Interleukin-8 and other agonists of Gi2 proteins: autocrine paracrine growth factors for human hematopoietic progenitors acting in synergy with colony stimulating factors

HIV-1 Tat protein inhibits the hematopoietic support function of human bone marrow mesenchymal stem cells

Most HIV-1-infected patients experience hematopoiesis suppression complications. Bone marrow mesenchymal stem cells (BMSCs) are involved in regulation of hematopoietic homeostasis, so we investigated the role of Tat, a protein released by infected cells in bone marrow and impacted differentiation potential of mesenchymal stem cells, in the BMSC hematopoietic support function. BMSCs were treated with HIV-1 Tat protein (BMSC_Tat-p), transfected with HIV-1 Tat mRNA (BMSC_Tat-m) or treated with solvent (PBS) (BMSC_con) for 20 days. Then, the hematopoietic support function of BMSC_Tat-p, BMSC_Tat-m and BMSC_con was analyzed via ex vivo expansion of hematopoietic stem cells (HSCs) grown on the BMSCs and via in vivo cotransplantation of HSCs and BMSCs. In addition, the hematopoiesis-supporting gene expression patterns of BMSC_Tat-p, BMSC_Tat-m and BMSC_con were compared. The results showed that BMSC_Tat-p and BMSC_Tat-m displayed reduced expansion, a decline in the number of colony forming units (CFUs) and a decreased proportion of the primitive subpopulation of hematopoietic stem cells under coculture conditions compared with BMSC_con. The ability of BMSC_Tat-p to support hematopoietic recovery was also impaired, which was further confirmed by the patterns in gene expression analysis. In conclusion, Tat treatment reduced the function of BMSCs in hematopoietic support, likely by downregulating the expression of a series of hematopoietic cytokines.

Specification and function of hemogenic endothelium during embryogenesis

Hemogenic endothelium is a specialized subset of developing vascular endothelium that acquires hematopoietic potential and can give rise to multilineage hematopoietic stem and progenitor cells during a narrow developmental window in tissues such as the extraembryonic yolk sac and embryonic aorta-gonad-mesonephros. Herein, we review current knowledge about the historical and developmental origins of hemogenic endothelium, the molecular events that govern hemogenic specification of vascular endothelial cells, the generation of multilineage hematopoietic stem and progenitor cells from hemogenic endothelium, and the potential for translational applications of knowledge gained from further study of these processes.

The Hen or the Egg: Inflammatory Aspects of Murine MPN Models

It has been known for some time that solid tumors, especially gastrointestinal tumors, can arise on the basis of chronic inflammation. However, the role of inflammation in the genesis of hematological malignancies has not been extensively studied. Recent evidence clearly shows that changes in the bone marrow niche can suffice to induce myeloid diseases. Nonetheless, while it has been demonstrated that myeloproliferative neoplasms (MPN) are associated with a proinflammatory state, it is not clear whether inflammatory processes contribute to the induction or maintenance of MPN. More provocatively stated: which comes first, the hen or the egg, inflammation or MPN? In other words, can chronic inflammation itself trigger an MPN? In this review, we will describe the evidence supporting a role for inflammation in initiating and promoting MPN development. Furthermore, we will compare and contrast the data obtained in gastrointestinal tumors with observations in MPN patients and models, pointing out the opportunities provided by novel murine MPN models to address fundamental questions regarding the role of inflammatory stimuli in the molecular pathogenesis of MPN.

Pathogenesis of Myeloproliferative Neoplasms: Role and Mechanisms of Chronic Inflammation

Myeloproliferative neoplasms (MPNs) are a heterogeneous group of clonal diseases characterized by the excessive and chronic production of mature cells from one or several of the myeloid lineages. Recent advances in the biology of MPNs have greatly facilitated their molecular diagnosis since most patients present with mutation(s) in the JAK2, MPL, or CALR genes. Yet the roles played by these mutations in the pathogenesis and main complications of the different subtypes of MPNs are not fully elucidated. Importantly, chronic inflammation has long been associated with MPN disease and some of the symptoms and complications can be linked to inflammation. Moreover, the JAK inhibitor clinical trials showed that the reduction of symptoms linked to inflammation was beneficial to patients even in the absence of significant decrease in the JAK2-V617F mutant load. These observations suggested that part of the inflammation observed in patients with JAK2-mutated MPNs may not be the consequence of JAK2 mutation. The aim of this paper is to review the different aspects of inflammation in MPNs, the molecular mechanisms involved, the role of specific genetic defects, and the evidence that increased production of certain cytokines depends or not on MPN-associated mutations, and to discuss possible nongenetic causes of inflammation.

Adenosine signaling promotes hematopoietic stem and progenitor cell emergence

Jing and colleagues show that adenosine signaling plays an important evolutionary role in the first step of hematopoietic stem cell generation in the embryonic aorta.

Hematopoietic stem cells (HSCs) emerge from aortic endothelium via the endothelial-to-hematopoietic transition (EHT). The molecular mechanisms that initiate and regulate EHT remain poorly understood. Here, we show that adenosine signaling regulates hematopoietic stem and progenitor cell (HSPC) development in zebrafish embryos. The adenosine receptor A_2b is expressed in the vascular endothelium before HSPC emergence. Elevated adenosine levels increased runx1⁺/cmyb⁺ HSPCs in the dorsal aorta, whereas blocking the adenosine pathway decreased HSPCs. Knockdown of A_2b adenosine receptor disrupted scl⁺ hemogenic vascular endothelium and the subsequent EHT process. A_2b adenosine receptor activation induced CXCL8 via cAMP–protein kinase A (PKA) and mediated hematopoiesis. We further show that adenosine increased multipotent progenitors in a mouse embryonic stem cell colony-forming assay and in embryonic day 10.5 aorta-gonad-mesonephros explants. Our results demonstrate that adenosine signaling plays an evolutionary conserved role in the first steps of HSPC formation in vertebrates.

Exosome-mediated crosstalk between chronic myelogenous leukemia cells and human bone marrow stromal cells triggers an interleukin 8-dependent survival of leukemia cells

Chronic myelogenous leukemia (CML) is a myeloproliferative disorder characterized by the Bcr-Abl oncoprotein with constitutive tyrosine kinase activity. Exosomes are nanovesicles released by cancer cells that are involved in cell-to-cell communication thus potentially affecting cancer progression. It is well known that bone marrow stromal microenvironment contributes to disease progression through the establishment of a bi-directional crosstalk with cancer cells. Our hypothesis is that exosomes could have a functional role in this crosstalk. Interleukin-8 (IL 8) is a proinflammatory chemokine that activates multiple signalling pathways downstream of two receptors (CXCR1 and CXCR2). We demonstrated that exosomes released from CML cells stimulate bone marrow stromal cells to produce IL 8 that, in turn, is able to modulate both in vitro and in vivo the leukemia cell malignant phenotype.

Transcription factor nuclear factor erythroid-2 mediates expression of the cytokine interleukin 8, a known predictor of inferior outcome in patients with myeloproliferative neoplasms

The transcription factor nuclear factor erythroid-2 is over-expressed in patients with myeloproliferative neoplasms irrespective of the presence of the JAK2(V617F) mutation. Our transgenic mouse model over-expressing nuclear factor erythroid-2, which recapitulates many features of myeloproliferative neoplasms including transformation to acute myeloid leukemia, clearly implicates this transcription factor in the pathophysiology of myeloproliferative neoplasms. Because the targets mediating nuclear factor erythroid-2 effects are not well characterized, we conducted microarray analysis of CD34(+) cells lentivirally transduced to over-express nuclear factor erythroid-2 or to silence this transcription factor via shRNA, in order to identify novel target genes. Here, we report that the cytokine interleukin 8 is a novel target gene. Nuclear factor erythroid-2 directly binds the interleukin 8 promoter in vivo, and these binding sites are required for promoter activity. Serum levels of interleukin 8 are known to be elevated in both polycythemia vera and primary myelofibrosis patients. Recently, increased interleukin 8 levels have been shown to be predictive of inferior survival in primary myelofibrosis patients in multivariate analysis. Therefore, one of the mechanisms by which nuclear factor erythroid-2 contributes to myeloproliferative neoplasm pathology may be increased interleukin 8 expression.

Bioregulators as prototypic nontraditional threat agents

Bioregulators are naturally occurring organic compounds that regulate a multitude of biologic processes. Under natural circumstances, bioregulators are synthesized in minute quantities in a variety of living organisms and are essential for physiologic homeostasis. In the wrong hands, these compounds have the capability to be used as nontraditional threat agents that are covered by the prohibitions of the Chemical Weapons Convention and the Biological and Toxin Weapons Convention. Unlike traditional biowarfare/bioterrorism agents that have a latency period of hours to days,the onset of action of bioregulators may occur within minutes after host exposure. Concerns regarding the potential misuse of bioregulators for nefarious purposes relate to the ability of these nontraditional agents to induce profound physiologic effects.

Erythropoietin-independent erythroid colony formation by bone marrow progenitors exposed to interleukin-11 and interleukin-8

OBJECTIVE

Endogenous erythroid colonies (EECs), formed in vitro without erythropoietin (EPo) or other exogenous cytokines, are characteristic of Polycythemia vera (PV). Our aim was to identify specific conditions of culture of bone marrow (BM) progenitors allowing formation of erythroid colonies without EPo.

METHODS

BM mononuclear cells (BMMCs), purified CD34+ cells, and purified CD36+ erythroid progenitors were cultured in serum-free media without and with cytokines: EPo, stem cell factor (SCF), and interleukin (IL)-11 and IL-8, produced by BM stromal cells and found elevated in PV.

RESULTS

EECs were formed in PV cultures of either BMMCs or CD34+ cells, which include cytokine-secreting cells, but not in cultures of purified CD36+ erythroid progenitors (EP). Despite expression of V617F JAK-2, no constitutive activation of JAK-2, Stat-5, or Erk-1/2 was detected in erythroblasts issued from PV CD36+ progenitors. However, when SCF was provided, PV CD36+ progenitors formed erythroid colonies without EPo. The ability to form erythroid colonies with SCF alone was conferred to BM progenitors of healthy donors and secondary erythrocytosis by exposure to IL-11 and IL-8. Both IL-11 and IL-8 enhanced formation of erythroid colonies in response to EPo and interfered with the activation of Erk-1/2 and Stat-5 induced, respectively, by SCF and EPo in erythroblasts. Anti-IL-11 antibody inhibited formation of erythroid colonies by PV BMMCs and CD34+ cells.

CONCLUSION

The data indicate that PV erythroid progenitors remain cytokine-dependent and that normal BM progenitors exposed to IL-11 and IL-8 can acquire the ability to form erythroid colonies without EPo.

Phenotypic and genotypic characteristics of new euploid–diploid lymphoblastoid B cell lines EBV+, normal human bone marrow derived, spontaneously overgrown in vitro

The present study describes the phenotypic and genotypic features of seven individual growth transformed, euploid-diploid EBV+ human B cell lines arisen spontaneously in vitro. The lines, obtained under general and standard culture conditions (un-manipulated), from seven individual bone marrow samples of 18 healthy young adults, Caucasian, of both sexes, display many traits of normal B cells and represent a mixture of EBV infected latently (latency type III) and producer cells (5-16% VCA+ by immunofluorescence) releasing seven individual different viral strains [Fruscalzo et al., 2001. DNA sequence heterogeneity within the Epstein-Barr virus family of repeats in the latent origin of replication. Gene 265, 165-173] similar to the B95-8 genotype as shown by results of Southern blot of BamHI-digested DNA fragment. These tests were planned to characterize more fully this panel of new bone marrow cell lines sharing normal B cell traits.

Secretion of cytokines and growth factors as a general cause of constitutive NFkappaB activation in cancer

The constitutive activation of nuclear factor kappaB (NFkappaB) helps a variety of tumors to resist apoptosis and desensitizes them to chemotherapy, but the causes are still largely unknown. We have analysed this phenomenon in eight mutant cell lines derived from human 293 cells, selected for NFkappaB-dependent expression of a marker gene, and also in seven tumor-derived cell lines. Conditioned media from all of these cells stimulated the activation of NFkappaB (up to 30-fold) in indicator cells carrying an NFkappaB-responsive reporter. Therefore, secretion of extracellular factors as the cause of constitutive activation seems to be general. The mRNAs encoding several different cytokines and growth factors were greatly overexpressed in the tumor and mutant cells. The pattern of overexpression was distinct in each cell line, indicating that the phenomenon is complex. Two secreted factors whose roles in the constitutive activation of NFkappaB are not well defined were investigated further as pure proteins: transforming growth factor beta2 (TGFbeta2) and fibroblast growth factor 5 (FGF5) were both highly expressed in some mutant clones and tumor cell lines, each activated NFkappaB alone, and the combination was synergistic. Our data indicate that a group of different factors, expressed at abnormally high levels, can contribute singly and synergistically to the constitutive activation of NFkappaB in all of the mutant and tumor cell lines we studied. Since several NFkappaB target genes encode secreted proteins that induce NFkappaB, autocrine loops are likely to be ubiquitously important in the constitutive activation of NFkappaB in cancer. We provide the first evidence of the general, complex, and synergistic activation of NFkappaB in tumor and mutant cell lines through the action of secreted factors and suggest that the same explanation is likely for the constitutive activation of NFkappaB in cancers.

Growth-related oncogene alpha induction of apoptosis in osteoarthritis chondrocytes

OBJECTIVE

To evaluate the apoptotic effect of the chemokine growth-related oncogene alpha (GROalpha), which we recently reported to be up-regulated in osteoarthritis (OA) chondrocytes. Chondrocyte apoptosis is considered to be a major determinant of cartilage damage in OA, a disease resulting from the aberrant production of inflammatory mediators (cytokines and chemokines) and effectors (matrix metalloproteinases and reactive oxygen and nitrogen species) by chondrocytes.

METHODS

We investigated the apoptotic effect of GROalpha on isolated human cells and on in vitro-cultured cartilage explants by conventional methods (morphology, detection of DNA fragmentation in situ and in solution, exposure of phosphatidylserine) and by analysis of "early" biochemical events (plasma membrane depolarization, activation of caspase 3, and phosphorylation of c-Jun N-terminal kinase/stress-activated protein kinase).

RESULTS

We clearly demonstrated that GROalpha was able to initiate a series of morphologic, biochemical, and molecular changes that led to chondrocyte apoptosis. Moreover, we found that additional signals delivered from the extracellular matrix (ECM) were essential in the control of chondrocyte susceptibility to GROalpha-induced apoptosis, since cell death was detected only when cells were stimulated after reestablishment of their proper interactions with the ECM, or in cartilage explant samples with reduced ECM, as indicated by decreased Safranin O staining.

CONCLUSION

GROalpha can induce apoptosis in articular chondrocytes, and the induction is dependent upon additional signals from the ECM. These findings are relevant to understanding the pathogenesis of OA, in view of the availability of the GROalpha chemokine in the joint space in the course of this rheumatic disease.

Abnormal production of interleukin (IL)-11 and IL-8 in polycythaemia vera

We studied the production of interleukin (IL)-11 and IL-8, two cytokines known to affect erythropoiesis, in polycythemia vera (PV). In vivo, IL-11 was detected more frequently in serum and bone marrow (BM) plasma of PV patients than in controls (healthy donors and patients with idiopathic erythrocytosis (IE)). In addition, serum IL-11 levels of PV patients were higher than those of controls. IL-8 was elevated in serum of both PV and IE patients (respective median levels: 38.6 and 242pg/ml, vs 4.4pg/ml for healthy donors). BM plasma IL-8 levels of PV patients (508pg/ml) were significantly higher than those of IE patients (120pg/ml). In vitro, bone marrow (BM) stromal cells (BMSC) of PV patients produced significantly more IL-11 (x6.4) and IL-8 (x8.3) than BMSC of healthy donors or IE patients. In conclusion, both IL-11 and IL-8 are overproduced in PV, apparently by BMSC; IL-8 is also overproduced in IE, by cells other than BMSC.

Constitutive activation of NF-kappa B and secretion of interleukin-8 induced by the G protein-coupled receptor of Kaposi's sarcoma-associated herpesvirus involve G alpha(13) and RhoA

The Kaposi's sarcoma herpesvirus (KSHV) open reading frame 74 encodes a G protein-coupled receptor (GPCR) for chemokines. Exogenous expression of this constitutively active GPCR leads to cell transformation and vascular overgrowth characteristic of Kaposi's sarcoma. We show here that expression of KSHV-GPCR in transfected cells results in constitutive transactivation of nuclear factor kappa B (NF-kappa B) and secretion of interleukin-8, and this response involves activation of G alpha(13) and RhoA. The induced expression of a NF-kappa B luciferase reporter was partially reduced by pertussis toxin and the G beta gamma scavenger transducin, and enhanced by co-expression of G alpha(13) and to a lesser extent, G alpha(q). These results indicate coupling of KSHV-GPCR to multiple G proteins for NF-kappa B activation. Expression of KSHV-GPCR led to stress fiber formation in NIH 3T3 cells. To examine the involvement of the G alpha(13)-RhoA pathway in KSHV-GPCR-mediated NF-kappa B activation, HeLa cells were transfected with KSHV-GPCR alone and in combination with the regulator of G protein signaling (RGS) from p115RhoGEF or a dominant negative RhoA(T19N). Both constructs, as well as the C3 exoenzyme from Clostritium botulinum, partially reduced NF-kappa B activation by KSHV-GPCR, and by a constitutively active G alpha(13)(Q226L). KSHV-GPCR-induced NF-kappa B activation is accompanied by increased secretion of IL-8, a function mimicked by the activated G alpha(13) but not by an activated G alpha(q)(Q209L). These results suggest coupling of KSHV-GPCR to the G alpha(13)-RhoA pathway in addition to other G proteins.

Gα16Couples Chemoattractant Receptors to NF-κB Activation

The guanine nucleotide-binding regulatory protein alpha-subunit, Galpha(16), is primarily expressed in hemopoietic cells, and interacts with a large number of seven-membrane span receptors including chemoattractant receptors. We investigated the biological functions resulting from Galpha(16) coupling of chemoattractant receptors in a transfected cell model system. HeLa cells expressing a kappaB-driven luciferase reporter, Galpha(16), and the formyl peptide receptor responded to fMLP with a approximately 7- to 10-fold increase in luciferase activity. This response was accompanied by phosphorylation of IkappaBalpha and elevation of nuclear kappaB-DNA binding activity, indicating activation of NF-kappaB. In contrast to Galpha(16), expression of Galpha(q), Galpha(13), and Galpha(i2) resulted in a marginal increase in kappaB luciferase activity. A GTPase-deficient, constitutively active Galpha(16) mutant (Q212L) could replace agonist stimulation for activation of NF-kappaB. Furthermore, expression of Galpha(16) (Q212L) markedly enhanced TNF-alpha-induced kappaB reporter activity. The Galpha(16)-mediated NF-kappaB activation was paralleled by an increase in phospholipase C-beta activity, and was blocked by pharmacological inhibitors of protein kinase C (PKC) and by buffering of intracellular Ca(2+). The involvement of a conventional PKC isoform was confirmed by the finding that expression of PKCalpha enhanced the effect of Galpha(16), and a dominant negative PKCalpha partially blocked Galpha(16)-mediated NF-kappaB activation. In addition to formyl peptide receptor, Galpha(16) also enhanced NF-kappaB activation by the C5a and C3a receptors, and by CXC chemokine receptor 2 and CCR8. These results suggest a potential role of Galpha(16) in transcriptional regulation downstream of chemoattractant receptors.