LEC5-8: Signal Transduction Flashcards

Question

what is signal branching? example?

Answer 1

when 1 receptor protein can activate more than 1 kind of G protein i.e. PKA has numerous substrates

Answer 2

because if signaling goes awry, that can result in disease 1) alpha subunit + RGS cause GTP hydrolysis to GDP 2) cAMP phosphodiesterase digests cAMP to AMP, which is a biologically inert signaling molecule 3) protein phosphotases inactivate substrates that require phosphate for activation

Answer 3

1) signal molecule activates its GPCR 2) **G_q** subunit of G protein binds & activates **phospholipase C-beta** 3) phospholipase C breaks down the membrane phospholipid **PIP₂** into **IP₃ and DAG** 4) **IP₃** can activate **release of Ca²⁺** inside the cell, which activates **PKC,** which causes other signaling functions **DAG** directly activates **PKC** also

Answer 4

secondary messengers! from the phospholipase C pathway

Answer 5

inhibits adenylyl cyclase

Answer 6

1) **rhodopsin** receptor activates G_t 2) **G_t** activates **cGMP phosphodiesterase** 3) cGMP phosphodiesterase **breaks down cGMP**

Answer 7

1) **cholera toxin** is an enzyme. it **ADP-ribosylates GS-alpha** 2) **ADP-ribosylated G_Scannot hydrolyze GTP to GDP** now 3) G_Sw/ GTP thus remains **permanently activated**, keeps **activating adenylyl cyclase ** 4) **activated adenylyl cyclase increases cAMP levels**, activates **PKA** 5) prolonged **PKA activation** in intestinal epithelium causes **efflux of Cl^- and water** into gut causes copious, watery diarrhea

Answer 8

1) **pertussis toxin ADP-ribosylates alpha-subnit of G_i** 2) **prevents G_i from binding to GPCRs** this **inhibits the inhibitor** 3) leads to **increased [cAMP]** causes bacteria colonization, leads to whooping cough

Answer 9

1) G_i activation, as it inhibits adenylyl cyclase, which activates cAMP which activates PKA 2) Block G_sfrom activating adenylyl cyclase 3) Block cAMP, as that is what adenylyl cyclase activates, and cAMP then activates PKA

Answer 10

- receptor with extracellular ligand-binding, membrane-spanning, and intracellular regions - receptors are **dimerized **(brought together) by ligand binding - receptors may be **homodimers** (same protein) or **heterodimers** (different proteins) - **enzyme activity** may be **intrinsic** to receptor, or **intracellular region** may bind to receptor **non-covalently**

Answer 11

receptor tyrosine kinases extracellular: ligand-binding domain single membrane spanning region intracellular: tyrosine-kinase domain

Answer 12

platelet-derived growth factor epidermal growth factor fibroblast growth factor insulin

Answer 13

RTKs exist as very weakly inactive in plasma membrane 1) **ligand binds RTK** **RTK dimerizes ** 2) dimerization causes receptors to be **phosphorylated** (auto or trans) **1st**: phosphorylation of **tyrosine-kinase domain** **2nd**: phosphorylation **outside of tyrosine-kinase domain** receptors are now **active** 3) phosphates provide **binding sites** for next factors in signal cascade, and activates receptor's **catalytic function**

Answer 14

SH2: binds phosphotyrosine regions SH3: binds polyproline regions *specific factors' SH2 or SH3 domains bind to phosphate of specific Tyr residues*

Answer 15

modular enzymes: contain SH2 and SH3 domains + an enzymatic component PLC-gamma: binds to RTKs PLC-beta: binds G_Q of G-protein alpha subunit

Answer 16

modular signaling protein with SH2 and SH3 domains but NO ENZYMATIC activity i.e. Grb2

Answer 17

Ras: s small G-protein which can bind GTP and GDP, has GTPase activity when **GTP-bound: active**; **GDP-bound: inactive** when signal enters, **GEF** (guanine nucleotide exchange factor) converts **GDP to GTP**, which turns Ras **ON** Ras needs a **GAP** (GTPase activating factor) to **hydrolyze GTP to GDP**, turns Ras **OFF**

Answer 18

1) prior to signaling, **Grb and SOS are bound ** 2) when **RTK activated by a ligand**, generates a **phosphotyrosine residue** 3) **Grb2** recognizes this residue, and **Grb2 activates ** 4) Grb2 recruits **SOS** 5) **SOS** causes Ras **nucleotide exchange** of GDP for GTP **Ras becomes activated**

Answer 19

growth factor binds from extracellular space 1) when **RTK is phosphorylated,** **Grb2 binds to it via SH2 domain** (phospho-tyrosine binding) **SOS is constituitively bound to Grb2** via its **SH3 domain** (which recognizes proline-rich area of Grb2) 2) **SOS** activates **Ras** 3) **Ras** activates **Raf** (MAPKKK) 4) **Raf** phosphorylates **MEK** (MAPKK) 5) **MEK** phosphorylates **ERK** (MAPK) causes *changes in protein activity* and *changes in gene expression*

Answer 20

MAP is a major pathway that's deregulated in cancer RTK may be multiplied or amplified Ras is activated by point mutations, most commonly mutated oncogen in cancers Raf sometimes also activated- esp in melanomas

Answer 21

breast cancer drug is antibody against a specific RTK that's innappropriately active in breast cancer, so interferes w/ MAP pathway

Answer 22

1) **PI-3K** is a complex of a **regulatory subunit,** p85, and **catalytic subunit,** p110 2) **p85** has **SH2** domain that **binds activated RTKs**, allows access of **p110 to PIP and PIP**₂ 3) **PI-3k phosphorylates** **PIP** and **PIP₂** on **3-position of inositol ring (= PIP3)** 4) **PIP3** activate **Akt, a ser/thr kinase** 5) activated **Akt** **phosphorylates** substrates that *promote cell survival & inhibit apoptosis*

Answer 23

tumor suppressor gene removes phosphate from 3-position of phosphoinotides (PI3) if mutated, the PI-3K pathway will not be turned off, and cell survival continues \> tumors

Answer 24

1) mutations in RTKs, mutations in Ras, muations in BRaf (a type of Raf) **drive pathway activation **in absence of growth factors 2) mutations leading to constitutive activation of **PI-3K **pathway, b/c promotes cell survival

Answer 25

**BOTH**: interact thru phospholipase C **only GPCRs:** turn on adenylyl cyclase **only RTKs:** turn on MAP kinase, Akt kinase pathways

Answer 26

prolactin, growth hormone, interferons, erythropoietin

Answer 27

RTK: single polypeptide BOTH RTK and Cytokine extracellular portion: amino terminus, binds ligands RTK intracellular portion: carboxy terminus, intrinsic tyrosine kinase activity Cytokine receptor intracellular portion: carboxy terminus, DOES NOT have intrinsic tyroskin kinase activity, or any other catalytic activity; non-covalently binds non-receptor tyrosine kinase that has intrinsic tyrosine kinase activity, JAK proteins

Answer 28

non-receptor tyrosine kinases associated w/ the intracellular portion of cytokine receptors when complexes with cytokine receptor, allows cytokine receptor to behave like RTKs in that they undergo ligand-induced dimerization

Answer 29

1) prolactin/interferons/growth hormone binds cytokine receptor/JAK complex extracellularly 2) cytokine receptor/JAK complex undergoes dimerization, cross-phosphorylation, activation of JAK proteins 3) JAK proteins phosphorylate intracellular portion of cytokine receptor 4) SH2-containg proteins bind to cytokine receptor

Answer 30

SH2-containing proteins: STAT (signal transducer and activator of transcription), are transcription factors 1) activated cytokine receptors phosphorylate STAT 2) receptors dimerize when pY of one STAT binds SH2 of its dimeric partner & vice versa 3) dimerized STATs translocate to nucleus, bind to DNA, activate gene expression

Answer 31

only ligands of the TGF (transforming growth factor)-beta/BMP (bone morphogenetic protein) family

Answer 32

heterodimers Type I and Type II both are single-pass transmembrane proteins; have extracellular ligand binding domain, intracellular ser/thr kinase domain

Answer 33

embryonic development, wound healing, disease-related fibrosis, cancer

Answer 34

1) **TGFbeta ligands** induce **Type I and II** receptors to **dimerize** 2) Type II receptors are constituitively active **Type II** receptors **phosphorylate Type I** receptors 3) **Type I** receptor **kinase activity** activates **Type I** receptors **phosphorylate SMAD** factors 4) **phosphorylated R-SMADs dimerize with co-SMADs** (non-phosphorylated) 5) **R-SMAD/co-SMAD dimer** enters nucleus, **induces expression** of specific genes

Answer 35

when a Delta or Jagged-expressing cell comes into direct physical contact w/ a Notch-expresing cell example of **contact-dependent signaling**

Answer 36

they are a target for many kinases, so for other pathways beyond the TGF-beta/BMP signaling pathway

Answer 37

1) Notch is bound by its ligand, **Delta** or Jagged **intracellular domain is proteolytically cleaved** 2) Cleaved Notch intracellular domain (**NICD**) enters **nucleus**, interacts w/ DNA-binding factor, **CSL** **CSL** usually **inhibits** Notch pathway target genes' expression 3) **CSL interaction w/ NICD** makes it **bind w/ transcriptional co-activators,** turns on **expression of notch-responsive target genes** signaling also **decreases Delta expression** - like on/off switch

Answer 38

1) lateral inhibition 2) note that no amplification occurs - so need NICD to go to nucleus to have transcription activation

Answer 39

large family of secreted proteins that have a covalently attached fatty acid

Answer 40

canonical complex of Frizzled & LRP5/6 **Frizzled:** 7 TM domains, bind Wnts via large extracellular N-terminus

Answer 41

If Wnt is inactive: B-cateninin undergoes proteolytic destruction by APC complex APC, axin, Ck1, GSK3-beta make up complex CK1 and GSK3-beta, ser/thr kinases, phosphorylate B-catenin, target it for proteolytic degradation by ubiquitin proteosome system in this state, in nucleus, TCF/LEF, DNA-binding factor, inhibits expression of Wnt pathway target genes

Answer 42

when Wnt is off, 1) TCF/LEF complex binds to DNA in nucleus, inhibits txn factors from binding and expressing Wnt-related genes 2) B-catenin undergoes constant degradation

Answer 43

1) Wnt binds Frizzled-LRP5/6 receptor complex 2) axin then binds to LRP5/6, disrupting the APC complex Dvl binds Frizzled, leads to inhibition of CK1 and GSK3-beta, they cannot phosphorylate B-catenin 3) B-catenin thus no longer exists in phosphorylated state, is stabilized 4) B-catenin migrates to nucleus, interacts w/ TCF/LEF and txn co-activators activates expression of Wnt pathway target genes P3000 and CBP act as transcriptional co-activators for Wnt

Answer 44

**cadherins:** B-catenin binds intracellular region of cell-cell adhesion molecules, tethers them to actin cytoskeleton, providng stability to cell-cell junctions keeps epithelia of epithelial cells together central area of B-cateinin protein is where binding occurs

Answer 45

1) important in embryonic development 2) regulates stem cells in homeostatic maintenance of adult tissues 3) involved in cancer, esp colorectal cancer

Answer 46

APC mutations means B-catenin is always produced, never degraded pathway is locked ON stem cells over-proliferate, develop polops in epithelial lining of gut b/c it's constantly regenerating thus APC = tumor suppressor gene, B-catenin=proto-oncogene

Answer 47

full-length protein has N-terminal signaling domain, C-terminal auto-processing domain C-terminal domain catalyzes proteolysis of itself into N- and C-terminal halves & simultaneously attaches a cholesterol molecuel to the new C-terminis of the N-terminal signaling domain signaling domain then has fatty acid molecule covalently added to its N-temrinus, results in **mature, dually lipidated HH ligand **

Answer 48

Ptch1, patched; 12 TM protein

Answer 49

1) Ptch1 inhibits signaling activity of Smo, another plasma membrane protein 2) If **no Smo** signaling, **Gli**, txn factor, is phosphorylated by **PKA, CK1, GSK3-beta,** Gli is thus proteolytically cleaved into **GliR**, repressor form 3) **GliR** enters nucleus, **inhibits HH pathway** target gene expression

Answer 50

1) **HH** binds **Ptch1**, relieves Ptch1-mediated inhibition of **Smo** 2) **Smo signals** to **prevent phosphorylation** & proteolytic **cleavage** of **Gli** 3) Full-length, activated **Gli** protein (**GliA**) **enters nucleus,** activates **expression of HH pathway** target genes

Answer 51

Ptch1 is actively inhibiting Smo without the binding of any ligand this is v different from GPCR or RTK pathways

Answer 52

primary cilium is microtubule-based organelle, present on almost all cell types HH signaling requires the primary cilium, most components of HH pathway localize to the primary cilium: Ptch1 is found there, Gli proteolytic cleave to GliR occurs there In HH presence, Ptch1 exits the cilium, Smo enteres the cilium, Gli cleave stops, leading to GliA formation

Answer 53

basal nevus syndrome mutations in Ptch1 result in Smo signlaling, leads to constituitive HH signaling Causes Gorlin syndrome, which causes basal cell carcinoma of skin/medulloblastoma Ptch1 = tumor suppressor gene, then!

Answer 54

holonprosencephaly - birth defect include cyclopia or embryonic death cyclopamine, chemical that binds and inhibits Smo, involved