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

Final: Ch 16 PI, SerK, Hedgehog Flashcards

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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
Q

in unstimulated cells, the Smads are located in the ______, but when activated they move into the ________ to regulate transcription

A

cytosol, nucleus (via NLS)

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26
Q

the primary function of the 3 human TGF-B isoforms is to….

A

strongly prevent cellular proliferation

induce synthesis of proteins that inhibit the cell cycle

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27
Q

TGF-B prevents growth in both…

A

the secreting cell (autocrine signaling)

neighboring cells (paracrine signaling)

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28
Q

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

A

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

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29
Q

how did researchers identify the receptor TGF-B1 bound to

A

radiolabeled purified TGF-B1 with iodine 125

Cross-linking

purification revealed 3 different receptors

30
Q

what are the 3 TGF-B receptor proteins called

A

RI, RII, RIII

31
Q

RIII (B-glycan)

A

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
Q

RI and RI receptor proteins are _____ transmembrane proteins with ______/_______ kinases as part of their cytosolic domains

A

dimeric, serine/threonine kinases

33
Q

RII exhibits constitutive ______ activity

A

kinase

34
Q

binding of TGF B to RI and RII causes what

A

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
Q

3 types of Smads

A

R-smads (receptor regulated – Smads2 and 3)

co-Smads (Smad4)

I-Smads (inhibitory Smads)

36
Q

what does the MH1 domain of R-Smads contain

A

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
Q

within the nucleus, R-Smads are continuously being _________ by…

A

dephosphorylated by a nuclear phosphatase

38
Q

______ feedback loops regulate TGF-B/Smad signaling

A

negative feedback loops

39
Q

in most signaling pathways, the response to a growth factor or other molecule decreases with _____

A

time (desensitization)

40
Q

which two cytosolic proteins downregulate TGF-B/Smad signaling

A

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
Q

what are the Wnts and Hedgehogs?

A

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
Q

similarities of Wnt and Hedgehog pathays 4 things

A

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
Q

NF-kB pathway controlled by ubiquitination

A

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
Q

another function of polyubiquitination other than signaling things for degradation by proteases is….

A

forming a scaffold to assemble a key signal transduction complex

45
Q

Wnt signaling triggers the release of a TF from a ______ protein complex

A

cytosolic

46
Q

proto-oncogene

A

a normal gene whose inappropriate expression promotes cancer

ex. Wnt-1

47
Q

Wnt means

A

wingless

48
Q

what does the Wnt pathway control

A

brain development

stem cells

development of osteoblasts

49
Q

Wnt proteins are secreted extracellular signaling molecules that are modified by addition of a ______ group near their N-termini

A

palmitate (hydrophobic)

tethers Wnt proteins to the membrane, limiting their action to nearby cells

50
Q

2 cell-surface receptors Wnt acts through

A

Frizzled (Fz) - 7 transmembrane helices and directly binds Wnt

co-receptor LRP - associated with Fz

51
Q

B-catenin (vertebrates) / Armadillo (flies)

A

major players in Wnt signaling

acts as a transcriptional activator and membrane-cytoskeleton linker protein

52
Q

Wnt pathway

A

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
Q

Hedgehog (Hh) signaling relieves ______ of target genes

A

repression

54
Q

the Hh pathway involves ______ of an intracellular complex containing a TF

A

disassembly

55
Q

unlike Wnt, the Hh protein undergoes distinctive ___-_________ processing

A

post-translational processing

56
Q

do the two Hh membrane receptors move between the plasma membrane and intracellular vesicles?

A

yes

57
Q

what happens to cells that receive a high or small amount of Hh

A

high: turn on genes to form certain structures
low: turn on different genes to form different structures

58
Q

morphogens

A

signals that induce different cell fates depending on their concentration in target cells

59
Q

how is Hh formed

A

from a precursor protein with autoproteolytic activity

cholesterol and palmitoyl is added, making it hydrophobic to limit its diffusion in the membrane

60
Q

Hh pathway in flies

A

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
Q

primary cilium

A

a single immotile cilium

62
Q

intraflagellar transport proteins (ITF)

A

move proteins and particles from the base of a cilium to the tip

63
Q

Hh pathway in vertebrates

A

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
Q

degradation of an inhibitor protein activates the _____ TF

A

NF-kB TF

65
Q

in the inactive state, the NF-kB TF is…

A

in the cytosol bound to an inhibitor

66
Q

activation of the NF-kB signaling pathway involves what

A

ubiquitination and degradation of the inhibitor, releasing the TF

rapidly activated in mammalian immune system cells in response to bacterial or viral infection

67
Q

toll like receptors NF-kB

A

activated when bacterial or fungal cell walls bind toll-like receptors on the cell surface

68
Q

NF-kB pathway

A

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
Q

what types of genes does NF-kB activate

A

those encoding cytokines and chemokines

causes immune cells to infiltrate the site of infection

70
Q

depending on the specific E3 ubiquitin ligase, ubiquitin forms multiple types of ______ that have different structures and functions

A

polymers

71
Q

polyubiquitin chains linked to activated IL-1 receptor forms a scaffold that…

A

brings the TAK1 kinase near I-kB kinase complex and phosphorylates it

Signal is transmitted this way

72
Q

When is NF-kB pathway activated

A

In response to viral or bacterial infection

Stress

Cellular and Molecular Biology (34 decks)

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