Signaling pathways recruited by the cardiotrophin-like cytokine/cytokine-like factor-1 composite cytokine: specific requirement of the membrane-bound form of ciliary neurotrophic factor receptor alpha component

Ciliary neurotrophic factor (CNTF) is a cytokine supporting the differentiation and survival of a number of neural cell types. Its receptor complex consists of a ligand-binding component, CNTF receptor (CNTFR), associated with two signaling receptor components, gp130 and leukemia inhibitory factor receptor (LIFR). Striking phenotypic differences between CNTF- and CNTFR-deficient mice suggest that CNTFR serves as a receptor for a second developmentally important ligand. We recently demonstrated that cardiotrophin-like cytokine (CLC) associates with the soluble orphan receptor cytokine-like factor-1 (CLF) to form a heterodimeric cytokine that displayed activities only on cells expressing the tripartite CNTF receptor on their surface. In this present study we examined the membrane binding of the CLC/CLF composite cytokine and observed a preferential interaction of the cytokine with the CNTFR subunit. Signaling pathways recruited by the CLC/CLF complex in human neuroblastoma cell lines were also analyzed in detail. The results obtained showed an activation of Janus kinases (JAK1, JAK2, and TYK2) leading to a tyrosine phosphorylation of the gp130 and LIFR. The phosphorylated signaling receptors served in turn as docking proteins for signal transducing molecules such as STAT3 and SHP-2. In vitro analysis revealed that the gp130-LIFR pathway could also stimulate the phosphatidylinositol 3-kinase and the mitogen-activated protein kinase pathways. In contrast to that reported before for CNTF, soluble CNTFR failed to promote the action CLC/CLF, and an absolute requirement of the membrane form of CNTFR was required to generate a functional response to the composite cytokine. This study reinforces the functional similarity between CNTF and the CLC/CLF composite cytokine defining the second ligand for CNTFR.

The ciliary neurotrophic factor receptor alpha component induces the secretion of and is required for functional responses to cardiotrophin-like cytokine

Ciliary neurotrophic factor (CNTF) is involved in the survival of a number of different neural cell types, including motor neurons. CNTF functional responses are mediated through a tripartite membrane receptor composed of two signalling receptor chains, gp130 and the leukaemia inhibitory factor receptor (LIFR), associated with a non-signalling CNTF binding receptor alpha component (CNTFR). CNTFR-deficient mice show profound neuronal deficits at birth, leading to a lethal phenotype. In contrast, inactivation of the CNTF gene leads only to a slight muscle weakness, mainly during adulthood, suggesting that CNTFR binds to a second ligand that is important for development. Modelling studies of the interleukin-6 family member cardiotrophin-like cytokine (CLC) revealed structural similarities with CNTF, including the conservation of a site I domain involved in binding to CNTFR. Co-expression of CLC and CNTFR in mammalian cells generates a secreted composite cytokine, displaying activities on cells expressing the gp130-LIFR complex on their surface. Correspondingly, CLC-CNTFR activates gp130, LIFR and STAT3 signalling components, and enhances motor neuron survival. Together, these observations demonstrate that CNTFR induces the secretion of CLC, as well as mediating the functional responses of CLC.

[Cerebral blood flow disturbances after anterior choroidal artery infarcts. Anatomical and functional correlates]

We have investigated the cortical and subcortical regional cerebral blood flow (rCBF) disorders resulting from infarcts of the anterior choroidal artery (AChA), and correlations with the severity of lesions, the physical and cognitive deficits, and the functional impairment. Eighteen patients presenting with recent anterior choroidal artery infarct without any other brain injury were examined at the secondary phase post-stroke using the single photon emission computed tomography technique and 133 Xenon inhalation. The rCBF and asymmetry indexes (AI) were calculated for 12 symmetrical hemispheric areas, and the cerebellum. The AI values were compared with those of 24 control subjects. The severity of the lesions was evaluated from CT scans or MRI. The neurological status (Orgogozo scale, walking disorders, MMSE, attention impairment, aphasia) and disability (functional independance measure: FIM) were assessed for each patient at the same time period. The relationships between rCBF disorders and brain lesions, and between the results of clinical investigations and rCBF disorders and brain lesions were assessed by linear regression analyses (stepwise variable selections, p=0.05). The AI values were significantly increased in the cerebral hemispheres, and this was most severe in the internal capsule (direct effect of the lesion) and the dorsolateral hemispheric cortex (diaschisis). Individual evaluations showed that AI were significantly increased in 13 patients in at least one ROI of the cerebral hemispheres, and in 3 patients in the internal capsule. Stepwise variable selections revealed that AI were best explained by the severity of the lesions in the internal capsule and the internal temporal area. The AI of the external temporal area and the internal capsule also helped explain the clinical (physical and cognitive) deficits. Thus, AChA infarcts may have relatively large effects on the central part of the lateral and dorsal cortex of the ipsilateral hemisphere. Subcortical and cortical consequences both contribute to explain the motor and cognitive deficits and disability.

[Neuropsychological correlates of cerebral blood flow anomalies and MRI lesions after rupture of anterior communicating artery aneurysms]

The aim of this study was to investigate relations between neuropsychological disorders resulting from rupture of aneurysms of the anterior communicating artery, regional cerebral blood flow anomalies and brain lesions revealed on MRI. Blood flow was analyzed in 22 consecutive patients at least 3 weeks after surgery using single photon emission computed tomography. Flow values were calculated in 10 regions of interest on each side of the brain. Attention, motor control, executive functions, short-term and long-term learning (verbal, visuo-spatial), categorical evocation, general intellectual performances were investigated. Flow drop was observed over frontal areas, which predominated on the right side. The correlation analyses showed that

CLF associates with CLC to form a functional heteromeric ligand for the CNTF receptor complex

Ciliary neurotrophic factor (CNTF) is a cytokine supporting the differentiation and survival of various cell types in the peripheral and central nervous systems. Its receptor complex consists of a non-signaling alpha chain, CNTFR, and two signaling beta chains, gp130 and the leukemia inhibitory factor receptor (LIFR). Striking phenotypic differences between CNTF- and CNTFR-deficient mice suggest that CNTFR serves as a receptor for a second, developmentally important ligand. We have identified this factor as a stable secreted complex of cardiotrophin-like cytokine (CLC) and the soluble receptor cytokine-like factor-1 (CLF). CLF expression was required for CLC secretion, and the complex acted only on cells expressing functional CNTF receptors. The CLF/CLC complex activated gp130, LIFR and signal transducer and activator of transcription 3 (STAT3) and supported motor neuron survival. Our results indicate that the CLF/CLC complex is a second ligand for CNTFR with potentially important implications in nervous system development.

Hepatocyte-derived cell lines express a functional receptor for cardiotrophin-1

Cardiotrophin-1 (CT-1) is a recently isolated cytokine belonging to the interleukin-6 cytokine family. In the present study, we show that CT-1 binds to hepatocyte-derived cell lines of rat and human origin with high (Kd = 600-800 pM) and low (Kd approximately 3-6 nM) binding affinities. Treatment of HepG2 cells with CT-1 resulted in the induction of tyrosine phosphorylation of both transducing receptor subunits, gp130 and LIF receptor, and this phosphorylation was completely inhibited by a neutralizing anti-gp130 mAb. Addition of CT-1 to HepG2 or H35 cell cultures induced a dose-dependent production of several acute phase proteins (haptoglobin, fibrinogen, alpha1-acid glycoprotein, alpha2-macroglobulin). Moreover, the use of a neutralizing mAb to gp130 in cultures of HepG2 cells grown in the presence of CT-1, inhibited the induction of acute phase protein secretion, indicating an absolute requirement of gp130 in the formation of a functional CT-1 receptor. Altogether, these results suggest that CT-1 could play an important role in the regulation of hepatocyte metabolism in inflammatory responses.

Regulation of interleukin 6 expression by cardiotrophin 1

Cardiotrophin 1 (CT-1) is a recently described cytokine sharing many biological properties with those reported previously for leukaemia inhibitory factor (LIF). In the present study we show that CT-1 binds to the KB epidermoid cancer cell surface through a tripartite receptor complex which includes the gp130 signal transducing protein, LIF receptor beta (LIFR beta) and a third component displaying a molecular weight of 80 kDa. CT-1 activates gp130 and LIFR beta transducing components, as attested by analysing their tyrosine phosphorylation level. The activation process is relayed to the nucleus by the recruitment of the STAT3 transcription factor. Analysis of KB cell line culture supernatants after CT-1 treatment indicates that CT-1 stimulates the production of interleukin 6 (IL-6) in a time- and dose-dependent manner. This stimulation of IL-6 production by CT-1 is associated with an increase in intracellular levels of IL-6 mRNA. This study suggests that at least in some pathological situations CT-1 might represent an immunomodulator regulating cytokine-induced gene products.

Alanine substitution for Thr268 and Asp269 of soluble ciliary neurotrophic factor (CNTF) receptor alpha component defines a specific antagonist for the CNTF response

Ciliary neurotrophic factor (CNTF) associates with an alpha subunit (CNTFRalpha) of the receptor complex to initiate signal transduction by facilitating heterodimerization of the gp130 transducing protein and the leukemia inhibitory factor receptor (LIFR) beta. CNTFRalpha is anchored to the membrane by a glycosylphosphatidylinositol linkage; however, a soluble form of the alpha subunit can still bind CNTF to recruit the signal transducing components of the receptor complex. In the present study we show that alanine substitution for residues Thr268 and Asp269 of the CNTFRalpha subunit results in a mutated receptor subunit (R3), which can bind CNTF with an affinity similar to that of the wild type CNTFRalpha but, when expressed as a soluble receptor subunit, lowers the binding of CNTF to its tripartite receptor. In addition, CNTFR3alpha inhibits the proliferation of the TF1 hematopoietic cell line triggered by CNTF plus soluble wild type CNTFRalpha but not by IL-6 or oncostatin M. Similarly, CNTFR3alpha specifically antagonizes the induction of gp130 and LIFRbeta tyrosine phosphorylation observed in response to CNTF and wild type soluble CNTFRalpha in the HepG2 hepatoma cell line, as well as the subsequent events leading to haptoglobin synthesis. Positions 268 and 269 of CNTFRalpha appear to be critical for its interaction with gp130 and LIFRbeta, whereby alanine substitution of the residues at these positions results in antagonism of the CNTF-induced response.

Nerve growth factor is involved in the supportive effect by bone marrow--derived stromal cells of the factor-dependent human cell line UT-7

We previously demonstrated that murine MS-5 and SI/SI4 cell lines induce the proliferation of human factor-dependent UT-7 cells in the absence of normally required human cytokines and also stimulate the differentiation of CD34+/CD38-LTC-ICs. We report in this study that the effect of MS-5 cells on UT-7 cells can be completely explained by the synergistic action of nerve growth factor (NGF) and stem cell factor (SCF) produced by these murine stromal cells. Purified murine NGF was able to support short-term clone formation and long-term growth of UT-7 cells in suspension cultures as efficiently as rhu-granulocyte-macrophage colony-stimulating factor. NGF action was mediated through the TrkA receptor, in which messenger RNA (mRNA) was easily detected in UT-7 cells by Northern blot. MS-5 cells strongly expressed NGF mRNA in Northern blot, and direct implication of MS-5-derived NGF in the induction of UT-7 cells proliferation was demonstrated in inhibition assays with an anti-NGF monoclonal antibody (MoAb) that neutralized by 84% +/- 4.1% (n = 5) UT-7 clone formation. However, NGF did not act alone, and several arguments demonstrated the synergistic action of MS-5-derived SCF: (1) an anti-c-kit partially inhibited UT-7 cells clone formation in coculture assays, (2) SCF and NGF synergized in an H3-TdR incorporation assay, and (3) the stimulatory effect of 10x-concentrated MS-5 supernatant was completely inhibited by an anti-c-kit but not by an anti-NGF, and levels of soluble NGF (1.2 ng/mL) detected by enzyme-linked immunosorbent assay in 10x supernatant of MS-5 cells cultures were below the biologically active concentrations. In contrast, although MS-5 cells also promoted the differentiation of very primitive CD34+/CD38- human stem cells both in colony assays and long-term cultures, we could not incriminate MS-5-derived NGF in the observed effect: an anti-NGF MoAb did not inhibit the synergistic effect of MS-5 cells in colony assays or long-term cultures nor did soluble muNGF duplicate MS-5 effect and survival of CD34+/CD38- clonogenic progenitor cells promoted by MS-5 was unaffected by an anti-NGF and was not induced by soluble NGF alone or combined with SCF. In contrast, NGF in synergy with SCF supported the short-term maintenance of high numbers of CD34+/CD38+ mature erythroid progenitors probably through an indirect mechanism implying macrophages. These results suggest that NGF, in which the primary target cells are outside the hematopoietic system, is present in the marrow environment and might act at some steps of hematopoietic stem cell development. These results also underline that the response of cell lines and normal stem cells to stromal cells is mediated by different pathways.

gp130 transducing receptor cross-linking is sufficient to induce interleukin-6 type responses

gP130 transducing receptor is involved in the formation of high affinity receptors for the cytokines of the interleukin-6 (IL-6) family. Recruitment of gp130 by IL-6 associated to its receptor leads to the dimerization of the transducing component. In the present study we did characterize the B-S12 monoclonal antibody raised against gp130 and able to elicit IL-6 type biological activities. B-S12 antibody triggered strongly the proliferation of TF1 and XGI hematopoietic cell lines and was able to increase the synthesis of acute phase proteins in HepG2 hepatoma cell line. B-S12 also behaved as a synergistic factor with granulocyte-macrophage colony-stimulating factor for both proliferation and differentiation of CD34-positive hematopoietic cell progenitors. By using a symmetric enzyme-linked immunosorbent assay, allowing the detection of dimeric forms of soluble gp130, we found that addition of B-S12 to gp130 led to its dimerization. Analysis of the tyrosine phosphorylation events in gp130 and Jak kinase family members revealed that B-S12 quickly induced the phosphorylation of gp130 in a neural derived cell line, and that Jak1 and Jak2 were also recruited. In conclusion, we show that gp130 cross-linking with the B-S12 monoclonal antibody was sufficient to generate functional IL-6 type responses in hematopoietic, neural, and hepatic cells.

Cerebral blood flow in lateral medullary infarcts

BACKGROUND AND PURPOSE

The aim of this study was to evaluate the diaschisis phenomenon in patients presenting with lateral medullary infarct (Wallenberg's syndrome).

METHODS

We examined all patients admitted between 1991 and 1993. The localization of lesions was evaluated by MRI. Single-photon emission computed tomographic technique was used to assess cerebral blood flow by two methods (133Xe and hexamethylpropyleneamine oxime) on five slices of brain tissue. Flow values were calculated in 11 regions of interest in each cerebral hemisphere and in the cerebellum and were compared with those obtained in 20 control subjects.

RESULTS

Three patients had selective lateral medullary infarct: Relative reduction of flow (133Xe) and of tracer uptake (HMPAO) were observed in one patient in the ipsilateral cerebellum and contralateral hemisphere; in two patients, hemispheric flow values were relatively low, without significant asymmetry. Two patients also presented with cerebellar infarct: Flow drop was severe in the ipsilateral cerebellum, and contralateral reduction in the brain hemisphere was observed in both cases.

CONCLUSIONS

Lateral medullary infarct can be associated with ipsilateral reduction of flow in the cerebellum, but this phenomenon is inconstant. Severe flow drop suggests infarction in the territory of the posterior inferior cerebellar artery. Contralateral hemispheric flow reduction can also be observed. These phenomena of cerebellar and crossed hemispheric diaschisis are probably related to lesions of tracts from the olivary and reticular nuclei.