Lecture 23: Cell signaling II Flashcards
Describe how vasopressin recruits aquaporin movement to the plasma membrane in kidney
cells
- Vasopressin binds GPCR V2R
2. G protein alpha activates adenylyl cyclase (AC)
- cAMP activates protein kinase A
(PKA) - PKA induces movement of
vesicles containing aquaporins
to move to plasma membrane
Vasopressin
is an antidiuretic hormone:
increases ion and water uptake from nephrons
– returns them to blood; reduces urine volume
How is vasopressin activity similar/ different to glucagon signaling?
Similar components as glucagon signaling (G protein alpha, adenylyl cyclase, PKA). The
difference in these cells is a.) different GPCR, b.) different targets of PKA
Describe how acetylcholine triggers smooth muscle contraction
Steps 1, 2: Kinases add phosphate
groups to phosphatidylinositols to
make PIP2.
Step 3: activation of
acetylcholine receptor
(a GPCR) by acetylcholine
Step 4: GP-alpha activates
phosphatidylinositiol specific phospholipase Cβ (PI-PLCβ)
Step5: PI-PLCβ splits PIP2 into DAG and IP3.
Step 7: IP3 diffuses into the
cytosol.
Step 8: IP3 binds to an IP3 receptor (a ligand gated
Ca2+ channel) in the membrane of the SER.
Step 9: binding of IP3 to receptor releases Ca2+ and
triggers muscle contraction
a. How does calcium release differ between smooth and skeletal muscle?
Ca2+ can be let into the cytosol by voltage dependent channels in nerves, some muscles and by
receptor-mediated calcium channels (like we just saw with the smooth muscle)
Where is Ca 2+ concentration low?
Remember that [Ca2+] is low in the
cytosol through the action of Ca2+
pumps and exchangers.
• fertilization,
mechanosensory calcium channels open up in oocytes following fertilization.
• prevent further sperm entry anywhere around the large cell (rapid, long distance)
• begins activation of cyclins, starting cell division (coordinating effect)
Nitric oxide (NO)
is an inorganic gas that acts as an extracellular messenger and as a second messenger (can go through membranes)
is synthesized by nitric oxide synthase
within cells using Arg as substrate
acts as autocrine, paracrine and
(likely) an endocrine hormone
Describe how nitric oxide relaxes smooth muscle
NO activates guanylyl cyclase to make
cGMP
• In blood vessels, acetylcholine stimulus
can induce NO synthase
– cGMP causes smooth muscle cells (around
blood vessels) to relax
– nitroglycerine applied under the tongue to
patients with congestive heart problems,
produces NO to relax arteries
- List the basic properties and functions of receptor tyrosine kinases (RTKs)
These receptors function as enzymes
• receptor tyrosine kinases phosphorylate target
proteins (including themselves) at particular tyrosines
• > 90 types of RTK receptors in humans
• all have similar structure – single trans-membrane segment • present in all multicellular organisms • involved in regulation of: • Cell division (defects lead to cancer) • Development (cells and tissues) • Cell survival and death (cancer!) • Cell attachments, migrations (more cancer!!) • Insulin perception and response
Describe how RTKs function
1. Binding of ligand induces dimerization either by: • One ligand binding to both monomers or • One ligand binds to each monomer, which causes them to dimerize • Either way, they dimerize!
2. The two monomers, once joined, moves amino acid loops out of the way and exposes the kinase domains. The kinase domains then trans- autophosphorylate each other
3. Once phosphorylated, they are activated and can bind to other signaling molecules
Describe RTKs and their different modes of action
A. Recruitment of docking and signaling molecules
without further kinase activity.
Here, the SH2 domain of Grb2 (a docking adaptor)
binds the phosphorylated tyrosine on the receptor.
Other domains of Grb2 have Sos and Ras bound to
it… so they’re now also associated with the receptor.
B. Recruitment of signaling molecules with further
kinase activity.
Here another protein binds to the receptor, then the
receptor further phosphorylates tyrosines on the
protein that was bound (IRS in this example). These
phosphorylation sites serve as docking sites for
other proteins to bind to.
C. Direct recruitment and phosphorylation of
transcription factors.
These then get transported into the nucleus to
modulate transcription of target genes (can you say
‘exposure of a NLS’?)
D. Direct recruitment of other proteins directly
involved in signaling cascades such as
phospholipases, kinases, phosphatases, etc.
growth factor
(also known as a cytokine), usually
a small protein, is a naturally occurring substance
capable of stimulating cellular growth, proliferation
and cellular differentiation, and cell survival. In
other words, these are the ligands of many RTKs.
Epidermal growth factor or EGF
i s a growth factor that plays an important role in the regulation of cell growth, proliferation, and differentiation by binding to its receptor epidermal growth factor receptor
This signaling results in changes in gene expression
•Transcription factors are activated, and genes
involved in cell proliferation such as the cyclins
(which drive the cell cycle) are transcribed
Describe how epidermal growth factor triggers cell proliferation
activate the MAP kinase pathway
1. EGF binds and activates the
epidermal growth factor receptor
(EGFR)
- EGFR autophosphorylates its
tyrosines - The phosphorylated tyrosines serve
as a docking station for Grb2/Sos,
which is recruited to the membrane - SOS is a GEF that activates RAS
- Once Ras is activated, it recruits to the
membrane a serine/threonine kinase
called Raf - Raf phosphorylates and activates MEK
- MEK phosphorylates and activates ERK
- ERK phosphorylates transcription factors,
which enter the nucleus and start
transcription of target genes that initiate
the cell cycle (e.g. cyclin D and TFs)
