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Cellular and Molecular Biology > Final: Ch 16 PI, SerK, Hedgehog > Flashcards

Final: Ch 16 PI, SerK, Hedgehog Flashcards

(72 cards)

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1
Q

do phosphoinositide pathways have long-term effects on gene expression?

A

yes

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2
Q

phosphoinositide pathways end with a variety of kinases, especially….

A

protein kinase C (PKC)

protein kinase B (PKB)

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3
Q

PKC & PKB play key roles in what 2 things

A

cellular growth and metabolism

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4
Q

hormonal stimulation of some GPCR leads to activation of ________ C

A

phospholipase C (PLC)

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5
Q

what does PLC do after activation

A

cleaves PIP2 to generate the second messengers DAG and IP3

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6
Q

signaling via the IP3/DAG pathway leads to…

A

an increase in cytosolic Ca and activation of PKC

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7
Q

which isoform of PLC is activated by GPCRs

A

beta

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8
Q

which isoform of PLC is activated by RTKs and cytokine receptors?

A

gamma - contains SH2 domains

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9
Q

what do the SH2 domains of PLC-gamma do

A

bind specific phosphotyrosines on the activated receptors

positions the PLC close to PIP2, and PLC gets phosphorylated

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10
Q

recruitment of PI-3 kinase to activated receptors leads to synthesis of _ phosphorylated phosphatidylinositols

A

2

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11
Q

how does the PI-3 kinase RTK/cytokine receptor pathway work

A

PI-3 kinase recruited to membrane by binding SH2 domains to phosphotyrosine on the cytosolic domain of activated RTK/cytokine receptors

catalytic domain of PI-3 kinase close to phosphoinositide substrates

phosphorylates 3’ carbon

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12
Q

what do the products of the PI-3 kinase pathway do

A

act as docking sites for signal transducing proteins so the signal is passed downstream

ex. cell division, prevent apoptosis

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13
Q

polyoma virus

A

DNA virus that transforms mammalian cells to uncontrolled growth

uses oncoprotein middle T

researchers discovered PI-3 kinase when studying middle T

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14
Q

protein kinase B (PKB)

A

serine/threonine kinase also called Akt

Also has a PH domain that binds to the 3-phosphates from PI-3

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15
Q

since the inositol phosphates are present on the cytosolic face of the membrane, binding recruits the ______ protein to the cell membrane

A

entire protein

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16
Q

following hormone stimulation (rise in PI 3-phosphates), what does PKB do

A

binds the membrane bound 3-phosphates via the PH domain (releases active catalytic site) and becomes localized at the plasma membrane

need two other kinases (PDK1 and PDK2 to be fully active)

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17
Q

PDK1 and PDK2

A

PDK1 is recruited to the membrane via binding of PH domain - eventually encounters PKB and phosphorylates a thr residue in the activation lip

PDK2 phosphorylates a serine not in the activation lip

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18
Q

once fully activated, PKB can…

A

dissociate from the membrane and phosphorylate target proteins within the cell

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19
Q

activated PKB can phosphorylate and inactivate ___-apoptotic proteins like ___

A

pro-apoptotic, Bad

short-term effect that prevents activation of an apoptosis pathway that leads to death

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20
Q

PKB and the Forkhead TF FOXO3a

A

PKB promotes survival of cultured cells by phosphorylating FOXO3a

this reduces the TF’s ability to induce expression of many pro-apoptotic genes

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21
Q

the PI-3 pathway is negatively regulated by ____ _________

A

PTEN phosphatase

overexpression in cultured mammalian cells promotes apoptosis by reducing the level of the PI 3-phosphates and hence activation and anti-apoptotic effect of PKB

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22
Q

is the PTEN gene deleted in many types of advanced human cancers?

A

yes, contributes to uncontrolled growth b/c of elevated levels of PI 3-phosphates

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23
Q

inositol phosphate (IP) releases stores of ____

A

Ca2+

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24
Q

transforming growth factor B (TGF-B) superfamily and the transforming growth factor B receptor superfamily

A

receptor serine kinases and signaling molecules

phosphorylate and activate the Smads TFs that regulate growth and differentiation pathways

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25
in unstimulated cells, the Smads are located in the ______, but when activated they move into the ________ to regulate transcription
cytosol, nucleus (via NLS)
26
the primary function of the 3 human TGF-B isoforms is to....
strongly prevent cellular proliferation induce synthesis of proteins that inhibit the cell cycle
27
TGF-B prevents growth in both...
the secreting cell (autocrine signaling) neighboring cells (paracrine signaling)
28
many animal cell types produce and secrete members of the TGF-B superfamily in an ________ form that is stored attached to cell-surface molecules or in the ECM
inactive form release of the active form from the matrix by protease digestion or inactivation of an inhibitor leads to a quick activation of signaling molecules already in place
29
how did researchers identify the receptor TGF-B1 bound to
radiolabeled purified TGF-B1 with iodine 125 Cross-linking purification revealed 3 different receptors
30
what are the 3 TGF-B receptor proteins called
RI, RII, RIII
31
RIII (B-glycan)
most abundant TGF-B receptor cell surface transmembrane proteoglycan binds and concentrates mature TGF-B molecules near the cell surface to aid their binding to RII
32
RI and RI receptor proteins are _____ transmembrane proteins with ______/_______ kinases as part of their cytosolic domains
dimeric, serine/threonine kinases
33
RII exhibits constitutive ______ activity
kinase
34
binding of TGF B to RI and RII causes what
induction of complexes containing 2 copies of each RI and RII RII phosphorylates serine and threonine residues in RI to activate RI kinase activity
35
3 types of Smads
R-smads (receptor regulated -- Smads2 and 3) co-Smads (Smad4) I-Smads (inhibitory Smads)
36
what does the MH1 domain of R-Smads contain
a nuclear localization signal that is hidden in the inactive form phosphorylation of serines in R-Smads by RI allows binding of an importin to the NLS, which allows transport to the nucleus
37
within the nucleus, R-Smads are continuously being _________ by...
dephosphorylated by a nuclear phosphatase
38
______ feedback loops regulate TGF-B/Smad signaling
negative feedback loops
39
in most signaling pathways, the response to a growth factor or other molecule decreases with _____
time (desensitization)
40
which two cytosolic proteins downregulate TGF-B/Smad signaling
SnoN and Ski block transcription activation by a bound Smad complex by deacetylating histones makes cells resistant to growth-inhibitory effects of TGF-B
41
what are the Wnts and Hedgehogs?
evolutionarily conserved families of signaling proteins play key roles in developmental pathways induce expression of genes required for a cell to acquire a new identity or fate
42
similarities of Wnt and Hedgehog pathays 4 things
bind receptors that are like GPCR, but don't activate G-proteins in resting state, key TFs are ubiquitinated and targeted for proteolytic cleavage activation of each pathway involves disassembly of cytosolic protein complexes, deubiquitination, and release of an active TF the kinase GSK3 is used
43
NF-kB pathway controlled by ubiquitination
an inhibitor of a TF is deactivated by ubiquitination in resting state, the TF NF-kB is in the cytosol bound to an inhibitor stress-inducing conditions cause deubiquitination and degradation of the inhibitor, allowing cells to activate gene transcription
44
another function of polyubiquitination other than signaling things for degradation by proteases is....
forming a scaffold to assemble a key signal transduction complex
45
Wnt signaling triggers the release of a TF from a ______ protein complex
cytosolic
46
proto-oncogene
a normal gene whose inappropriate expression promotes cancer ex. Wnt-1
47
Wnt means
wingless
48
what does the Wnt pathway control
brain development stem cells development of osteoblasts
49
Wnt proteins are secreted extracellular signaling molecules that are modified by addition of a ______ group near their N-termini
palmitate (hydrophobic) tethers Wnt proteins to the membrane, limiting their action to nearby cells
50
2 cell-surface receptors Wnt acts through
Frizzled (Fz) - 7 transmembrane helices and directly binds Wnt co-receptor LRP - associated with Fz
51
B-catenin (vertebrates) / Armadillo (flies)
major players in Wnt signaling acts as a transcriptional activator and membrane-cytoskeleton linker protein
52
Wnt pathway
Wnt binds to Fz and the LRP co-receptor kinases phosphorylate LRP and Axin binds phosphorylation of B-catenin is blocked, allowing it to accumulate B-catenin translocates to the nucleus and binds to TF as a co-activator
53
Hedgehog (Hh) signaling relieves ______ of target genes
repression
54
the Hh pathway involves ______ of an intracellular complex containing a TF
disassembly
55
unlike Wnt, the Hh protein undergoes distinctive ___-_________ processing
post-translational processing
56
do the two Hh membrane receptors move between the plasma membrane and intracellular vesicles?
yes
57
what happens to cells that receive a high or small amount of Hh
high: turn on genes to form certain structures low: turn on different genes to form different structures
58
morphogens
signals that induce different cell fates depending on their concentration in target cells
59
how is Hh formed
from a precursor protein with autoproteolytic activity cholesterol and palmitoyl is added, making it hydrophobic to limit its diffusion in the membrane
60
Hh pathway in flies
Hh binds to Patched (Ptc) to stop inhibition of Smo Smo moves to the membrane, gets phosphorylated Ci (a TF) moves to nucleus and recruits CREB-binding activator protein to express target genes
61
primary cilium
a single immotile cilium
62
intraflagellar transport proteins (ITF)
move proteins and particles from the base of a cilium to the tip
63
Hh pathway in vertebrates
Hh binding triggers movement of Smo to the ciliary memb and the KIF7 motor protein up the microtubule to the ciliary tip Gli (a TF) accumulates and is transported down the cilium and released into cytosol --> nucleus
64
degradation of an inhibitor protein activates the _____ TF
NF-kB TF
65
in the inactive state, the NF-kB TF is...
in the cytosol bound to an inhibitor
66
activation of the NF-kB signaling pathway involves what
ubiquitination and degradation of the inhibitor, releasing the TF rapidly activated in mammalian immune system cells in response to bacterial or viral infection
67
toll like receptors NF-kB
activated when bacterial or fungal cell walls bind toll-like receptors on the cell surface
68
NF-kB pathway
kinase phosphorylates inhibitor of NF-kB, which gets ubiquitinated and degraded by proteasomes nuclear localization signal in NF-kB dimer is revealed, and it is transported to nucleus NF-kB activates many genes
69
what types of genes does NF-kB activate
those encoding cytokines and chemokines causes immune cells to infiltrate the site of infection
70
depending on the specific E3 ubiquitin ligase, ubiquitin forms multiple types of ______ that have different structures and functions
polymers
71
polyubiquitin chains linked to activated IL-1 receptor forms a scaffold that...
brings the TAK1 kinase near I-kB kinase complex and phosphorylates it Signal is transmitted this way
72
When is NF-kB pathway activated
In response to viral or bacterial infection Stress

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