Intro

Conj532 - Cytokine - Jak/STAT Pathways

1T-helper cell subsets and cytokine profiles

Th1, Th2 and Th17 cells are a separate lineage of CD4+ T cells, distinct from other T cell subsets. Every specific T helper cells produce its specific cytokines. T-bet, T-box expressed in T cells; FoxP3, forkhead box P3; ROR, retinoid-related orphan receptor. Makoto Kudo, et al. Front Microbiol. 2013;4:263.

Nature Reviews Immunology 10, 236-247 TH1 like response TH2 like response AntigenCytokines secreted by immune cells instruct T-cellsEffector B cells ('Be1' and 'Be2' cells) can secrete cytokines, such as interferon- (IFN), interleukin-12 (IL-12), IL-4 and IL-2, that reinforce and stabilize the cytokine profile of effector T helper 1 (TH1) and TH2 cells. In addition, the effector B cells can recruit additional naive T cells into the inflammatory response. Effector and regulatory B cells can present antigen to CD4+ T cells and provide co-stimulation and cytokines. Effector B cells ('Be1' and 'Be2' cells) can secrete cytokines, such as interferon- (IFN), interleukin-12 (IL-12), IL-4 and IL-2, that reinforce and stabilize the cytokine profile of effector T helper 1 (TH1) and TH2 cells. In addition, the effector B cells can recruit additional naive T cells into the inflammatory response. By contrast, the regulatory B cells produce IL-10, which suppresses the inflammatory potential of effector T cells, alters the activity of antigen-presenting dendritic cells (DCs) and promotes regulatory T cell development and expansion. Therefore, effector B cells function as accelerators of CD4+ T cell responses, but regulatory B cells function as 'brakes' on the response. In autoimmune disease, the ratio between effector B and T cells and regulatory B and T cells probably favours the effector B cells. Drugs that selectively deplete the effector B cells could be highly effective in resetting the balance in favour of the regulatory populations. APC, antigen-presenting cell; BCR, B cell receptor.3Cellular Mechanisms in Rheumatoid ArthritisPathogenesis of RA: synovial and systemic inflammation. Inflammation in RA is caused by activation of T cells, B cells and macrophages, which releases cytokines such as IL-1, IL-6 and TNF. These cytokines cause local joint damage through increased production of metalloproteinases and activation of osteoclasts. IL-1, IL-6 and TNF also leak out to the blood stream resulting in systemic inflammation: anaemia, thrombocytosis, fatigue, osteoporosis and the acute-phase response. Abbreviations: IL, interleukin; RA, rheumatoid arthritis. Choy, E. H. et al. Nat. Rev. Rheumatol. 9, 154163 (2013)

Figure 1 | Pathogenesis of RA: synovial and systemic inflammation. Inflammation in RA is caused by activation of T cells, B cells and macrophages, which releases cytokines such as IL-1, IL-6 and TNF. These cytokines cause local joint damage through increased production of metalloproteinases and activation of osteoclasts. IL-1, IL-6 and TNF also leak out to the blood stream resulting in systemic inflammation: anaemia, thrombocytosis, fatigue, osteoporosis and the acute-phase response. Abbreviations: IL, interleukin; RA, rheumatoid arthritis.43 General types of cytokine receptorsQ: why did nature evolve multiple chain receptors?

Epo, GH, Prl, GM-CSFClass ISingle chain (dimer)

a aClass IIClass IIIIL-2, Interferons

Multiple unique chains (2 or 3)abgIL-6, LIF, IL-11, CNTF), CT-1, CLC, OSM, IL-27 and IL-31.

Unique + Common chains (tetramer)b (gp130)a5Describe 3 classes, pictured as monomers that dimerize when cytokine binds Differences are in the number and types of subunits Some single chain. WHY? A: Various combinations of subunits allow greater specificity for signalingIL-6, LIF, IL-11, ciliary neurotrophic factor (CNTF), cardiotrophin-1 (CT-1), cardiotrophin-like cytokine (CLC), leukemia inhibitoryfactor (LIF), and oncostatin M (OSM)(1) and is now supplemented by the addition of two newly characterized cytokines,IL-27 and IL-31 Some partner with Gp130 Some Have unique multiple chainsThree sequential tyrosine phosphorylations triggered by cytokinereceptor interaction. Receptor dimerization allows transphosphorylation and activation of Janus kinases (JAKs). This is followed by phosphorylation of receptor tails and the recruitment of the Signal Transducers and Activators of Transcription (STAT) proteins through their Src-homology-2 domains. STAT tyrosine phosphorylation then occurs. Dimerization of activated (tyrosine phosphorylated) STAT is followed by nuclear entry. Nature Reviews Molecular Cell Biology 3; 651-662Canonical JAKSTAT pathway

Activating cross Tyr PO4 of JAK

PO4 of JAK

Binding & PO4 of STATTHM: 3 Tyr-P required; catalyzed by a kinase that is NOT a part of the receptor

Dimerization of STATs6SH2 Domains on STATS provide binding sites for P-Tyr on receptorPO4 STAT can then dimerizeDimerized STAT then capable of activating transcription

So, lets go into more detail about each of these players8Structural organization of STATsThe domain structure of STAT. The contact regions of STAT-interacting proteins are indicated by red lines. DBD: DNA binding domain; SH3: Src homology 3 domain (poly Pro); SH2: Src homology 2 domain (pY); TAD: Transcription activation domain; FERM ( band4.1, ezrin,radixin, & moesin) binds to STATS and other proteins FERM DBD SH3 SH2 TADStat2/p300(CBP)Stat1/p300(CBP)Stat5/ERKStat1/MCM5Stat5/NmiStat2/p48Stat1/p300(CBP)Stat1/PIAS1Stat1/p48Stat3/c-JunYPSPSignal Transducers and Activators of TranscriptionDifferent regions have different functions or bind different transcriptional regulatorsAt least 6 families of STATS8The amino terminal (NH2) end (JH4-JH7) of Jaks is called a FERM domain (short for band 4.1 ezrin, radixin and moesin); this domain is also found in the focal adhesion kinase (FAK) family and is involved in association of JAKs with cytokine receptors and/or other kinases.[SH3 interacts with poly proline sites on other signaling proteins SH2 binds to P tyr TAD = Transcription activation domain DBD = DNA binding domain

TyrTyrSH2STAT monomersSTAT dimer(binds DNA)Phosphorylation and SH2-phosphotyrosine bindingHow do SH2 and DNB domains work? FERM DBD SH3 SH2 TADYPSPP

(a) Crystal structure of an N and C-terminally truncated Stat1 molecule bound to DNA. The structure of truncated Stat3 is virtually superimposible with that of Stat1 (Chen et al., 1998). SH2 domainLinker domainDNA-binding domainCoiled coil domainStructure of STAT bound to DNANutcracker Model10Note the domains, SH2 required for dimerization (pTyr)11

The core structure (amino acids 130712) shows binding of a STAT1 dimer to DNA and the location of binding sites of various proteins in various domains. The amino-terminal structure, the placement of which in the intact structure is undefined, also interacts with various partners, as does the carboxy-terminal transactivation domain, the structure of which is unknown. CBP, CREB binding protein; IRF, interferon regulatory factor; Mcm, mini chromosome maintenance; Nmi, N-Myc interactor; PIAS, protein inhibitor of activated STAT. Nature Reviews Molecular Cell Biology 3; 651-662STAT domain structure and protein binding sites11Note that there are a lot of different regulatory molecules that bind to various places around the structure. Importin allows nuclear entry12Structure & number of JaksSeven domains, termed Jak homology (JH) domains 1-7 are shared among Jaks. The JH1 domain is the kinase domain and the JH2 domain is a pseudokinase domain whose precise function has not yet been determined. Pseudokinase DomainKinase DomainN C JH7 JH6 JH5 JH4 JH3 JH2 JH1Tyk2140 kDa 36%19p13.2UbquitousJak1135 kDa36% 1p31.2UbiquitousJak2130 kDa47%10p23UbiquitousJak3120 kDa - 4q31Myeloid/LymphoidSize Identity Chromosome ExpressionJANUS KINASESQ: What does acronym, JAK stand for? FERM 12The gene encodes an essential kinase (= an enzyme phosphorylating other proteins) that functions in the internal signalling system of cells. In the Janus kinases, there are two phosphate-transferring domains. Thus, it got its name from the Roman two-faced gatekeeper of the heaven Janus.The abbreviation JAK is also said to stand for "just another kinase" as there are so overwhelmingly many kinases in the body that no-one can remember them all anyway. The V617F mutation in the Jak2 pseudokinase domain causes myeloproliferative neoplasms, and the equivalent mutation in Jak1 (V658F) is found in T-cell leukemias. Crystal structures of wild-type and V658F-mutant human Jak1 pseudokinase reveal a conformational switch that remodels a linker segment encoded by exon 12, which is also a site of mutations in Jak2. This switch is required for V617F-mediated Jak2 activation and possibly for physiologic Jak activation. (Nature Structural & Molecular Biology 20, 12211223 (2013))13

Janus - the two-faced god, keeper of the gateThe Janus kinases, were thought to contain 2 types of phosphate-transferring domains. Thus, it is named after Janus, the Roman two-faced gatekeeper of the heavens.

13Janus in Myth JUST ANOTHER KINASE Tony Hunter Janus was the god of gates in Roman mythology. And in his role as the numen of gates and doors, Janus was also thought to represent beginnings. The explanation for this belief comes from the idea that one must emerge through a gate or door before entering a new place. As the god of beginnings, Janus also lent his name to the first month of the year. This month was referred to by the ancient Romans as Ianuarius - you can see how similar this word is to our own version (which is, of course, January). The god Janus has a distinctive appearance in art, as he is often depicted with two faces. Some sources claim that the reason Janus was represented in this peculiar fashion was due to the notion that doors and gates look in two directions. In this way, one of the god's faces could look forward, while the other looked backward. In addition, the Romans had an important temple to Janus, which was called the Ianus geminus. This temple served a symbolic function. When the gates of the structure were closed, this represented peace in the Roman Empire; but when the gates were open, it meant that the Romans were at war. It worth noting that Janus was well respected and highly regarded by the ancient Romans. From his role as the guardian of gates and his position as the god of beginnings, to the honor of having the first month of the year named after him, it is clear that Janus played a significant part in Roman myth and religion. Janus did not have a counterpart in Greek mythologyJanuary is named for the Greek god Janus, the god of beginnings and endings, who looked both backward and forward with his two faces. He was considered the door-keeper of the new year. Interestingly enough, our word janitor comes from Janus, as the person who tends the buildings, keeps the place neat and clean, the keeper of the keys. The term janitor does not carry much honor or authority in todays world, but the role is just as essential and significant it was when it was when honored by the name of an important god, Janus.Greek God who opens doors???Just another kinase14Different cytokine receptors bind different combinations of Jaks TYPE HORMONE PHOSPHORYLATIONSingle specificity Growth Hormone Homo-phosphorylationPromiscuous IL-6Multi- phosphorylation (all JAKs)Obligate Hetero INFa, INFgHetero-phosphorylation (2 different JAKs)INFgJak1Jak2INFaJak1Tyk2(Mutate Jak1 ---> no Tyk2 PO4(Mutate Jak1 ---> no Jak2 PO4 PO4OHow determined?Why important?Different Jaks PO4 different STATS14Why is it important that different receptors can bind different combinations of Jaks?, A: Different subunits bind different STATS and different Jaks preferentially phosphorylate different STATS15Interferon receptors and activation of classicalJAKSTAT pathways by type I and type II interferons

From Nat Rev Immunol 376 | MAY 2005All type I interferons (IFNs) bind a common receptor which is known as the type I IFN receptor. The type I IFN receptor is composed of two subunits, IFNAR1 and IFNAR2, which are associated with the Janus activated kinases (JAKs), tyrosine kinase 2 (TYK2) and JAK1, respectively. A single type II IFN, IFN-g, binds a distinct cell-surface receptor, which is known as the type II IFN receptor. This receptor is also composed of 2 subunits, IFNGR1 and IFNGR2, which are associated with JAK1 and JAK2, respectively. Activation of the JAKs that are associated with the type I IFN receptor results in tyrosine phosphorylation of STAT2 (signal transducer and activator of transcription 2) and STAT1; this leads to the formation of STAT1STAT2IRF9 (IFN-regulatory factor 9) complexes, which are known as ISGF3 (IFN-stimulated gene (ISG) factor 3) complexes. These complexes translocate to the nucleus and bind IFN-stimulated response elements (ISREs) to initiate gene transcription. Both type I and II IFNs also induce formation of STAT1STAT1 homodimers that translocate to the nucleus and bind GAS elements in the promoter of some ISGs, thereby initiating transcription of these genes. The GAS element and ISRE sequences are shown.Example of how one can get specificity of function by different interferons by expressing and utilizing different combinations of cytokine receptors, Jaks and STATS 15Example of how different interferon can give different signals by binding to different heterodimeric cytokine receptors that in turn bind different Jaks.How is Cytokine Function Regulated?A: Several types of negative feedbackDiagram of domains in STAT-induced STAT Inhibitors, SOCS & CIS proteins

At least eight proteins belong to the SOCS family of proteins are shown (upper panel). They are characterized by the presence of an SH2 central domain and the SOCS box domain at the C-terminus. A small domain called kinase inhibitory region (KIR), only found in SOCS1 and SOCS3, is shown as a small box at the N-terminal region. SOCS proteins can interact with phosphotyrosine phosphorylated proteins through their SH2 domain and with Elongin BC through their SOCS box domain. Other proteins containing a SOCS box domain but lacking a SH2 domain are also shown (lower panel). Rico-Bautista et al 2006

Other SOCS Box containing proteinsCIS = Cytokine-Induced SH2 protein; SOCS = Suppressor of Cytokine SignalingSSI = STAT-induced STAT InhibitorKinase domain binding (Kinase Inhibitor)P-tyrosine binding (STAT competitorElongin B/C binding (ubiquitination)18(a) Binding of JAK to cytokine receptors and activation of STAT. (b) SSI-type inhibition of cytokine signaling. The gene encoding SSI-1 is induced by STAT dimers, resulting in the production of SSI-1 and inhibition of cytokine signaling by binding of SSI-1 to the kinase domain of the JAK family. (c) CIS1-type inhibition of cytokine signaling. The gene encoding CIS1 is induced by STAT5 dimers, resulting in the production of CIS1 and inhibition of cytokine signaling by binding of CIS1 to the STAT binding site of cytokine receptors.Abbreviations used: CIS1, cytokine-inducible SH2 protein 1; GAS motif, -Stat activated site; JAK, Janus tyrosine kinase, SSI, STAT-induced STAT inhibitor; STAT, signal transducers and activators of transcription.Negative regulation of cytokine signaling: STAT-induced STAT inhibitor Naka et al.,TiBs, 24:394-398

SSI-1 type inhibition

CIS-1 type inhibitionTHM - 2 sites of inhibition (Jaks or STAT binding to Receptor)= SOCS1SOCS bind to and inhibit JAKsCIS inhibits STAT bindingQuestion: what would the difference be for this pathway in the cell to be feedback inhibited by SOCS vs CIS (ie Jak inhibition vs more direct STAT inhibition?1819

Phosphatases (a) and suppressors of cytokine signalling (SOCS proteins) (b) block further STAT activation in the cell cytoplasm. In the nucleus, nuclear phosphatases (c) can mediate STAT dephosphorylation, and interactions with proteins that inhibit activated STAT proteins (PIAS) (d) can also occur. In addition, naturally occurring short forms of STATs can potentially act as dominant-negative proteins by occupying DNA as non-functional protein or by binding to a wild-type STAT protein (e). JAK, Janus kinase; STAT, signal transducers and activators of transcription. Note, also shown in green is a likely regulation of JAKs by ubiquitination/phosphorylationNature Reviews Molecular Cell Biology 3; 651-662 (2002); STATS: Transcriptional control and biological impactOther negative regulators of STAT proteins

Why so many different mechanisms for controlling STATS?

19Point here is that there are additional regulators, eg ptases in both cytoplasm and nucleus (different)WHY so many regulators? A: Because so important signaling switch. Run amok and you have big problems.20

Fig 4 | Different PIAS (protein inhibitor of activated STAT) proteins can inhibit the Janus kinase (JAK)signal transducer and activator of transcription (STAT) pathway through distinct mechanisms. a | PIAS1 and PIAS3 block the DNA-binding activity of STAT dimers. b | PIASX and PIASY might act as transcriptional co-repressors of STAT by recruiting other co-repressor proteins such as histone deacetylase (HDAC). c | PIAS proteins can promote the conjugation of small ubiquitin-related modifier (SUMO) to STAT1. The significance of STAT1 sumoylation in regulating STAT1 activity is controversial and needs to be clarifiedNature Reviews Immunology 3; 900-911Proposed mechanisms for inhibiting the JAKSTAT pathway by PIAS proteinsBlock DNA bindingAct as co-repressorsPromote sumoylation21Pias Proteins act as E3 ligases for SUMO

Left - Ubiquitin is coupled to E-1 ubiquitin-activating enzyme and in turn transferred to E-2 ubiquitin-conjugating enzyme. E3 ubiquitin ligase combines with the charged E2 and forms an isopeptide bond between ubiquitin and the target protein. PIAS proteins act as E3 ligases for SUMO. SUMO shares 18% homology with ubiquitin. Right - PIAS1, PIAS3 and PIASx sumoylate STAT1 at Lys-703- close to Tyr-701 where JAK is phosphorylated. STAT1 can be modified by SUMO at lysine residue 703. Direct interactions between PIAS1 and STAT1 may interfere with the STAT1 ability to bind DNA.

Biochemical Pharmacology 70 (2005) 649657Ubiquitin is a 76 AA small modifying protein added to Lys residues. Classically it targets to degradation esp when multi ub groups put on.21Example of Feedback Regulation by SOCS23Leptin induces SOCS-3, but not CIS, SOCS-1, or SOCS-2, mRNA in CHO cells expressing the long form of the leptin receptor. The role of SOCS-3 in Leptin signaling and resistanceJ Flier lab JBC 274:30059 99

CIS mRNASOCS-1 mRNASOCS-2 mRNASOCS-3 mRNACHO-OBRIO hr 1hr 2 hr 4hr stimulation with leptinTHM - specificity of induction and different time courses

THM - induction of SOCS-3 causes decreased cytokine coupling23Left shows transient induction of SOCS-3 but not 1,2 or CIS in CHO cells by long form of leptin receptorRight shows that only SOCS-3 will inhibit JAK-2 PO4 (lower panel stats from upper)THM note specificity for only Jak-2 and also transient time courseHow important are SSI proteins?Studies with SOCS1 KO mice25In SOCS1 knockout mice, negative regulation of cytokine signaling is diminished

Lack of binding of SSI-1 to JAK leads to prolonged activation of the JAK/STAT pathway and prolonged action of cytokines. Abbreviations: JAK, Janus tyrosine kinase, SSI, STAT-induced STAT inhibitor; STAT, signal transducers and activators of transcription.Naka et al.,Trends in Biochemical Sciences, 24:394-398SOCS-1 KO ---> Post-Embryonic LethalRescued by cross of heterozygotes to INF-g KO25Point is that SOCS-1 KO is lethal2nd point is that INFg KO is able to rescue; therefore phenotype due largely to to much INFgamma signaling in absence of normal SOCS feedbackCross talk between Jak/STAT and other signaling pathwaysTHM1: Other pathways can be activated by ligand binding to "cytokine" receptorsTHM2: Jaks can bind & activate other tyrosine kinase pathwaysTHM3: Other serine kinase pathways can modulate Jak/STAT functionTHM4: SOCS proteins can modulate other pathwaysActivation of CRKL by the type I INF receptor, and role of CRKL in type-I INF-mediated signaling

Fig 2 CRKL is present as a latent cytoplasmic form that constitutively associates with the guanine-nucleotide-exchange factor (GEF) C3G. A member of the STAT (signal transducer and activator of transcription) family of proteins, STAT5, is associated with tyrosine kinase 2 (TYK2) that is bound to the type I interferon (IFN) receptor subunit IFNAR1. After engagement of the type I IFN receptor by an IFN, CRKL associates with TYK2 and undergoes rapid tyrosine phosphorylation. The activated form of CRKL forms a signaling complex with STAT5, which also undergoes TYK2-dependent tyrosine phosphorylation. The CRKLSTAT5 complex translocates to the nucleus and binds specific GAS (IFN-activated site) elements that are present in the promoters of certain IFN-stimulated genes (ISGs), which initiates transcription of these genes. The specific GAS sequence bound by CRKLSTAT5 is shown. The IFN-dependent phosphorylation (activation) of CRKL also results in induction of the GEF activity of C3G. C3G subsequently regulates the small G-protein RAP1, resulting in activation of this GTPase, which may then promote growth-inhibitory responses JAK, Janus activated kinase.Nat Rev Immunol 376 | MAY 2005 | Jak2 can also phosphorylate CRKL allowing it to be active itself just like a STAT and form a heterodimer

It can also scaffold and activate C3G, (GEF) leading to increased RAP1 activity.27Major message here is that Jak2 can also phosphorylate CRKL allowing it to be active itself just like a STAT and form a heterodimerIt can also scaffold and activate C3G, a small GTP exchange protein ieading to increased RAP1 activity.28

Interferon (IFN)-activated JAKs regulate the phosphorylation (activation) of VAV or other guanine-nucleotide-exchange factors (GEFs), resulting in downstream activation of RAC1 and, possibly, other small G proteins (SGPs) that can regulate the signaling pathway of the mitogenactivated protein kinase (MAPK) p38. A MAPK kinase kinase (MAPKKK) is subsequently activated and regulates downstream activation of the MAPK kinases MAPKK3 and MAPKK6, which directly phosphorylate p38, resulting in its activation. Activated p38 subsequently regulates activation of multiple downstream effectors, including MAPK-activated protein kinase 2 (MAPKAPK2), MAPKAPK3, mitogen- and stress-activated kinase 1 (MSK1) and MAPK-interacting protein kinase 1 (MNK1). IFNAR1, type I IFN receptor subunit 1; IFNAR2, type I IFN receptor subunit 2; TYK2, tyrosine kinase 2.Mechanisms of activation of MAP kinase, p38 and its downstream effectors by type I interferonsNat Rev Immunol 376 MAY 2005THM: Tyk2 and Jak1 can also directly activate GEFs28Tyk2 and Jak1 can also directly activate GEFs29JAK2-mediated activation of STATs and ERK/MAPK by GH or a growth factor (GF)

Current Biology Linda A. Winston, Tony Hunter 1996, 6:668-671THM: Just because effect is due to a cytokine, doesnt mean that it has to be STAT pathwayPI3KAKT29Basically, the map kinases can activate STATS while bound to cytokine receptors, receptor probably is needed but in the absence of or decreased activity of JAKs, Map kinase can do the job. See next slide for example. Perhaps for example in the presence of SOCs. Q: can activation of map kinase pathway overcome normal SOCs inhibition?

MSH5HTJAK-STAT 1:4, 250256; Ang II activates JAK2 via the G protein-dependent and -independent mechanisms leading to gene transcription and vasoconstriction. Various second messengers including PKC, Pyk2, Arhgef1 and SHP2 are involved in these pathways. Activation of the JAK-STAT pathway via AT1R30JAK-STAT 1:4, 250256; Figure 1. Scheme illustrating the activation of the JAK-STAT pathway by Ang II through AT1R. Ang II activates JAK2 via the G protein-dependent and -independent mechanisms leading to gene transcription and vasoconstriction. Various second messengers including PKC, Pyk2, Arhgef1 and SHP2 are involved in these pathways.

31Please - Dont get behind on reading. You can be sure that some of exam questions will come from the readings.For example, in the research paper I assigned that came out just last week,Do you think that the authors are correct when they say that these inflamasomes that contain NLRP3 are direct binders and effectors for cAMP action on immune system??

32SOCS proteins inhibit insulin receptor signaling by binding to the insulin receptor, thereby blocking access of signaling intermediates and inhibiting insulin receptor tyrosine kinase activity, leading to a reduction in insulin-receptor directed phosphorylation of IRS-1 and its downstream events, and by targeting IRS-1 and IRS-2 for proteosomal degradation. Abbreviations: PKB, protein kinase B (also known as Akt); PDK1 and 2, phosphoinositide-dependent kinase 1 and 2; PI(4,5)P2, phosphatidylinositol (4,5)- bisphosphate; PI(3,4,5)P3, phosphatidylinositol (3,4,5)-trisphosphate); Shr, C-terminal SH2 domain-containing adaptor protein.

SOCS can regulate insulin pathway at several pointsFlier 0633Termination of STAT1 signaling via acetylation

IFNs induce STAT1 signaling. The nuclear HAT CBP catalyzes acetylation of phosphorylated nuclear STAT1. Subsequently, TCP45 is recruited and STAT1 becomes dephosphorylated, exits the nucleus, and acquires latency.Kramer & Heinzel, Molecular and Cellular Endocrinology (2009) THM: One more mechanism of regulationHATTyr PtaseTCP45 is a tyrosine phosphatase

CBP is a HAT and CBP is a CREB binding protein 33TCP45 is a tyrosine phosphatase; CBP is a HAT and CBP is a CREB binding protein, CREP = Cyclic AMP Response Element Binding Protein34A phospho-acetyl switch controls STAT1 signaling

A phospho-acetyl switch controls STAT1 signaling. Modifications of STAT1 are dynamically regulated. A phospho-acetyl switch controls STAT1 upon activation by IFN. Serine phosphorylation of STAT1 regulates repressive sumoylation of STAT1 (pY, tyrosine phosphorylation; Ac, lysine acetylation; pS, serine phosphorylation; Su,sumoylation; MAPK,MAPkinases). STAT1/STAT2 heterodimers serve as example.Kramer & Heinzel, Molecular and Cellular Endocrinology (2009)

Acetylation of STAT1 antagonizes its IFN-induced phosphorylation. The balance between STAT1 acetylation and phosphorylation determines STAT1 activity and IFN signaling. STAT1 homodimers serve as an example.

34Histone acetyltransferases (HATs); histone deacetylases (HDACs); histone deacetylase inhibitors (HDACIs),gamma interferon activated sequences (GAS)

Intracellular sensors in innate immunity to viruses: a mechanism for control of cytokine synthesisPRRs = pattern recognition receptors TLRs ( Toll-like), RLRs (RIG-1-like), CLRs (C-type lectin), & NLRs (nucleotide binding domain leucine rich repeatsCARD = caspase recruitment domainAfter induction many cytokines need to be activated by proteolytic clipping of the prohormoneFigure 1 | Intracellular sensors in innate immunity to viruses. Viral pathogen-associated molecular patterns (PAMPs) activate nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) and inflammasomes to initiate signalling cascades that lead to the production of pro-inflammatory cytokines, thereby amplifying antiviral innate immune responses. In the presence of viral PAMPs, NLR family PYD-containing protein 3 (NLRP3) and absent in melanoma 2 (AIM2) oligomerize and recruit the adaptor protein apoptosis-associated speck-like protein containing a CARD (ASC) through homotypic pyrin domain (PYD) interactions. The caspase-recruitment domain (CARD) of ASC binds the CARD of pro-caspase1, leading to caspase1 activation and the production of interleukin1 (IL1) and IL18 through cleavage of pro-IL1 and pro-IL18. Retinoic acid inducible geneI (RIGI) contains an RNA helicase domain and an amino-terminal CARD. The helicase domain of RIGI senses the 5-triphosphate moiety of single-stranded (ss)RNA virus genomes and then signals through CARDCARD interactions with the adaptor molecule mitochondrial antiviral signalling protein (MAVS). This results in the phosphorylation and activation of interferon (IFN) response factor 3 (IRF3) and IRF7 to turn on the transcription of typeI IFN (IFN/) genes. RIGI also regulates IL1 production transcriptionally and post-translationally following recognition of 5-triphosphate double-stranded (ds)RNA. Whereas RIGI-triggered transcription of pro-IL1 depends on nuclear factor-B (NF-B) activation and is mediated by MAVS, inflammasome formation, caspase1 activation, and IL1 and IL18 production in response to RIGI activation involve ASC. The NLRs NOD2, NLR family member X1 (NLRX1) and NLR family CARD-containing protein 5 (NLRC5) associate with MAVS. Whereas NOD2 mediates the induction of typeI IFNs, NLRX1 and NLRC5 inhibit RIGIMAVS interactions and thereby negatively regulate typeI IFN production. LRR, leucine-rich repeat; MAPK, mitogen-activated protein kinase; MYD88, myeloid differentiation primary-response protein 88; RIPK2, receptor-interacting serine-threonine protein kinase 2; ROS, reactive oxygen species; TLR, Toll-like receptor; TNF, tumour necrosis factor; TRIF, TIR-domain-containing adaptor protein inducing IFN.

3536Figure 1 | Intracellular sensors in innate immunity to viruses. Viral pathogen-associated molecular patterns (PAMPs) activate nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) and inflammasomes to initiate signalling cascades that lead to the production of pro-inflammatory cytokines, thereby amplifying antiviral innate immune responses. In the presence of viral PAMPs, NLR family PYD-containing protein 3 (NLRP3) and absent in melanoma 2 (AIM2) oligomerize and recruit the adaptor protein apoptosis-associated speck-like protein containing a CARD (ASC) through homotypic pyrin domain (PYD) interactions. The caspase-recruitment domain (CARD) of ASC binds the CARD of pro-caspase1, leading to caspase1 activation and the production of interleukin1 (IL1) and IL18 through cleavage of pro-IL1 and pro-IL18. Retinoic acid inducible geneI (RIGI) contains an RNA helicase domain and an amino-terminal CARD. The helicase domain of RIGI senses the 5-triphosphate moiety of single-stranded (ss)RNA virus genomes and then signals through CARDCARD interactions with the adaptor molecule mitochondrial antiviral signalling protein (MAVS). This results in the phosphorylation and activation of interferon (IFN) response factor 3 (IRF3) and IRF7 to turn on the transcription of typeI IFN (IFN/) genes. RIGI also regulates IL1 production transcriptionally and post-translationally following recognition of 5-triphosphate double-stranded (ds)RNA. Whereas RIGI-triggered transcription of pro-IL1 depends on nuclear factor-B (NF-B) activation and is mediated by MAVS, inflammasome formation, caspase1 activation, and IL1 and IL18 production in response to RIGI activation involve ASC. The NLRs NOD2, NLR family member X1 (NLRX1) and NLR family CARD-containing protein 5 (NLRC5) associate with MAVS. Whereas NOD2 mediates the induction of typeI IFNs, NLRX1 and NLRC5 inhibit RIGIMAVS interactions and thereby negatively regulate typeI IFN production. LRR, leucine-rich repeat; MAPK, mitogen-activated protein kinase; MYD88, myeloid differentiation primary-response protein 88; RIPK2, receptor-interacting serine-threonine protein kinase 2; ROS, reactive oxygen species; TLR, Toll-like receptor; TNF, tumour necrosis factor; TRIF, TIR-domain-containing adaptor protein inducing IFN.