R E V I E W S
`
`Recent insights into targeting the
`IL-6 cytokine family in inflammatory
`diseases and cancer
`
`Simon A. Jones1,2* and Brendan J. Jenkins3,4*
`
`Abstract | The IL-6 family of cytokines consists of IL-6, IL-11, IL-27 , IL-31, oncostatin M (OSM),
`leukaemia inhibitory factor (LIF), ciliary neurotrophic factor (CNTF), cardiotrophin 1 (CT-1) and
`cardiotrophin- like cytokine factor 1 (CLCF1). Membership of this cytokine family is defined by
`usage of common β- receptor signalling subunits, which activate various intracellular signalling
`pathways. Each IL-6 family member elicits responses essential to the physiological control
`(cid:81)(cid:72)(cid:124)(cid:75)(cid:79)(cid:79)(cid:87)(cid:80)(cid:71)(cid:2)(cid:74)(cid:81)(cid:79)(cid:71)(cid:81)(cid:85)(cid:86)(cid:67)(cid:85)(cid:75)(cid:85)(cid:14)(cid:2)(cid:74)(cid:67)(cid:71)(cid:79)(cid:67)(cid:86)(cid:81)(cid:82)(cid:81)(cid:75)(cid:71)(cid:85)(cid:75)(cid:85)(cid:14)(cid:2)(cid:75)(cid:80)(cid:72)(cid:78)(cid:67)(cid:79)(cid:79)(cid:67)(cid:86)(cid:75)(cid:81)(cid:80)(cid:14)(cid:2)(cid:70)(cid:71)(cid:88)(cid:71)(cid:78)(cid:81)(cid:82)(cid:79)(cid:71)(cid:80)(cid:86)(cid:2)(cid:67)(cid:80)(cid:70)(cid:2)(cid:79)(cid:71)(cid:86)(cid:67)(cid:68)(cid:81)(cid:78)(cid:75)(cid:85)(cid:79)(cid:16)(cid:2)
`(cid:35)(cid:69)(cid:69)(cid:81)(cid:84)(cid:70)(cid:75)(cid:80)(cid:73)(cid:78)(cid:91)(cid:2)(cid:14)(cid:124)(cid:70)(cid:75)(cid:85)(cid:86)(cid:81)(cid:84)(cid:86)(cid:75)(cid:81)(cid:80)(cid:2)(cid:81)(cid:72)(cid:2)(cid:86)(cid:74)(cid:71)(cid:85)(cid:71)(cid:2)(cid:69)(cid:91)(cid:86)(cid:81)(cid:77)(cid:75)(cid:80)(cid:71)(cid:2)(cid:67)(cid:69)(cid:86)(cid:75)(cid:88)(cid:75)(cid:86)(cid:75)(cid:71)(cid:85)(cid:2)(cid:81)(cid:72)(cid:86)(cid:71)(cid:80)(cid:2)(cid:82)(cid:84)(cid:81)(cid:79)(cid:81)(cid:86)(cid:71)(cid:85)(cid:2)(cid:69)(cid:74)(cid:84)(cid:81)(cid:80)(cid:75)(cid:69)(cid:2)(cid:70)(cid:75)(cid:85)(cid:71)(cid:67)(cid:85)(cid:71)(cid:2)(cid:67)(cid:80)(cid:70)(cid:2)(cid:69)(cid:67)(cid:80)(cid:69)(cid:71)(cid:84)(cid:2)(cid:29)(cid:2)
`the pathological importance of this is exemplified by the successful treatment of certain
`autoimmune conditions with drugs that target the IL-6 pathway. Here, we discuss the emerging
`roles for IL-6 family members in infection, chronic inflammation, autoimmunity and cancer and
`review therapeutic strategies designed to manipulate these cytokines in disease.
`
`Lymphokines
`A subset of cytokines that are
`released by lymphocytes.
`
`1Division of Infection and
`Immunity, School of Medicine,
`Cardiff University, Cardiff,
`Wales, UK.
`
`2Systems Immunity,
`University Research Institute,
`School of Medicine, Cardiff
`University, Cardiff, Wales, UK.
`
`3Centre for Innate Immunity
`and Infectious Diseases,
`Hudson Institute of Medical
`Research, Clayton, Victoria,
`Australia.
`
`4Department of Molecular
`and Translational Science,
`Faculty of Medicine, Nursing
`and Health Sciences, Monash
`University, Clayton, Victoria,
`Australia.
`
`*e- mail: JonesSA@
`cardiff.ac.uk;
`brendan.jenkins@
`hudson.org.au
`
`https://doi.org/10.1038/
`s41577-018-0066-7
`
`Cytokines contribute to all aspects of human biology
`and have evolved to enable the sensing and interpreta-
`tion of environmental cues relevant to the maintenance
`of normal host physiology1. Although these secretory
`proteins are best known for their role as custodians of
`immune homeostasis and the inflammatory response
`to infection, trauma or injury, their diverse functions
`also affect embryonic development, cognitive func-
`tion and behaviour, tissue integrity and ageing. In this
`regard, cytokines often display pleiotropic or overlapping
`functional properties1.
`The IL-6 cytokine family comprises IL-6, IL-11,
`IL-27, IL-31, oncostatin M (OSM), leukaemia inhibi-
`tory factor (LIF), ciliary neurotrophic factor (CNTF),
`cardiotrophin 1 (CT-1) and cardiotrophin- like cytokine
`factor 1 (CLCF1), and among all cytokine families, it
`arguably displays the highest degree of functional pleio-
`tropy and redundancy in eliciting responses relevant to
`health and disease2. Members of this family play prom-
`inent roles in chronic inflammation, autoimmunity,
`infectious disease and cancer (BOX 1), where they often
`act as diagnostic or prognostic indicators of disease
`activity and response to therapy1,3–6. Moreover, IL-6
`family cytokines are now viewed as major therapeutic
`targets for clinical intervention3–9. This is epitomized
`by the treatment of chronic immune- related conditions,
`such as inflammatory arthritis, giant cell arteritis and
`Castleman disease, with drugs that target IL-6 (REFS5,10–12).
`In this Review, we draw on recent advances to provide
`a timely update on the biology of IL-6 family cytokines
`
`and their clinical potential as therapeutic targets or
`disease modifiers in autoimmunity, inflammation,
`infection and cancer.
`
`What constitutes IL-6 family membership?
`IL-6 remains the archetypal member of the IL-6 cytokine
`family and regulates a diverse array of functions relevant
`to haematopoiesis, tissue homeostasis, metabolism and
`immunity5,13 (BOXES 1,2). Since the discovery of IL-6,
`subsequent investigations have revealed a high degree of
`functional redundancy among IL-6 family cytokines14.
`As a consequence, cytokines within this family are
`often described with activities attributed to lymphokines,
`adipokines or myokines, which reflect their broad expres-
`sion and cellular distribution among all major cell types
`within the body. This redundancy is characterized by a
`precise hierarchical involvement in inflammation, meta-
`bolism, development, tissue regeneration, neurogenesis
`and oncogenesis15 (BOXES 1,2).
`A defining feature of this cytokine family is its usage
`of common cytokine receptor subunits. These recep-
`tor complexes comprise the shared signal- transducing
`receptor β- subunit, membrane glycoprotein 130 (gp130;
`also known as IL-6Rβ), together with either a ligand-
`binding non- signalling receptor α- subunit or a signal-
`ling receptor β- subunit that resembles gp130 (REFS2,15,16)
`(FIG. 1). The receptor signalling complexes for IL-6 and
`IL-11 contain a gp130 homodimer, whereas other fam-
`ily members signal via a heterodimeric receptor com-
`plex containing gp130 and an alternative signalling
`
`NATURE REVIEWS | IMMUNOLOGY
`
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` VOLUME 18 | DECEMBER 2018 | 773
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`Lassen - Exhibit 1020, p. 1
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`

`

`R E V I E W S
`
`Box 1 | Signalling mechanisms for IL-6 family cytokines and links with physiological and disease processes
`
`Intracellular signalling mechanisms linked to the membrane glycoprotein
`130 (gp130) receptor system are triggered via activation of receptor-
`associated cytoplasmic tyrosine kinases (Janus kinase 1 (JAK1), JAK2
`and non- receptor tyrosine- protein kinase 2 (TYK2)). Activation of these
`proteins leads to distinct patterns of tyrosine phosphorylation and
`subsequent activation of the latent transcription factors signal transducer
`and activator of transcription 1 (STAT1), STAT3 and, to a lesser extent,
`STAT5. Additional signalling mechanisms associated with cytokine
`activation of the gp130 receptor system include processes controlled
`through the tyrosine- protein phosphatase SH- PTP2 (SHP2). The activation
`of this protein promotes signalling through the RAS–RAF pathway
`and the SRC–YAP–NOTCH pathway. Activation of the RAS–RAF
`cascade also regulates several downstream modifiers that include
`the phosphory lation of mitogen- activated protein kinases (MAPKs)
`
`and the RAC serine/threonine-protein kinase (AKT) and mechanistic target
`of rapamycin complex 1 (mTORC1) pathways and activities associated with
`the transcription factors nuclear factor NF- IL-6 (a CAAT/enhancer
`binding protein (C/EBP) family member) and activator protein 1 (AP-1)
`(a heterodimer of proto- oncogene JUN and proto- oncogene FOS). Other
`kinases with less defined involvements with this receptor system include
`serine/threonine- protein kinase SAK (also known as PLK4), tyrosine-protein
`kinase HCK, tyrosine- protein kinase FES/FPS (FES), tyrosine-protein kinase
`BTK and tyrosine- protein kinase TEC16. Each of these signal transduction
`mechanisms controls various biological processes, as indicated. The heat
`map depicted in the right- hand panel details how individual IL-6 cytokine
`family members contribute to specific physiological and immunological
`processes and emphasizes their relative importance in certain disease
`settings (depicted below the blue line).
`
`Intracellular cytokine receptor signals and downstream activities
`
`IL-6 family cytokine
`
`IL-6
`
`(cid:43)(cid:46)(cid:15)(cid:19)(cid:19)
`
`IL-27
`
`(cid:43)(cid:46)(cid:15)(cid:21)(cid:19)
`
`O S M
`
`LIF
`
`(cid:37) (cid:48)(cid:54)(cid:40)
`
`(cid:37)(cid:54)(cid:15)(cid:19)
`
`(cid:37)(cid:46)(cid:37)(cid:40)(cid:19)
`
`JAK
`
`SHP2
`
`(cid:114)(cid:2)(cid:53)(cid:54)(cid:35)(cid:54)(cid:19)
`(cid:114)(cid:2)(cid:53)(cid:54)(cid:35)(cid:54)(cid:21)
`(cid:114)(cid:2)(cid:53)(cid:54)(cid:35)(cid:54)(cid:23)
`
`(cid:114)(cid:2)(cid:52)(cid:35)(cid:53)
`(cid:114)(cid:2)(cid:52)(cid:35)(cid:40)
`(cid:114)(cid:2)(cid:47)(cid:35)(cid:50)(cid:45)
`
`(cid:114)(cid:2)(cid:35)(cid:45)(cid:54)
`(cid:114)(cid:2)(cid:50)(cid:43)(cid:21)(cid:45)
`(cid:114)(cid:2)(cid:10)(cid:79)(cid:54)(cid:49)(cid:52)(cid:37)(cid:19)(cid:11)
`
`(cid:114)(cid:2)(cid:53)(cid:52)(cid:37)
`(cid:114)(cid:2)(cid:59)(cid:35)(cid:50)
`(cid:114)(cid:2)(cid:48)(cid:49)(cid:54)(cid:37)(cid:42)
`
`(cid:114) Proliferation
`(cid:114) Survival
`(cid:114) Differentiation
`(cid:114) Migration
`(cid:114) Maturation
`(cid:114) Self-renewal
`(cid:114) Immune regulation
`(cid:114) Angiogenesis
`(cid:114) Metabolism
`(cid:114) Oxidative stress
`
`Proliferation
`
`(cid:114) Proliferation
`(cid:114)(cid:2)(cid:54)(cid:75)(cid:85)(cid:85)(cid:87)(cid:71)(cid:2)
`generation
`
`(cid:114) Proliferation
`(cid:114) Survival
`(cid:114) Apoptosis
`(cid:114) Growth
`(cid:114) Fate
`(cid:114) Metabolism
`(cid:114) Oxidative stress
`
`Innate immunity
`
`Adaptive immunity
`
`(cid:54)(cid:75)(cid:85)(cid:85)(cid:87)(cid:71)(cid:2)(cid:74)(cid:81)(cid:79)(cid:71)(cid:81)(cid:85)(cid:86)(cid:67)(cid:85)(cid:75)(cid:85)
`
`Haematopoeisis
`
`Oncogenesis
`
`Pain
`
`Mental well-being
`
`(cid:48)(cid:71)(cid:87)(cid:84)(cid:81)(cid:86)(cid:84)(cid:81)(cid:82)(cid:74)(cid:75)(cid:69)(cid:2)(cid:72)(cid:67)(cid:69)(cid:86)(cid:81)(cid:84)
`
`(cid:37)(cid:67)(cid:80)(cid:69)(cid:71)(cid:84)
`
`Autoimmunity
`
`(cid:43)(cid:80)(cid:561)(cid:67)(cid:79)(cid:79)(cid:67)(cid:86)(cid:75)(cid:81)(cid:80)
`
`(cid:37)(cid:81)(cid:80)(cid:86)(cid:84)(cid:75)(cid:68)(cid:87)(cid:86)(cid:75)(cid:81)(cid:80)
`
`Less
`
`More Unknown
`
`CLCF1, cardiotrophin-like cytokine factor 1; CNTF, ciliary neurotrophic factor; CT-1, cardiotrophin 1; LIF, leukaemia inhibitory factor; OSM, oncostatin M;
`PI3K, phosphoinositide 3-kinase.
`
`β- subunit (FIG. 1). The exception to this ‘gp130 rule’ is
`IL-31, which binds a cytokine receptor complex con-
`taining the OSM- specific receptor subunit- β (OSMRβ)
`and a cognate IL-31-binding receptor termed IL-31
`receptor subunit- α (IL-31Rα)17–19.
`Phylogenetic analysis of cytokine families reveals that
`members of the IL-6 family share a close relationship
`with IL-12 family cytokines20–22. This link is illustrated
`by the heterodimeric composition of IL-27 (comprising
`IL-27p28 (also known as IL-27α) and Epstein–Barr virus-
`induced gene 3 protein (EBI3; also known as IL-27β)),
`which is structurally related to the IL-12 (IL-12p40 (also
`known as IL-12β)–IL-12p35 (also known as IL-12α)),
`IL-23 (IL-23p19 (also known as IL-23α)–IL-12p40),
`IL-35 (IL-12p40–EBI3) and IL-39 (IL-23p19–EBI3)
`hetero dimers23–25. Interestingly, both IL-27p28 and IL-35
`can also signal via gp130 (REFS26,27), although the biolog-
`ical importance of this engagement with gp130 requires
`further substantiation, and thus their membership to the
`IL-6 family of cytokines is premature.
`The functional diversity and redundancy associated
`with IL-6 family cytokines is partially explained by the
`
`presence of the ubiquitously expressed common gp130
`signal- transducing receptor (FIG. 1). Use of the common
`gp130 receptor subunit contributes to the regulation
`of a wide range of overlapping activities that are con-
`trolled by IL-6 family cytokines. As a consequence,
`these cytokines play key roles in many physiological
`processes, including development, as evidenced by the
`embryonic lethality of gp130-deficient mice28. In con-
`trast to gp130, the receptor subunits specific to individ-
`ual family members display a more restricted cellular
`expression profile, and the phenotype of mice lacking
`individual cytokine family members or their associated
`receptor subunits is often less severe than their apparent
`pleiotropic properties would suggest28–31.
`While the tissue distribution of these receptors offers
`some distinction as to how individual family members
`act in defined cellular compartments, certain cytokines
`within the family have evolved several mechanisms that
`amplify or broaden their cellular activities. For example,
`human OSM can signal via gp130–LIF receptor (LIFR)
`or gp130–OSMRβ complexes to mediate responses typi-
`cally associated with LIF (for example, haematopoiesis)17.
`
`Adipokines
`A subset of cytokines that are
`secreted by adipose tissue and
`are sometimes called
`adipocytokines.
`
`Myokines
`Cytokines produced and
`released by myocytes in
`response to muscle
`contraction.
`
`774 | DECEMBER 2018 | VOLUME 18
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`Lassen - Exhibit 1020, p. 2
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`

`

`Box 2 | IL-6 family cytokines as regulators of metabolic processes
`
`IL-6 family cytokines
`
`IL-6
`
`IL-11
`
`IL-27
`
`IL-31
`
`O S M
`
`LIF
`
`C N TF
`
`C T-1
`
`C L C F1
`
`Bone metabolism
`
`Energy metabolism
`
`Glucose metabolism
`
`Lipid metabolism
`
`Iron transport
`
`Thermogenesis
`
`Contribution
`
`Less
`
`More
`
`Unknown
`
`CLCF1, cardiotrophin-like cytokine factor 1.
`
`Members of the IL-6
`cytokine family perform
`integral roles in health and
`disease, and their capacity
`to influence the
`maintenance of immune
`homeostasis and well-
`being can occur via
`regulation of various
`metabolic processes.
`(cid:54)(cid:74)(cid:71)(cid:124)(cid:70)(cid:71)(cid:82)(cid:75)(cid:69)(cid:86)(cid:71)(cid:70)(cid:2)(cid:74)(cid:71)(cid:67)(cid:86)(cid:2)(cid:79)(cid:67)(cid:82)(cid:2)
`summarizes the relative
`contribution of individual
`members of the IL-6
`cytokine family to
`metabolism and
`emphasizes the types of
`metabolic processes that they affect. Certain family members, such as IL-6 and oncostatin
`M (OSM), elicit these effects in various stromal tissue compartments (for example, muscle,
`liver, bone and brain) and inflammatory cells (for example, lymphocytes and
`macrophages)242–244. On the other hand, IL-27 displays a more restricted activity profile on
`select immune cell types, where it controls the expression of enzymes responsible for
`oxysterol generation in effector and regulatory CD4+(cid:2)(cid:54)(cid:124)(cid:69)(cid:71)(cid:78)(cid:78)(cid:85)245. Importantly, several of
`these associations with metabolism have been identified through clinical observations in
`patients receiving biological drugs. For example, hypoferraemia is a common response to
`systemic infection, and patients with autoimmune conditions, such as rheumatoid arthritis,
`frequently suffer from inflammatory anaemia246. Here, biological drugs against IL-6
`(cid:10)(cid:72)(cid:81)(cid:84)(cid:124)(cid:71)(cid:90)(cid:67)(cid:79)(cid:82)(cid:78)(cid:71)(cid:14)(cid:2)(cid:86)(cid:81)(cid:69)(cid:75)(cid:78)(cid:75)(cid:92)(cid:87)(cid:79)(cid:67)(cid:68)(cid:11)(cid:2)(cid:69)(cid:81)(cid:79)(cid:68)(cid:67)(cid:86)(cid:2)(cid:86)(cid:74)(cid:71)(cid:2)(cid:70)(cid:71)(cid:88)(cid:71)(cid:78)(cid:81)(cid:82)(cid:79)(cid:71)(cid:80)(cid:86)(cid:2)(cid:81)(cid:72)(cid:2)(cid:67)(cid:80)(cid:67)(cid:71)(cid:79)(cid:75)(cid:67)(cid:2)(cid:67)(cid:80)(cid:70)(cid:2)(cid:75)(cid:80)(cid:74)(cid:75)(cid:68)(cid:75)(cid:86)(cid:2)(cid:86)(cid:74)(cid:71)(cid:2)
`hepatic-derived generation of hepcidin and haptoglobin247,248. These latter responses are
`also associated with OSM and leukaemia inhibitory factor (LIF)249. Further roles for IL-6 in
`metabolic processes have been identified in Il6−/− mice, which develop mature- onset
`obesity, hypertriglyceridaemia and glucose intolerance, and patients on tocilizumab
`experience changes in serum cholesterol and triglyceride levels, along with increases in
`body weight10,250,251. The control of adipogenesis and lipolysis is also attributed to other IL-6
`family cytokines, and these are reviewed elsewhere252–254. For instance, ciliary neurotrophic
`factor (CNTF) treatment in mice reduced adiposity and body weight and improved various
`(cid:82)(cid:67)(cid:84)(cid:67)(cid:79)(cid:71)(cid:86)(cid:71)(cid:84)(cid:85)(cid:2)(cid:81)(cid:72)(cid:2)(cid:70)(cid:75)(cid:67)(cid:68)(cid:71)(cid:86)(cid:71)(cid:85)(cid:2)(cid:67)(cid:80)(cid:70)(cid:2)(cid:74)(cid:71)(cid:82)(cid:67)(cid:86)(cid:75)(cid:69)(cid:2)(cid:85)(cid:86)(cid:71)(cid:67)(cid:86)(cid:81)(cid:85)(cid:75)(cid:85)(cid:14)(cid:2)(cid:67)(cid:2)(cid:72)(cid:75)(cid:80)(cid:70)(cid:75)(cid:80)(cid:73)(cid:2)(cid:86)(cid:74)(cid:67)(cid:86)(cid:2)(cid:78)(cid:71)(cid:70)(cid:2)(cid:86)(cid:81)(cid:2)(cid:86)(cid:74)(cid:71)(cid:124)(cid:70)(cid:71)(cid:88)(cid:71)(cid:78)(cid:81)(cid:82)(cid:79)(cid:71)(cid:80)(cid:86)(cid:2)(cid:81)(cid:72)(cid:2)
`recombinant CNTF therapy (axokine), which suppressed appetite, increased energy
`expenditure and caused sustained weight loss in humans255–257. Consistent with a role for
`IL-6 family cytokines in regulating energy and glucose metabolism, acute infusion of IL-6 in
`mice increased glucose uptake and fatty acid oxidation in skeletal muscle, which was
`(cid:67)(cid:85)(cid:85)(cid:81)(cid:69)(cid:75)(cid:67)(cid:86)(cid:71)(cid:70)(cid:2)(cid:89)(cid:75)(cid:86)(cid:74)(cid:2)(cid:75)(cid:79)(cid:82)(cid:84)(cid:81)(cid:88)(cid:71)(cid:70)(cid:2)(cid:75)(cid:80)(cid:85)(cid:87)(cid:78)(cid:75)(cid:80)(cid:2)(cid:85)(cid:71)(cid:80)(cid:85)(cid:75)(cid:86)(cid:75)(cid:88)(cid:75)(cid:86)(cid:91)(cid:2)(cid:67)(cid:80)(cid:70)(cid:124)(cid:82)(cid:84)(cid:81)(cid:86)(cid:71)(cid:69)(cid:86)(cid:75)(cid:81)(cid:80)(cid:2)(cid:72)(cid:84)(cid:81)(cid:79)(cid:2)(cid:70)(cid:75)(cid:71)(cid:86)(cid:15)(cid:2)(cid:75)(cid:80)(cid:70)(cid:87)(cid:69)(cid:71)(cid:70)(cid:2)(cid:81)(cid:68)(cid:71)(cid:85)(cid:75)(cid:86)(cid:91)258.
`Here, IL-6 released from contracting muscle drives the production of glucagon- like
`peptide 1 (GLP-1) within the gut and pancreas and contributes to the maintenance of
`glucose homeostasis through GLP-1 control of insulin secretion259. An important aspect
`of these metabolic- associated outcomes regulated by IL-6 family members is their link with
`alterations in mitochondrial activity. These include changes in mitochondrial remodelling
`because of cachexia, alterations in mitochondrial calcium mobilization and membrane
`(cid:82)(cid:81)(cid:86)(cid:71)(cid:80)(cid:86)(cid:75)(cid:67)(cid:78)(cid:124)(cid:67)(cid:80)(cid:70)(cid:2)(cid:86)(cid:74)(cid:71)(cid:2)(cid:84)(cid:71)(cid:73)(cid:87)(cid:78)(cid:67)(cid:86)(cid:75)(cid:81)(cid:80)(cid:2)(cid:81)(cid:72)(cid:2)(cid:86)(cid:74)(cid:71)(cid:84)(cid:79)(cid:81)(cid:73)(cid:71)(cid:80)(cid:71)(cid:85)(cid:75)(cid:85)(cid:2)(cid:86)(cid:74)(cid:84)(cid:81)(cid:87)(cid:73)(cid:74)(cid:2)(cid:84)(cid:71)(cid:73)(cid:87)(cid:78)(cid:67)(cid:86)(cid:75)(cid:81)(cid:80)(cid:2)(cid:81)(cid:72)(cid:2)(cid:79)(cid:75)(cid:86)(cid:81)(cid:69)(cid:74)(cid:81)(cid:80)(cid:70)(cid:84)(cid:75)(cid:67)(cid:78)(cid:2)(cid:68)(cid:84)(cid:81)(cid:89)(cid:80)(cid:2)
`fat uncoupling protein 1 (REFS260–266).
`
`R E V I E W S
`
`In addition to these classical mechanisms of cytokine
`receptor signalling, several members of the IL-6 family
`employ alternative modes of gp130 activation termed
`cytokine trans- signalling (relevant to IL-6, IL-11 and
`CNTF) and trans- presentation (relevant to IL-6) (BOX 3).
`These alternative modes of cytokine signalling are best
`epitomized by the action of IL-6, and we refer the
`reader to several recent articles that review the regula-
`tion and biological properties of classical IL-6 receptor
`(IL-6R) signalling and IL-6 trans- signalling in health
`and disease5,15,17,37–40. Briefly, classical IL-6R signalling
`describes activities mediated via the membrane- bound
`IL-6R complex and is restricted to cells that express
`both IL-6Rα and gp130 (REF.37). By contrast, IL-6 trans-
`signalling denotes a process that involves IL-6 binding
`to a soluble form of IL-6Rα (sIL-6R), which maintains
`the circulating half- life of IL-6 and increases its bio-
`availability41,42. Interestingly, sIL-6R shares sequence
`identity with both IL-12p40 and EBI3, and once bound
`with IL-6 resembles a heterodimeric cytokine sim-
`ilar to IL-12-related cytokines5,20,43. In this regard, the
`IL-6–sIL-6R complex is able to directly engage and acti-
`vate membrane- bound gp130 to facilitate IL-6 signalling
`in cell types that would not normally respond to IL-6
`(REF.37). Thus, trans- signalling serves to broaden the tar-
`get cell repertoire of IL-6 and is considered the primary
`mechanism for IL-6 involvement in numerous chronic
`diseases and cancers5,37,39. Intriguingly, similar cytokine
`trans- signalling mechanisms have been described for
`IL-11 and CNTF, and recent in vitro observations imply
`that both IL-27p28 and EBI3 can also induce sIL-6R-
`mediated forms of trans- signalling2,15,36,44–46 (BOX  3).
`While the in vivo consequences of these latter signal-
`ling modes require further evaluation, the identifica-
`tion of soluble variants of gp130 (sgp130) in human
`serum, urine and inflammatory exudates that antago-
`nize both IL-6 and IL-11 trans- signalling emphasizes
`the biological importance of these alternative signalling
`mechanisms17,37,40,46.
`
`Regulation of intracellular signalling
`All IL-6-related cytokine receptor complexes transduce
`intracellular signals via t he Janus kinase–signal transducer and
`activator of transcription pathway (JAK–STAT pathway),
`where receptor- associated JAKs (namely, JAK1, JAK2 and
`TYK2) activate the latent transcription factors STAT1,
`STAT3 and (to a lesser extent) STAT5 (REFS6,9,16) (BOX 1).
`Other signalling intermediates activated in response
`to IL-6 family cytokines include, first, the protein
`tyrosine phosphatase SH- PTP2 (SHP2; also known as
`PTPN11), which promotes activation of the RAS–RAF–
`extracellular- signal-regulated kinase 1 (ERK1)/ERK2
`mitogen- activated protein kinase (MAPK) and the
`phosphoinositide 3-kinase (PI3K)–protein kinase B
`(PKB; also known as AKT) pathways, and, second, the
`transcription factor nuclear factor NF- IL-6 (also known
`as C/EBPβ)16 (BOX 1). Recently, IL-6-induced and IL-11-
`induced activation of PI3K was shown to regulate the
`mechanistic target of rapamycin (mTOR) complex 1
`(mTORC1) system, which controls telomerase activity
`and protein synthesis and influences various cellular
`processes including metabolism and redox stress47,48
`
`Receptor promiscuity can also elicit defined forms of
`cytokine receptor crosstalk. For instance, CNTF displays
`a low affinity interaction with IL-6 receptor subunit- α
`(IL-6Rα) that can lead to the formation and activation of
`an IL-6Rα–gp130–LIFR signalling receptor complex2,32.
`Such cross- regulation may afford CNTF the capacity
`to control IL-6-related processes not normally associ-
`ated with its primary involvement in the nervous sys-
`tem (for example, metabolism, bone remodelling and
`immune regulation)33,34 (BOXES 1,2). The complexities of
`IL-6Rα usage also extend to cytokines beyond the IL-6
`cytokine family, with a recent example being IL-27p28,
`which moderates inflammatory activities through
`engagement of an IL-6Rα–gp130 receptor system27,35,36.
`
`Janus kinase–signal
`transducer and activator of
`transcription pathway
`(JAK–STAT pathway). A
`cytokine receptor signalling
`mechanism used by certain
`cytokines to sense and
`interpret environmental cues
`during inflammation and
`immune homeostasis.
`
`NATURE REVIEWS | IMMUNOLOGY
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` VOLUME 18 | DECEMBER 2018 | 775
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`Lassen - Exhibit 1020, p. 3
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`

`

`R E V I E W S
`
`a
`
`b gp130 homodimer receptors
`
`c gp130 heterodimer receptors
`
`LIF
`
`CT-1 OSM
`
`IL-31
`
`IL-27
`
`CLCF1 CNTF
`
`Unpaired 3
`
`IL-6
`
`IL-11
`
`Domeless
`
`Hopscotch
`
`Stat92E
`
`OSMRβ
`
`IL-6R
`
`IL-11R
`
`LIFR
`
`IL-31Rα
`
`IL-27Rα
`
`gp130
`
`CNTFRα
`(GPI anchored)
`
`Fig. 1 | Cytokine receptor usage by the IL-6 family of cytokines. Members of the IL-6 cytokine family share a common
`ancestral link to an innate immune sensing mechanism found in Drosophila melanogaster (part a). This system consists of
`Unpaired 3 (IL-6-like), Domeless (gp130-like), Hopscotch (Drosophila melanogaster homologue of mammalian Janus kinase
`(cid:10)(cid:44)(cid:35)(cid:45)(cid:11)(cid:11)(cid:2)(cid:67)(cid:80)(cid:70)(cid:2)(cid:85)(cid:75)(cid:73)(cid:80)(cid:67)(cid:78)(cid:2)(cid:86)(cid:84)(cid:67)(cid:80)(cid:85)(cid:70)(cid:87)(cid:69)(cid:71)(cid:84)(cid:2)(cid:67)(cid:80)(cid:70)(cid:2)(cid:67)(cid:69)(cid:86)(cid:75)(cid:88)(cid:67)(cid:86)(cid:81)(cid:84)(cid:2)(cid:81)(cid:72)(cid:2)(cid:86)(cid:84)(cid:67)(cid:80)(cid:85)(cid:69)(cid:84)(cid:75)(cid:82)(cid:86)(cid:75)(cid:81)(cid:80)(cid:2)(cid:82)(cid:84)(cid:81)(cid:86)(cid:71)(cid:75)(cid:80)(cid:2)(cid:67)(cid:86)(cid:2)(cid:27)(cid:20)(cid:39)(cid:2)(cid:10)(cid:53)(cid:86)(cid:67)(cid:86)(cid:27)(cid:20)(cid:39)(cid:29)(cid:2)(cid:67)(cid:78)(cid:85)(cid:81)(cid:2)(cid:84)(cid:71)(cid:72)(cid:71)(cid:84)(cid:84)(cid:71)(cid:70)(cid:2)(cid:86)(cid:81)(cid:2)(cid:67)(cid:85)(cid:2)(cid:47)(cid:67)(cid:84)(cid:71)(cid:78)(cid:78)(cid:71)(cid:11)(cid:16)(cid:2)(cid:43)(cid:80)(cid:2)(cid:79)(cid:67)(cid:79)(cid:79)(cid:67)(cid:78)(cid:85)(cid:14)(cid:2)
`all cytokines within the family activate cells through receptor complexes that contain the signal- transducing receptor
`β- subunit membrane glycoprotein 130 (gp130) (parts b and c). Three distinct forms of cytokine receptor arrangements are
`utilized by these cytokines. Receptor complexes for IL-6 and IL-11 (part b) contain a cognate non- signalling receptor
`α- subunit and gp130 (termed a gp130 homodimer receptor complex), with gp130 existing as a homodimer to elicit
`signalling. On the basis of the proposed structural arrangement of the IL-6 receptor (IL-6R), a functioning receptor is
`composed of an IL-6–IL-6R–gp130 complex that is clustered into a dimer structure16,268(cid:16)(cid:2)(cid:36)(cid:91)(cid:124)(cid:69)(cid:81)(cid:80)(cid:86)(cid:84)(cid:67)(cid:85)(cid:86)(cid:14)(cid:2)(cid:84)(cid:71)(cid:69)(cid:71)(cid:82)(cid:86)(cid:81)(cid:84)(cid:2)(cid:69)(cid:81)(cid:79)(cid:82)(cid:78)(cid:71)(cid:90)(cid:71)(cid:85)(cid:2)
`for leukaemia inhibitory factor (LIF), cardiotrophin 1 (CT-1), oncostatin M (OSM) and IL-27 (part c) comprise gp130 and
`a second receptor subunit, which contains structural features similar to gp130 (termed a gp130 heterodimer receptor
`complex). These include LIF receptor (LIFR), OSM- specific receptor subunit- β (OSMRβ) and IL-27 receptor subunit- α
`(IL-27Rα). The receptor for ciliary neurotrophic factor (CNTF) and cardiotrophin- like cytokine factor 1 (CLCF1) comprises
`three individual receptor subunits formed between CNTF receptor subunit- α (CNTFRα), LIFR and gp130. Currently , IL-31
`remains the only exception to this ‘gp130 rule’, and the IL-31 receptor consists of IL-31 receptor subunit- α (IL-31Rα) and
`OSMRβ. These alternative receptors provide cytokine specificity and couple directly to signal transduction pathways
`required for cellular activation (BOX 1)(cid:16)(cid:2)(cid:41)(cid:50)(cid:43)(cid:14)(cid:2)(cid:73)(cid:78)(cid:91)(cid:69)(cid:81)(cid:85)(cid:91)(cid:78)(cid:82)(cid:74)(cid:81)(cid:85)(cid:82)(cid:74)(cid:67)(cid:86)(cid:75)(cid:70)(cid:91)(cid:78)(cid:75)(cid:80)(cid:81)(cid:85)(cid:75)(cid:86)(cid:81)(cid:78)(cid:29)(cid:2)(cid:43)(cid:46)(cid:15)(cid:19)(cid:19)(cid:52)(cid:2)(cid:14)(cid:2)(cid:43)(cid:46)(cid:15)(cid:19)(cid:19)(cid:2)(cid:84)(cid:71)(cid:69)(cid:71)(cid:82)(cid:86)(cid:81)(cid:84)(cid:16)
`
`(BOX 1). The diverse signalling networks activated by
`IL-6 also extend to NOTCH and Yes- associated protein
`(YAP), which upon gp130–SRC kinase- dependent acti-
`vation facilitate epithelial cell proliferation and tissue
`remodelling or regeneration49 (BOX 1).
`The pathophysiological consequences of dysregulated
`gp130 activation on immune homeostasis and suscep-
`tibility to infection, autoimmunity or cancer have been
`widely reported, thus highlighting the importance of
`restricting the magnitude or duration of IL-6 cytokine
`family signalling in disease50–54. In this respect, multiple
`negative regulatory mechanisms have evolved to curtail
`gp130-dependent signalling. These include receptor
`internalization, deactivation of receptors and signal-
`ling intermediates by protein tyrosine phosphatases,
`microRNA (miRNA)-mediated translational repression
`and degradation of target mRNAs encoding cytokines or
`their receptors and the STAT- driven induction of protein
`inhibitor of activated STAT protein (PIAS) and suppressor
`of cytokine signalling (SOCS) factors9,16,55,56. Among these,
`SOCS3 plays the predominant negative regulatory role by
`inhibiting JAK–STAT3 activation and targeting cytokine
`receptor complexes for proteasome degradation55.
`Considering the global cellular processes activated
`by the above signalling cascades, it is not surprising
`
`that IL-6 family cytokines display widespread func-
`tional pleiotropy (BOX 1). So, how do individual family
`members acquire unique biological specificity? Early
`investigations of STAT factors and their interaction with
`the genome provided evidence of cooperative mecha-
`nisms with other transcription factors, competition for
`overlapping transcription factor binding sites in gene
`promoter regions and interaction with other transcrip-
`tional co- activators or co- repressors9,55,57. For example,
`the STAT3-mediated transcriptional output of IL-6
`family cytokines can be influenced by the interaction of
`STAT3 with co- activators (such as p300–CREB- binding
`protein (CBP)) and other transcription factors, includ-
`ing nuclear factor- κB (NF- κB). NF- κB complexes with
`STAT3 in an unphosphorylated state to drive a distinct
`transcriptional signature enriched for genes involved
`in oncogenic and immune responses58. Interestingly,
`there is also an alternative mode of transcriptional con-
`trol employed by STAT3. This occurs downstream of
`IL-6 and IL-11 and involves the induction of specific
`miRNAs implicated in tumorigenesis and epithelial–
`mesenchymal transition (EMT) (for example, miR-21
`and miR-200 family members)59,60.
`Another mechanism by which individual IL-6 fam-
`ily members achieve biological specificity involves
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`776 | DECEMBER 2018 | VOLUME 18
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`

`Box 3 | Receptor signalling mechanisms used by the IL-6 family of cytokines
`
`Several members of the IL-6 family adopt alternative modes of cellular activation via
`membrane glycoprotein 130 (gp130). For example, IL-6 classical cytokine receptor
`signalling transduced via a gp130 homodimer is facilitated by membrane- bound forms of
`IL-6 receptor subunit- α (IL-6Rα) and gp130 (for schematic purposes, only one gp130
`molecule is shown). Soluble forms of the cognate non- signalling receptor α- subunits for
`IL-6 (sIL-6Rα), IL-11 (sIL-11R) and ciliary neurotrophic factor (CNTF) (sCNTFR) are readily
`detected in serum. These soluble receptors retain cytokine- binding kinetics and form
`receptor–ligand complexes that activate cells through binding interactions with
`cell-associated gp130. Cytokine binding to soluble receptors also increases the
`circulating half- life of the cytokine and offers protection from proteolytic degradation40.
`These forms of cellular activation are termed cytokine trans- signalling and provide a
`mechanism to broaden the types of cells that are responsive to IL-6, IL-11 or CNTF2.
`Recent evidence has identified another form of receptor engagement termed IL-6 trans-
`presentation267. Here, IL-6 bound to membrane- bound IL-6Rα is displayed on the surface
`of cells (for example, specialized dendritic cells) and presented to gp130 expressed on a
`nearby cell type (for example, a lymphocyte) to elicit signalling via a gp130 homodimer
`(for schematic purposes, only one gp130 molecule is shown). These additional forms of
`cytokine receptor signalling contribute to the regulation of innate and adaptive
`immunity and direct responses in target cells that lack specific receptors for these
`cytokines. Also shown are the numerous cellular processes associated with each of
`these signalling modes.
`
`IL-6 +
`sIL-6Rα
`
`IL-11 +
`sIL-11R
`
`CNTF +
`sCNTFR
`
`e.g. IL-6
`
`IL-