Signal transduction through cytokine receptors

Receptors for interleukins, colony stimulating factors, and hormones have a homology in their extracellular regions, characterized by the conserved cysteine residues and the tryptophan-serine-x-tryptophan-serine motif, thus, they are classified to the type 1 cytokine receptor superfamily. Janus tyrosine kinase (JAKs) have been found to be involved in the signal transduction through type I cytokine receptors. JAKs associate with the membrane proximal region in the cytoplasmic domain having box1 and box2, which are conserved among the family, and upon the stimulation JAKs can be aggregated following the receptor dimerization and activated probably by transphosphorylation. JAKs then phosphorylate the receptor and various signal transducing molecules, including STATs (signal transducer and activator of transcriptions) and other SH2-containing adapter molecules. STATs were initially identified as transcription factors containing a SH2 domain and regulating interferons-inducible genes. STATs can be tyrosine phosphorylated by JAKs and form dimer (either hetero- or homo-dimers) to enter the nucleus, resulting in the expression of a set of genes. On the other hand, adapter molecules such as Shc, GRB2, and SHP-2 have been shown to link the cytokine receptors to Ras, followed by the activation of the Raf-MEK-MAP kinase pathway, leading to the activation of various transcription factors in the nucleus. These two signals are generated by different ways upon the stimulation of the receptors and they elicit a variety of biological functions in various cell types. In this review, we will discuss the mechanism by which cytokines activate JAKs, STATs, and a variety of adapter molecules. We further discuss the roles of each signal transduction pathways in the expression of biological activities of cytokines.

STAT3 is required for the gp130-mediated full activation of the c-myc gene

The signal transducers and activators of transcription (STAT) family members have been implicated in regulating the growth, differentiation, and death of normal and transformed cells in response to either extracellular stimuli, including cytokines and growth factors, or intracellular tyrosine kinases. c-myc expression is coordinately regulated by multiple signals in these diverse cellular responses. We show that STAT3 mostly mediates the rapid activation of the c-myc gene upon stimulation of the interleukin (IL)-6 receptor or gp130, a signal transducing subunit of the receptor complexes for the IL-6 cytokine family. STAT3 does so most likely by binding to cis-regulatory region(s) of the c-myc gene. We show that STAT3 binds to a region overlapping with the E2F site in the c-myc promoter and this site is critical for the c-myc gene promoter- driven transcriptional activation by IL-6 or gp130 signals. This is the first identification of the linkage between a member of the STAT family and the c-myc gene activation, and also explains how the IL-6 family of cytokines is capable of inducing the expression of the c-myc gene.

[Postoperative mediastinitis after the coronary artery bypass grafting using internal thoracic artery graft]

It has been pointed out in general that the resistance against infection is decreased in the diabetic patients. This problem is very important in patients undergoing major surgery. In cardiovascular surgery, the median wound infection may result in life threatening sequelae. We have used the internal thoracic artery as the appropriate graft for its excellent long-term patency. In this series of the diabetic patients who underwent coronary artery bypass grafting with bilateral internal thoracic artery grafts, the incidence of postoperative mediastinitis was significantly higher than other cases. Therefore the use of bilateral internal thoracic artery grafts should be avoided, if possible in the diabetic patients.

Signaling through Gp130: toward a general scenario of cytokine action

Cytokines play roles in a wide range of responses such as immune response, hematopoiesis and inflammation. A large volume of studies revealed that cytokines show functional pleiotropy and redundancy. Gp130 is a receptor subunit shared by the interleukin-6 family of cytokines. We describe and discuss signaling through gp130 in relation to a general scenario for cytokine signaling regulating cell growth, differentiation and survival.

[The long-term anterior chest median wound keloid after the cardiac surgery]

We discussed on the long-term anterior chest median wound keloid after the cardiac surgery by using a questionnaire. The risk of the anterior chest median wound keloid was high significantly in the cases using the bilateral internal thoracic artery compared with the cases using no internal thoracic artery. Participation of the decreased blood supply was highly suggested as the cause of this keloid formation.

Left ventricular free wall rupture following mitral valve replacement

During a 10-year period, 110 patients underwent mitral valve replacement (MVR). We experienced three left ventricular ruptures among these patients. Two had a type I immediate rupture, and one had a type III delayed rupture. Two patients (type I, III) survived after repair of the rupture. It was possible to control bleeding by manual compression with oxidized cellulose, collagen mat and fibrin glue with or without external mattress sutures. Following the repair, an intra-aortic balloon pump and sedative agents were used in both patients. In the other patient with a type I early rupture, control of bleeding was attempted by external direct suture using Teflon felt. The bleeding was controlled by this repair and the use of a left ventricular assist device, but the patient died of a brain infarction 5 days after the operation. The manual compression technique using oxidized cellulose, collagen mat and fibrin glue may be useful for minor lacerations, and for reinforcing repairs. The intra-aortic balloon pump and continuous sedation are useful for unloading the ventricle and reducing the tension on repairs.

STAT3 orchestrates contradictory signals in cytokine-induced G1 to S cell-cycle transition

The signal transducer and activator of transcription molecules (STATs) play key roles in cytokine-induced signal transduction. However, their role in cell growth has not been clear. In the present study, we show that STAT3 plays a key role in the G1 to S phase cell-cycle transition induced by the cytokine receptor subunit gp130, through the upregulation of cyclins D2, D3 and A, and cdc25A, and the concomitant downregulation of p21 and p27. Furthermore, unexpectedly, we found that gp130 could induce the expression of p21 when STAT3 activation was suppressed. Such contradictory signals regulating cell-cycle progression could be simultaneously delivered from distinct cytoplasmic regions of gp130. We propose an 'orchestrating model' for cytokine and growth factor action in which contradictory signals are orchestrated to produce a specific effect in a target cell.

[Coronary artery bypass grafting performed by the simple and convenient graft supporter]

We have experienced a simple, safe and convenient technique for supporting the arterial or saphenous vein graft in the coronary artery bypass grafting. This graft supporter is made of cotton cloth with a 50 percent polyester mix. The supporter is twenty centimeters long and two centimeters wide. This supporter provides the complete fixation of the graft without the holding by the co-operater. Therefore the supporter allows very easy, safe and accurate graft anastomosis with the native coronary artery or the ascendinbg aorta. No complication was encountered in association with this procedure in 127 operations.

A novel homeobox gene, dharma, can induce the organizer in a non-cell-autonomous manner

The formation of Spemann organizer is one of the most important steps in dorsoventral axis determination in vertebrate development. However, whether the organizer forms autonomously or is induced non-cell-autonomously is controversial. In this report we have isolated a novel zebrafish homeobox gene, dharma, capable of inducing the organizer ectopically. The expression of dharma was first detected in several blastomeres at one side of the margin soon after the mid-blastula transition and continued in the dorsal side of the yolk syncytial layer (YSL) under the embryonic shield, the zebrafish organizer, until the onset of gastrulation. Furthermore, dharma expressed in the YSL induced the organizer in a non-cell-autonomous manner. These results provided the first identification of a zygotic gene to be implicated in the formation of an organizer-inducing center.

Gab1 acts as an adapter molecule linking the cytokine receptor gp130 to ERK mitogen-activated protein kinase

Gab1 has structural similarities with Drosophila DOS (daughter of sevenless), which is a substrate of the protein tyrosine phosphatase Corkscrew. Both Gab1 and DOS have a pleckstrin homology domain and tyrosine residues, potential binding sites for various SH2 domain-containing adapter molecules when they are phosphorylated. We found that Gab1 was tyrosine phosphorylated in response to various cytokines, such as interleukin-6 (IL-6), IL-3, alpha interferon (IFN-alpha), and IFN-gamma. Upon the stimulation of IL-6 or IL-3, Gab1 was found to form a complex with phosphatidylinositol (PI)-3 kinase and SHP-2, a homolog of Corkscrew. Mutational analysis of gp130, the common subunit of IL-6 family cytokine receptors, revealed that neither tyrosine residues of gp130 nor its carboxy terminus was required for tyrosine phosphorylation of Gab1. Expression of Gab1 enhanced gp130-dependent mitogen-activated protein (MAP) kinase ERK2 activation. A mutation of tyrosine 759, the SHP-2 binding site of gp130, abrogated the interactions of Gab1 with SHP-2 and PI-3 kinase as well as ERK2 activation. Furthermore, ERK2 activation was inhibited by a dominant negative p85 PI-3 kinase, wortmannin, or a dominant negative Ras. These observations suggest that Gab1 acts as an adapter molecule in transmitting signals to ERK MAP kinase for the cytokine receptor gp130 and that SHP-2, PI-3 kinase, and Ras are involved in Gab1-mediated ERK activation.

[The long-term anterior chest wound pain after the cardiac surgery]

We discussed on the long-term anterior chest wound pain after the cardiac surgery by using a questionnaire. The risk of the left anterior chest wound pain was high significantly in the cases using the left internal thoracic artery compared with other cases. Participation of the division of the left upper pericardium and the adjacent soft tissue was highly suggested as the cause of this pain.

Rupture of the innominate artery following tracheostomy: report of a case

A 23-year-old man underwent a tracheostomy. A massive hemorrhage from the tracheostomy site occurred 50 days later. An emergency operation was immediately performed and an erosion was noted on the innominate artery. The artery was divided and the hemorrhage was successfully stopped.

[Coronary artery bypass grafting under the excellent heart exposure provided by the use of the coronary artery exposing tape]

We have used the coronary artery exposing tape devised by Akio Matsuura in 93 patients undergoing coronary artery bypass grafting. We could perform graft anastomosis more easily and safely by the use of this tape than by the conventional simple compression method of the heart with the gauzes. The heart was lifted anteriorly with the rotation by the tape pulled to the left side or to the caudal side. The right coronary artery branches were exposed excellently by the simple traction of the tape to the caudal side. The circumflex coronary artery branches were well exposed by one tape pulled to the left side and another tape to the right side over the heart with the counterclockwise rotation of the heart. In these procedures no complication was encountered in association with the traction of this tape.

[Cardiac surgery by the safe and easy insertion method with the J-shaped left ventricular vent catheter]

We experienced the safe and easy insertion method with the J-shaped left ventricular vent catheter. The catheter tip (about 15 cm) was vended in the J shape with the inner stainless steel introducer. This J-shaped catheter was inserted into the left atrium through the right upper pulmonary vein. Then this catheter was held vertically and only the outer silicone catheter was pushed into the left ventricle. In this method the catheter tip is turned to the front in the left atrium and inserted easily into the left ventricle along the anterior wall of the left atrium through the anterior margin of the mitral valve orifice.

Overexpression of neurogenin induces ectopic expression of HuC in zebrafish

Several basic helix-loop-helix (bHLH) transcription factors are known to be involved in vertebrate neurogenesis. To investigate their roles in zebrafish neurogenesis, we isolated cDNAs for homologues of neurogenin and Math(-1)/atonal. The transcription of neurogenin was first detectable in zebrafish nervous system at late gastrulation stage. The expression of zebrafish neurogenin precedes and overlaps that of HuC, one of the earliest neuronal precursor markers. Injection of neurogenin mRNA into early stage zebrafish embryos induced ectopic expression of HuC. These results suggest that neurogenin may participate in the generation of HuC-expressing cells, implying its role in neuronal determination in zebrafish.

Signaling mechanisms through gp130: a model of the cytokine system

The interleukin-6 cytokine family plays roles in a wide variety of tissues and organs, including the immune hematopoietic and nervous systems. Gp130 is a signal-transducing subunit shared by the receptors for the IL-6 family of cytokines. The binding of a ligand to its receptor induces the dimerization of gp130, leading to the activation of JAK tyrosine kinase and tyrosine phosphorylation of gp130. These events lead to the activation of multiple signal-transduction pathways, such as the STAT, Ras-MAPK and PI-3 kinase pathways whose activation is controlled by distinct regions of gp130. We propose a model showing that the outcome of the signal transduction depends on the balance or interplay among the contradictory signal transduction pathways that are simultaneously generated through a cytokine receptor in a given target cell.

Lateral origin of the right internal thoracic artery: report of a case

We report herein the unusual case of a patient in whom postoperative angiography following coronary artery bypass grafting (CABG) revealed a lateral origin of the right internal thoracic artery (ITA) and a normal origin of the left ITA, both of which were demonstrated to be patent and did not follow a tortuous course. The CABG had involved revascularization of the left anterior descending artery (LAD) with the right ITA, and the obtuse marginal artery with the left ITA. The patient had an uneventful postoperative course and developed no respiratory symptoms.

Dual control of neurite outgrowth by STAT3 and MAP kinase in PC12 cells stimulated with interleukin-6

IL-6 induces differentiation of PC12 cells pretreated with nerve growth factor (NGF). We explored the signals required for neurite outgrowth of PC12 cells by using a series of mutants of a chimeric receptor consisting of the extracellular domain of the granulocyte-colony stimulating factor (G-CSF) receptor and the cytoplasmic domain of gp130, a signal-transducing subunit of the IL-6 receptor. The mutants incapable of activating the MAP kinase cascade failed to induce neurite outgrowth. Consistently, a MEK inhibitor, PD98059, inhibited neurite outgrowth, showing that activation of the MAP kinase cascade is essential for the differentiation of PC12 cells. In contrast, a mutation that abolished the ability to activate STAT3 did not inhibit, but rather stimulated neurite outgrowth. This mutant did not require NGF pretreatment for neurite outgrowth. Dominant-negative STAT3s mimicked NGF pretreatment, and NGF suppressed the IL-6-induced activation of STAT3, supporting the idea that STAT3 might regulate the differentiation of PC12 cells negatively. These results suggest that neurite outgrowth of PC12 cells is regulated by the balance of MAP kinase and STAT3 signal transduction pathways, and that STAT3 activity can be regulated negatively by NGF.

A clinical study for the durability of oxygenators on cardiopulmonary support

Cardiopulmonary support (CPS) requires durability of the oxygenator. The life span of the oxygenator is affected by various clinical factors, including patient condition, perfusion condition, and equipment usage. Predictors for the durability of oxygenators were evaluated clinically in this study. Thirty-two patients, who had undergone CPS during the last 3 years in our institute were assigned to this study. Fifty oxygenators had been used (Capiox SX in 19, CB Maxima in 23, and AL-6000 in 8). Significant predictors for the durability of oxygenators were evaluated by nonparametric survival analysis and proportional hazards regression analysis. Univariate regression analysis revealed 6 significant predictors for the life span of oxygenators. These were the oxygenator type, type of centrifugal pump, acidosis with blood pH less than 7.35, base excess less than -5, blood glutamic-oxaloacetic transaminase (GOT) levels greater than 1,000 IU, and blood lactate dehydrogenase (LDH) levels greater than 3,000 IU. After multivariate analysis, there remained only 2 significant predictors. An oxygenator used with a noncoated CPS system (Capiox SX with Capiox EBS) proved to have a significantly shorter life span than one used with a heparin-coated system (CB Maxima or AL-6000 with CB BP-80) (hazards ratio, 3.588, p = 0.0065). Patient conditions, which revealed acidosis with less than -5 of base excess, significantly shortened the life of the oxygenator (hazards ratio, 3.595, p = 0.0188).

Tec tyrosine kinase links the cytokine receptors to PI-3 kinase probably through JAK

Tec/Btk tyrosine kinases are members of a subgroup of Src tyrosine kinase family. They are reported to be activated in response to cytokines, such as IL-3 and IL-6. Janus kinases (JAKs) are known to associate with certain cytokine receptors, e.g. gp130, the signal transducing subunit of IL-6 receptor, and the common beta chain of IL-3 receptor, which can be activated upon receptor dimerization in response to cytokines. Here we show the association between Jak1/Jak2 and Tec or Jak1 and Btk. Furthermore, Jak1 but not Jak2 induces tyrosine phosphorylation of Btk, but not Tec. These observations suggest that upon cytokine stimulation JAKs activate Tec/Btk or induce their dimerization resulting in endogenous tyrosine phosphorylation. Furthermore using a yeast two-hybrid system we have identified the target molecules for Tec, the p85 and p55PIK subunits of PI-3 kinase, and Vav. Tec associated with Vav through its SH2 domain independently of its kinase activity. In contrast the p85 and p55PIK subunits of PI-3 kinase associated with the SH2-kinase domain of Tec, dependent on Tec kinase activity. Consistent with these, IL-6 or IL-3 induced the association between Tec and the p85 subunit of PI-3 kinase in mammalian cells. These findings suggest that Tec tyrosine kinase links cytokine receptors to PI-3 kinase probably through JAKs.

Involvement of a common 10-amino-acid segment in the cytoplasmic region of CD40 but different MAP kinases in different CD40-mediated responses

CD40-mediated signals can induce cell aggregation, proliferation and rescue from apoptosis in WEHI231. To define which segment of cytoplasmic domain of CD40 and how signals are involved in those events, we generated mutant CD40 transfectants. We demonstrated the same 10 amino acid segment that could bind to tumor necrosis factor receptor associated factor-2 and -3 mediated all those responses. However, activation pattern of mitogen activated protein kinases was different. Immunoglobulin M-mediated apoptosis was inhibited by CD40-mediated signal that activated c-Jun aminoterminal kinase synergistically. While, CD40 stimulus through the 10 amino acid segment alone that induced cell aggregation and proliferation resulted in activation of extracellular signal-regulated protein kinase 2.

Blood concentrations of G-CSF and myelopoiesis in patients undergoing aortocoronary bypass surgery

The pattern of changes in leukocyte counts and the blood concentration of G-CSF were observed in 15 patients undergoing aortocoronary bypass surgery. Myelopoietic function was assessed by examining the myelogram and performing flow cytometry to identify human leukocyte differentiation antigens on bone marrow aspirates obtained from the sternum when opening and closing the sternotomy. The blood concentration of G-CSF increased gradually after removal of the aortic cross clamp and peaked on the first postoperative day (232 +/- 98 ngml). The white blood cell count also increased during the operation and peaked on the second postoperative day, demonstrating a threefold increase (15,800 +/- 2700). Granulocytes represented most of the increase, while lymphocytes and monocytes showed no significant changes. The myelogram showed that the percentages of myeloblasts, promyelocytes, and metamyelocytes did not change; however, the percentage of myelocytes increased significantly during surgery (14.0 +/- 2.5% vs. 17.3 +/- 3.5%, p < 0.05). The number of mature myelocytes (LFA-1 beta and Leu-15 positive) decreased significantly (p < 0.01 and p < 0.05) during surgery. With the two-color method, the ratio of immature myelocytes (MCS-2 negative and Leu-15 negative) increased significantly (p < 0.01). The ratio of myeloblasts (Leu-11 and HLA-DR positive) and the ratio of stem cells (CD 34 and MY-9 positive) did not increase significantly during the operation. G-CSF concentrations increase substantially during aortocoronary bypass surgery and may be responsible for the rise in granulocyte and total leukocyte counts, as well as for the increase in immature myelocytes seen on bone marrow examination.

Omental transfer as a method of preventing residual persistent subcutaneous infection after mediastinitis

Currently, poststernotomy mediastinitis frequently is being treated by debridement and immediate closure with omental drainage. This method is useful, but subcutaneous infection occasionally occurs. Divided omental transfer to the presternal space may be helpful in preventing this complication.

An alternative pathway for STAT activation that is mediated by the direct interaction between JAK and STAT

JAK is believed to be an essential tyrosine kinase that mediates signals from the cytokine receptor to its downstream events. JAK associates with the cytoplasmic domain of the type I cytokine receptor superfamily and upon the ligand stimulation it can be activated, resulting in the receptor phosphorylation. In signaling from gp130, a common signal transducer for the IL-6 family cytokines, STAT3, a transcription factor that contains an SH2 domain, is recruited by phosphotyrosines on gp130 and is subsequently phosphorylated by gp130-associated JAKs. In this study, we attempted to find a new target for JAK that is directly activated by JAK, independent of gp130 tyrosine phosphorylation, by using a yeast two-hybrid system. In the process we found that the JH2 domain of JAK1, JAK2 or JAK3 could specifically associate with the carboxy-terminal portion of STAT5, but not with STAT3 or STAT1. The interaction was confirmed using both a transient expression system in a cell line and a GST-fusion protein binding assay. Furthermore, we showed that the activation of STAT5 via gp130 did not need any phosphotyrosines on gp130 while that of STAT3 strictly depended on phosphotyrosines on gp130. Mutations of STAT5 that eliminated the interaction with JAK1 reduced the activation of STAT5 upon the gp130 stimulation, although such mutants could be still activated through erythropoietin receptor. These results indicate that STATs are activated through cytokine receptors by two distinct mechanisms, one dependent on receptor tyrosine phosphorylation and the other mediated by the JAK-STAT direct interaction.

Syk-dependent and -independent signaling cascades in B cells elicited by osmotic and oxidative stress

It was found that Syk protein-tyrosine kinase is rapidly activated in B cells after H2O2 treatment (oxidative stress) or increased extracellular NaCl concentration (osmotic stress) as well as in response to B cell receptor activation. In this study we examined the involvement of Syk in responses elicited by these types of extracellular stress, particularly Ca2+ responses and c-Jun amino-terminal kinase (JNK) activation, using a chicken B cell line, DT40, as well as the DT40-derived mutant DT40/Syk(-), which does not express Syk. Osmotic stress evokes increases in [Ca2+]i by stimulating an extracellular Ca2+ influx in both DT40 and DT40/Syk(-) cells. In comparison, oxidative stress elicits an increase in [Ca2+]i by stimulating both an extracellular Ca2+ influx and Ca2+ release from internal stores in DT40 cells, but this Ca2+ response is partially abolished in DT40/Syk(-) cells, indicating that the oxidative stress-induced Ca2+ response is at least partly dependent on Syk. Interestingly, the depletion of Ca2+ results in a significantly decreased level of Syk activation in DT40 cells stimulated by oxidative but not osmotic stress. Furthermore, JNK is activated to different extents by these two types of stress. The extent of JNK activation in DT40/Syk(-) cells in response to osmotic stress is comparable to that observed in DT40 cells. Intriguingly, oxidative stress-induced JNK activation is significantly compromised in DT40/Syk(-) cells. Collectively, these results indicate that both the Ca2+ response and JNK activity induced by oxidative stress are partly dependent on Syk, whereas those induced by osmotic stress are independent of Syk.