change in the confirmation of a RECEPTOR, and subsequently, in the way a series of cytoplasmic and nuclear proteins interact with one another.
-These changes ultimately lead to SIGNAL TRANSDUCTION thus “transducing” the extra-cellular signal to the NUCLEUS
Examples of Signal Transduction Pathways
- TNF alpha
- JAK/STAT
- Hedgehog
- RAS
5.FGF
TNF alpha Pathway
-Part of the Immune System
1. TNF alpha binds to receptor
2. Conformational change of receptor leads to a phosphorylation of IKK complex
3. IKB is bound to NFkappaB inhibiting the transactivator, IKK binds to IKB and phosphorylating IKB causing it to degrade
4. NFkB is free, translocates to nucleus binds on to a sequence of DNA and increases transcription
(IKB is a decoy)
1st step of the TNF alpha pathway
- TNF alpha binds to receptor
2nd step of the TNF alpha pathway
- Conformational change leads to a phosphorylation of IKK complex
3rd step of the TNF alpha pathway
3.IKB is bound to NFkappaB inhibiting the transactivator, IKK binds to IKB and phosphorylating IKB causing it to degrade
4th step of TNF alpha pathway
- NFkB is free, translocates to nucleus and increases transcription
JAK/STAT1 pathway
-Plays a part with interferons
1. A cytokine (IFN) will bind to the cytokine receptor and cause the two subunits to come together
2. This will cause JAK to cross phosphorylate each other and the receptor. This will attract STAT (transactivator)
3. STAT will phosphorylated, it will dimerize, hide the phosphates and translocate to the nuclease to increase transcription
1st step of the JAK/STAT1 pathway
- A cytokine (IFN) will bind to the cytokine receptor and cause the two subunits to come together
2nd step of JAK/STAT1 pathway
- This will cause JAK to cross phosphorylate each other and the receptor. This will attract STAT (transactivator)
3rd step of JAK/STAT1 pathway
- STAT will phosphorylated, it will dimerize, hide the phosphates and translocate to the nuclease to increase transcription
What Is the connection between STAT1 dimerization and position of phosphorylation sites?
Phosphates get internalized
Example of interferons that are part of the JAK/STAT pathway
-Interferon(gamma)
-Interferon (alpha)
Why is that the STAT protein phosphorylation does not interfere with the STAT protein binding to DNA?
Phosphate is in the middle of the dimer
JAK stands for
Janus kinase
STAT stands for
Signal transducer & activator of transcription
What is the disease caused by a consistently active Hedgehog pathway?
Basel cell carcinoma
(WITHOUT) Hedgehog pathway
- No hedgehog, PATCH binds to smoothened inactivating it
- Inactivated smoothened, Protease free to cleave Ci protein (transactivator)
- Cleavage of Ci protein exposes the Co-repressor binding sites
- Ci co-repessor binding site translocate to nucleus and decrease transcription (specifically proliferation genes-NO proliferation)
1st step of the (WITHOUT) Hedgehog pathway
- No hedgehog, PATCH binds to smoothened inactivating it
2nd step of the (WITHOUT) Hedgehog pathway
- Inactivated smoothened, Protease free to cleave Ci protein (transactivator)
3rd step of the (WITHOUT) Hedgehog pathway
- Cleavage of Ci protein exposes the Co-repressor binding sites
4th step of the (WITHOUT) Hedgehog pathway
- Ci co-repessor binding site translocate to nucleus and decrease transcription (specifically proliferation genes-NO proliferation)
Which of the following protein interactions is defective in basal cell carcinoma?
PATCHED to SMOOTHENED
(WITH) Hedgehog Pathway
- Hedgehog will interact with PATCHED, patched cannot inhibit smoothened
- Smoothened interacts with protease, Protease cannot cleave the Ci protein
- Ci protein is now a co-activator (rather than repressor)
- Leads to transcription of proliferation
1st step of (WITH) Hedgehog Pathway
- Hedgehog will interact with PATCHED, patched cannot inhibit smoothened
2nd step of (WITH) Hedgehog Pathway
- Smoothened interacts with protease, Protease cannot cleave the Ci protein
3rd and 4th step of (WITH) Hedgehog Pathway
- Ci protein is now a co-activator (rather than repressor)
- Leads to transcription of proliferation
Receptor Tyrosine Kinase Pathway (RAS)
- Two receptors come together and phosphorylate each other (own tyrosine kinase activity)
- Binds to lose GDP
- GTP exchange:
-Inactive State-when RAS is bound to GDP
-Active State-when RAS is bound to GTP
4.Leading to RAF, MEK, ERK which phosphorylate the transcription factors (Downstream signals)
1st step of Receptor Tyrosine Pathway
- External ligand binds to cell membrane and brings two receptors come together and phosphorylate each other (own tyrosine kinase activity)
2nd step of Receptor Tyrosine Pathway
Binds to lose GDP
3rd step of Receptor Tyrosine Pathway
GTP exchange (GDP to GTP to activate RAS prortein):
-Inactive State-when RAS is bound to GDP
-Active State-when RAS is bound to GTP
4th step of Receptor Tyrosine Pathway
Leading to RAF (MAP3K), MEK (MAP2K), ERK(MAPK) which phosphorylate the transcription factors (Downstream signals)
Fibroblast growth factor (FGF) pathway—- receptor mutation
Activating FGF mutation lead to INCREASED GROWTH of spermatocytes
How does FGF lead to increased growth of spermatocytes?
- Men age and acquire more FGF mutations
- More spermatocytes with those mutations
- More sperm have these FGF receptor mutations
FGF mutations in offspring leads to what and why does this occur?
Leads to achondroplasia (dwarfism; shortening of bones). This is because chondrocytes are in growth plates and they can divide to lengthen bone due to the the FGF receptor mutations
What are three main points of FGF
- Occurs in spermatocyte development
- Occurs in chondrocytes (cartilage)
- Signaling pathway can occur even without PIC
Peptide hormones binds to receptor inside or outside the cell? And why?
outside (because it requires an EXTRAcellular receptor)
Steroid hormones binds to receptor inside or outside
Inside—-AKA Intracellular in cytoplasm or nucleus (because steroid hormones can diffuse through lipid bilayer membrane)