Cellular mechanisms of tumour suppression by the retinoblastoma gene

The retinoblastoma (RB) tumour suppressor gene is functionally inactivated in a broad range of paediatric and adult cancers, and a plethora of cellular functions and partners have been identified for the RB protein. Data from human tumours and studies from mouse models indicate that loss of RB function contributes to both cancer initiation and progression. However, we still do not know the identity of the cell types in which RB normally prevents cancer initiation in vivo, and the specific functions of RB that suppress distinct aspects of the tumorigenic process are poorly understood.

CSF-1 receptor structure/function in MacCsf1r-/- macrophages: regulation of proliferation, differentiation, and morphology

CSF-1 is the major regulator of tissue macrophage development and function. A GM-CSF-dependent, CSF-1 receptor (CSF-1R)-deficient F4/80(hi)Mac-1(+)Gr1(-)CD11c(+) bone marrow macrophage (BMM) line (MacCsf1r-/-) was developed to study the roles of the eight intracellular CSF-1R tyrosines phosphorylated upon receptor activation. Retroviral expression of the wild-type CSF-1R rescued the CSF-1-induced survival, proliferation, differentiation, and morphological characteristics of primary BMM. Mutation of all eight tyrosines failed to rescue, whereas the individual Y --> F mutants (544, 559, 697, 706, 721, 807, 921, 974) rescued these CSF-1-inducible phenotypes to varying degrees. The juxtamembrane domain Y559F and activation loop Y807F mutations severely compromised proliferation and differentiation, whereas Y706, Y721F, and Y974F mutations altered morphological responses, and Y706F increased differentiation. Despite their retention of significant in vitro tyrosine kinase activity, Y559F and Y807F mutants exhibited severely impaired in vivo receptor tyrosine phosphorylation, consistent with the existence of cellular mechanisms inhibiting CSF-1R tyrosine phosphorylation that are relieved by phosphorylation of these two sites. The MacCsf1r-/- macrophage line will facilitate genetic and proteomic approaches to CSF-1R structure/function studies in the major disease-related CSF-1R-expressing cell type.

Cyclin E phosphorylation regulates cell proliferation in hematopoietic and epithelial lineages in vivo

Phosphorylations within N- and C-terminal degrons independently control the binding of cyclin E to the SCF(Fbw7) and thus its ubiquitination and proteasomal degradation. We have now determined the physiologic significance of cyclin E degradation by this pathway. We describe the construction of a knockin mouse in which both degrons were mutated by threonine to alanine substitutions (cyclin E(T74A T393A)) and report that ablation of both degrons abolished regulation of cyclin E by Fbw7. The cyclin E(T74A T393A) mutation disrupted cyclin E periodicity and caused cyclin E to continuously accumulate as cells reentered the cell cycle from quiescence. In vivo, the cyclin E(T74A T393A) mutation greatly increased cyclin E activity and caused proliferative anomalies. Cyclin E(T74A T393A) mice exhibited abnormal erythropoiesis characterized by a large expansion of abnormally proliferating progenitors, impaired differentiation, dysplasia, and anemia. This syndrome recapitulates many features of early stage human refractory anemia/myelodysplastic syndrome, including ineffective erythropoiesis. Epithelial cells also proliferated abnormally in cyclin E knockin mice, and the cyclin E(T74A T393A) mutation delayed mammary gland involution, implicating cyclin E degradation in this anti-mitogenic response. Hyperproliferative mammary epithelia contained increased apoptotic cells, suggesting that apoptosis contributes to tissue homeostasis in the setting of cyclin E deregulation. Overall these data show the critical role of both degrons in regulating cyclin E activity and reveal that complete loss of Fbw7-mediated cyclin E degradation causes spontaneous and cell type-specific proliferative anomalies.

Retinoblastoma function is essential for establishing lung epithelial quiescence after injury

The retinoblastoma gene product (RB) regulates cell cycle, quiescence, and survival in a cell type-dependent and environment-dependent manner. RB function is critical in the pulmonary epithelium, as evidenced by nearly universal RB inactivation in lung cancer and increased lung cancer risk in persons with germline RB gene mutations. Lung carcinomas occur in the context of epithelial remodeling induced by cytotoxic damage. Whereas the role of RB in development and normal organ homeostasis has been extensively studied, RB function in the context of cellular injury and repair has remained largely unexplored. In the current studies, the RB gene was selectively deleted in the respiratory epithelium of the mouse. Although RB was not required for establishing or maintaining quiescence during lung homeostasis, RB was essential for establishing quiescence during epithelial repair after injury. Notably, aberrant cell cycle progression was sustained for 9 months after injury in RB-deficient lungs. Prenatal and postnatal RB ablation had similar effects, providing evidence that timing of RB loss was not critical to the outcome and that the injury-induced phenotype was not secondary to compensatory alterations occurring during development. These data show that RB is essential for repair of the respiratory epithelium after cytotoxic damage and support a critical unique role for RB in the context of epithelial remodeling after injury. Because human cancers are associated with chronic cellular damage, these findings have important new implications for RB-mediated tumor suppression.

Resident and "inflammatory" dendritic cells in human skin

Dendritic cells (DCs) are a heterogeneous group of antigen-presenting leukocytes that are important in activation of both the innate and adaptive arms of the immune system. Although there are several different DC populations in the body, DCs are globally defined by their capacity for potent antigen presentation and naive T-cell activation. In noninflamed human skin during steady state, there are three main cutaneous DC populations: epidermal Langerhans cells, dermal myeloid DCs, and dermal plasmacytoid DCs. In psoriasis, a model for cutaneous inflammation, there is an additional population of myeloid dermal DCs--"inflammatory DCs"--which appears to be critical for disease pathogenesis.

Blood monocyte subsets differentially give rise to CD103+ and CD103- pulmonary dendritic cell populations

There are two major myeloid pulmonary dendritic cell (DC) populations: CD103+ DCs and CD11bhigh DCs. In this study, we investigated in detail the origins of both myeloid DC pools using multiple experimental approaches. We show that, in resting lung, Ly-6ChighCCR2high monocytes repopulated CD103+ DCs using a CCR2-dependent mechanism, and these DCs preferentially retained residual CCR2 in the lung, whereas, conversely, Ly-6ClowCCR2low monocytes repopulated CD11bhigh DCs. CX3CR1 was required to generate normal numbers of pulmonary CD11bhigh DCs, possibly because Ly-6Clow monocytes in the circulation, which normally express high levels of CX3CR1, failed to express bcl-2 and may have diminished survival in the circulation in the absence of CX3CR1. Overall, these data demonstrate that the two circulating subsets of monocytes give rise to distinct tissue DC populations.

Epidermal receptor activator of NF-kappaB ligand controls Langerhans cells numbers and proliferation

Langerhans cells (LC) are the dendritic APC population of the epidermis, where they reside for long periods and are self-replicating. The molecular signals underlying these characteristics are unknown. The TNF superfamily member receptor activator of NF-kappaB ligand (RANKL, TNFSF11) has been shown to sustain viability of blood dendritic cells in addition to its role in promoting proliferation and differentiation of several cell types, notably osteoclasts. In this study, we have studied expression of the RANKL system in skin and have defined a key role for this molecule in LC homeostasis. In vitro and in vivo, human KC expressed RANKL and epidermal LC expressed cell surface RANK. In vitro, RANKL sustained CD34(+) progenitor-derived LC viability following 72-h cultures in cytokine-free medium (79.5 +/- 1% vs 55.2 +/- 5.7% live cells, respectively; n = 4; p < 0.05). In vivo, RANKL-deficient mice displayed a marked reduction in epidermal LC density (507.1 +/- 77.2 vs 873.6 +/- 41.6 LC per mm(2); n = 9; p < 0.05) and their proliferation was impaired without a detectable effect on apoptosis. These data indicate a key role for the RANKL system in the regulation of LC survival within the skin and suggest a regulatory role for KC in the maintenance of epidermal LC homeostasis.

GFP reporter mice for the retinoblastoma-related cell cycle regulator p107

The RB tumor suppressor gene is mutated in a broad range of human cancers, including pediatric retinoblastoma. Strikingly, however, Rb mutant mice develop tumors of the pituitary and thyroid glands, but not retinoblastoma. Mouse genetics experiments have demonstrated that p107, a protein related to pRB, is capable of preventing retinoblastoma, but not pituitary tumors, in Rb-deficient mice. Evidence suggests that the basis for this compensatory function of p107 is increased transcription of the p107 gene in response to Rb inactivation. To begin to address the context-dependency of this compensatory role of p107 and to follow p107 expression in vivo, we have generated transgenic mice carrying an enhanced GFP (eGFP) reporter inserted into a bacterial artificial chromosome (BAC) containing the mouse p107 gene. Expression of the eGFP transgene parallels that of p107 in these transgenic mice and identifies cells with a broad range of expression level for p107, even within particular organs or tissues. We also show that loss of Rb results in the upregulation of p107 transcription in specific cell populations in vivo, including subpopulations of hematopoietic cells. Thus, p107 BAC-eGFP transgenic mice serve as a useful tool to identify distinct cell types in which p107 is expressed and may have key functions in vivo, and to characterize changes in cellular networks accompanying Rb deficiency.

The B cell antigen receptor and overexpression of MYC can cooperate in the genesis of B cell lymphomas

A variety of circumstantial evidence from humans has implicated the B cell antigen receptor (BCR) in the genesis of B cell lymphomas. We generated mouse models designed to test this possibility directly, and we found that both the constitutive and antigen-stimulated state of a clonal BCR affected the rate and outcome of lymphomagenesis initiated by the proto-oncogene MYC. The tumors that arose in the presence of constitutive BCR differed from those initiated by MYC alone and resembled chronic B cell lymphocytic leukemia/lymphoma (B-CLL), whereas those that arose in response to antigen stimulation resembled large B-cell lymphomas, particularly Burkitt lymphoma (BL). We linked the genesis of the BL-like tumors to antigen stimulus in three ways. First, in reconstruction experiments, stimulation of B cells by an autoantigen in the presence of overexpressed MYC gave rise to BL-like tumors that were, in turn, dependent on both MYC and the antigen for survival and proliferation. Second, genetic disruption of the pathway that mediates signaling from the BCR promptly killed cells of the BL-like tumors as well as the tumors resembling B-CLL. And third, growth of the murine BL could be inhibited by any of three distinctive immunosuppressants, in accord with the dependence of the tumors on antigen-induced signaling. Together, our results provide direct evidence that antigenic stimulation can participate in lymphomagenesis, point to a potential role for the constitutive BCR as well, and sustain the view that the constitutive BCR gives rise to signals different from those elicited by antigen. The mouse models described here should be useful in exploring further the pathogenesis of lymphomas, and in preclinical testing of new therapeutics.

It has long been suspected that the malignant proliferation of B lymphocytes known as lymphomas might represent a perversion of how the cells normally respond to antigen. In particular, the molecular receptor on the surface of the cells that signals the presence of antigen might be abnormally active in lymphomas. We have tested this hypothesis by engineering the genome of mice so that virtually all of the B cells are commandeered by a single version of the surface receptor, then stimulated that receptor with the molecule it is designed to recognize. Our results indicate that both the unstimulated and stimulated states of the receptor can cooperate with an oncogene known as MYC in the genesis of lymphomas. But the two states of the receptor give rise to different forms of lymphoma. In particular, the stimulated form cooperates with MYC to produce a disease that closely resembles Burkitt lymphoma. These results illuminate the mechanisms that are responsible for lymphomas and could inform the development of new strategies to treat the disease.

A series of genetically engineered mice were used to substantiate a long-standing speculation that chronic immune-stimulus may be involved in the genesis of certain lymphomas, illuminating the pathogenesis of B cell lymphomas and suggesting new strategies to treat several forms of this malignancy, including Burkitt lymphoma.

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.

Bone remodeling: Multiple cellular interactions required for coupling of bone formation and resorption

The dynamic nature of the skeleton is achieved by a process called "remodeling" which involves the co-ordinated actions of osteoclasts, osteoblasts, osteocytes within the bone matrix and osteoblast-derived lining cells that cover the surface of bone. Remodeling commences with signals that initiate osteoclast formation followed by osteoclast-mediated bone resorption, a reversal period, and then a long period of bone matrix formation mediated by osteoblasts, followed by mineralisation of the matrix. This review will discuss each of these steps with particular emphasis on the communication pathways between each cell type involved and the roles of ephrins, sclerostin, RANKL and PTHrP.

Pyridyl and thiazolyl bisamide CSF-1R inhibitors for the treatment of cancer

The bisamide class of kinase inhibitors was identified as being active against CSF-1R. The synthesis and SAR of pyridyl and thiazolyl bisamides are reported, along with the pharmacokinetic properties and in vivo activity of selected examples.

Colony-stimulating factors in inflammation and autoimmunity

Although they were originally defined as haematopoietic-cell growth factors, colony-stimulating factors (CSFs) have been shown to have additional functions by acting directly on mature myeloid cells. Recent data from animal models indicate that the depletion of CSFs has therapeutic benefit in many inflammatory and/or autoimmune conditions and as a result, early-phase clinical trials targeting granulocyte/macrophage colony-stimulating factor and macrophage colony-stimulating factor have now commenced. The distinct biological features of CSFs offer opportunities for specific targeting, but with some associated risks. Here, I describe these biological features, discuss the probable specific outcomes of targeting CSFs in vivo and highlight outstanding questions that need to be addressed.

B-cell lymphoma 6 and the molecular pathogenesis of diffuse large B-cell lymphoma

PURPOSE OF REVIEW

The B-cell lymphoma 6 transcriptional repressor is the most commonly involved oncogene in B-cell lymphomas. Sustained expression of B-cell lymphoma 6 causes malignant transformation of germinal center B cells. Understanding the mechanism of action of B-cell lymphoma 6 is crucial for the study of how aberrant transcriptional programming leads to lymphomagenesis and development of targeted antilymphoma therapy.

RECENT FINDINGS

Identification of B-cell lymphoma 6 target genes indicates a critical role for B-cell lymphoma 6 in facilitating a state of physiological genomic instability required for germinal center B cells to undergo affinity maturation, and suggests its contribution to several additional cellular functions. The discovery of several layers of counterregulatory mechanisms reveals how B cells can control and fine-tune the potentially lymphomagenic actions of B-cell lymphoma 6. From the biochemical standpoint, B-cell lymphoma 6 can regulate distinct biological pathways through different cofactors. This observation explains how the biological actions of B-cell lymphoma 6 can be physiologically controlled through separate mechanisms and affords the means for improved therapeutic targeting. The fact that patients with B-cell lymphoma 6-dependent lymphoma can be identified on the basis of gene signatures suggests that therapeutic trials of B-cell lymphoma 6 inhibitors could be personalized to these individuals.

SUMMARY

B-cell lymphoma 6 plays a fundamental role in lymphomagenesis and is an excellent therapeutic target for development of improved antilymphoma therapeutic regimens.

Effects of the cFMS kinase inhibitor 5-(3-methoxy-4-((4-methoxybenzyl)oxy)benzyl)pyrimidine-2,4-diamine (GW2580) in normal and arthritic rats

The cFMS (cellular homolog of the V-FMS oncogene product of the Susan McDonough strain of feline sarcoma virus) (Proc Natl Acad Sci U S A 83:3331-3335, 1986) kinase inhibitor 5-(3-methoxy-4-((4-methoxybenzyl)oxy)benzyl)pyrimidine-2,4-diamine (GW2580) inhibits colony-stimulating factor (CSF)-1-induced monocyte growth and bone degradation in vitro and inhibits CSF-1 signaling through cFMS kinase in 4-day models in mice (Proc Natl Acad Sci U S A 102:16078, 2005). In the present study, the kinase selectivity of GW2580 was further characterized, and the effects of chronic treatment were evaluated in normal and arthritic rats. GW2580 selectively inhibited cFMS kinase compared with 186 other kinases in vitro and completely inhibited CSF-1-induced growth of rat monocytes, with an IC(50) value of 0.2 microM. GW2580 dosed orally at 25 and 75 mg/kg 1 and 5 h before the injection of lipopolysaccharide inhibited tumor necrosis factor-alpha production by 60 to 85%, indicating a duration of action of at least 5 h. In a 21-day adjuvant arthritis model, GW2580 dosed twice a day (b.i.d.) from days 0 to 21, 7 to 21, or 14 to 21 inhibited joint connective tissue and bone destruction as assessed by radiology, histology and bone mineral content measurements. In contrast, GW2580 did not affect ankle swelling in the adjuvant model nor did it affect ankle swelling in a model where local arthritis is reactivated by peptidoglycan polysaccharide polymers. GW2580 administered to normal rats for 21 days showed no effects on tissue histology and only modest changes in serum clinical chemistry and blood hematology. In conclusion, GW2580 was effective in preserving joint integrity in the adjuvant arthritis model while showing minimal effects in normal rats.

Monocyte-mediated defense against microbial pathogens

Circulating blood monocytes supply peripheral tissues with macrophage and dendritic cell (DC) precursors and, in the setting of infection, also contribute directly to immune defense against microbial pathogens. In humans and mice, monocytes are divided into two major subsets that either specifically traffic into inflamed tissues or, in the absence of overt inflammation, constitutively maintain tissue macrophage/DC populations. Inflammatory monocytes respond rapidly to microbial stimuli by secreting cytokines and antimicrobial factors, express the CCR2 chemokine receptor, and traffic to sites of microbial infection in response to monocyte chemoattractant protein (MCP)-1 (CCL2) secretion. In murine models, CCR2-mediated monocyte recruitment is essential for defense against Listeria monocytogenes, Mycobacterium tuberculosis, Toxoplasma gondii, and Cryptococcus neoformans infection, implicating inflammatory monocytes in defense against bacterial, protozoal, and fungal pathogens. Recent studies indicate that inflammatory monocyte recruitment to sites of infection is complex, involving CCR2-mediated emigration of monocytes from the bone marrow into the bloodstream, followed by trafficking into infected tissues. The in vivo mechanisms that promote chemokine secretion, monocyte differentiation and trafficking, and finally monocyte-mediated microbial killing remain active and important areas of investigation.

T-cell-mediated and antigen-dependent differentiation of human monocyte into different dendritic cell subsets: a feedback control of Th1/Th2 responses

It is well established that human monocytes differentiate into dendritic cells (DCs) when cultured with certain cytokine cocktails, such as granulocyte-macrophage colony-stimulating factor and interleukin-4. Conversely, it is not completely established which cell population synthesizes the cytokines required for monocyte differentiation and how their secretion is regulated. We show that on specific activation T cells induce the differentiation into DCs of antigen-presenting and bystander monocytes. Monocytes exposed to cytokines released by Th1 and Th0 lymphocytes differentiate into DCs with a reduced antigen uptake and antigen presentation capacity. Moreover, these DCs show a limited capacity to induce Th1 polarization of naive T cells but are capable of priming interleukin-10-secreting T cells. Conversely, DCs derived from monocytes sensing cytokines released by Th2 lymphocytes are antigen-presenting-cell (APC) endowed with a marked Th1 polarization capacity. Monocytes are corecruited with lymphocytes in chronic inflammation sites; thus our results suggest that functionally different DCs can be generated in environments characterized by the prevalent release of Th1-, Th0-, or Th2-associated cytokines. Because the APC capacities of these DCs have opposite functional consequences, a contribution in the regulation of the ongoing immune response by monocyte-derived inflammatory DCs is envisaged.

Id2 intrinsically regulates lymphoid and erythroid development via interaction with different target proteins

Inhibitors of DNA binding (Id) family members are key regulators of cellular differentiation and proliferation. These activities are related to the ability of Id proteins to antagonize E proteins and other transcription factors. As negative regulators of E proteins, Id proteins have been implicated in lymphocyte development. Overexpression of Id1, Id2, or Id3 has similar effects on lymphocyte development. However, which Id protein plays a physiologic role during lymphocyte development is not clear. By analyzing Id2 knock-out mice and retroviral transduced hematopoietic progenitors, we demonstrated that Id2 is an intrinsic negative regulator of B-cell development. Hematopoietic progenitor cells overexpressing Id2 did not reconstitute B-cell development in vivo, which resembled the phenotype of E2A null mice. The B-cell population in bone marrow was significantly expanded in Id2 knock-out mice compared with their wild-type littermates. Knock-down of Id2 by shRNA in hematopoietic progenitor cells promoted B-cell differentiation and induced the expression of B-cell lineage-specific genes. These data identified Id2 as a physiologically relevant regulator of E2A during B lymphopoiesis. Furthermore, we identified a novel Id2 function in erythroid development. Overexpression of Id2 enhanced erythroid development, and decreased level of Id2 impaired normal erythroid development. Id2 regulation of erythroid development is mediated via interacting with transcription factor PU.1 and modulating PU.1 and GATA-1 activities. We conclude that Id2 regulates lymphoid and erythroid development via interaction with different target proteins.

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.

Dendritic cells in chronic obstructive pulmonary disease: new players in an old game

Dendritic cells (DCs) are professional antigen-presenting cells responsible for immune homeostasis. In the lung's responses to tissue damage or infection, they initiate and orchestrate innate and adaptive immunity. There are immature and mature states and at least three phenotypic and functional subsets. DCs circulate in the blood and localize to mucosal surfaces in immature form where they act as sentinels, sampling constituents of the external environment that breach the epithelium. With internalization of antigen, they are activated, mature, and migrate to draining lymph nodes to induce the proliferation and regulate the balance of Th1/Th2 T cells or to induce a state of tolerance, the last dependent on maturation status, extent of cell surface costimulatory molecule expression, and cytokine release. Cigarette smoke has modulatory effects varying with species, dose, the location examined within the lung, and the marker or technique used to identify DCs. Healthy smokers (and smokers with asthma) have reduced numbers of large airway mature DCs. In chronic obstructive pulmonary disease, the number of immature DCs is increased in small airways, whereas in smokers with chronic obstructive pulmonary disease, the total number of DCs appears to be reduced in large airways. We hypothesize that the long-term effects of cigarette smoke include reduction of DC maturation and function, changes that favor repeated infection, increased exacerbation frequency, and the altered (CD8(+) T-cell predominant) pattern of inflammation associated with this progressive chronic disease.

Critical roles for macrophages in islet angiogenesis and maintenance during pancreatic degeneration

OBJECTIVE

Chronic pancreatitis, characterized by pancreatic exocrine tissue destruction with initial maintenance of islets, eventually leads to insulin-dependent diabetes in most patients. Mice deficient for the transcription factors E2F1 and E2F2 suffer from a chronic pancreatitis-like syndrome and become diabetic. Surprisingly, onset of diabetes can be prevented through bone marrow transplantation. The goal of the described studies was to determine the hematopoietic cell type responsible for maintaining islets and the associated mechanism of this protection.

RESEARCH DESIGN AND METHODS

Mouse models of acute and chronic pancreatitis, together with mice genetically deficient for macrophage production, were used to determine roles for macrophages in islet angiogenesis and maintenance.

RESULTS

We demonstrate that macrophages are essential for preventing endocrine cell loss and diabetes. Macrophages expressing matrix metalloproteinase-9 migrate to the deteriorating pancreas. E2f1/E2f2 mutant mice transplanted with wild-type, but not macrophage-deficient colony stimulating factor 1 receptor mutant (Csf1r(-/-)), bone marrow exhibit increased angiogenesis and proliferation within islets, coinciding with increased islet mass. A similar macrophage dependency for islet and islet vasculature maintenance is observed during caerulein-induced pancreatitis.

CONCLUSIONS

These findings demonstrate that macrophages promote islet angiogenesis and protect against islet loss during exocrine degeneration, could explain why most patients with chronic pancreatitis develop diabetes, and suggest an avenue for preventing pancreatitis-associated diabetes.

Discovery of a cytokine and its receptor by functional screening of the extracellular proteome

To understand the system of secreted proteins and receptors involved in cell-cell signaling, we produced a comprehensive set of recombinant secreted proteins and the extracellular domains of transmembrane proteins, which constitute most of the protein components of the extracellular space. Each protein was tested in a suite of assays that measured metabolic, growth, or transcriptional responses in diverse cell types. The pattern of responses across assays was analyzed for the degree of functional selectivity of each protein. One of the highly selective proteins was a previously undescribed ligand, designated interleukin-34 (IL-34), which stimulates monocyte viability but does not affect responses in a wide spectrum of other assays. In a separate functional screen, we used a collection of extracellular domains of transmembrane proteins to discover the receptor for IL-34, which was a known cytokine receptor, colony-stimulating factor 1 (also called macrophage colony-stimulating factor) receptor. This systematic approach is thus useful for discovering new ligands and receptors and assessing the functional selectivity of extracellular regulatory proteins.

The receptor tyrosine kinase Flt3 is required for dendritic cell development in peripheral lymphoid tissues

Dendritic cell (DC) development begins in the bone marrow but is not completed until after immature progenitors reach their sites of residence in lymphoid organs. The hematopoietic growth factors regulating these processes are poorly understood. Here we examine the effects of FMS-like tyrosine kinase 3 (Flt3) signaling on macrophage DC progenitors (MDP) in the bone marrow and on peripheral DCs. We find that the MDP compartment is responsive to super–physiologic levels of Flt3 ligand (Flt3L) but is not dependent on Flt3 for its homeostatic maintenance in vivo. In contrast, Flt3 is essential in regulation of homeostatic DC development in the spleen where it is required to maintain normal numbers of DCs by controlling their division in the periphery.

The diverse functions of Src family kinases in macrophages

Macrophages are key components of the innate immune response. These cells possess a diverse repertoire of receptors that allow them to respond to a host of external stimuli including cytokines, chemokines, and pathogen-associated molecules. Signals resulting from these stimuli activate a number of macrophage functional responses such as adhesion, migration, phagocytosis, proliferation, survival, cytokine release and production of reactive oxygen and nitrogen species. The cytoplasmic tyrosine kinase Src and its family members (SFKs) have been implicated in many intracellular signaling pathways in macrophages, initiated by a diverse set of receptors ranging from integrins to Toll-like receptors. However, it has been difficult to implicate any given member of the family in any specific pathway. SFKs appear to have overlapping and complementary functions in many pathways. Perhaps the function of these enzymes is to modulate the overall intracellular signaling network in macrophages, rather than operating as exclusive signaling switches for defined pathways. In general, SFKs may function more like rheostats, influencing the amplitude of many pathways.

Colony-stimulating factor-1 transfection of myoblasts improves the repair of failing myocardium following autologous myoblast transplantation

AIMS

Skeletal myoblasts are used in repair of ischaemic myocardium. However, a large fraction of grafted myoblasts degenerate upon engraftment. Colony-stimulating factor-1 (CSF-1) accelerates myoblast proliferation and angiogenesis. We hypothesized that CSF-1 overexpression improves myoblast survival and cardiac function in ischaemia-induced heart failure.

METHODS AND RESULTS

Three weeks following myocardial infarction, rats developed heart failure and received intramyocardial injections of mouse CSF-1-transfected or untransfected primary autologous rat myoblasts, recombinant human CSF-1, mouse CSF-1 expressing plasmids, or culture medium. Tissue gene and protein expression was measured by quantitative RT-PCR (reverse transcription-polymerase chain reaction) and western blotting. Fluorescence imaging and immunocytochemistry were used to analyse myoblasts, endothelial cells, macrophages, and infarct wall thickening. Electrocardiograms were recorded online using a telemetry system. Left ventricular function was assessed by echocardiography over time, and improved significantly only in the CSF-1-overexpressing myoblast group. CSF-1-overexpression enhanced myoblast numbers and was associated with an increased infarct wall thickness, enhanced angiogenesis, increased macrophage recruitment and upregulated matrix metalloproteases (MMP)-2 and -12 in the zone bordering the infarction. Transplantation of CSF-1-overexpressing myoblasts did not result in major arrhythmias.

CONCLUSION

Autologous intramyocardial transplantation of CSF-1 overexpressing myoblasts might be a novel strategy in the treatment of ischaemia-induced heart failure.

BCL6 represses NFkappaB activity in diffuse large B-cell lymphomas

BCL6 is a transcriptional repressor whose deregulated expression plays a key role in diffuse large B-cell lymphomas (DLBCLs). BCL6 expression characterizes one of the two main subtypes (GC type) of DLBCL, while the other (ABC type) is recognized by increased NFkappaB activation. The mechanistic basis of this distinction remains unclear and the BCL6 targets have been only partially explored. Here we describe how NFkappaB activity is increased after BCL6 silencing by shRNA in DLBCL cells, leading us to propose that BCL6 represses NFkappaB activity. We also demonstrate that this repression is brought about by a mechanism involving protein-protein interaction between BCL6 and NFkappaB members, both in vitro and in vivo. Analysis of a series of DLBCLs shows a negative correlation between the expression of NFkappaB target genes and BCL6. This combined approach using silenced cells and a series of human DLBCL samples leads us to a better understanding of the role of BCL6 as an NFkappaB regulator in B-cells.

PU.1 and C/EBPalpha/beta convert fibroblasts into macrophage-like cells

Earlier work has shown that the transcription factor C/EBPalpha induced a transdifferentiation of committed lymphoid precursors into macrophages in a process requiring endogenous PU.1. Here we have examined the effects of PU.1 and C/EBPalpha on fibroblasts, a cell type distantly related to blood cells and akin to myoblasts, adipocytes, osteoblasts, and chondroblasts. The combination of the two factors, as well as PU.1 and C/EBPbeta, induced the up-regulation of macrophage/hematopoietic cell surface markers in a large proportion of NIH 3T3 cells. They also up-regulated these markers in mouse embryo- and adult skin-derived fibroblasts. Based on cell morphology, activation of macrophage-associated genes, and extinction of fibroblast-associated genes, cell lines containing an attenuated form of PU.1 and C/EBPalpha acquired a macrophage-like phenotype. The lines also display macrophage functions: They phagocytose small particles and bacteria, mount a partial inflammatory response, and exhibit strict CSF-1 dependence for growth. The myeloid conversion is primarily induced by PU.1, with C/EBPalpha acting as a modulator of macrophage-specific gene expression. Our data suggest that it might become possible to induce the transdifferentiation of skin-derived fibroblasts into cell types desirable for tissue regeneration.

Serum level of macrophage colony-stimulating factor is increased in prostate cancer patients with bone metastasis

Recent evaluation of human prostate tissues has shown predominantly high expression of the macrophage colony-stimulating factor receptor in prostatic intra-epithelial neoplasia or prostate cancer. However, the expression of its ligand, the macrophage colony-stimulating factor (M-CSF), and the biological role of this signaling in prostate cancer has not been analyzed. In this research we determined the relationship of serum M-CSF level to clinical parameters of prostate cancer progression. We measured the serum level of M-CSF in 170 patients with histologically confirmed prostatic adenocarcinoma and in 54 patients in whom prostate cancer was not detected. We also investigated the M-CSF expression in prostate cancer tissues by immunohistochemistry. The serum levels of M-CSF in bone metastatic prostate cancer patients was significantly higher than those in non-metastatic patients, while M-CSF did not differ with regards to histological grade, Gleason score or local tumor progression. M-CSF expression was detected in prostate cancer cells themselves by immunohistochemistry. These results suggest that M-CSF may have a functional role in prostate cancer progression.

Blood monocytes: distinct subsets, how they relate to dendritic cells, and their possible roles in the regulation of T-cell responses

Monocytes can have important effects on the polarization and expansion of lymphocytes and may contribute to shaping primary and memory T-cell responses in humans and mice. However, their precise contribution in terms of cellular subsets and the molecular mechanisms involved remains to be determined. Mouse monocytes originate from a bone marrow progenitor, the macrophage and DC precursor (MDP), which also gives rise to conventional dendritic cells through a separate differentiation pathway. Mouse monocytes may be grouped in different functional subsets. The CD115(+) Gr1(+) 'inflammatory' monocyte subset can give rise not only to immunostimulatory 'TipDCs' in infected mice but also to immunosuppressive 'myeloid-derived suppressor cells' in tumor-bearing mice. CD115(+) Gr1(+) monocytes can also contribute to the renewal of several resident subsets of macrophages and DCs, such as microglia and Langerhans cells, in inflammatory conditions. The CD115(+) Gr1(-) 'resident' monocyte subset patrols blood vessels in the steady state and extravasates during infection with Listeria monocytogenes or in the healing myocardium. CD115(+) Gr1(-) monocytes are responsible for an early and transient inflammatory burst during Lm infection, which may play a role in the recruitment of other effector cells and subsequently differentiate toward 'M2'-like macrophages that may be involved in wound healing. More research will no doubt confirm the existence of more functional subsets, the developmental relationship between mouse subsets as well as the correspondence between mouse subsets and human subsets of monocytes. We will discuss here the potential roles of monocytes in the immune response, the existence of functional subsets and their relationship with other myeloid cells, including dendritic cells.

The function of heme-regulated eIF2alpha kinase in murine iron homeostasis and macrophage maturation

Heme-regulated eIF2alpha kinase (HRI) plays an essential protective role in anemias of iron deficiency, erythroid protoporphyria, and beta-thalassemia. In this study, we report that HRI protein is present in murine macrophages, albeit at a lower level than in erythroid precursors. Hri-/- mice exhibited impaired macrophage maturation and a weaker antiinflammatory response with reduced cytokine production upon LPS challenge. The level of production of hepcidin, an important player in the pathogenesis of the anemia of inflammation, was significantly decreased in Hri-/- mice, accompanied by decreased splenic macrophage iron content and increased serum iron content. Hepcidin expression was also significantly lower, with a concomitant increase in serum iron in Hri-/- mice upon LPS treatment. We also demonstrated an impairment of erythrophagocytosis by Hri-/- macrophages both in vitro and in vivo under chronic hemolytic anemia, providing evidence for the role of HRI in recycling iron from senescent red blood cells. This work demonstrates that HRI deficiency attenuates hepcidin expression and iron homeostasis in mice, indicating a potential role for HRI in the anemia of inflammation.

The function of heme-regulated eIF2alpha kinase in murine iron homeostasis and macrophage maturation

Heme-regulated eIF2alpha kinase (HRI) plays an essential protective role in anemias of iron deficiency, erythroid protoporphyria, and beta-thalassemia. In this study, we report that HRI protein is present in murine macrophages, albeit at a lower level than in erythroid precursors. Hri-/- mice exhibited impaired macrophage maturation and a weaker antiinflammatory response with reduced cytokine production upon LPS challenge. The level of production of hepcidin, an important player in the pathogenesis of the anemia of inflammation, was significantly decreased in Hri-/- mice, accompanied by decreased splenic macrophage iron content and increased serum iron content. Hepcidin expression was also significantly lower, with a concomitant increase in serum iron in Hri-/- mice upon LPS treatment. We also demonstrated an impairment of erythrophagocytosis by Hri-/- macrophages both in vitro and in vivo under chronic hemolytic anemia, providing evidence for the role of HRI in recycling iron from senescent red blood cells. This work demonstrates that HRI deficiency attenuates hepcidin expression and iron homeostasis in mice, indicating a potential role for HRI in the anemia of inflammation.

New strategies for the treatment of metastatic bone disease

The introduction of bisphosphonates represents an important advance in the care of patients with metastatic bone disease. Nonetheless, we remain unable to prevent metastatic bone destruction. This review will discuss several novel therapies, including inhibitors of receptor activator of nuclear factor-kappabeta, c-Src, mammalian target of rapamycin, cathepsin K, and alpha(5)beta(3) integrins, which could improve our control over this devastating complication.

Building bone to reverse osteoporosis and repair fractures

An important, unfilled clinical need is the development of new approaches to improve fracture healing and to treat osteoporosis by increasing bone mass. Recombinant forms of bone morphogenetic protein 2 (BMP2) and BMP7 are FDA approved to promote spinal fusion and fracture healing, respectively, and the first FDA-approved anabolic drug for osteoporosis, parathyroid hormone, increases bone mass when administered intermittently but can only be given to patients in the US for two years. As we discuss here, the tremendous explosion over the last two decades in our fundamental understanding of the mechanisms of bone remodeling has led to the prospect of mechanism-based anabolic therapies for bone disorders.

Monocyte-derived dendritic cells in innate and adaptive immunity

Monocytes have been classically considered essential elements in relation with innate immune responses against pathogens, and inflammatory processes caused by external aggressions, infection and autoimmune disease. However, although their potential to differentiate into dendritic cells (DCs) was discovered 14 years ago, their functional relevance with regard to adaptive immune responses has only been uncovered very recently. Studies performed over the last years have revealed that monocyte-derived DCs play an important role in innate and adaptive immunity, due to their microbicidal potential, capacity to stimulate CD4(+) and CD8(+) T-cell responses and ability to regulate Immunoglobulin production by B cells. In addition, monocyte-derived DCs not only constitute a subset of DCs formed at inflammatory foci, as previously thought, but also comprise different subsets of DCs located in antigen capture areas, such as the skin and the intestinal, respiratory and reproductive tracts.

The orally-active and selective c-Fms tyrosine kinase inhibitor Ki20227 inhibits disease progression in a collagen-induced arthritis mouse model

Macrophage colony-stimulating factor (M-CSF) is important in the development of macrophages and osteoclasts. Previous studies have also shown that CD11b(+) myeloblasts and osteoclasts play key roles during inflammation and bone destruction in arthritic lesions. In this study, we investigated whether N-{4-[(6,7-dimethoxy-4-quinolyl)oxy]-2-methoxyphenyl}-N'-[1-(1,3-thiazole-2-yl)ethyl] urea (Ki20227), an inhibitor of the M-CSF receptor (c-Fms), suppressed disease progression in a type II collagen (CII)-induced arthritis (CIA) mouse model. We found that Ki20227 inhibited M-CSF-dependent reactions, such as lipopolysaccharide-induced tumor necrosis factor-alpha production, which were enhanced by M-CSF in vitro. Oral administration of Ki20227 in vivo prevented inflammatory cell infiltration and bone destruction, and consequently suppressed disease progression. In addition, the number of CD11b(+), Gr-1(+), and Ly-6G(+) cells in the spleen decreased in the Ki20227-treated mice, and the CII-induced cytokine production in splenocytes isolated from the Ki20227-treated arthritic mice was also reduced. These observations indicate that Ki20227 might exert its therapeutic effects in the CIA mouse model by suppressing the M-CSF-dependent accumulation of both inflammatory and osteoclast cells, as well as by inhibiting inflammatory cytokine production. Hence, inhibitors of the c-Fms tyrosine kinase might act as anti-inflammatory or anti-osteolytic agents against arthritis.

Understanding the pathology and mechanisms of type I diabetic bone loss

Type I (T1) diabetes, also called insulin dependent diabetes mellitus (IDDM), is characterized by little or no insulin production and hyperglycemia. One of the less well known complications of T1-diabetes is bone loss which occurs in humans and animal models. This complication is receiving increased attention because T1-diabetics are living longer due to better therapeutics, and are faced with their existing health concerns being compounded by complications associated with aging, such as osteoporosis. Both male and female, endochondrial and intra-membranous, and axial and appendicular bones are susceptible to T1-diabetic bone loss. Exact mechanisms accounting for T1-diabetic bone loss are not known. Existing data indicate that the bone defect in T1-diabetes is anabolic rather than catabolic, suggesting that anabolic therapeutics may be more effective in preventing bone loss. Potential contributors to T1-diabetic suppression of bone formation are discussed in this review and include: increased marrow adiposity, hyperlipidemia, reduced insulin signaling, hyperglycemia, inflammation, altered adipokine and endocrine factors, increased cell death, and altered metabolism. Differences between T1-diabetic- and age-associated bone loss underlie the importance of condition specific, individualized treatments for osteoporosis. Optimizing therapies that prevent bone loss or restore bone density will allow T1-diabetic patients to live longer with strong healthy bones.

Systems biology of transcription control in macrophages

The study of the mammalian immune system offers many advantages to systems biologists. The cellular components of the mammalian immune system are experimentally tractable; they can be isolated or differentiated from in vivo and ex vivo sources and have an essential role in health and disease. For these reasons, the major effectors cells of the innate immune system, macrophages, have been a particular focus in international genome and transcriptome consortia. Genome-scale analysis of the transcriptome, and transcription initiation has enabled the construction of predictive models of transcription control in macrophages that identify the points of control (the major nodes of networks) and the ways in which they interact.

Expression and synthesis of bone morphogenetic proteins by osteoclasts: a possible path to anabolic bone remodeling

Skeletal remodeling is a finely orchestrated process coupling bone formation to bone resorption. The dynamics of coupling is regulated by the microenvironment at the bone remodeling site, which in turn is influenced by the intercellular communication between cells like osteoclasts and osteoblasts. Understanding the dynamics of coupling is important in devising new therapeutic approaches to the treatment of skeletal diseases characterized by disturbances in the bone remodeling process. In this study, we report the localization of bone morphogenetic proteins (BMPs) in osteoclasts generated from primary cocultures of bone marrow cells from mouse femur and tibia with mouse calvarial osteoblasts, using immunocytochemistry and in situ hybridization. Positive staining was seen in osteoclasts for BMP-2, -4, -6, and -7. Real-time PCR was used to quantitatively confirm the expression of transcripts for BMP-2, BMP-4, and BMP-6 mRNA in murine osteoclasts. Finally, the presence of BMP-2, -4, -6, and-7 proteins was confirmed in osteoclast lysates by Western blotting. Overall, our data suggest a possible direct role for osteoclasts in promoting bone formation via expression and synthesis of BMPs, which then would play an important role in promoting the recruitment, proliferation, and differentiation of osteoblasts at bone resorption sites.

DNA damage, apoptosis and langerhans cells--Activators of UV-induced immune tolerance

Solar UVR is highly mutagenic but is only partially absorbed by the outer stratum corneum of the epidermis. UVR can penetrate into the deeper layers of the epidermis, depending on melanin content, where it induces DNA damage and apoptosis in epidermal cells, including those in the germinative basal layer. The cellular decision to initiate either cellular repair or undergo apoptosis has evolved to balance the acute need to maintain skin barrier function with the long-term risk of retaining precancerous cells. Langerhans cells (LCs) are positioned suprabasally, where they may sense UV damage directly, or indirectly through recognition of apoptotic vesicles and soluble mediators derived from surrounding keratinocytes. Apoptotic vesicles will contain UV-induced altered proteins that may be presented to the immune system as foreign. The observation that UVR induces immune tolerance to skin-associated antigens suggests that this photodamage response has evolved to preserve the skin barrier by protecting it from autoimmune attack. LC involvement in this process is not clear and controversial. We will highlight some basic concepts of photobiology and review recent advances pertaining to UV-induced DNA damage, apoptosis regulation, novel immunomodulatory mechanisms and the role of LCs in generating antigen-specific regulatory T cells.

Molecular genetic studies of gene identification for osteoporosis

This review comprehensively summarizes the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of September 2007. It is intended to constitute a sequential update of our previously published reviews covering the available data up to the end of 2004. Evidence from candidate gene-association studies, genome-wide linkage and association studies, as well as functional genomic studies (including gene-expression microarray and proteomics) on osteogenesis and osteoporosis, are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. The major results of all studies are tabulated for comparison and ease of reference. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.