Molecular cloning of a complementary DNA encoding human macrophage-specific colony-stimulating factor (CSF-1)

A timeline of tumour-associated macrophage biology

Tumour progression is modulated by the local microenvironment. This environment is populated by many immune cells, of which macrophages are among the most abundant. Clinical correlative data and a plethora of preclinical studies in mouse models of cancers have shown that tumour-associated macrophages (TAMs) play a cancer-promoting role. Within the primary tumour, TAMs promote tumour cell invasion and intravasation and tumour stem cell viability and induce angiogenesis. At the metastatic site, metastasis-associated macrophages promote extravasation, tumour cell survival and persistent growth, as well as maintain tumour cell dormancy in some contexts. In both the primary and metastatic sites, TAMs are suppressive to the activities of cytotoxic T and natural killer cells that have the potential to eradicate tumours. Such activities suggest that TAMs will be a major target for therapeutic intervention. In this Perspective article, we chronologically explore the evolution of our understanding of TAM biology put into the context of major enabling advances in macrophage biology.

Neoplasia-associated Chromosome Translocations Resulting in Gene Truncation

Chromosomal translocations in cancer as well as benign neoplasias typically lead to the formation of fusion genes. Such genes may encode chimeric proteins when two protein-coding regions fuse in-frame, or they may result in deregulation of genes via promoter swapping or translocation of the gene into the vicinity of a highly active regulatory element. A less studied consequence of chromosomal translocations is the fusion of two breakpoint genes resulting in an out-of-frame chimera. The breaks then occur in one or both protein-coding regions forming a stop codon in the chimeric transcript shortly after the fusion point. Though the latter genetic events and mechanisms at first awoke little research interest, careful investigations have established them as neither rare nor inconsequential. In the present work, we review and discuss the truncation of genes in neoplastic cells resulting from chromosomal rearrangements, especially from seemingly balanced translocations.

Functions of macrophage colony-stimulating factor (CSF1) in development, homeostasis, and tissue repair

Macrophage colony-stimulating factor (CSF1) is the primary growth factor required for the control of monocyte and macrophage differentiation, survival, proliferation and renewal. Although the cDNAs encoding multiple isoforms of human CSF1 were cloned in the 1980s, and recombinant proteins were available for testing in humans, CSF1 has not yet found substantial clinical application. Here we present an overview of CSF1 biology, including evolution, regulation and functions of cell surface and secreted isoforms. CSF1 is widely-expressed, primarily by cells of mesenchymal lineages, in all mouse tissues. Cell-specific deletion of a floxed Csf1 allele in mice indicates that local CSF1 production contributes to the maintenance of tissue-specific macrophage populations but is not saturating. CSF1 in the circulation is controlled primarily by receptor-mediated clearance by macrophages in liver and spleen. Administration of recombinant CSF1 to humans or animals leads to monocytosis and expansion of tissue macrophage populations and growth of the liver and spleen. In a wide variety of tissue injury models, CSF1 administration promotes monocyte infiltration, clearance of damaged cells and repair. We suggest that CSF1 has therapeutic potential in regenerative medicine.

Monopoiesis in humans and mice

Monocytes are a widely conserved cell population in vertebrates with important roles in both inflammation and homeostasis. Under both settings, monocytes continuously arise from hematopoietic progenitors in the bone marrow and, on demand, migrate into tissues through the bloodstream. Monocytes are classified into three subsets-classical, intermediate and non-classical-based on their cell surface expression of CD14 and CD16 in humans and Ly6C, CX3CR1 and CCR2 in mice. In tissues, monocytes differentiate further into monocyte-derived macrophages and dendritic cells to mediate innate and adaptive immune responses and maintain tissue homeostasis. Recently, the progenitors that strictly give rise to monocytes were identified in both humans and mice, thereby revealing the monocyte differentiation pathways.

Selective deletion of the soluble Colony-Stimulating Factor 1 isoform in vivo prevents estrogen-deficiency bone loss in mice

Neutralizing CSF1 in vivo completely prevents ovariectomy (OVX)-induced bone loss in mice. There are two isoforms of CSF1, soluble (sCSF1), and membrane-bound (mCSF1), but their individual biological functions are unclear. It had been previously reported that mCSF1 knockout (K/O) and wild type (Wt) female mice experience the same degree of bone loss following OVX. In Wt mice the expression of sCSF1 was elevated fourfold in skeletal tissue following OVX while expression of mCSF1 was unchanged. To examine the role of sCSF1 in OVX-induced bone loss, mice were engineered in which sCSF1 was not expressed but expression of mCSF1 was unaffected (sCSF1 K/O). Isoform-specific reverse transcription PCR confirmed the absence of transcripts for sCSF1 in bone tissue isolated from these animals and no circulating CSF1 was detected by ELISA. Surprisingly, there were no significant differences in bone mineral density (BMD) between sCSF1 K/O mice and Wt controls as assessed by dual-energy X-ray absorptiometry and micro-CT. However, one month after OVX, femoral, spinal and total BMD had declined by 11.2%, 8.9%, and 8.7% respectively in OVX-Wt animals as compared to Sham-OVX. In contrast OVX sCSF1 K/O mice showed changes of +0.1%, -2.4%, and +2.3% at the same 3 sites compared to Sham-OVX sCSF1 K/O mice. These data indicate important non-redundant functions for the two isoforms of CSF1 and suggest that sCSF1, but not mCSF1, plays a key role in estrogen-deficiency bone loss.

Non-apoptotic functions of caspases in myeloid cell differentiation

Subtle caspase activation is associated with the differentiation of several myeloid lineages. A tightly orchestrated dance between caspase-3 activation and the chaperone HSP70 that migrates to the nucleus to protect the master regulator GATA-1 from cleavage transiently occurs in basophilic erythroblasts and may prepare nucleus and organelle expel that occurs at the terminal phase of erythroid differentiation. A spatially restricted activation of caspase-3 occurs in maturing megakaryocytes to promote proplatelet maturation and platelet shedding in the bloodstream. In a situation of acute platelet need, caspase-3 could be activated in response to IL-1α and promote megakaryocyte rupture. In peripheral blood monocytes, colony-stimulating factor-1 provokes the formation of a molecular platform in which caspase-8 is activated, which downregulates nuclear factor-kappa B (NF-κB) activity and activates downstream caspases whose target fragments such as those generated by nucleophosmin (NPM1) cleavage contribute to the generation of resting macrophages. Human monocytes secrete mature IL-1β in response to lipopolysaccharide through an alternative inflammasome activation that involves caspase-8, a pathway that does not lead to cell death. Finally, active caspase-3 is part of the proteases contained in secretory granules of mast cells. Many questions remain on how these proteases are activated in myeloid cell lineages, which target proteins are cleaved, whereas other are protected from proteolysis, the precise role of cleaved proteins in cell differentiation and functions, and the link between these non-apoptotic functions of caspases and the death of these diverse cell types. Better understanding of these functions may generate therapeutic strategies to control cytopenias or modulate myeloid cell functions in various pathological situations.

Diverse in vivo effects of soluble and membrane-bound M-CSF on tumor-associated macrophages in lymphoma xenograft model

Macrophage colony-stimulating factor (M-CSF) is an important cytokine for monocyte/macrophage lineage. Secretory M-CSF (sM-CSF) and membrane-bound M-CSF (mM-CSF) are two major alternative splicing isoforms. The functional diversity of these isoforms in the activation of tumor-associated macrophages (TAMs), especially in lymphoma microenvironment, has not been documented. Here, we studied the effects of M-CSF isoforms on TAMs in xenograft mouse model. More infiltrating TAMs were detected in microenvironment with mM-CSF and sM-CSF. TAMs could be divided into three subpopulations based on their expression of CD206 and Ly6C. While sM-CSF had greater potential to recruit and induce differentiation of TAMs and TAM subpopulations, mM-CSF had greater potential to induce proliferation of TAMs and TAM subpopulations. Though both isoforms educated TAMs and TAM subpopulations to M2-like macrophages, mM-CSF and sM-CSF induced different spectrums of phenotype-associated genes in TAMs and TAM subpopulations. These results suggested the diverse effects of M-CSF isoforms on the activation of TAMs and TAM subpopulations in lymphoma microenvironments.

Regulation of Embryonic and Postnatal Development by the CSF-1 Receptor

Macrophages are found in all tissues and regulate tissue morphogenesis during development through trophic and scavenger functions. The colony stimulating factor-1 (CSF-1) receptor (CSF-1R) is the major regulator of tissue macrophage development and maintenance. In combination with receptor activator of nuclear factor κB (RANK), the CSF-1R also regulates the differentiation of the bone-resorbing osteoclast and controls bone remodeling during embryonic and early postnatal development. CSF-1R-regulated macrophages play trophic and remodeling roles in development. Outside the mononuclear phagocytic system, the CSF-1R directly regulates neuronal survival and differentiation, the development of intestinal Paneth cells and of preimplantation embryos, as well as trophoblast innate immune function. Consistent with the pleiotropic roles of the receptor during development, CSF-1R deficiency in most mouse strains causes embryonic or perinatal death and the surviving mice exhibit multiple developmental and functional deficits. The CSF-1R is activated by two dimeric glycoprotein ligands, CSF-1, and interleukin-34 (IL-34). Homozygous Csf1-null mutations phenocopy most of the deficits of Csf1r-null mice. In contrast, Il34-null mice have no gross phenotype, except for decreased numbers of Langerhans cells and microglia, indicating that CSF-1 plays the major developmental role. Homozygous inactivating mutations of the Csf1r or its ligands have not been reported in man. However, heterozygous inactivating mutations in the Csf1r lead to a dominantly inherited adult-onset progressive dementia, highlighting the importance of CSF-1R signaling in the brain.

The amphibian (Xenopus laevis) type I interferon response to frog virus 3: new insight into ranavirus pathogenicity

The increasing prevalence of ranavirus (RV; Iridoviridae) infections of wild and commercially maintained aquatic species is raising considerable concerns. While Xenopus laevis is the leading model for studies of immunity to RV, amphibian antiviral interferon (IFN) responses remain largely uncharacterized. Accordingly, an X. laevis type I interferon was identified, the expression of the gene for this IFN was examined in RV (frog virus 3 [FV3])-infected tadpoles and adult frogs by quantitative PCR, and a recombinant form of this molecule (recombinant X. laevis interferon [rXlIFN]) was produced for the purpose of functional studies. This rXlIFN protected the kidney-derived A6 cell line and tadpoles against FV3 infection, decreasing the infectious viral burdens in both cases. Adult frogs are naturally resistant to FV3 and clear the infection within a few weeks, whereas tadpoles typically succumb to this virus. Hence, as predicted, virus-infected adult X. laevis frogs exhibited significantly more robust FV3-elicited IFN gene expression than tadpoles; nevertheless, they also tolerated substantially greater viral burdens following infection. Although tadpole stimulation with rXlIFN prior to FV3 challenge markedly impaired viral replication and viral burdens, it only transiently extended tadpole survival and did not prevent the eventual mortality of these animals. Furthermore, histological analysis revealed that despite rXlIFN treatment, infected tadpoles had considerable organ damage, including disrupted tissue architecture and extensive necrosis and apoptosis. Conjointly, these findings indicate a critical protective role for the amphibian type I IFN response during ranaviral infections and suggest that these viruses are more pathogenic to tadpole hosts than was previously believed, causing extensive and fatal damage to multiple organs, even at very low titers.

IMPORTANCE

Ranavirus infections are threatening wild and commercially maintained aquatic species. The amphibian Xenopus laevis is extensively utilized as an infection model for studying ranavirus-host immune interactions. However, little is known about amphibian antiviral immunity and, specifically, type I interferons (IFNs), which are central to the antiviral defenses of other vertebrates. Accordingly, we identified and characterized an X. laevis type I interferon in the context of infection with the ranavirus frog virus 3 (FV3). FV3-infected adult frogs displayed more robust IFN gene expression than tadpoles, possibly explaining why they typically clear FV3 infections, whereas tadpoles succumb to them. Pretreatment with a recombinant X. laevis IFN (rXlIFN) substantially reduced viral replication and infectious viral burdens in a frog kidney cell line and in tadpoles. Despite reducing FV3 loads and extending the mean survival time, rXlIFN treatments failed to prevent tadpole tissue damage and mortality. Thus, FV3 is more pathogenic than was previously believed, even at very low titers.

A (selective) history of Australian involvement in cytokine biology

This review focuses on contributions to cytokine biology made by Australians in Australia. It is clearly biased by my own experiences and selective recollections especially related to the colony-stimulating factors in which Australian involvement has been pre-eminent from discovery to clinical use. Nevertheless Australian scientists have also made profound contributions to other areas of cytokine and growth factor biology (including interferons, inflammatory cytokines, chemokines and epidermal, insulin-like and vascular endothelial growth factors) that are briefly described in this review as well as other chapters in this volume.

Colony-stimulating factor-1-responsive macrophage precursors reside in the amphibian (Xenopus laevis) bone marrow rather than the hematopoietic subcapsular liver

Macrophage precursors originate from and undergo lineage commitment within designated sites of hematopoiesis, such as the mammalian bone marrow. These cells subsequently differentiate in response to stimulation with macrophage colony-stimulating factor-1 (CSF-1). The amphibian bone marrow, unlike that of mammals, has been overlooked as a source of leukocyte precursors in favor of the liver subcapsular region, where hematopoiesis occurs in anurans. Here we report that the bone marrow rather than the liver periphery provides macrophage progenitors to the amphibian Xenopus laevis. We identified the amphibian CSF-1, examined its gene expression in developing and virally infected X. lae vis and produced it in recombinant form (rXlCSF-1). This rXlCSF-1 did not bind or elicit proliferation/differentiation of subcapsular liver cells. Surprisingly, a subpopulation of bone marrow cells engaged this growth factor and formed rXlCSF-1 concentration-dependent colonies in semisolid medium. Furthermore, rXlCSF-1-treated bone marrow (but not liver) cultures comprised of cells with characteristic macrophage morphology and high gene expression of the macrophage marker CSF-1 receptor. Together, our findings indicate that in contrast to all other vertebrates studied to date, committed Xenopus macrophage precursor populations are not present at the central site of hematopoiesis, but reside in the bone marrow.

Transcriptional control of macrophage identity, self-renewal, and function

Macrophages not only are prominent effector cells of the immune system that are critical in inflammation and innate immune responses but also fulfill important functions in tissue homeostasis. Transcription factors can define macrophage identity and control their numbers and functions through the induction and maintenance of specific transcriptional programs. Here, we review the mechanisms employed by lineage-specific transcription factors to shape macrophage identity during the development from hematopoietic stem and progenitor cells. We also present current insight into how specific transcription factors control macrophage numbers, by regulating coordinated proliferation and differentiation of myeloid progenitor cells and self-renewal of mature macrophages. We finally discuss how functional specialization of mature macrophages in response to environmental stimuli can be induced through synergistic activity of lineage- and stimulus-specific transcription factors that plug into preexisting transcriptional programs. Understanding the mechanisms that define macrophage identity, numbers, and functions will provide important insights into the differential properties of macrophage populations under various physiological and pathological conditions.

Functional role of monocytes and macrophages for the inflammatory response in acute liver injury

Different etiologies such as drug toxicity, acute viral hepatitis B, or acetaminophen poisoning can cause acute liver injury or even acute liver failure (ALF). Excessive cell death of hepatocytes in the liver is known to result in a strong hepatic inflammation. Experimental murine models of liver injury highlighted the importance of hepatic macrophages, so-called Kupffer cells, for initiating and driving this inflammatory response by releasing proinflammatory cytokines and chemokines including tumor necrosis factor (TNF), interleukin-6 (IL-6), IL-1beta, or monocyte-chemoattractant protein-1 (MCP-1, CCL2) as well as activating other non-parenchymal liver cells, e.g., endothelial or hepatic stellate cells. Many of these proinflammatory mediators can trigger hepatocytic cell death pathways, e.g., via caspase activation, but also activate protective signaling pathways, e.g., via nuclear factor kappa B (NF-κB). Recent studies in mice demonstrated that these macrophage actions largely depend on the recruitment of monocytes into the liver, namely of the inflammatory Ly6c+ (Gr1+) monocyte subset as precursors of tissue macrophages. The chemokine receptor CCR2 and its ligand MCP-1/CCL2 promote monocyte subset infiltration upon liver injury. In contrast, the chemokine receptor CX3CR1 and its ligand fractalkine (CX3CL1) are important negative regulators of monocyte infiltration by controlling their survival and differentiation into functionally diverse macrophage subsets upon injury. The recently identified cellular and molecular pathways for monocyte subset recruitment, macrophage differentiation, and interactions with other hepatic cell types in the injured liver may therefore represent interesting novel targets for future therapeutic approaches in ALF.

Selective deletion of the membrane-bound colony stimulating factor 1 isoform leads to high bone mass but does not protect against estrogen-deficiency bone loss

To better define the biologic function of membrane-bound CSF1 (mCSF1) in vivo, we have generated mCSF1 knockout (k/o) mice. Spinal bone density (BMD) was 15.9% higher in k/o mice compared to wild-type (wt) controls (P < 0.01) and total BMD was increased by 6.8% (P < 0.05). A higher mean femur BMD was also observed but did not reach statistical significance (6.9% P = NS). The osteoclastogenic potential of bone marrow isolated from mCSF1 k/o mice was reduced compared to wt marrow. There were no defects in osteoblast number or function suggesting that the basis for the high bone mass phenotype was reduced resorption. In addition to a skeletal phenotype, k/o mice had significantly elevated serum triglyceride levels (123 ± 7 vs. 88 ± 3.2 mg/dl; k/o vs. wt, P < 0.001), while serum cholesterol levels were similar (122 ± 6 vs. 116 ± 6 mg/dl; k/o vs. wt, P = NS). One month after surgery, 5-month-old k/o and wt female mice experienced the same degree of bone loss following ovariectomy (OVX). OVX induced a significant fourfold increase in the expression of the soluble CSF1 isoform (sCSF1) in the bones of wt mice while expression of mCSF1 was unchanged. These findings indicate that mCSF1 is essential for normal bone remodeling since, in its absence, BMD is increased. Membrane-bound CSF1 does not appear to be required for estrogen-deficiency bone loss while in contrast; our data suggest that sCSF1 could play a key role in this pathologic process. The reasons why mCSF1 k/o mice have hypertriglyceridemia are currently under study.

Therapeutic applications of macrophage colony-stimulating factor-1 (CSF-1) and antagonists of CSF-1 receptor (CSF-1R) signaling

Macrophage-colony stimulating factor (CSF-1) signaling through its receptor (CSF-1R) promotes the differentiation of myeloid progenitors into heterogeneous populations of monocytes, macrophages, dendritic cells, and bone-resorbing osteoclasts. In the periphery, CSF-1 regulates the migration, proliferation, function, and survival of macrophages, which function at multiple levels within the innate and adaptive immune systems. Macrophage populations elicited by CSF-1 are associated with, and exacerbate, a broad spectrum of pathologies, including cancer, inflammation, and bone disease. Conversely, macrophages can also contribute to immunosuppression, disease resolution, and tissue repair. Recombinant CSF-1, antibodies against the ligand and the receptor, and specific inhibitors of CSF-1R kinase activity have been each been tested in a range of animal models and in some cases, in patients. This review examines the potential clinical uses of modulators of the CSF-1/CSF-1R system. We conclude that CSF-1 promotes a resident-type macrophage phenotype. As a treatment, CSF-1 has therapeutic potential in tissue repair. Conversely, inhibition of CSF-1R is unlikely to be effective in inflammatory disease but may have utility in cancer.

The colony-stimulating factors and cancer

The four colony-stimulating factors (CSFs) are glycoproteins that regulate the generation and some functions of infection-protective granulocytes and macrophages. Recombinant granulocyte-CSF (G-CSF) and granulocyte-macrophage-CSF (GM-CSF) have now been used to increase dangerously low white blood cell levels in many millions of cancer patients following chemotherapy. These CSFs also release haematopoietic stem cells to the peripheral blood, and these cells have now largely replaced bone marrow as more effective populations for transplantation to cancer patients who have treatment-induced bone marrow damage.

Development of monocytes, macrophages, and dendritic cells

Monocytes and macrophages are critical effectors and regulators of inflammation and the innate immune response, the immediate arm of the immune system. Dendritic cells initiate and regulate the highly pathogen-specific adaptive immune responses and are central to the development of immunologic memory and tolerance. Recent in vivo experimental approaches in the mouse have unveiled new aspects of the developmental and lineage relationships among these cell populations. Despite this, the origin and differentiation cues for many tissue macrophages, monocytes, and dendritic cell subsets in mice, and the corresponding cell populations in humans, remain to be elucidated.

Blood monocytes: development, heterogeneity, and relationship with dendritic cells

Monocytes are circulating blood leukocytes that play important roles in the inflammatory response, which is essential for the innate response to pathogens. But inflammation and monocytes are also involved in the pathogenesis of inflammatory diseases, including atherosclerosis. In adult mice, monocytes originate in the bone marrow in a Csf-1R (MCSF-R, CD115)-dependent manner from a hematopoietic precursor common for monocytes and several subsets of macrophages and dendritic cells (DCs). Monocyte heterogeneity has long been recognized, but in recent years investigators have identified three functional subsets of human monocytes and two subsets of mouse monocytes that exert specific roles in homeostasis and inflammation in vivo, reminiscent of those of the previously described classically and alternatively activated macrophages. Functional characterization of monocytes is in progress in humans and rodents and will provide a better understanding of the pathophysiology of inflammation.

Development of macrophages of cyprinid fish

The innate immune responses of early vertebrates, such as bony fishes, play a central role in host defence against infectious diseases and one of the most important effector cells of innate immunity are macrophages. In order for macrophages to be effective in host defence they must be present at all times in the tissues of their host and importantly, the host must be capable of rapidly increasing macrophage numbers during times of need. Hematopoiesis is a process of formation and development of mature blood cells, including macrophages. Hematopoiesis is controlled by soluble factors known as cytokines, that influence changes in transcription factors within the target cells, resulting in cell fate changes and the final development of specific effector cells. The processes involved in macrophage development have been largely derived from mammalian model organisms. However, recent advancements have been made in the understanding of macrophage development in bony fish, a group of organisms that rely heavily on their innate immune defences. Our understanding of the growth factors involved in teleost macrophage development, as well as the receptors and regulatory mechanisms in place to control them has increased substantially. Furthermore, model organisms such as the zebrafish have emerged as important instruments in furthering our understanding of the transcriptional control of cell development in fish as well as in mammals. This review highlights the recent advancements in our understanding of teleost macrophage development. We focused on the growth factors identified to be important in the regulation of macrophage development from a progenitor cell into a functional macrophage and discuss the important transcription factors that have been identified to function in teleost hematopoiesis. We also describe the findings of in vivo studies that have reinforced observations made in vitro and have greatly improved the relevance and importance of using teleost fish as model organisms for studying developmental processes.

A special linker between macrophage and hematopoietic malignant cells: membrane form of macrophage colony-stimulating factor

The membrane form of macrophage colony-stimulating factor (mM-CSF) is an alternative splicing variant of this cytokine. Although its high expression was detected in hematopoietic malignancies, its physiologic and pathologic roles in hematopoietic system have not been established. In this report, stable transfectant clones expressing mM-CSF (Namalwa-M and Ramos-M) were obtained, which showed reduced proliferation potential in vitro. Moreover, the in vivo study showed that Namalwa-M and Ramos-M exhibited enhanced oncogenicity in tumor size in nude mice model, which could be inhibited by M-CSF monoclonal antibody. A remarkable increase in infiltrating macrophage and the vessel densities was found in tumor tissues formed by lymphoma cell lines that stably expressed mM-CSF, which suggested the involvement of macrophages in this process. The in vitro results using coculture system showed that macrophages could promote Namalwa-M and Ramos-M proliferation and activate extracellular signal-regulated kinase/mitogen-activated protein kinase signal pathway. In addition, the expression of murine origin vascular endothelial growth factor, basic fibroblast growth factor, and hepatocyte growth factor was elevated in Namalwa-M formed tumor tissues. These results suggested that mM-CSF should be a positive regulator in the development of hematopoietic malignancies by abnormally activating infiltrating macrophages, which in turn promote the malignant development. Thus, mM-CSF may be a critical linker between macrophages and malignant cells in the development of hematopoietic malignancies.

Macrophage colony stimulating factor: not just for macrophages anymore! A gateway into complex biologies

Macrophage colony stimulating factor (M-CSF, also called colony stimulating factor-1) has traditionally been viewed as a growth/differentiation factor for monocytes, macrophages, and some female-specific tumors. As a result of alternative mRNA splicing and post-translational processing, several forms of M-CSF protein are produced: a secreted glycoprotein, a longer secreted form containing proteoglycan, and a short membrane-bound isoform. These different forms of M-CSF all initiate cell signaling in cells bearing the M-CSF receptor, called c-fms. Here we review the biology of M-CSF, which has important roles in bone physiology, the intestinal tract, cancer metastases to the bone, macrophage-mediated tumor cell killing and tumor immunity. Although this review concentrates mostly on the membrane form of human M-CSF (mM-CSF), the biology of the soluble forms and the M-CSF receptor will also be discussed for comparative purposes. The mechanisms of the biological effects of the membrane-bound M-CSF reveal that this cytokine is unexpectedly involved in many complex molecular events. Recent experiments suggest that a tumor vaccine based on membrane-bound M-CSF-transduced tumor cells, combined with anti-angiogenic therapy, should be evaluated further for use in clinical trials.

Hematopoietic cytokines

The production of hematopoietic cells is under the tight control of a group of hematopoietic cytokines. Each cytokine has multiple actions mediated by receptors whose cytoplasmic domains contain specialized regions initiating the various responses-survival, proliferation, differentiation commitment, maturation, and functional activation. Individual cytokines can be lineage specific or can regulate cells in multiple lineages, and for some cell types, such as stem cells or megakaryocyte progenitors, the simultaneous action of multiple cytokines is required for proliferative responses. The same cytokines control basal and emergency hematopoietic cell proliferation. Three cytokines, erythropoietin, granulocyte colony-stimulating factor, and granulocyte-macrophage colony-stimulating factor, have now been in routine clinical use to stimulate cell production and in total have been used in the management of many millions of patients. In this little review, discussion will be restricted to those cytokines well established as influencing the production of hematopoietic cells and will exclude newer candidate regulators and those active on lymphoid cells. As requested, this account will describe the cytokines in a historical manner, using a sequential format of discovery, understanding, validation, and puzzlement, a sequence that reflects the evolving views on these cytokines over the past 50 years.

Cell surface colony-stimulating factor 1 can be cleaved by TNF-alpha converting enzyme or endocytosed in a clathrin-dependent manner

CSF-1 is a hemopoietic growth factor, which plays an essential role in macrophage and osteoclast development. Alternative splice variants of CSF-1 are synthesized as soluble or membrane-anchored molecules, although membrane CSF-1 (mCSF-1) can be cleaved from the cell membrane to become soluble CSF-1. The activities involved in this proteolytic processing, also referred to as ectodomain shedding, remain poorly characterized. In the present study, we examined the properties of the mCSF-1 sheddase in cell-based assays. Shedding of mCSF-1 was up-regulated by phorbol ester treatment and was inhibited by the metalloprotease inhibitors GM6001 and tissue inhibitor of metalloproteases 3. Moreover, the stimulated shedding of mCSF-1 was abrogated in fibroblasts lacking the TNF-alpha converting enzyme (TACE, also known as a disintegrin and metalloprotease 17) and was rescued by expression of wild-type TACE in these cells, strongly suggesting that the stimulated shedding is TACE dependent. Additionally, we observed that mCSF-1 is predominantly localized to intracellular membrane compartments and is efficiently internalized in a clathrin-dependent manner. These results indicate that the local availability of mCSF-1 is actively regulated by ectodomain shedding and endocytosis. This mechanism may have important implications for the development and survival of monocyte lineage cells.

The Cell-Surface Isoform of Colony Stimulating Factor 1 (CSF1) Restores but Does Not Completely Normalize Fecundity in CSF1-Deficient Mice1

The complete genetic absence of colony stimulating factor 1 (CSF1) in CSF1-deficient Csf1(op)/Csf1(op) mice leads to reproductive defects in males and females. Although the cell-surface or membrane-bound isoform of CSF1 (mCSF1) is biologically active in bone, little is known about its role in reproduction. Transgenic mice expressing mCSF1 under the control of the 2.4-kb rat collagen type I alpha promoter were developed [Tg(Col1a1-mCSF1)1Gqy] and bred onto a Csf1(op)/Csf1(op) background [Csf1(op)/Csf1(op); Tg(Col1a1-mCSF1)1Gqy] to examine the effects of the mCSF1 isoform in bone in vivo. Surprisingly, when interbred, these mice were fertile. The Csf1(op)/Csf1(op); Tg(Col1a1-mCSF1)1Gqy transgenic male mice have normal libido, sperm number and percent of motile sperm. In Csf1(op)/Csf1(op); Tg(Col1a1-mCSF1)1Gqy females, puberty and estrus cycles are at expected age and duration. Further, females are able to carry pregnancies to term and nurse their offspring. Crosses of Csf1(op)/Csf1(op); Tg(Col1a1-mCSF1)1Gqy males or females with their control littermates showed no significant differences in either number or viability of offspring. However, crossing Csf1(op)/Csf1(op); Tg(Col1a1-mCSF1)1Gqy males with Csf1(op); Tg(Col1a1-mCSF1)1Gqy females resulted in a decline in both the number and viability of offspring, suggesting that a subtle reproductive defect might persist in the transgenic animals that was only manifest when the animals were interbred. Although the gravid murine uterus expresses extremely high levels of CSF1 that are thought to be important for reproduction, uterine tissue levels of CSF1 remained low and unchanged during pregnancy in Csf1(op)/Csf1(op); Tg(Col1a1-mCSF1)1Gqy mice. Low levels of CSF1 protein were detected in serum and in lung and uterine tissue in Csf1(op)/Csf1(op); Tg(Col1a1-mCSF1)1Gqy mouse, which likely result from the known proteolytic shedding of mCSF1 from the cell surface. These data are consistent with the conclusion that mCSF1, when shed from the cell surface, can support reproduction and that high uterine tissue levels of CSF1 may not be required for mouse reproduction.

Glyceraldehyde-3-phosphate dehydrogenase binds to the AU-Rich 3' untranslated region of colony-stimulating factor-1 (CSF-1) messenger RNA in human ovarian cancer cells: possible role in CSF-1 posttranscriptional regulation and tumor phenotype

The overexpression of the colony-stimulating factor-1(CSF-1) by epithelial ovarian cancer cells enhances invasiveness and metastatic properties, contributing to the poor prognosis of the patients. It has been suggested that CSF-1 3' untranslated region containing AU-rich elements (ARE) could regulate CSF-1 posttranscriptional expression and be responsible for its aberrant abundance in such cancer cells. In this study, normal (NOSE.1) and malignant (Hey) ovarian epithelial cells were used to examine CSF-1 expression and regulation. CSF-1 overexpression in Hey cells was found to associate with increased invasiveness, motility, urokinase activity, and virulence of tumorigenicity, compared with NOSE.1 cells, which expressed little CSF-1. CSF-1 ARE was further found to serve as an mRNA decay element that correlates with down-regulation of protein translation. Moreover, such down-regulation was found more prominent in NOSE.1 than in Hey cells, suggesting differences in posttranscriptional regulation. As a variety of trans-acting factors [AU-binding protein (AUBP)] are known to modulate messenger stability through binding to such elements, we examined the protein content of both cell lines for their ability to bind the CSF-1 ARE. Our results strongly suggested the abundance of such AUBP activity in Hey cells. We isolated a 37-kDa AUBP, which was identified as glyceraldehyde-3-phosphate dehydrogenase (GAPDH). To summarize, our study identified GAPDH as an AUBP abundant in Hey cells, where it binds to CSF-1 ARE that imparts mRNA decay. These data suggest that GAPDH binding to CSF-1 ARE sequence prevents CSF-1 mRNA decay and subsequent down-regulation of CSF-1 protein translation, leading to CSF-1 overexpression and increased metastatic properties seen in ovarian cancer.

Human monocytes differentiate into macrophages under the influence of human KPB-M15 conditioned medium

Culture medium conditioned by the L929 murine fibroblast cell line contains macrophage colony-stimulating factor (M-CSF), providing an alternative to recombinant M-CSF for in vitro generation of murine macrophages. No such alternative has been described for in vitro studies requiring human macrophages. We tested the differentiation of human blood monocytes into mature macrophages by culturing in media conditioned by the human KPB-M15 cell line, which produces M-CSF and interleukin 6 (IL-6). The phenotypes of macrophages cultured in KPB-M15 conditioned media and recombinant M-CSF were compared by examining viability, expression of cell surface markers, phagocytic/pinocytic activity, and cytokine/chemokine secretion in response to bacterial lipopolysaccharide (LPS). In conditioned medium, monocytes differentiated into a homogeneous population of large cells that exhibited higher expression of CD14 and the macrophage mannose receptor (CD206) than did M-CSF-cultured cells. Cells matured in KPB-M15 conditioned medium exhibited macrophage morphology, were phagocytic, and were activated in response to LPS. These data demonstrate that KPB-M15 conditioned medium can be used to differentiate human blood monocytes into macrophages in vitro.

Macrophage Colony-Stimulating Factor (M-CSF), As Well As Granulocyte Colony-Stimulating Factor (G-CSF), Accelerates Neovascularization

It has been reported that bone marrow cells (BMCs) differentiate into endothelial cells of blood vessels, and that granulocyte colony-stimulating factor (G-CSF) mobilizes progenitors in the BMCs to the peripheral blood, while macrophage colony-stimulating factor (M-CSF) augments the production of monocytes. We examined whether M-CSF augments the differentiation of BMCs into endothelial cells of blood vessels using a hindlimb-ischemic model. Either G-CSF or M-CSF, or both, was administered to the hindlimb-ischemic mice for 3 days. Both M-CSF and G-CSF augmented the differentiation of BMCs into endothelial cells of blood vessels through vascular endothelial cell growth factor (VEGF), resulting in early recovery of blood flow in the ischemic limbs.

Prostanoid receptor expression by human airway smooth muscle cells and regulation of the secretion of granulocyte colony-stimulating factor

The prostanoid receptors on human airway smooth muscle cells (HASMC) that augment the release by IL-1β of granulocyte colony-stimulating factor (G-CSF) have been characterized and the signaling pathway elucidated. PCR of HASM cDNA identified products corresponding to EP2, EP3, and EP4receptor subtypes. These findings were corroborated at the protein level by immunocytochemistry. IL-1β promoted the elaboration of G-CSF, which was augmented by PGE2. Cicaprost (IP receptor agonist) was approximately equiactive with PGE2, whereas PGD2, PGF2α, and U-46619 (TP receptor agonist) were over 10-fold less potent. Neither SQ 29,548 nor BW A868C (TP and DP1receptor antagonists, respectively) attenuated the enhancement of G-CSF release evoking any of the prostanoids studied. With respect to PGE2, the EP receptor agonists 16,16-dimethyl PGE2(nonselective), misoprostol (EP2/EP3selective), 17-phenyl-ω-trinor PGE2(EP1selective), ONO-AE1-259, and butaprost (both EP2selective) were full agonists at enhancing G-CSF release. AH 6809 (10 μM) and L-161,982 (2 μM), which can be used in HASMC as selective EP2and EP4receptor antagonists, respectively, failed to displace to the right the PGE2concentration-response curve that described the augmented G-CSF release. In contrast, AH 6809 and L-161,982 in combination competitively antagonized PGE2-induced G-CSF release. Augmentation of G-CSF release by PGE2was mimicked by 8-BrcAMP and abolished in cells infected with an adenovirus vector encoding an inhibitor protein of cAMP-dependent protein kinase (PKA). These data demonstrate that PGE2facilitates G-CSF secretion from HASMC through a PKA-dependent mechanism by acting through EP2and EP4prostanoid receptors and that effective antagonism is realized only when both subtypes are blocked concurrently.

Interstitial gene delivery in human xenograft prostate tumors using titanium metal seeds

Gene therapy is a promising approach for the treatment of cancers. Strategies for gene vector delivery include systemic and local-regional approaches. Intratumoral delivery of vectors has generally employed direct injections into single or multiple locations throughout the tumor volume. However, this approach leads to nonuniform distributions of reagents within tumors and becomes cumbersome as the required number of injections is increased. We have investigated the effectiveness of an interstitial plasmid gene delivery based on using tiny metallic seeds (GeneSeeds) analogous to technology used for brachytherapy. Feasibility for interstitial use of GeneSeeds was demonstrated expressing reporter plasmids (green fluorescence protein or β-galactosidase) in human xenograft prostate tumors. Immunohistochemical analysis confirmed effective interstitial delivery, vector expression, and distributions of reporter genes within tumors. Applicability of GeneSeeds for delivery of radiosensitizing cytokines was examined by generating a cytokine [tumor necrosis factor-α (TNF-α)] expressing vector under the cytomegaloviral promoter and interstitially implanting GeneSeeds with this vector into prostate cancer tumors. TNF-α protein expression was observed around the ends of seeds and decreasing in an exponential gradient as a function of distance. The expression of TNF-α resulted in tumor growth delay of a human prostate cancer xenograft. These results demonstrate the feasibility of applying interstitial delivery of gene expressing vectors for the treatment of human cancers.

Quantitation of bovine macrophage colony-stimulating factor in bovine serum by ELISA

We established an enzyme-linked immunosorbent assay (ELISA) system for the quantitation of bovine macrophage colony-stimulating factor (M-CSF) and used it to measure the serum M-CSF levels in bovine fetuses and calves. The average serum M-CSF level was 2.7+/-1.5 ng/ml in 39 calves under 100 days old, and 1.8+/-0.8 ng/ml in 15 cattle between 101 and 418 days old. Fetal sera samples (n = 6) prepared from cattle between 150 and 280 days of gestational age had a higher average level of M-CSF (8.8+/-1.4 ng/ml). Alteration in serum M-CSF levels in each individual calf was also measured. The serum levels of M-CSF in calves at 0-1 day after birth ranged from 0.52 to 7.3 ng/ml. During the period 113-125 days after birth, serum levels were around 1.4+/-0.39 ng/ml. Although serum M-CSF levels generally decreased as the age of calves advanced, differences among individuals, especially among newborn calves, were observed.

Incomplete restoration of colony-stimulating factor 1 (CSF-1) function in CSF-1-deficient Csf1op/Csf1op mice by transgenic expression of cell surface CSF-1

The primary macrophage growth factor, colony-stimulating factor 1 (CSF-1), is expressed as a secreted glycoprotein or proteoglycan found in the circulation or as a biologically active cell surface glycoprotein (csCSF-1). To investigate the in vivo roles of csCSF-1, we created mice that exclusively express csCSF-1, in a normal tissue-specific and developmental manner, by transgenic expression of csCSF-1 in the CSF-1-deficient osteopetrotic (Csf1(op)/Csf1(op)) background. The gross defects of Csf1(op)/Csf1(op) mice, including growth retardation, failure of tooth eruption, and abnormal male and female reproductive functions were corrected. Macrophage densities in perinatal liver, bladder, sublinguinal salivary gland, kidney cortex, dermis, and synovial membrane were completely restored, whereas only partial or no restoration was achieved in adult liver, adrenal gland, kidney medulla, spleen, peritoneal cavity, and intestine. Residual osteopetrosis, significantly delayed trabecular bone resorption in the subepiphyseal region of the long bone, and incomplete correction of the hematologic abnormalities in the peripheral blood, bone marrow, and spleens of CSF-1-deficient mice were also found in mice exclusively expressing csCSF-1. These data suggest that although csCSF-1 alone is able to normalize several aspects of development in Csf1(op)/Csf1(op) mice, it cannot fully restore in vivo CSF-1 function, which requires the presence of the secreted glycoprotein and/or proteoglycan forms.

Effect of polysaccharide Krestin on the up-regulation of macrophage colony-stimulating factor gene expression in protecting mouse peritoneal macrophages from oxidative injury

Oxidative injury caused by oxidatively modified low density lipoprotein (Ox-LDL) plays an important role in the transformation of macrophages into foam cells and atherogenesis. Treatments to protect macrophages from oxidative injury will be effective in treating atherosclerosis. A macrophage-specific growth factor, macrophage colony-stimulating factor (M-CSF), was reported to be able to prevent the progression of atherosclerosis in Watanabe heritable hypercholesterolemic (WHHL) rabbits. A protein-bound polysaccharide, polysaccharide Krestin (PSK), was also proven to have effects in preventing atherosclerosis in our previous work. We proposed that, both M-CSF and PSK could protect macrophages from oxidative injury, and the effects of PSK were associated with its capability of inducing M-CSF expression. In our present results, M-CSF could alleviate the Ox-LDL- or tert-butyl hydroperoxide (tbOOH)-induced injury to mouse peritoneal macrophages, and PSK exhibited some similar effects. PSK treatment could induce M-CSF gene expression and secretion in mouse peritoneal macrophages. Furthermore actinomycin D and cycloheximide could attenuate that induction. We concluded that, maybe PSK exerted its effects on macrophages partly through the transcriptional induction of M-CSF in the cells.

Differential mRNA expression of inflammatory cytokines in cultured human fetal membrane cells responding to influenza virus infection

We examined the expression of mRNAs for inflammatory cytokines and Fas in cultured human fetal membrane cells responding to influenza virus (IV) infection using the reverse transcriptase-polymerase chain reaction (RT-PCR). Primary cultured chorion and amnion cells prepared from human fetal membranes were infected with IV. Chorion cells expressed significant amounts of interleukin (IL)-1beta, IL-6, tumor necrosis factor (TNF)-alpha, interferon (IFN)-beta, IFN-gamma and granulocyte macrophage colony-stimulating factor (GM-CSF) mRNAs and small amounts of Fas mRNA in response to IV infection. Amnion cells expressed TNF-alpha and IFN-beta mRNAs in response to IV infection, while expression of the other mRNAs was not altered. We also examined whether or not TNF-alpha, IFN-beta, IFN-gamma and Fas participated in IV infection-induced apoptotic DNA fragmentation in chorion cells. Neutralizing antibodies against them did not inhibit DNA fragmentation. These results suggested that chorion cells expressed significant amounts of mRNAs for inflammatory cytokines in response to IV infection, and that, in contrast, mRNA expression was quiescent in amnion cells. Moreover, TNF-alpha, IFN-beta, IFN-gamma and Fas do not appear to be directly involved in the apoptosis induction of IV-infected chorion cells. The results indicated that chorion cells may play a role in defense against IV through an antiviral immune response and apoptosis to eliminate own cells and viral pathogens in infected organs, whereas amnion cells do not play such a role.

Expression of macrophage-colony stimulating factor in normal and inflammatory bowel disease intestine

Mucosal macrophages have been implicated in the pathogenesis of inflammatory bowel disease (IBD). Macrophage-colony stimulating factor (M-CSF) influences monocyte/macrophage proliferation, differentiation, and activation. Serum levels are increased in active IBD, but little is known about its role in mucosal inflammation. This study was undertaken to determine the distribution, frequency, and level of M-CSF expression in normal and IBD-affected intestine. RNA and tissue were studied from patients with Crohn's disease (CD) and ulcerative colitis (UC) as well as from histologically normal colon. Tissue from intestinal tuberculosis and ischaemic colitis patients served as controls. M-CSF mRNA and protein were examined by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), in situ hybridisation, and immunohistochemistry, respectively. M-CSF mRNA and protein were detected in histologically normal intestine, but their expression was largely confined to the mucosa. In active IBD, the frequency of M-CSF-expressing cells was significantly increased and their distribution markedly altered, although no increase in mucosal M-CSF mRNA levels in intestinal tissue was observed. The changes were not specific to IBD, as there were similar findings in intestinal tuberculosis and ischaemic colitis. The marked alteration observed in M-CSF expression in IBD and the importance of this cytokine in stimulating macrophage functions suggest that M-CSF may contribute to the pathogenesis of the IBD lesion.

Rescue of the colony-stimulating factor 1 (CSF-1)-nullizygous mouse (Csf1(op)/Csf1(op)) phenotype with a CSF-1 transgene and identification of sites of local CSF-1 synthesis

Colony-stimulating factor 1 (CSF-1) regulates the survival, proliferation, and differentiation of mononuclear phagocytes. It is expressed as a secreted glycoprotein or proteoglycan found in the circulation or as a biologically active cell-surface glycoprotein. To investigate tissue CSF-1 regulation, CSF-1-null Csf1(op)/Csf1(op) mice expressing transgenes encoding the full-length membrane-spanning CSF-1 precursor driven by 3.13 kilobases of the mouse CSF-1 promoter and first intron were characterized. Transgene expression corrected the gross osteopetrotic, neurologic, weight, tooth, and reproductive defects of Csf1(op)/Csf1(op) mice. Detailed analysis of one transgenic line revealed that circulating CSF-1, tissue macrophage numbers, hematopoietic tissue cellularity, and hematopoietic parameters were normalized. Tissue CSF-1 levels were normal except for elevations in 4 secretory tissues. Skin fibroblasts from the transgenic mice secreted normal amounts of CSF-1 but also expressed some cell-surface CSF-1. Also, lacZ driven by the same promoter/first intron revealed beta-galactosidase expression in hematopoietic, reproductive, and other tissue locations proximal to CSF-1 cellular targets, consistent with local regulation by CSF-1 at these sites. These studies indicate that the 3.13-kilobase promoter/first intron confers essentially normal CSF-1 expression. They also pinpoint new cellular sites of CSF-1 expression, including ovarian granulosa cells, mammary ductal epithelium, testicular Leydig cells, serous acinar cells of salivary gland, Paneth cells of the small intestine, as well as local sites in several other tissues.

A Rep recognition sequence is necessary but not sufficient for nicking of DNA by adeno-associated virus type-2 Rep proteins

The strand-specific, site-specific endonuclease (nicking) activity of the Rep68 and Rep78 (Rep68/78) proteins of adeno-associated virus type 2 (AAV) is involved in AAV replication, and appears to be involved in AAV site-specific integration. Rep68/78 cuts within the inverted terminal repeats (ITRs) of the AAV genome and in the AAV preferred integration locus on human chromosome 19 (AAVS1). The known endonuclease cut sites are 11-16 bases away from the primary binding sites, known as Rep recognition sequences (RRSs). A linear, double-stranded segment of DNA, containing an RRS and a cut site, has previously been shown to function as a substrate for the Rep68/78 endonuclease activity. We show here that mutation of the Rep recognition sequence, within such a DNA segment derived from the AAV ITRs, eliminates the ability of this substrate to be cleaved detectably by Rep78. Rep78 nicks the RRS-containing site from AAVS1 about half as well as the linear ITR sequence. Eighteen other RRS-containing sequences found in the human genome, but outside AAVS1, are not cleaved by Rep78. These results may help to explain the specificity of AAV integration.

Interleukin-6 and other gp130-dependent cytokines selectively inhibit proliferation of macrophage-lineage hemopoietic progenitor cells

OBJECTIVE

Hemopoiesis is regulated by cytokines with positive or negative effects on proliferation of lineage-committed or multipotent hemopoietic stem cells. We have investigated the roles of interleukin-6 and other gp130-dependent ligands on the proliferation of macrophage-lineage hemopoietic progenitor cells.

METHODS

The responses of human and murine hemopoietic cells to combinations of cytokines involving interleukin-6 or related factors were assessed in short-term culture by clonogenic assay.

RESULTS

Interleukin-6, leukemia inhibitory factor, and ciliary neurotrophic factor inhibited formation of colonies stimulated by macrophage colony-stimulating factor. These effects were dose dependent and selective for macrophage-lineage precursors. Progenitors from murine peripheral blood were inhibited by 37-93% in cultures containing interleukin-6 (11 experiments; median, 68%). Macrophage progenitors from murine bone marrow were also inhibited by interleukin-6 but were less sensitive (seven experiments; median, 48%). In cultures costimulated with leukemia inhibitory factor, peripheral blood and bone marrow progenitors were inhibited by 82% and 58%, respectively. Ciliary neurotrophic factor inhibited macrophage colonies by 66%. Multilineage bone marrow colony formation was not affected. In cultures of human bone marrow cells stimulated with macrophage colony stimulating factor and stem cell factor, interleukin-6 inhibited colony formation by 51-74%. Bone marrow colonies stimulated by granulocyte-macrophage colony stimulating factor were not inhibited by costimulation with interleukin-6.

CONCLUSIONS

These results suggest a novel mechanism for the negative regulation of macrophage-lineage hemopoietic cells. They also demonstrate new properties of interleukin-6 and certain other gp 130-dependent ligands.

Liver fibrosis

Knowledge on the development and progression of liver fibrosis has grown exponentially in the past decade. At present, liver fibrogenesis is referred to as a dynamic process involving complex cellular and molecular mechanisms, resulting from the chronic activation of the tissue repair mechanisms that follows reiterated liver tissue injury. The identification and characterization of the cell types and of the different mediators involved in this process has allowed a "re-visitation" of several issues related to liver cirrhosis and its immediate consequences. Among these, evaluation of the relationships occurring between fibrogenesis and portal hypertension, cholestasis and the development of hepatocellular carcinoma, represent some of the hottest areas of research in this field of hepatology. The elucidation of many of the cellular and molecular mechanisms responsible for the progression of liver fibrosis has provided a sound basis for the development of pharmacological strategies able to modulate this important pathophysiological process.

Roles of adeno-associated virus Rep protein and human chromosome 19 in site-specific recombination

Adeno-associated virus type 2 (AAV) is the only known eucaryotic virus capable of targeted integration in human cells. AAV integrates preferentially into human chromosome (ch) 19q13.3qter. The nonstructural proteins of AAV-2, Rep78 and Rep68, are essential for targeted integration. Rep78 and Rep68 are multifunctional proteins with diverse biochemical activities, including site-specific binding to AAV and ch-19 target sequences, helicase activity, and strand-specific, site-specific endonuclease activities. Both a Rep DNA binding element (RBE) and a nicking site essential for AAV replication present within the viral terminal repeats are also located on ch-19. Recently, identical RBE sequences have been identified at other locations in the human genome. This fact raises numerous questions concerning AAV targeted integration; specifically, how many RBE sequences are in the human genome? How does Rep discriminate between these and the ch-19 RBE sequence? Does Rep interact with all sites and, if so, how is targeted integration within a fixed time frame facilitated? To better characterize the role of Rep in targeted integration, we established a Rep-dependent filter DNA binding assay using a highly purified Rep-68 fusion protein. Electron microscopy (EM) analysis was also performed to determine the characteristics of the Rep-RBE interaction. Our results determined that the Rep affinity for ch-19 is not distinct compared to other RBEs in the human genome when utilizing naked DNA. In fact, a minimum-binding site (GAGYGAGC) efficiently associated with Rep, suggesting that as many as 2 x 10(5) sites may exist. In addition, such sites also exist frequently in nonprimate mammalian genomes, although AAV integrates site specifically into primate genomes. EM analysis demonstrated that only one Rep-DNA complex was formed on ch-19 target DNA. Surprisingly, identically sized complexes were observed on all substrates containing a RBE sequence, but never on DNA lacking an RBE. Rep-DNA complexes involved a multimeric protein structure that spanned ca. 60 bp. Immunoprecipitation of AAV latently infected cells determined that 1,000 to 4,000 copies of Rep78 and Rep68 protein are expressed per cell. Comparison of the Rep association constant with those of established DNA binding proteins indicates that sufficient molecules of Rep are present to interact with all potential RBE sites. Moreover, Rep expression in the absence of AAV cis-acting substrate resulted in Rep-dependent amplification and rearrangement of the target sequence in ch-19. This result suggests that this locus is a hot spot for Rep-dependent recombination. Finally, we engineered mice to carry a single 2.7-kb human ch-19 insertion containing the AAV ch-19 target locus. Using cells derived from these mice, we demonstrated that this sequence was sufficient for site-specific recombination after infection with transducing vectors expressing Rep. This result indicates that any host factors required for targeting are conserved between human and mouse. Furthermore, the human ch-19 cis sequences and chromatin structure required for site-specific recombination are contained within this fragment. Overall, these results indicate that the specificity of targeted recombination to human ch-19 is not dictated by differential Rep affinities for RBE sites. Instead, specificity is likely dictated by human ch-19 sequences that serve as a Rep protein-mediated origin of replication, thus facilitating viral targeting through Rep-Rep interactions and host enzymes, resulting in site-specific recombination. Control of specificity is clearly dictated by the ch-19 sequences, since transfer of these sequences into the mouse genome are sufficient to achieve Rep-dependent site-specific integration.

Membrane-bound macrophage colony-stimulating factor and its receptor play adhesion molecule-like roles in leukemic cells

Membrane-bound macrophage colony-stimulating factor (m-M-CSF) is the membrane form M-CSF by alternative splicing. J6-1 leukemic cell line spontaneously forms cell clusters, whose growth depends on the auto-juxtacrine mediated by m-M-CSF and its receptor (M-CSFR). In this study, M-CSFR isolated from J6-1 cells and recombinant human M-CSF soluble receptor (rh-M-CSFsR) were used to study their effects on J6-1 cells. Both receptors inhibited cell proliferation. Use of M-CSFR monoclonal antibodies, M-CSFR or rh-M-CSFsR to block either M-CSFR or m-M-CSF on cell surface inhibited the cluster forming process, while both receptors stimulated cells adhering to culture plate. Furthermore, M-CSFR and/or rh-M-CSFsR caused multiple cellular changes including cytoplasmic pH, multinuclear cell ratio, antigen expression and cell diameter. A [Ca(2+)] rise was induced within 90 s by both receptors. Western blot experiments showed that rh-M-CSFsR caused tyrosine phosphorylation on multiple cytoplasmic proteins of 45 kDa and 55-90 kDa, which could be blocked by H7. These observations suggested that m-M-CSF and M-CSFR mediate J6-1 cell intercellular adhesion with bi-directional signal transduction, and Ca(2+), protein tyrosine kinases, PKC and/or other H7 sensitive kinase(s) involve in the counter-directional signal transduction.

Macrophage colony-stimulating factor reduces tert-butyl hydroperoxide induced oxidative injury to monocytes/macrophages

The transformation of macrophages into foam cells is an important event in the development of atherosclerosis, and the oxidative injury caused by oxidized low density lipoprotein (Ox-LDL) plays an essential role in that process. It has been proved that macrophage colony-stimulating factor (M-CSF) could prevent the progression of atherosclerosis in Watanabe heritable hypercholesterolemic (WHHL) rabbits. We proposed that the anti-atherogenic effect of M-CSF was partly associated with its protective effect on monocyte-derived macrophages from Ox-LDL induced oxidative injury. In order to prove this, we investigated the effect of M-CSF on the oxidative injury caused by tert-butyl hydroperoxide (tbOOH) to mouse peritoneal macrophages and U937/J774 cell lines. The results showed that M-CSF could protect mouse peritoneal macrophages from oxidative injury (presented by cell morphology and cell survival rate); L929 cell-conditioned medium (L929-CM) had the same effect as M-CSF; and anti-M-CSF monoclonal antibody could mostly block the protective effect of L929-CM on macrophages. L929-CM was proved to be also able to decrease the impact of plasma membrane fluidity in U937 and J774 cells treated with tbOOH. Incubation with tbOOH caused DNA fragmentation in U937 cells. The presence of L929-CM greatly reduced the number of apoptotic U937 cells characterized by DNA fragmentation. From these results, we concluded that M-CSF could protect monocytes/macrophages from oxidative injury. It may be one of the mechanisms which explain the anti-atherogenic effect of exogenous M-CSF in WHHL rabbits.

The release of acetylcholine receptor inducing activity (ARIA) from its transmembrane precursor in transfected fibroblasts

Acetylcholine receptor inducing activity (ARIA) is made by motoneurons and is released at the neuromuscular synapse to stimulate the synthesis of acetylcholine receptors by skeletal muscle. ARIA is derived from a transmembrane precursor (pro-ARIA) via proteolytic cleavage of the ectodomain. We studied requirements in the amino acid sequence at the cleavage site with various substitution and deletion mutations. Wild type (WT) and mutant proteins were transiently expressed in COS cells, and release of ARIA into the conditioned medium was measured by tyrosine phosphorylation of its receptor, p185, in L6 cells. Removal of all potential cleavage sites between the extracellular epidermal growth factor domain and the transmembrane domain by substitution and small deletions (<11 amino acid residues out of 21) did not significantly reduce ARIA release, whereas larger deletions abolished it. We propose that cleavage occurs independently of amino acid sequence at a short distance from the epidermal growth factor domain, unless sterically hindered by the nearby secondary structure. A mutant with shorter cytoplasmic domain ("c" isoform) released significantly less ARIA than the WT ("a" isoform), suggesting that the c isoform may be suitable for signaling through direct cell-cell contact. Alternatively, proteolytic conversion of the a isoform to the c isoform may rapidly down-regulate release of ARIA.

Combined therapy with anti-P-glycoprotein antibody and macrophage colony-stimulating factor gene transduction for multiorgan metastases of multidrug-resistant human small cell lung cancer in NK cell-depleted SCID mice

Our aim was to determine the antimetastatic potential of anti-P-glycoprotein (P-gp) antibodies (Abs) against multidrug-resistant (MDR) human small cell lung cancer (SCLC) cells expressing P-gp. Human SCLC cells H69 (P-gp negative) and its etoposide-resistant variant H69/YP (P-gp positive) were used. H69 and H69/VP cells injected i.v. metastasized to the liver, kidneys and systemic lymph nodes of NK cell-depleted severe combined immunodeficient (SCID) mice. H69/VP cells, but not H69 cells, were resistant to treatments with vindesine. Treatment with mouse-human chimeric anti-P-gp Ab (MH162) and its mouse counterpart (MRK-16) reduced metastasis of H69/VP cells in various organs and prolonged the survival of tumor-bearing mice, although they were less effective if injected at late times (after 28 days). Treatment with another mouse anti-Pgp Ab, MRK-17, was effective only against liver metastasis. MH162 and MRK-16 efficiently induced Ab-dependent cellular cytotoxicity (ADCC) by peritoneal macrophages against H69/VP cells in vitro, but MRK-17 was less effective, in accordance with their in vivo antimetastatic potential. Gene transfection of macrophage colony-stimulating factor (M-CSF) into H69/VP cells to augment macrophage-mediated ADCC resulted in inhibition of metastasis to the liver and lymph nodes, but not kidneys. Combined treatment with a low dose of MRK-16 completely cured metastasis of M-CSF transfectant, but not of the mock transfectant. Our findings suggest that while anti-P-gp Abs had antimetastatic potential against SCLC cells expressing P-gp, combined treatment with M-CSF gene transduction to augment the therapeutic efficacy of anti-P-gp Abs may be beneficial for eradicating metastatic MDR SCLC in humans.