Cross-talk between IGF-I and TGF-beta signaling pathways

Insulin-like growth factor-I (IGF-I) has gained broad recognition as an important survival factor for epithelial cells in numerous tissues. The IGF-I receptor signaling pathway is deregulated in the majority of carcinomas, and such deregulation has also been reported to be tightly associated with enhanced tumor progression and metastasis. One of the key proteins that transduces IGF-I signals and is phospho-activated downstream of the IGF-I receptor, is the non-receptor serine/threonine kinase proto-oncogene protein kinase B (PKB, also known as Akt). This kinase serves as a major molecular node to control the function of many cell survival and death proteins through phosphorylation-mediated protein modification. The end result of the activation of Akt is enhanced cell survival and proliferation, pre-requisites for malignant transformation. Recent studies show that IGF-I signals cross-talk at multiple levels with various components of the TGF-beta signaling pathway, which depending on context may function either as tumor suppressor or as tumor promoter. Thus, a better understanding of how the IGF-I and TGF-beta signaling pathways are mutually interconnected is likely to unveil novel targets for the therapeutic intervention of many cancers.     

Cross-talk between IL-1 and IL-6 signaling pathways in rheumatoid arthritis synovial fibroblasts.

The balance between pro- and anti-inflammatory cytokines plays an important role in determining the severity of inflammation in rheumatoid arthritis (RA). Antagonism between opposing cytokines at the level of signal transduction plays an important role in many other systems. We have begun to explore the possible contribution of signal transduction cross-talk to cytokine balance in RA by examining the effects of IL-1, a proinflammatory cytokine, on the signaling and action of IL-6, a pleiotropic cytokine that has both pro- and anti-inflammatory actions, in RA synovial fibroblasts. Pretreatment with IL-1 suppressed Janus kinase-STAT signaling by IL-6, modified patterns of gene activation, and blocked IL-6 induction of tissue inhibitor of metalloproteases 1 expression. These results suggest that proinflammatory cytokines may contribute to pathogenesis by modulating or blocking signal transduction by pleiotropic or anti-inflammatory cytokines. The mechanism of inhibition did not require de novo gene activation and did not depend upon tyrosine phosphatase activity, but, instead, was dependent on the p38 stress kinase. These results identify a molecular basis for IL-1 and IL-6 cross-talk in RA synoviocytes and suggest that, in addition to levels of cytokine expression, modulation of signal transduction also plays a role in regulating cytokine balance in RA.     

Cross-talk between aldosterone and angiotensin signaling in vascular smooth muscle cells

In hypertension or other forms of cardiovascular disease, the chronic activation of the renin-angiotensin-aldosterone system (RAAS) leads to dysfunction of the vasculature, including, increased vascular tone, inflammation, fibrosis and thrombosis. Cross-talk between the main mediators of the RAAS, aldosterone and angiotensin (Ang) II, participates in the development of this vascular dysfunction. Recent studies have highlighted the molecular mechanisms supporting this cross-talk in vascular smooth muscle cells (VSMCs). Some of the signaling pathways activated by the Ang II type 1 receptor (AT₁R) are dependent on the mineralocorticoid receptor (MR) and vice versa. VSMC signaling pathways involved in migration and growth are under the control of cross-talk between aldosterone and Ang II. A synergistic mechanism leads to potentiation of signaling pathways activated by each agent. The genomic and non-genomic mechanisms activated by aldosterone cooperate with Ang II to regulate vascular tone and gene expression of pro-inflammatory and pro-fibrotic molecules. This cross-talk is dependent on the non-receptor tyrosine kinase c-Src, and on receptor tyrosine kinases, EGFR and PDGFR, and leads to activation of MAP kinases and growth, migration and inflammatory effects. These new findings will contribute to development of better treatments for conditions in which the RAAS is excessively activated.     

Cross-talk between hematopoiesis and angiogenesis signaling pathways

The relationship between hematopoietic cells and endothelial cells has been seen as an indication that a common progenitor, the hemangioblast, gives rise to both cell types in the yolk sac, the initial site of hematopoiesis and blood vessel formation during mammalian development. The existence of angioblast-like circulating endothelial precursor cells in adults humans has recently been suggested. In this review, we have summarized the principle mechanisms involved in the cross-talk signaling pathway between hematopoiesis and angiogenesis in order to further understand how the hematopoietic and vascular systems are established during the development.     

Cross-talk between estrogen and leptin signaling in the hypothalamus

Obesity, characterized by enhanced food intake (hyperphagia) and reduced energy expenditure that results in the accumulation of body fat, is a major risk factor for various diseases, including diabetes, cardiovascular disease, and cancer. In the United States, more than half of adults are overweight, and this number continues to increase. The adipocyte-secreted hormone leptin and its downstream signaling mediators play crucial roles in the regulation of energy balance. Leptin decreases feeding while increasing energy expenditure and permitting energy-intensive neuroendocrine processes, such as reproduction. Thus, leptin also modulates the neuroendocrine reproductive axis. The gonadal steroid hormone estrogen plays a central role in the regulation of reproduction and also contributes to the regulation of energy balance. Estrogen deficiency promotes feeding and weight gain, and estrogen facilitates, and to some extent mimics, some actions of leptin. In this review, we examine the functions of estrogen and leptin in the brain, with a focus on mechanisms by which leptin and estrogen cooperate in the regulation of energy homeostasis.     

Cross-talk between sulfur assimilation and ethylene signaling in plants

Sulfur (S) deficiency is prevailing all over the world and becoming an important issue for crop improvement through maximising its utilization efficiency by plants for sustainable agriculture. Its interaction with other regulatory molecules in plants is necessary to improve our understanding on its role under changing environment. Our knowledge on the influence of S on ethylene signaling is meagre although it is a constituent of cysteine (Cys) required for the synthesis of reduced glutathione (GSH) and S-adenosyl methionine (SAM), a precursor of ethylene biosynthesis. Thus, there may be an interaction between S assimilation, ethylene signaling and plant responses under optimal and stressful environmental conditions. The present review emphasizes that responses of plants to S involve ethylene action. This evaluation will provide an insight into the details of interactive role of S and ethylene signaling in regulating plant processes and prove profitable for developing sustainability under changing environmental conditions.     

Up-regulation of production of TGF-beta and IL-4 and down-regulation of IL-6 by apoptotic human bronchial epithelial cells

Human bronchial epithelial cells secrete cytokines that play a role in immune responses in the lung. However, the roles of these cytokines in regulating epithelial repair following acute lung injury are largely unknown. Responses to injury include hyperplasia of epithelial cells and squamous metaplasia. The resolution stage is characterized by discontinuation of hyperplasia. Apoptosis is considered to be the most efficient mechanism of removal of unwanted cells without causing inflammation. The presence of TGF-beta1 increases apoptosis, induces squamous metaplasia and inhibits proliferation of airway epithelial cells. Interleukin-4 increases the ability of macrophages to phagocytose epithelial cells and produce inflammatory cytokines. The purpose of this study was to investigate the hypothesis that apoptotic lung epithelial cells produce cytokines, which could act in an autocrine manner to control hyperplasia and induce squamous differentiation following acute lung injury. A bronchial epithelial cell line (16 HBE) was used as an in vitro model, to study the production of TGF-beta, IL-4 and IL-6 by lung epithelial cells undergoing apoptosis. Apoptotic and live cells were sorted on the basis of bright and negative staining with FITC-conjugated Annexin V, respectively. Intracellular IL-6, TGF-beta and IL-4 was measured using flow cytometric techniques. Electron microscopy, immunohistochemistry and ELISA were used as supportive techniques. Apoptotic cells produced significantly more TGF-beta and IL-4 (but less IL-6) than viable cells. Increased production of TGF-beta and IL-4 by epithelial cells undergoing apoptosis may contribute to the inhibition of proliferation, squamous metaplasia, and reduction of the inflammatory response in acute lung injury.     

Influence of IL-6 on MDR and MRP-mediated multidrug resistance in human hepatoma cells.

The objective of this study was to examine effects of interleukin-6 (IL-6) on the expression and activity of the drug resistance transporters (MDR1 and MRP) in human hepatoma cell lines. Expression and activity of MDR1 and MRP transporters were examined in IL-6-treated and control HuH 7 and HepG2 cells using semi-quantitative RT-PCR analysis and by rhodamine 123 and 5-carboxyfluorescin efflux assays. Results from RT-PCR demonstrated expression of MRP3, MRP6, and MDR1 in HuH 7 cells and expression of MRP1, MRP2, MRP3, MRP6, and MDR1 in HepG2 cells. Compared with controls, treatment of HuH 7 cells with IL-6 (10 ng/mL, 24 h) resulted in a 1.8-fold increase in MRP-mediated efflux of 5-CF with a corresponding 1.5-fold induction of MRP3 mRNA levels (p < 0.05). Similarly, in HepG2 cells, a 2-fold increase in MRP functional activity and a 1.8-fold induction of MRP1 mRNA levels were seen in the IL-6 treated cells (p < 0.05). Treatment of cells with IL-6 was also found to cause significant reductions in the expression and activity of MDR1 in HuH 7 cells, but not in HepG2 cells. Our data suggest that IL-6 induces MRP expression and activity in human hepatoma cell lines. Suppressive effects of IL-6 on MDR1 expression and activity were also observed in HuH 7 cells. This underscores the importance of examining the regulation of multiple drug resistance proteins as these proteins may have opposing regulatory mechanisms in malignant cells.     

Cross-talk between the ATP and ADP nucleotide receptor signalling pathways in glioma C6 cells

In this review we summarize the present status of our knowledge on the enzymes involved in the extracellular metabolism of nucleotides and the receptors involved in nucleotide signalling. We focus on the mechanism of the ATP and ADP signalling pathways in glioma C6, representative of the type of nonexcitable cells. In these cells, ATP acts on the P2Y(2) receptor coupled to phospholipase C, whereas ADP on two distinct P2Y receptors: P2Y(1) and P2Y(12). The former is linked to phospholipase C and the latter is negatively coupled to adenylyl cyclase. The possible cross-talk between the ATP-, ADP- and adenosine-induced pathways, leading to simultaneous regulation of inositol 1,4,5-trisphosphate and cAMP mediated signalling, is discussed.     

Association between IL-6 and CD40 signaling. IL-6 induces phosphorylation of CD40 receptors.

CD40 mAb at subsaturating doses inhibit the growth of transformants of the M12 murine cell line expressing intact full length CD40 molecules (M12/CD40+ cells) but do not inhibit the growth of two M12 transformants expressing either a mutant CD40 cDNA missing most of the cytoplasmic tail (CD40/tailless) or a mutant cDNA with a substitution at residue 234 (CD40/234A, Ala for Thr). Using these transformants, we tested a panel of cytokines for the ability to mimic CD40 mAb. rIL-6 behaved like CD40 mAb and inhibited the growth of M12/CD40+ cells but not of CD40/tailless or CD40/234A mutants. The effect of IL-6 on M12/CD40+ cells not only required intact CD40 including threonine 234 but also was specific because IL-6 mAb blocked the inhibitory activity. The M12/CD40+ cells responsive to IL-6 expressed greater than 300,000 CD40 molecules/cells but, like M12/CD40-controls, expressed only small numbers (less than 50/cell) of high affinity IL-6R, indicating that CD40 is not a receptor for IL-6. Nevertheless, IL-6 utilizes intact CD40 efficiently when it signals these cells: treatment of M12/CD40+ cells with IL-6 induced increased phosphorylation of CD40. Conversely, triggering CD40 on M12/CD40+ cells leads to IL-6 production. Similar effects were evident in human CD40+ B cells: IL-6 increased the phosphorylation of CD40 in the IL-6-responsive cell line, CESS, and CD40 mAb induced IL-6 production in activated human B cells. Thus, CD40 may function to receive and regulate IL-6-dependent signals in B cells.     

TGF-beta1 and IL-6 gene polymorphism in Spanish brucellosis patients

Polymorphisms in the cytokine genes have allowed for the understanding of the genetic determinants in several diseases. We investigated the polymorphism of the transforming growth factor (TGF)-beta1 and IL-6 genes in relation to susceptibility to human brucellosis. We typed 82 Spanish brucellosis patients and 102 healthy controls for TGF-beta1 polymorphisms in codons 10 and 25, and IL-6 promoter polymorphism at position -174 by PCR-SSP methods. The T/T G/G genotype of the TGF-beta1 gene was significantly increased in patients compared to controls (49% vs. 32%) P=0.02; OR=1.99 (1.05-3.80) and the T/C G/G genotype was significantly less common in the patients compared to the controls (32% vs. 49%) P=0.01; OR=0.48 (0.25-0.92). The CC genotype of codon 10 was significantly increased in the patients who had focal forms of the disease as compared with those who did not develop focal forms (19% vs. 4%), P=0.03; OR=0.19 (0.02-1.10). No differences were found in the IL-6 variants between the patients and the controls. These results suggest that polymorphism of the TGF-beta1 gene may be involved in susceptibility to brucellosis and to developing focal forms of the disease in a group of patients from southern Spain.     

Protein-tyrosine phosphatase-1B negatively regulates insulin signaling in l6 myocytes and Fao hepatoma cells

Insulin signaling is regulated by tyrosine phosphorylation of the signaling molecules, such as the insulin receptor and insulin receptor substrates (IRSs). Therefore, the balance between protein-tyrosine kinases and protein-tyrosine phosphatase activities is thought to be important in the modulation of insulin signaling in insulin-resistant states. We thus employed the adenovirus-mediated gene transfer technique, and we analyzed the effect of overexpression of a wild-type protein-tyrosine phosphatase-1B (PTP1B) on insulin signaling in both L6 myocytes and Fao cells. In both cells, PTP1B overexpression blocked insulin-stimulated tyrosine phosphorylation of the insulin receptor and IRS-1 by more than 70% and resulted in a significant inhibition of the association between IRS-1 and the p85 subunit of phosphatidylinositol 3-kinase and Akt phosphorylation as well as mitogen-activated protein kinase phosphorylation. Moreover, insulin-stimulated glycogen synthesis was also inhibited by PTP1B overexpression in both cells. These effects were specific for insulin signaling, because platelet-derived growth factor (PDGF)-stimulated PDGF receptor tyrosine phosphorylation and Akt phosphorylation were not inhibited by PTP1B overexpression. The present findings demonstrate that PTP1B negatively regulates insulin signaling in L6 and Fao cells, suggesting that PTP1B plays an important role in insulin resistance in muscle and liver.     

Differential effects of LPS and TGF-beta on the production of IL-6 and IL-12 by Langerhans cells, splenic dendritic cells, and macrophages

We examined modulatory effects of lipopolysaccharide (LPS) on IL-6 and IL-12 production by mouse Langerhans cells (LC), spleen-derived CD11c+ dendritic cells (DC), and macrophages (Mphi). Low dose LPS (1 ng/ml) increased IL-6 and IL-12 p40 production by Mphi. LPS slightly augmented IL-6 production but showed no effect on IL-12 p40 production by DC. In contrast, only high dose LPS (1 microg/ml) induced IL-6 but not IL-12 p40 production by LC. CD14 expression was the highest on Mphi and then on DC, but not on LC, which may explain the difference in responsiveness to LPS. We also found that TGF-beta inhibited IL-6 and IL-12 p40 production by LPS-stimulated Mphi. However, TGF-beta did not inhibit IL-6 production and even enhanced IL-12 p40 production by anti-CD40/IFN-gamma-stimulated Mphi. Concerning LC, TGF-beta enhanced IL-6 and IL-12 p40 production when stimulated with anti-CD40/IFN-gamma alone or with anti-CD40/IFN-gamma and LPS. Taken together, these findings indicate diverse effects of LPS and TGF-beta on these antigen presenting cells, which probably represents their differential roles in the innate immunity.     

Cross-talk between Wnt signaling pathways in human mesenchymal stem cells leads to functional antagonism during osteogenic differentiation

Wnt signaling is involved in developmental processes and in adult stem cell homeostasis. This study analyzes the role(s) of key Wnt signaling mediators in the maintenance and osteogenesis of mesenchymal stem cells (MSCs). We focus specifically on the involvement of low-density lipoprotein-related protein 5 (LRP5), T-cell factor 1 (TCF1), and Frizzled (Fz) receptors, in the presence or absence of exogenous, prototypical canonical (Wnt3a), and non-canonical (Wnt5a) Wnts. In undifferentiated MSCs, LRP5 and TCF1 mediate canonical Wnt signal transduction, leading to increased proliferation, enhanced synergistically by Wnt3a. However, LRP5 overexpression inhibits osteogenic differentiation, further suppressed by Wnt3a. Wnt5a does not affect cell proliferation but enhances osteogenesis of MSCs. Interestingly, Wnt5a inhibits Wnt3a effects on MSCs, while Wnt3a suppresses Wnt5a-mediated enhancement of osteogenesis. Flow cytometry revealed that LRP5 expression elicits differential changes in Fz receptor profiles in undifferentiated versus osteogenic MSCs. Taken together, these results suggest that Wnt signaling crosstalk and functional antagonism with the LRP5 co-receptor are key signaling regulators of MSC maintenance and differentiation.