The Significance of HMGB1, a Late-Acting Pro-inflammatory Cytokine

(1)

Pro-inflammatory Cytokine

E. Abraham

Introduction

Multiple organ failure is a frequent occurrence after sepsis or multisystem acci- dental trauma associated with severe hemorrhage [1–4]. Acute lung injury (ALI), characterized by the accumulation of activated neutrophils into the lungs as well as epithelial and endothelial dysfunction that leads to the development of interstitial edema, is a common organ dysfunction in these clinical settings. Pro- inﬂammatory cytokines, such as tumor necrosis factor (TNF)-

α

and interleukin (IL)-1

β

, are increased in the lungs after blood loss, endotoxemia, or sepsis and appear to contribute to the development of ALI in this setting, but the mechanisms by which they induce ALI are incompletely characterized [5–7]. Although these same cytokines have been shown to participate in organ dysfunction and mortality associated with sepsis, recent data indicate that many of their actions may actually be through inducing the downstream release of high mobility group box 1 protein (HMGB1), a late acting pro-inﬂammatory mediator [8–18].

There are three HMGB chromosomal proteins: HMGB1 (previously known as HMG1), HMGB2 (previously HMG2), and HMGB3 (previously HMG4 or HMG2) [8, 10, 13, 19, 20]. HMGBs are composed of three different domains, including the homologous DNA binding boxes A and B, and the C-terminal domain [8–10, 13, 19, 21, 22]. The amino acid sequence within the HMGB family members exhibits 85% similarity, but the proteins have a distinctly different tissue expression pattern. HMGB1 is ubiquitously present in all vertebrate nuclei, but the expression of HMGB2 and HMGB3 is more restricted. HMGB2 is widely present during embryonic development, but is expressed only in the testes and lymphoid tissue of the adult mouse. HMGB3 expression is only present during embryogenesis.

HMGB1 is a 215 amino acid protein with a uniquely conserved sequence among species. Mouse HMGB1 differs from the human form by only two amino acids [10, 16,19,23]. HMGB1 deﬁcient mice die within a few hours of birth, demonstrating the crucial role of this protein in cellular function. The two homologous DNA binding domains, HMGB boxes A and B, are each approximately 75 amino acids in length.

The C terminal domain is highly negatively charged, consisting of a continuous stretch of glutamate or aspartate residues.

The truncated HMGB1 protein containing the B box motif is a potent inducer of TNF-

α

production in cultured macrophages [8, 13, 21, 22]. Similarly, synthe-

(2)

sized B box protein also stimulates TNF-

α

release [8]. Afﬁnity puriﬁed anti-B box antibodies inhibit TNF-

α

release induced by either full length HMGB1 or the B box protein, showing that the macrophage stimulating effects of HMGB1 are B box specific. In vivo experiments have also shown that the HMGB1 B box has pro-inflammatory effects. In particular, administration of the HMGB1 B box to lipopolysaccharide (LPS)-resistant C3H/HeJ mice was lethal and also significantly increased serum levels of TNF-

α

^{, IL-1}

β

, and IL-6 [8]. Mice given anti-HMGB1 B box antibodies were signiﬁcantly protected against lethal endotoxemia, indicating that selective inhibition of the HMGB1 B box decreases the toxicity of endogenous HMGB1 [8].

Unlike the B box of HMGB1, the A box does not stimulate pro-inﬂammatory cytokine production by cultured macrophages [8, 13, 21, 22]. In contrast, the A box functions as a competitive inhibitor of HMGB1. Such inhibitory actions of the HMGB1 A box are demonstrated by the fact that addition of the A box to macrophage cultures decreases HMGB1 induced release of IL-1

β

^{and TNF-}

α

ⁱⁿ

a dose dependent manner and displaces¹²⁵I-labelled HMGB1 from macrophage binding [8]. The HMGB1 A box also has in vivo anti-inﬂammatory effects. In par- ticular, administration of recombinant A box protein to mice subjected to sepsis induced by cecal ligation and puncture (CLP) improved survival [8]. Remarkably, injection of the A box of HMGB1 as late as 24 hours after cecal perforation still rescued mice from the lethal effects of sepsis [8].

HMGB1 appears to have two distinct functions in cellular systems. First, it has been shown to have an intracellular role as a regulator of transcription and, second, an extracellular role in which it promotes tumor metastasis and inﬂammation [8–10, 12, 19, 20, 24, 25]. Monocytes/macrophages stimulated by LPS, TNF-

α

^{, or}

IL-1 secrete HMGB1 [24, 26]. Addition of HMGB1 to monocytes in culture induces the release of TNF-

α

^{, IL-1}

α

^{, IL-1}

β

, IL-1 receptor antagonist (IL-1ra), IL-6, IL- 8, macrophage inﬂammatory protein (MIP)-1

α

^{, MIP-1}

β

, but not IL-10 or IL-12 [24, 26]. Activation of macrophages by HMGB1 occurs with delayed kinetics as compared to LPS-induced stimulation. For example, culture of macrophages with LPS results in increases in TNF-

α

that are apparent within less than one hour, whereas TNF-

α

synthesis after HMGB1 exposure only begins to occur after 2 hours and then persists for as long as 8 hours [12, 26]. In the in vivo setting, increases in circulating HMGB1 levels are found after serum TNF-

α

^{and IL-1}

β

levels have returned to basal levels [8–12, 20, 26]. Administration of anti-HMGB1 antibodies decrease the severity of LPS induced ALI, even though pulmonary concentrations of pro-inﬂammatory cytokines, such as IL-1

β

^{or TNF-}

α

, remain elevated [27].

Similarly, in septic mice with peritonitis, mortality can be reduced even if anti- HMGB1 antibodies are given as long as 24 hours after CLP [8, 28]. Such results indicate that HMGB1 is a late mediator of lethal inﬂammation, whose effects are independent of those of early acting pro-inﬂammatory mediators, such as TNF-

α

or IL-1

β

^.

(3)

HMGB1 and Sepsis

Serum concentrations of HMGB1 increase 8 to 32 hours after administration of LPS or TNF-

α

to mice [8, 26]. Systemic administration of puriﬁed recombinant HMGB1 is lethal in LPS sensitive C3H/HeN mice as well as in the LPS resistant C3H/HeJ mice, indicating that HMGB1 can mediate lethal toxicity in the absence of signal transduction by LPS [26]. These results also indicate that receptors other than the type 4 Toll-like receptor (TLR4), which is responsible for LPS-induced cellular activation, are involved in the inﬂammatory response initiated by HMGB1.

Administration of anti-HMGB1 antibodies protects mice from LPS-induced lethality even if the therapy is delayed several hours, and is administered after the appearance of the early pro-inﬂammatory cytokine response [8, 12, 13, 26].

Similarly, anti-HMGB1 antibodies can improve survival of mice subjected to peritonitis induced by CLP, even if administered 24 hours after the initiation of the septic insult [28].

In patients with severe sepsis, serum HMGB1 levels are increased, and the highest levels were initially reported to be present in non-survivors [26]. However, more recent studies have brought the relationship between HMGB1 levels and outcome from sepsis into question. In particular, although Sunden-Cullberg et al.

found persistent increases in circulating HMGB1 levels in septic patients, there was no apparent relationship between HMGB1 levels and mortality in that study [29].

An important question is the mechanism through which HMGB1 may contribute to organ dysfunction and lethality in sepsis. Interestingly, there is evidence that HMGB1 itself does not cause hypotension, but rather may induce organ dysfunction through its effects on the epithelium and, in particular, through produc- ing epithelial dysfunction that results in interstitial edema [15, 21]. Such ﬁndings are somewhat surprising, given the ability of HMGB1 to induce macrophages to produce TNF-

α

, which itself causes profound hypotension.

In addition to being secreted by activated macrophages, HMGB1 is also released into the extracellular milieu when cells die by necrosis, but not when cellular death occurs through apoptosis, when it remains bound to chromatin [23, 25].

In this respect, HMGB1 appears to function as a true ‘danger signal’, indicating when cells meet a fate that results in unexpected death. While enhanced apoptosis, particularly of lymphocytes and epithelial cells, is found in sepsis [30], the presence of increased circulating HMGB1 levels in this setting may also reﬂect enhanced rates of cell death by necrosis, a hypothesis that will require conﬁrmation in future experiments.

HMGB1, Hemorrhage, and Burns

As with sepsis, persistent elevations in serum HMGB1 levels are present in humans after life threatening hemorrhage, with increases occurring within the ﬁrst 24 hours after the onset of blood loss and then continuing for more than 72 hours [31].

(4)

Of note, serum levels of HMGB1 after hemorrhage, up to 70

µ

^g

/

l, are similar to those found in severe sepsis. Additionally, increased HMGB1 expression is found in experimental burn injury models [32]. In those thermal injury experiments, signiﬁcant correlations were found between pulmonary HMGB1 expression and MPO activity, suggesting a role for HMGB1 in burn-induced ALI.

Hemorrhage results in increased expression of multiple pro-inﬂammatory cytokines in the lungs, including TNF-

α

^{and IL-1}

β

[33–39]. Because pro-inﬂammatory cytokines, including TNF-

α

, are known to stimulate the production of HMGB1 by macrophages, endothelial cells, and other cell populations [9, 10, 12, 24, 26, 40, 41], it seemed likely that hemorrhage would be associated with increased generation of HMGB1 in the lungs. Recent experiments in murine models of hemorrhage have conﬁrmed increased pulmonary levels of HMGB1 in this setting [42]. Addition- ally, anti-HMGB1 antibodies decreased the severity of hemorrhage-induced ALI, demonstrating a role for HMGB1 in this pathophysiologic process.

HMGB1 and Acute Lung Injury

Intratracheal administration of HMGB1 produces ALI, and antibodies against HMGB1 decrease LPS- or hemorrhage-induced lung edema and neutrophil accumulation [27, 42]. Anti-HMGB1 antibodies did not signiﬁcantly reduce the levels of the pro-inﬂammatory cytokines TNF-

α

^{, IL-1}

β

, or MIP-2 in LPS-induced ALI, indicating that HMGB1 occupies a more distal position in endotoxin-induced pro-inﬂammatory cascades. In addition, these results suggest that the previously described roles of early appearing pro-inﬂammatory cytokines, such as TNF-

α

and IL-1

β

, in inducing LPS and perhaps sepsis-induced ALI may not all have been due to direct effects, but rather to their ability to produce generation of HMGB1.

Receptors for HMGB1 Include RAGE, TLR2, and TLR4

The receptor for advanced glycation end products (RAGE), a multiligand mem- ber of the immunoglobulin superfamily of cell surface molecules, interacts with HMGB1 and triggers activation of key cell signaling pathways [43–47]. Binding of HMGB1 to RAGE leads to neurite outgrowth and enhanced expression of plasminogen activator by macrophages [40,48–53]. Although RAGE is a major receptor for HMGB1 in neural tissue and some malignant cells [44, 48–50, 54], this receptor appears to be less important in HMGB1 signaling among other cell populations. For example, incubation of microvascular endothelial cells with anti-RAGE antibodies only decreased HMGB1-induced IL-8 production by 14% and TNF-

α

^production

by 17% [40].

Because the pattern of kinase activation and release of pro-inﬂammatory cytokines induced by HMGB1 in macrophages is similar to that which occurs after incubation with the Gram-negative bacterial product LPS that interacts with TLR4

(5)

or with the Gram-positive products peptidoglycan or lipotechoic acid that interact with TLR2, it seemed possible that HMGB1 might interact with these same receptors. Subsequent experiments, using transfection of TLR2 or TLR4 into HEK cells that normally do not bear these receptors, as well as studies that directly exam- ined the interaction of HMGB1 with TLR2 or TLR4 on macrophages, showed that HMGB1 does produce cellular activation through TLR2 and TLR4 [55]. Interest- ingly, RAGE appears to be less important than either TLR2 or TLR4 for macrophage stimulation by HMGB1 [56].

Cellular Activation Pathways Induced by HMGB1

Interaction of bacterial products with TLR2 or TLR4 leads to enhanced nuclear translocation of nuclear factor kappa B (NF-

κ

B), occurring through activation of the IKK

α

^/

β

kinase complex. In neutrophils and macrophages, the p38 mitogen activated protein kinase pathway (p38 MAPK) as well as the phosphoinositide-3 kinase (PI3-K) pathways are also activated when signaling is induced through TLR2 and TLR4, and also appear to contribute to inducing nuclear translocation of NF-

κ

^{B [57].}

Since the primary signaling initiated by HMGB1 in neutrophils and macrophages occurs through TLR2 and TLR4, it is not surprising that exposure of these cell populations to HMGB1 produces nuclear translocation of NF-

κ

B and activation of the p38 and PI3-K kinase pathways with patterns resembling those induced by LPS [40, 41, 56]. However, gene array studies show that the patterns of gene expression induced by LPS and HMGB1, although similar in many respects, also demonstrate signiﬁcant differences, consistent with the use of receptors other than TLR4 by HMGB1 [41].

Signaling pathways involving cellular activation by HMGB1 are shown in Fig. 1.

Release of HMGB1 from Necrotic Cells Triggers Inflammation

When cells die by necrosis rather than apoptosis, they lose their membrane in- tegrity and release intracellular contents. Necrotic cell death is common in the setting of trauma and blood loss. HMGB1 is passively released by necrotic or damaged cells [23, 25]. Transgenic cells lacking HMGB1 (HMGB1 -/-) have greatly reduced ability to promote inflammation when they die by necrosis, showing that the release of HMGB1 by necrotic cell death can initiate inflammatory responses in neighboring cells [19,25,58]. In contrast, apoptotic cells do not release HMGB1 even after undergoing secondary necrosis, and fail to promote inflammation even if not cleared promptly by phogocytic cells. In apoptotic cells, HMGB1 remains bound to chromatin because of generalized underacetylation of histones. If chromatin deacetylation is prevented during the apoptosis process, HMGB1 is released into the intracellular space and can promote inflammation. The in vivo role of HMGB1

(6)

Fig. 1. Signaling pathways activated by high mobility group box protein 1 (HMGB1)

in mediating inﬂammation after cellular necrosis is shown in experiments where anti-HMGB1 antibodies reduce damage and inﬂammatory cell recruitment to the liver after acetaminophen-induced necrosis [25].

Conclusion

HMGB1 is a novel late mediator of inﬂammatory responses that contributes to ALI and lethal sepsis. It appears to interact with at least three receptors, including RAGE, TLR2, and TLR4, potentially explaining the similarities in cellular activation induced by HMGB1 and bacterial products, such as LPS or peptidoglycan. However, the multiple receptors involved in HMGB1 signaling also provide insights into the differences in gene expression produced by cellular interaction with this mediator.

Unlike the situation with classically described pro-inﬂammatory cytokines, such as TNF-

α

^{or IL-1}

β

, where blockade is only effective in improving outcome from experimental sepsis if administered before or very early in the course of sepsis, inhibition of HMGB1 with speciﬁc antibodies or the HMGB1 A box sequence still reduces mortality even if performed up to 24 hours after the initiation of the septic insult. Such ﬁndings suggest that HMGB1 may be an appropriate therapeutic target

(7)

in patients with sepsis or ALI, since it may participate in the pathogenesis of organ dysfunction and mortality even at later time points when such patients present for hospital or ICU admission.

Acknowledgement. This work was supported in part by NIH awards HL68743 and GM49222.

References

1. Moore FA, Moore EE, Sauaia A (1997) Blood transfusion. An independent risk factor for postinjury multiple organ failure. Arch Surg 132:620–624

2. Sauaia A, Moore FA, Moore EE, et al (1994) Early predictors of postinjury multiple organ failure. Arch Surg 129:39–45

3. Sauaia A, Moore FA, Moore EE, Lezotte DC (1996) Early risk factors for postinjury multiple organ failure. World J Surg 20:392–400

4. Sauaia A, Moore FA, Moore EE, et al (1998) Multiple organ failure can be predicted as early as 12 hours after injury. J Trauma 45:291–301

5. Abraham E, Allbee J (1994) Effects of therapy with interleukin-1 receptor antagonist on pulmonary cytokine expression following hemorrhage and resuscitation. Lymphokine Cytokine Res 13:343–347

6. Abraham E, Coulson WF, Schwartz MD, Allbee J (1994) Effects of therapy with soluble tumour necrosis factor receptor fusion protein on pulmonary cytokine expression and lung injury following haemorrhage and resuscitation. Clin Exp Immunol 98:29–34

7. Abraham E, Jesmok G, Tuder R, et al (1995) Contribution of tumor necrosis factor-alpha to pulmonary cytokine expression and lung injury after hemorrhage and resuscitation. Crit Care Med 23:1319–1326

8. Andersson U, Erlandsson-Harris H, Yang H, Tracey KJ (2002) HMGB1 as a DNA-binding cytokine. J Leukoc Biol 72:1084–1091

9. Czura CJ, Tracey KJ (2003) Targeting high mobility group box 1 as a late-acting mediator of inﬂammation. Crit Care Med 31:S46–50

10. Czura CJ, Wang H, Tracey KJ (2001) Dual roles for HMGB1: DNA binding and cytokine. J Endotoxin Res 7:315–321

11. Ulloa L, Ochani M, Yang H, et al (2002) Ethyl pyruvate prevents lethality in mice with established lethal sepsis and systemic inﬂammation. Proc Natl Acad Sci USA 99:12351–12356 12. Wang H, Yang H, Czura CJ, et al (2001) HMGB1 as a late mediator of lethal systemic inﬂam-

mation. Am J Respir Crit Care Med 164:1768–1773

13. Yang H, Wang H, Czura CJ, Tracey KJ (2002) HMGB1 as a cytokine and therapeutic target. J Endotoxin Res 8:469–472

14. Chen G, Ward MF, Sama AE, Wang H (2004) Extracellular HMGB1 as a proinﬂammatory cytokine. J Interferon Cytokine Res 24:329–333

15. Czura CJ, Yang H, Amella CA, Tracey KJ (2004) HMGB1 in the Immunology of Sepsis (Not Septic Shock) and Arthritis. Adv Immunol 84:181–200

16. Erlandsson Harris H, Andersson U (2004) Mini-review: The nuclear protein HMGB1 as a proinﬂammatory mediator. Eur J Immunol 34:1503–1512

17. Sadikot RT, Christman JW, Blackwell TS (2004) Molecular targets for modulating lung in- ﬂammation and injury. Curr Drug Targets 5:581–588

18. Wang H, Yang H, Tracey KJ (2004) Extracellular role of HMGB1 in inﬂammation and sepsis.

J Intern Med 255:320–331

(8)

19. Muller S, Scafﬁdi P, Degryse B, et al (2001) New EMBO members’ review: the double life of HMGB1 chromatin protein: architectural factor and extracellular signal. Embo J 20:4337–

4340

20. Yang H, Wang H, Tracey KJ (2001) HMG-1 rediscovered as a cytokine. Shock 15:247–253 21. Sappington PL, Yang R, Yang H, et al (2002) HMGB1 B box increases the permeability of Caco-

2 enterocytic monolayers and impairs intestinal barrier function in mice. Gastroenterology 123:790–802

22. Taudte S, Xin H, Bell AJ Jr, Kallenbach NR (2001) Interactions between HMG boxes. Protein Eng 14:1015–1023

23. Bustin M (2002) At the crossroads of necrosis and apoptosis: signaling to multiple cellular targets by HMGB1. Sci STKE 151:PE39

24. Andersson U, Wang H, Palmblad K, et al (2000) High mobility group 1 protein (HMG-1) stimulates proinﬂammatory cytokine synthesis in human monocytes. J Exp Med 192:565–

570

25. Scafﬁdi P, Misteli T, Bianchi ME (2002) Release of chromatin protein HMGB1 by necrotic cells triggers inﬂammation. Nature 418:191–195

26. Wang H, Bloom O, Zhang M, et al (1999) HMG-1 as a late mediator of endotoxin lethality in mice. Science 285:248–251

27. Abraham E, Arcaroli J, Carmody A, et al (2000) HMG-1 as a mediator of acute lung inﬂam- mation. J Immunol 165:2950–2954

28. Yang H, Ochani M, Li J, et al (2004) Reversing established sepsis with antagonists of endogenous high-mobility group box 1. Proc Natl Acad Sci USA 101:296–301

29. Sunden-Cullberg J, Norrby-Teglund A, Rouhiainen A, et al (2005) Persistent elevation of high mobility group box-1 protein (HMGB1) in patients with severe sepsis and septic shock. Crit Care Med 33:564–573

30. Hotchkiss RS, Karl IE (2003) The pathophysiology and treatment of sepsis. N Engl J Med 348:138–150

31. Ombrellino M, Wang H, Ajemian MS, et al (1999) Increased serum concentrations of high- mobility-group protein 1 in haemorrhagic shock. Lancet 354:1446–1447

32. Fang WH, Yao YM, Shi ZG, et al (2002) The signiﬁcance of changes in high mobility group-1 protein mRNA expression in rats after thermal injury. Shock 17:329–333

33. Le Tulzo Y, Shenkar R, Kaneko D, et al (1997) Hemorrhage increases cytokine expression in lung mononuclear cells in mice: involvement of catecholamines in nuclear factor-kappaB regulation and cytokine expression. J Clin Invest 99:1516–1524

34. Moine P, Shenkar R, Kaneko D, et al (1997) Systemic blood loss affects NF-kappa B regulatory mechanisms in the lungs. Am J Physiol 273: L185–192

35. Parsey MV, Tuder RM, Abraham E (1998) Neutrophils are major contributors to intraparenchymal lung IL-1 beta expression after hemorrhage and endotoxemia. J Immunol 160:1007–1013

36. Shenkar R, Abraham E (1997) Hemorrhage induces rapid in vivo activation of CREB and NF-kappaB in murine intraparenchymal lung mononuclear cells. Am J Respir Cell Mol Biol 16:145–152

37. Shenkar R, Abraham E (1993) Effects of hemorrhage on cytokine gene transcription. Lym- phokine Cytokine Res 12:237–247

38. Shenkar R, Coulson WF, Abraham E (1994) Hemorrhage and resuscitation induce alterations in cytokine expression and the development of acute lung injury. Am J Respir Cell Mol Biol 10:290–297

39. Shenkar R, Yum HK, Arcaroli J, et al (2001) Interactions between CBP, NF-kappaB, and CREB in the lungs after hemorrhage and endotoxemia. Am J Physiol Lung Cell Mol Physiol 281:L418–426

40. Fiuza C, Bustin M, Talwar S, et al (2003) Inﬂammation-promoting activity of HMGB1 on human microvascular endothelial cells. Blood 101:2652–2660

(9)

41. Park JS, Arcaroli J, Yum HK, et al (2003) Activation of gene expression in human neutrophils by high mobility group box 1 protein. Am J Physiol Cell Physiol 284:C870–C879

42. Kim JY, Park JS, Strassheim D, et al (2005) HMGB1 contributes to the development of acute lung injury after hemorrhage. Am J Physiol Lung Cell Mol Physiol 288:L958–L965

43. Bucciarelli LG, Wendt T, Rong L, et al (2002) RAGE is a multiligand receptor of the immunoglobulin superfamily: implications for homeostasis and chronic disease. Cell Mol Life Sci 59:1117–1128

44. Huttunen HJ, Fages C, Kuja-Panula J, et al (2002) Receptor for advanced glycation end products-binding COOH-terminal motif of amphoterin inhibits invasive migration and metastasis. Cancer Res 62:4805–4811

45. Schmidt AM, Yan SD, Yan SF, Stern DM (2001) The multiligand receptor RAGE as a progres- sion factor amplifying immune and inﬂammatory responses. J Clin Invest 108:949–955 46. Sparatore B, Pedrazzi M, Passalacqua M, et al (2002) Stimulation of erythroleukaemia cell

differentiation by extracellular high-mobility group-box protein 1 is independent of the receptor for advanced glycation end-products. Biochem J 363:529–535

47. Stern D, Du Yan S, Fang Yan S, Marie Schmidt A (2002) Receptor for advanced glycation endproducts: a multiligand receptor magnifying cell stress in diverse pathologic settings.

Adv Drug Deliv Rev 54:1615–1625

48. Hori O, Brett J, Slattery T, et al (1995) The receptor for advanced glycation end products (RAGE) is a cellular binding site for amphoterin. Mediation of neurite outgrowth and co- expression of rage and amphoterin in the developing nervous system. J Biol Chem 270:25752–

25761

49. Huttunen HJ, Fages C, Rauvala H (1999) Receptor for advanced glycation end products (RAGE)-mediated neurite outgrowth and activation of NF-kappaB require the cytoplasmic domain of the receptor but different downstream signaling pathways. J Biol Chem 274:19919–

19924

50. Sajithlal G, Huttunen H, Rauvala H, Munch G (2002) Receptor for advanced glycation end products plays a more important role in cellular survival than in neurite outgrowth during retinoic acid-induced differentiation of neuroblastoma cells. J Biol Chem 277:6888–6897 51. Schmidt AM, Hori O, Cao R, et al (1996) RAGE: a novel cellular receptor for advanced

glycation end products. Diabetes 45 (Suppl 3):S77–80

52. Taniguchi N, Kawahara K, Yone K, et al (2003) High mobility group box chromosomal protein 1 plays a role in the pathogenesis of rheumatoid arthritis as a novel cytokine. Arthritis Rheum 48:971–981

53. Parkkinen J, Raulo E, Merenmies J, et al (1993) Amphoterin, the 30-kDa protein in a family of HMG1-type polypeptides. Enhanced expression in transformed cells, leading edge localization, and interactions with plasminogen activation. J Biol Chem 268:19726–19738 54. Huttunen HJ, Kuja-Panula J, Rauvala H (2002) Receptor for advanced glycation end prod-

ucts (RAGE) signaling induces CREB-dependent chromogranin expression during neuronal differentiation. J Biol Chem 277:38635–38646

55. Park JS, Gamboni-Robertson F, He Q, et al (2005) High Mobility Group Box 1 protein (HMGB1) interacts with multiple Toll like receptors. Am J Physiol Cell Physiol 290:C917–924 56. Park JS, Svetkauskaite D, He Q, et al (2004) Involvement of Toll-like receptors 2 and 4 in

cellular activation by High Mobility Group Box 1 protein. J Biol Chem 279:7370–7377 57. O’Neill LA (2002) Signal transduction pathways activated by the IL-1 receptor/toll-like re-

ceptor superfamily. Curr Top Microbiol Immunol 270:47–61

58. Bianchi ME, Beltrame M (2000) Upwardly mobile proteins. Workshop: the role of HMG proteins in chromatin structure, gene expression and neoplasia. EMBO Rep 1:109–114