Editorial
Editorial: NFAT signaling: no FAT as new weapon to fight shock By Shuang Zhang,*,† Min Wu,*,1 and Hongwei Gao‡,1 *Department of Basic Sciences, University of North Dakota, Grand Forks, North Dakota, USA; †State Key Laboratory of Biotherapy and Cancer Center/Collaborative Innovation Center of Biotherapy, West China Hospital, Sichuan University, Chengdu, China; and ‡ Center for Experimental Therapeutics and Reperfusion Injury, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, USA RECEIVED DECEMBER 21, 2014; REVISED JANUARY 29, 2015; ACCEPTED MARCH 15, 2015. DOI: 10.1189/jlb.4CE1214-616R
< SEE CORRESPONDING ARTICLE ON PAGE 1003
S
treptococcus pyogenes is a significant human pathogen causing a wide array of infections, ranging from mild skin infections to life-threatening infections, such as bacteremia, pneumonia, and STSS. Unlike many emerging multiantibiotic-resistant bacteria in recent years, S. pyogenes show low antibiotic resistance, and almost all strains are susceptible to penicillin. Paradoxically, this fact does not fully explain the clinical observations: many patients with invasive S. pyogenes infections die, despite complete eradication of the invading pathogen. To corroborate better the complex pathogenic mechanism involving this pathogen, scientists suggest that it is the host, not the germ, to drive the pathogenesis of systemic inflammation [1]. Immunity is definitely a double-edged sword, as the same functions that protect the host against pathogens can also damage normal tissues, ultimately impairing structure and function of multiple organs. Overzealous immune activation underlies several inflammatory diseases, including systemic inflammatory response syndrome, sepsis, sepsis shock, and multiorgan dysfunction syndrome. Thus, a better mechanistic understanding of systematic immune responses, accompanied by a detailed description of the relevant molecular pathways, will constitute a critical step in Abbreviations: BTP = bis-trifluoromethyl-pyrazole compound, Ca2+ = calcium ion, HBP = heparinbinding protein, Mac-1 = macrophage 1, MNL = monomorphonuclear leukocyte, MPO = myeloperoxidase, PMNL = polymorphonuclear leukocytes, STSS = streptococcal toxic shock syndrome
0741-5400/15/0097-997 © Society for Leukocyte Biology
designing potential treatment and prevention strategies against these lethal inflammatory diseases. The NFAT proteins are a family of transcription factors whose activation is regulated by calcineurin, a Ca2+-dependent phosphatase. Originally identified as inducers of cytokine gene expression, NFAT proteins play varied roles in the immune system. In this issue of the Journal of Leukocyte Biology, Zhang and colleagues [2] have shown that NFAT signaling controls pulmonary infiltration of neutrophils in response to streptococcal M1 protein via CXC chemokines and neutrophil expression of Mac-1, which results in lung dysfunction, immunity defect, and gaseous exchange impairment. STSS is defined as isolation of S. pyogenes from a normally sterile or nonsterile site in the organism, hypotension, and more than 1 of the following signs: acute respiratory distress syndrome, liver involvement, renal impairment, erythematous rash, coagulopathy, or soft tissue necrosis. M Protein represents the classic virulence determinant of S. pyogenes, which is normally associated with the bacterial cell wall but can be released spontaneously or by the proteinase secreted from the bacteria. More than 80 different M serotypes have been documented in S. pyogenes, and accumulating evidence has demonstrated that the M1 serotype is most prevalently associated with STSS. Furthermore, patients dying from STSS, caused by M1 strains, were found to have low antibody titers toward the M1 protein. These
observations demonstrate that the M1 protein participates in the inflammatory molecular mechanism, which contributes to this lethal clinical condition. It has been reported that M1 protein forms complexes with fibrinogen, and these complexes bind to b2-integrins on the neutrophil surface and induce release of HBP. This process is dependent on extracellular-divalent metal ions and causes severe pulmonary damage characterized by leakage of plasma and blood cells [3]. It has also been reported that M1 protein-fibrinogen complexes cause neutrophil degranulation and acute lung damage. Recent studies have expanded virulence mechanisms of M1 protein, including cytokine release from monocytes and chemokine expression in epithelial cells, which may contribute directly to the lung damage observed in STSS patients [4]. As the lung is one of the most critical organs that is compromised by STSS, Zhang and colleagues [2], in this report, timely defined the significance of NFAT signaling in controlling CXC chemokine production, neutrophil activation, as well as edema formation in acute lung injury provoked by streptococcal M1 protein. Extracellular stress signals trigger 1. Correspondence: H.G., Center for Experimental Therapeutics and Reperfusion Injury, Dept. of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, Harvard Medical School, 20 Shattuck St., Boston, MA 02115, USA. E-mail: hgao@zeus. bwh.harvard.edu; M.W., Dept. of Biochemistry and Molecular Biology, University of North Dakota, 501 North Columbia Rd., P.O. Box 9037, Grand Forks, ND 58203, USA. E-mail: [email protected]
Volume 97, June 2015
Journal of Leukocyte Biology 997
intracellular signaling cascades on specific transcription factors, controlling gene expression and effector functions. Ca2+ serves as a universal second messenger in virtually all eukaryotic cells, which is a key determinant in the activation of immune cells. NFAT consists of 4 isoforms (NFATc1–c4), which are heavily phosphorylated and located in the cytosol under quiescent conditions. Upon stimulation with prolonged elevation of Ca2+ levels, NFAT is dephosphorylated by calcineurin, allowing nuclear translocation [5]. NFAT activation initiates a cascade of transcriptional events regulating several physiologic states. Meanwhile, accumulating data suggest that NFAT activity also plays an important role in pathologic inflammations, including autoimmune diseases, atherosclerosis, and acute pancreatitis [6, 7]. Mechanistically, Zhang et al. [2] used NFAT-luciferase reporter mice and demonstrated that M1 protein triggers NFATdependent transcriptional activity, not only in the lung but also in the spleen and liver, prompting that NFAT is systemically activated in M1 protein-induced inflammation. Moreover, compared with the solvent control, administration of the NFAT inhibitor A-285222 reached 66% inhibition against lung edema and tissue damage in the lungs of mice exposed to M1 protein. Lung edema and epithelial injury are often accompanied by an influx of neutrophils into the alveolar interstitium; thus, neutrophils are considered a key player in the progression of M1 protein-induced lung damage. It is also interesting to reveal that treatment with A-285222 reduced MPO levels in the lungs by ;77% in response to M1 protein. Notably, the A-285222mediated decrease in MPO activity correlated well with the reduction in neutrophils in the alveolar compartment in M1 proteintreated mice [2]. Controversially, the authors observed that challenge with M1 protein decreased the circulating number of PMNL and MNL. However, inhibition of NFAT activity reversed this M1 proteininduced reduction in PMNL and MNL in the peripheral blood. It is mainly the consequence of M1 protein-induced neutrophil recruitment in lungs and other organs. However, the brisk bone marrow response that includes the release of immature immune cells has been documented during the course of various 998 Journal of Leukocyte Biology
inflammatory events. It would be interesting to investigate further the relationship between NFAT activity and bone marrowderived hemopoietic cell recruitment in the peripheral blood. Neutrophil infiltration is an insidious characteristic in acute lung injury, although the molecular mechanisms mediating pulmonary recruitment of neutrophils remain elusive. In the inflammatory area, evidence is now emerging that neutrophil activation and trafficking are controlled by CXC chemokines, such as CXCL1 and CXCL2. Meanwhile, activated neutrophils express high levels of integrins (mainly Mac-1 and LFA-1), which are crucial to promote firm adhesion of neutrophils to the vessel endothelial cells [8]. Zhang et al. [2] found that inhibiting NFAT activity greatly attenuated M1 protein-induced expression of Mac-1 on neutrophils. Furthermore, NFAT inhibition markedly suppressed M1 protein-induced pulmonary formation of CXCL1 and CXCL2. With the consideration that CXC chemokines and their receptor CXCR2 are important in up-regulating Mac-1 expression in neutrophils, inhibition of CXC chemokine formation could be 1 mechanism that explains the inhibitory effect of A-285222 on neutrophil activation, Mac-1 expression, and recruitment into the lung in response to M1 protein. Most importantly, this is the first study to elaborate that NFAT signaling executes a significant function in streptococcal M1 protein-provoked neutrophil recruitment and acute lung injury [2]. Despite recent advances in understanding the molecular mechanisms of NFAT inflammatory signaling, the main mechanism—that M1 protein increases intracellular Ca2+ concentration—has not been studied in great detail. A good example shows that an influx of Ca2+ into the cytosol occurs following the engagement of receptors on the surface of immune cells [9]. In this case, antigens bind to the TCR or the BCR, and antigen-antibody complexes bind to FcRs on dendritic cells or macrophages, which is essential for the activation of calcium signals and cytokine gene expression. Recent studies also show that M1 protein interacts with TLR2 or b2integrins on the immune cells, which may evoke the calcium signals that are attributed to the pathophysiological
Volume 97, June 2015
consequences seen in severe streptococcal infections [3, 9]. This study also provides insight into translational medicine. A-285222 belongs to the BTPs, a novel class of immunosuppressive agents that inhibit NFAT activity by maintaining NFAT in an inactive phosphorylated state. Although A-285222 is applied by intraperitoneal injection in several animal models, including acute lung injury, atherosclerosis, diabetes mellitus, and spontaneous pulmonary hypertension, it is not translatable to clinical application. Intravenous or oral administration, the clinically relevant methods of drug delivery, should be attempted in the subsequent experiments. Meanwhile, NFAT proteins play many physiologic roles, such as heartvalve formation, neuronal growth, skeletal muscle growth, as well as organization of developing blood vessels. A-285222 tends to cause certain predictable, on-target, adverse events, which are those that result from the mechanism of inhibition of NFAT signaling in normal tissues. For example, the neurotoxic side-effects of A-285222 occur when animals are dosed excessively. The high concentration of A-285222 in cerebrospinal fluid may be the cause of neurotoxicity as a result of its pharmacokinetic properties. Thus, the development of new BTPs with diminished ability to cross the blood-brain barrier may avoid neurotoxic adverse effects. It is important to note that the mechanisms of NFAT activation have been studied extensively in immune cells. Moreover, ubiquitous expression and activation of NFAT in mammalian tissues have been observed recently in the tumor and its microenvironment. NFAT isoforms are overexpressed in solid and hematologic malignancies and important for fibroblast proliferation, epithelial tumor cell invasion, endothelial cell growth, and angiogenesis. The knowledge of the roles played by NFAT in tumor progression and metastasis may provide insight into effective therapeutics targeting the NFAT pathway in cancer [10]. We illustrate the works by Zhang and colleagues [2] and other investigators in Fig. 1 [3, 4, 9]. Although the work by Zhang et al. [2] has increased our understanding of NFAT signaling and its
www.jleukbio.org
EDITORIAL Zhang et al.
NFAT signaling in shock
Figure 1. Scheme describes the cascade of events by which neutrophils are recruited and activated in response to streptococcal M1 protein in the pulmonary blood-gas barrier. M1 Protein forms complexes with fibrinogen and then binds to b2integrins on the neutrophil surface, resulting in release of HBP and neutrophil granules. M1 Protein also induces cytokine release from monocytes. Most importantly, upon stimulation with M1 protein, NFAT is dephosphorylated by calcineurin, allowing nuclear translocation, which markedly increases Mac-1 expression on neutrophils and up-regulates pulmonary formation of CXCL1 and CXCL2. CaN, calcineurin.
potential role in bacterial infection, much remains to be learned regarding the deeper molecular mechanisms in host response. It may be interesting to delve into the molecular events by which NFAT is expressed, and the pathway is regulated, such as the precise molecular interaction with the target proteins and their domains, as well as the possible involvement of posttranscriptional regulation. Given this new findings, selective and specific inhibition of NFAT signaling might cause robust efficacy in severe invasive infections, cancer, and autoimmune diseases. It is also reported that cyclosporine and FK506, 2 calcineurin inhibitors, can protect the host against endotoxemia and acute lung injury. As NFAT activity is regulated by calcineurin, it provides another therapeutic option by use of calcineurin inhibitors on STSS and other diseases. As the current mortality rate of STSS is rather high, any new format of therapeutics is required to enter the research domains or
www.jleukbio.org
pharmaceutic market. Although much remains to be learned, further elucidation of the functions of NFAT signaling may help understand its translational importance.
REFERENCES
1. Angus, D. C., van der Poll, T. (2013) Severe sepsis and septic shock. N. Engl. J. Med. 369, 2063. 2. Zhang, S., Zhang, S., Garcia-Vaz, E., Herwald, H., Gomez, M. F., Thorlacius, H. (2015) Streptococcal M1 protein triggers chemokine formation, neutrophil infiltration, and lung injury in an NFAT-dependent manner. J. Leukoc. Biol. 97, 1003–1010. 3. Herwald, H., Cramer, H., M¨orgelin, M., Russell, W., Sollenberg, U., Norrby-Teglund, A., Flodgaard, H., Lindbom, L., Bj¨orck, L. (2004) M Protein, a classical bacterial virulence determinant, forms complexes with fibrinogen that induce vascular leakage. Cell 116, 367–379. 4. Soehnlein, O., Oehmcke, S., Ma, X., Rothfuchs, A. G., Frithiof, R., van Rooijen, N., Mo¨ rgelin, M., Herwald, H., Lindbom, L. (2008) Neutrophil degranulation mediates severe lung damage triggered by streptococcal M1 protein. Eur. Respir. J. 32, 405–412.
5. Feske, S. (2007) Calcium signalling in lymphocyte activation and disease. Nat. Rev. Immunol. 7, 690–702. 6. Horsley, V., Pavlath, G. K. (2002) NFAT: ubiquitous regulator of cell differentiation and adaptation. J. Cell Biol. 156, 771–774. 7. Awla, D., Zetterqvist, A. V., Abdulla, A., Camello, C., Berglund, L. M., Sp´egel, P., Pozo, M. J., Camello, P. J., Regn´er, S., Gomez, M. F., Thorlacius, H. (2012) NFATc3 regulates trypsinogen activation, neutrophil recruitment, and tissue damage in acute pancreatitis in mice. Gastroenterology 143, 1352–1360, e1–e7. 8. Phillipson, M., Kubes, P. (2011) The neutrophil in vascular inflammation. Nat. Med. 17, 1381–1390. 9. P˚ahlman, L. I., M¨orgelin, M., Eckert, J., Johansson, L., Russell, W., Riesbeck, K., Soehnlein, O., Lindbom, L., NorrbyTeglund, A., Schumann, R. R., Bj¨orck, L., Herwald, H. (2006) Streptococcal M protein: a multipotent and powerful inducer of inflammation. J. Immunol. 177, 1221–1228. 10. Mancini, M., Toker, A. (2009) NFAT proteins: emerging roles in cancer progression. Nat. Rev. Cancer 9, 810–820.
KEY WORDS: Streptococcus pyogenes neutrophil cytokine chemokine
Volume 97, June 2015
•
•
•
Journal of Leukocyte Biology 999
Editorial: NFAT signaling: no FAT as new weapon to fight shock By Shuang Zhang,*,† Min Wu,*,1 and Hongwei Gao‡,1 *Department of Basic Sciences, University of North Dakota, Grand Forks, North Dakota, USA; †State Key Laboratory of Biotherapy and Cancer Center/Collaborative Innovation Center of Biotherapy, West China Hospital, Sichuan University, Chengdu, China; and ‡ Center for Experimental Therapeutics and Reperfusion Injury, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, USA RECEIVED DECEMBER 21, 2014; REVISED JANUARY 29, 2015; ACCEPTED MARCH 15, 2015. DOI: 10.1189/jlb.4CE1214-616R
< SEE CORRESPONDING ARTICLE ON PAGE 1003
S
treptococcus pyogenes is a significant human pathogen causing a wide array of infections, ranging from mild skin infections to life-threatening infections, such as bacteremia, pneumonia, and STSS. Unlike many emerging multiantibiotic-resistant bacteria in recent years, S. pyogenes show low antibiotic resistance, and almost all strains are susceptible to penicillin. Paradoxically, this fact does not fully explain the clinical observations: many patients with invasive S. pyogenes infections die, despite complete eradication of the invading pathogen. To corroborate better the complex pathogenic mechanism involving this pathogen, scientists suggest that it is the host, not the germ, to drive the pathogenesis of systemic inflammation [1]. Immunity is definitely a double-edged sword, as the same functions that protect the host against pathogens can also damage normal tissues, ultimately impairing structure and function of multiple organs. Overzealous immune activation underlies several inflammatory diseases, including systemic inflammatory response syndrome, sepsis, sepsis shock, and multiorgan dysfunction syndrome. Thus, a better mechanistic understanding of systematic immune responses, accompanied by a detailed description of the relevant molecular pathways, will constitute a critical step in Abbreviations: BTP = bis-trifluoromethyl-pyrazole compound, Ca2+ = calcium ion, HBP = heparinbinding protein, Mac-1 = macrophage 1, MNL = monomorphonuclear leukocyte, MPO = myeloperoxidase, PMNL = polymorphonuclear leukocytes, STSS = streptococcal toxic shock syndrome
0741-5400/15/0097-997 © Society for Leukocyte Biology
designing potential treatment and prevention strategies against these lethal inflammatory diseases. The NFAT proteins are a family of transcription factors whose activation is regulated by calcineurin, a Ca2+-dependent phosphatase. Originally identified as inducers of cytokine gene expression, NFAT proteins play varied roles in the immune system. In this issue of the Journal of Leukocyte Biology, Zhang and colleagues [2] have shown that NFAT signaling controls pulmonary infiltration of neutrophils in response to streptococcal M1 protein via CXC chemokines and neutrophil expression of Mac-1, which results in lung dysfunction, immunity defect, and gaseous exchange impairment. STSS is defined as isolation of S. pyogenes from a normally sterile or nonsterile site in the organism, hypotension, and more than 1 of the following signs: acute respiratory distress syndrome, liver involvement, renal impairment, erythematous rash, coagulopathy, or soft tissue necrosis. M Protein represents the classic virulence determinant of S. pyogenes, which is normally associated with the bacterial cell wall but can be released spontaneously or by the proteinase secreted from the bacteria. More than 80 different M serotypes have been documented in S. pyogenes, and accumulating evidence has demonstrated that the M1 serotype is most prevalently associated with STSS. Furthermore, patients dying from STSS, caused by M1 strains, were found to have low antibody titers toward the M1 protein. These
observations demonstrate that the M1 protein participates in the inflammatory molecular mechanism, which contributes to this lethal clinical condition. It has been reported that M1 protein forms complexes with fibrinogen, and these complexes bind to b2-integrins on the neutrophil surface and induce release of HBP. This process is dependent on extracellular-divalent metal ions and causes severe pulmonary damage characterized by leakage of plasma and blood cells [3]. It has also been reported that M1 protein-fibrinogen complexes cause neutrophil degranulation and acute lung damage. Recent studies have expanded virulence mechanisms of M1 protein, including cytokine release from monocytes and chemokine expression in epithelial cells, which may contribute directly to the lung damage observed in STSS patients [4]. As the lung is one of the most critical organs that is compromised by STSS, Zhang and colleagues [2], in this report, timely defined the significance of NFAT signaling in controlling CXC chemokine production, neutrophil activation, as well as edema formation in acute lung injury provoked by streptococcal M1 protein. Extracellular stress signals trigger 1. Correspondence: H.G., Center for Experimental Therapeutics and Reperfusion Injury, Dept. of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, Harvard Medical School, 20 Shattuck St., Boston, MA 02115, USA. E-mail: hgao@zeus. bwh.harvard.edu; M.W., Dept. of Biochemistry and Molecular Biology, University of North Dakota, 501 North Columbia Rd., P.O. Box 9037, Grand Forks, ND 58203, USA. E-mail: [email protected]
Volume 97, June 2015
Journal of Leukocyte Biology 997
intracellular signaling cascades on specific transcription factors, controlling gene expression and effector functions. Ca2+ serves as a universal second messenger in virtually all eukaryotic cells, which is a key determinant in the activation of immune cells. NFAT consists of 4 isoforms (NFATc1–c4), which are heavily phosphorylated and located in the cytosol under quiescent conditions. Upon stimulation with prolonged elevation of Ca2+ levels, NFAT is dephosphorylated by calcineurin, allowing nuclear translocation [5]. NFAT activation initiates a cascade of transcriptional events regulating several physiologic states. Meanwhile, accumulating data suggest that NFAT activity also plays an important role in pathologic inflammations, including autoimmune diseases, atherosclerosis, and acute pancreatitis [6, 7]. Mechanistically, Zhang et al. [2] used NFAT-luciferase reporter mice and demonstrated that M1 protein triggers NFATdependent transcriptional activity, not only in the lung but also in the spleen and liver, prompting that NFAT is systemically activated in M1 protein-induced inflammation. Moreover, compared with the solvent control, administration of the NFAT inhibitor A-285222 reached 66% inhibition against lung edema and tissue damage in the lungs of mice exposed to M1 protein. Lung edema and epithelial injury are often accompanied by an influx of neutrophils into the alveolar interstitium; thus, neutrophils are considered a key player in the progression of M1 protein-induced lung damage. It is also interesting to reveal that treatment with A-285222 reduced MPO levels in the lungs by ;77% in response to M1 protein. Notably, the A-285222mediated decrease in MPO activity correlated well with the reduction in neutrophils in the alveolar compartment in M1 proteintreated mice [2]. Controversially, the authors observed that challenge with M1 protein decreased the circulating number of PMNL and MNL. However, inhibition of NFAT activity reversed this M1 proteininduced reduction in PMNL and MNL in the peripheral blood. It is mainly the consequence of M1 protein-induced neutrophil recruitment in lungs and other organs. However, the brisk bone marrow response that includes the release of immature immune cells has been documented during the course of various 998 Journal of Leukocyte Biology
inflammatory events. It would be interesting to investigate further the relationship between NFAT activity and bone marrowderived hemopoietic cell recruitment in the peripheral blood. Neutrophil infiltration is an insidious characteristic in acute lung injury, although the molecular mechanisms mediating pulmonary recruitment of neutrophils remain elusive. In the inflammatory area, evidence is now emerging that neutrophil activation and trafficking are controlled by CXC chemokines, such as CXCL1 and CXCL2. Meanwhile, activated neutrophils express high levels of integrins (mainly Mac-1 and LFA-1), which are crucial to promote firm adhesion of neutrophils to the vessel endothelial cells [8]. Zhang et al. [2] found that inhibiting NFAT activity greatly attenuated M1 protein-induced expression of Mac-1 on neutrophils. Furthermore, NFAT inhibition markedly suppressed M1 protein-induced pulmonary formation of CXCL1 and CXCL2. With the consideration that CXC chemokines and their receptor CXCR2 are important in up-regulating Mac-1 expression in neutrophils, inhibition of CXC chemokine formation could be 1 mechanism that explains the inhibitory effect of A-285222 on neutrophil activation, Mac-1 expression, and recruitment into the lung in response to M1 protein. Most importantly, this is the first study to elaborate that NFAT signaling executes a significant function in streptococcal M1 protein-provoked neutrophil recruitment and acute lung injury [2]. Despite recent advances in understanding the molecular mechanisms of NFAT inflammatory signaling, the main mechanism—that M1 protein increases intracellular Ca2+ concentration—has not been studied in great detail. A good example shows that an influx of Ca2+ into the cytosol occurs following the engagement of receptors on the surface of immune cells [9]. In this case, antigens bind to the TCR or the BCR, and antigen-antibody complexes bind to FcRs on dendritic cells or macrophages, which is essential for the activation of calcium signals and cytokine gene expression. Recent studies also show that M1 protein interacts with TLR2 or b2integrins on the immune cells, which may evoke the calcium signals that are attributed to the pathophysiological
Volume 97, June 2015
consequences seen in severe streptococcal infections [3, 9]. This study also provides insight into translational medicine. A-285222 belongs to the BTPs, a novel class of immunosuppressive agents that inhibit NFAT activity by maintaining NFAT in an inactive phosphorylated state. Although A-285222 is applied by intraperitoneal injection in several animal models, including acute lung injury, atherosclerosis, diabetes mellitus, and spontaneous pulmonary hypertension, it is not translatable to clinical application. Intravenous or oral administration, the clinically relevant methods of drug delivery, should be attempted in the subsequent experiments. Meanwhile, NFAT proteins play many physiologic roles, such as heartvalve formation, neuronal growth, skeletal muscle growth, as well as organization of developing blood vessels. A-285222 tends to cause certain predictable, on-target, adverse events, which are those that result from the mechanism of inhibition of NFAT signaling in normal tissues. For example, the neurotoxic side-effects of A-285222 occur when animals are dosed excessively. The high concentration of A-285222 in cerebrospinal fluid may be the cause of neurotoxicity as a result of its pharmacokinetic properties. Thus, the development of new BTPs with diminished ability to cross the blood-brain barrier may avoid neurotoxic adverse effects. It is important to note that the mechanisms of NFAT activation have been studied extensively in immune cells. Moreover, ubiquitous expression and activation of NFAT in mammalian tissues have been observed recently in the tumor and its microenvironment. NFAT isoforms are overexpressed in solid and hematologic malignancies and important for fibroblast proliferation, epithelial tumor cell invasion, endothelial cell growth, and angiogenesis. The knowledge of the roles played by NFAT in tumor progression and metastasis may provide insight into effective therapeutics targeting the NFAT pathway in cancer [10]. We illustrate the works by Zhang and colleagues [2] and other investigators in Fig. 1 [3, 4, 9]. Although the work by Zhang et al. [2] has increased our understanding of NFAT signaling and its
www.jleukbio.org
EDITORIAL Zhang et al.
NFAT signaling in shock
Figure 1. Scheme describes the cascade of events by which neutrophils are recruited and activated in response to streptococcal M1 protein in the pulmonary blood-gas barrier. M1 Protein forms complexes with fibrinogen and then binds to b2integrins on the neutrophil surface, resulting in release of HBP and neutrophil granules. M1 Protein also induces cytokine release from monocytes. Most importantly, upon stimulation with M1 protein, NFAT is dephosphorylated by calcineurin, allowing nuclear translocation, which markedly increases Mac-1 expression on neutrophils and up-regulates pulmonary formation of CXCL1 and CXCL2. CaN, calcineurin.
potential role in bacterial infection, much remains to be learned regarding the deeper molecular mechanisms in host response. It may be interesting to delve into the molecular events by which NFAT is expressed, and the pathway is regulated, such as the precise molecular interaction with the target proteins and their domains, as well as the possible involvement of posttranscriptional regulation. Given this new findings, selective and specific inhibition of NFAT signaling might cause robust efficacy in severe invasive infections, cancer, and autoimmune diseases. It is also reported that cyclosporine and FK506, 2 calcineurin inhibitors, can protect the host against endotoxemia and acute lung injury. As NFAT activity is regulated by calcineurin, it provides another therapeutic option by use of calcineurin inhibitors on STSS and other diseases. As the current mortality rate of STSS is rather high, any new format of therapeutics is required to enter the research domains or
www.jleukbio.org
pharmaceutic market. Although much remains to be learned, further elucidation of the functions of NFAT signaling may help understand its translational importance.
REFERENCES
1. Angus, D. C., van der Poll, T. (2013) Severe sepsis and septic shock. N. Engl. J. Med. 369, 2063. 2. Zhang, S., Zhang, S., Garcia-Vaz, E., Herwald, H., Gomez, M. F., Thorlacius, H. (2015) Streptococcal M1 protein triggers chemokine formation, neutrophil infiltration, and lung injury in an NFAT-dependent manner. J. Leukoc. Biol. 97, 1003–1010. 3. Herwald, H., Cramer, H., M¨orgelin, M., Russell, W., Sollenberg, U., Norrby-Teglund, A., Flodgaard, H., Lindbom, L., Bj¨orck, L. (2004) M Protein, a classical bacterial virulence determinant, forms complexes with fibrinogen that induce vascular leakage. Cell 116, 367–379. 4. Soehnlein, O., Oehmcke, S., Ma, X., Rothfuchs, A. G., Frithiof, R., van Rooijen, N., Mo¨ rgelin, M., Herwald, H., Lindbom, L. (2008) Neutrophil degranulation mediates severe lung damage triggered by streptococcal M1 protein. Eur. Respir. J. 32, 405–412.
5. Feske, S. (2007) Calcium signalling in lymphocyte activation and disease. Nat. Rev. Immunol. 7, 690–702. 6. Horsley, V., Pavlath, G. K. (2002) NFAT: ubiquitous regulator of cell differentiation and adaptation. J. Cell Biol. 156, 771–774. 7. Awla, D., Zetterqvist, A. V., Abdulla, A., Camello, C., Berglund, L. M., Sp´egel, P., Pozo, M. J., Camello, P. J., Regn´er, S., Gomez, M. F., Thorlacius, H. (2012) NFATc3 regulates trypsinogen activation, neutrophil recruitment, and tissue damage in acute pancreatitis in mice. Gastroenterology 143, 1352–1360, e1–e7. 8. Phillipson, M., Kubes, P. (2011) The neutrophil in vascular inflammation. Nat. Med. 17, 1381–1390. 9. P˚ahlman, L. I., M¨orgelin, M., Eckert, J., Johansson, L., Russell, W., Riesbeck, K., Soehnlein, O., Lindbom, L., NorrbyTeglund, A., Schumann, R. R., Bj¨orck, L., Herwald, H. (2006) Streptococcal M protein: a multipotent and powerful inducer of inflammation. J. Immunol. 177, 1221–1228. 10. Mancini, M., Toker, A. (2009) NFAT proteins: emerging roles in cancer progression. Nat. Rev. Cancer 9, 810–820.
KEY WORDS: Streptococcus pyogenes neutrophil cytokine chemokine
Volume 97, June 2015
•
•
•
Journal of Leukocyte Biology 999
