Tandem linkage of human CSF-1 receptor (c-fms) and PDGF receptor genes

Molecular Pathogenesis of Gastrointestinal Stromal Tumor: A Paradigm for Personalized Medicine

Over the past three to four decades, the molecular pathogenesis of gastrointestinal stromal tumors (GISTs) has been elucidated in great detail. In this review, we discuss the biological genesis of GISTs, identification of the various primary activating driver mutations (focusing on KIT and PDGFRA), oncogene addiction and targeted therapies with imatinib and other tyrosine kinase inhibitors, and the subsequent characterization of the various mechanisms of drug resistance. We illustrate how GIST has become a quintessential paradigm for personalized medicine. Expected final online publication date for the Annual Review of Pathology: Mechanisms of Disease, Volume 17 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The equine mononuclear phagocyte system: The relevance of the horse as a model for understanding human innate immunity

The mononuclear phagocyte system (MPS) is a family of cells of related function that includes bone marrow progenitors, blood monocytes and resident tissue macrophages. Macrophages are effector cells in both innate and acquired immunity. They are a major resident cell population in every organ and their numbers increase in response to proinflammatory stimuli. Their function is highly regulated by a wide range of agonists, including lymphokines, cytokines and products of microorganisms. Macrophage biology has been studied most extensively in mice, yet direct comparisons of rodent and human macrophages have revealed many functional differences. In this review, we provide an overview of the equine MPS, describing the variation in the function and phenotype of macrophages depending on their location and the similarities and differences between the rodent, human and equine immune response. We discuss the use of the horse as a large animal model in which to study macrophage biology and pathological processes shared with humans. Finally, following the recent update to the horse genome, facilitating further comparative analysis of regulated gene expression between the species, we highlight the importance of future transcriptomic macrophage studies in the horse, the findings of which may also be applicable to human as well as veterinary research.

Gastrointestinal stromal tumors (GISTs) and second malignancies: A novel "sentinel tumor"? A monoinstitutional, STROBE-compliant observational analysis

Several evidences showed that patients with gastrointestinal stromal tumors (GISTs) develop additional malignancies. However, thorough incidence of second tumors remains uncertain as the possibility of a common molecular pathogenesis.A retrospective series of 128 patients with histologically proven GIST treated at our institution was evaluated. Molecular analysis of KIT and PDGFR-α genes was performed in all patients. Following the involvement of KRAS mutation in many tumors' pathogenesis, analysis of KRAS was performed in patients with also second neoplasms.Forty-six out of 128 GIST patients (35.9%) had a second neoplasm. Most second tumors (52%) raised from gastrointestinal tract and 19.6% from genitourinary tract. Benign neoplasms were also included (21.7%). Molecular analysis was available for 29/46 patients with a second tumor: wild-type GISTs (n. 5), exon 11 (n. 16), exon 13 (n. 1), exon 9 (n. 1) KIT mutations, exon 14 PDGFR-α mutation (n. 2) and exon 18 PDGFR-α mutation (n. 4). KIT exon 11 mutations were more frequent between patients who developed a second tumor (P = 0.0003). Mutational analysis of KRAS showed a wild-type sequence in all cases. In metachronous cases, the median time interval between GIST and second tumor was 21.5 months.The high frequency of second tumors suggests that an unknown common molecular mechanism might play a role, but it is not likely that KRAS is involved in this common pathogenesis. The short interval between GIST diagnosis and the onset of second neoplasms asks for a careful follow-up, particularly in the first 3 years after diagnosis.

Clinical utility of lenalidomide in the treatment of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) represent a heterogeneous group of acquired clonal hematopoietic disorders characterized by peripheral blood cytopenias, paradoxical BM hypercellularity, ineffective hematopoiesis, and increased risk of leukemic transformation. Risk stratification, using different prognostic scores and markers, is at the core of MDS management. Deletion 5q [del(5q)] MDS is a distinct class of MDS characterized by the haploinsufficiency of specific genes, microRNAs, and proteins, which has been linked to increased sensitivity to the drug lenalidomide. Phase II and III clinical trials have demonstrated the efficacy of lenalidomide in improving clinical outcomes of patients with del(5q) MDS, including reduction in red blood cell transfusion requirements and improvements in quality of life. Lenalidomide has also demonstrated some activity in non-del(5q) lower-risk MDS as well as higher-risk MDS, especially in combination with other agents. In this paper, we review the pathogenesis of del(5q) MDS, the proposed mechanisms of action of lenalidomide, the major clinical trials that documented the activity of lenalidomide in different MDS populations, potential predictors of benefit from the drug and suggested mechanisms of resistance, and the use of combination strategies to expand the clinical utility of lenalidomide in MDS.

CSF-1 receptor signaling in myeloid cells

The CSF-1 receptor (CSF-1R) is activated by the homodimeric growth factors colony-stimulating factor-1 (CSF-1) and interleukin-34 (IL-34). It plays important roles in development and in innate immunity by regulating the development of most tissue macrophages and osteoclasts, of Langerhans cells of the skin, of Paneth cells of the small intestine, and of brain microglia. It also regulates the differentiation of neural progenitor cells and controls functions of oocytes and trophoblastic cells in the female reproductive tract. Owing to this broad tissue expression pattern, it plays a central role in neoplastic, inflammatory, and neurological diseases. In this review we summarize the evolution, structure, and regulation of expression of the CSF-1R gene. We discuss the structures of CSF-1, IL-34, and the CSF-1R and the mechanism of ligand binding to and activation of the receptor. We further describe the pathways regulating macrophage survival, proliferation, differentiation, and chemotaxis downstream from the CSF-1R.

Advances in the 5q- syndrome

The 5q- syndrome is the most distinct of all the myelodysplastic syndromes with a clear genotype/phenotype relationship. The significant progress made during recent years has been based on the determination of the commonly deleted region and the demonstration of haploinsufficiency for the ribosomal gene RPS14. The functional screening of all the genes in the commonly deleted region determined that RPS14 haploinsufficiency is the probable cause of the erythroid defect in the 5q- syndrome. A mouse model of the human 5q- syndrome has now been created by chromosomal engineering involving a large-scale deletion of the Cd74-Nid67 interval (containing RPS14). A variety of lines of evidence support the model of ribosomal deficiency causing p53 activation and defective erythropoiesis, including most notably the crossing of the "5q- mice" with p53-deficient mice, thereby ameliorating the erythroid progenitor defect. Emerging evidence supports the notion that the p53 activation observed in the mouse model may also apply to the human 5q- syndrome. Other mouse modeling data suggest that haploinsufficiency of the microRNA genes miR-145 and miR-146a may contribute to the thrombocytosis seen in the 5q- syndrome. Lenalidomide has become an established therapy for the 5q- syndrome, although its precise mode of action remains uncertain.

Gain-of-function PDGFRA mutations, earlier reported in gastrointestinal stromal tumors, are common in small intestinal inflammatory fibroid polyps. A study of 60 cases

The inflammatory fibroid polyp is a rare benign lesion occurring throughout the digestive tract. It usually forms a solitary mass, characterized by a proliferation of fibrovascular tissue infiltrated by a variable number of inflammatory cells. The etiology of this lesion is unknown and conflicting histogenetic theories have been proposed. Recently, mutations in platelet-derived growth factor receptor (PDGFRA) and PDGFRA expression were reported in gastric inflammatory fibroid polyps. In this study, PDGFRA exons 12, 14, and 18 were screened for activating mutations in 60 small intestinal inflammatory fibroid polyps. In addition, the PDGFRA expression was evaluated immunohistochemically. Mutations in PDGFRA were identified in 33 of 60 (55%) cases, whereas 95% expressed PDGFRA. There were 26 deletions, three deletion-insertions, duplication, and single nucleotide substitution in exon 12, and a single nucleotide substitution and deletion in exon 18. The majority (n=23) of exon 12 deletions were 1837_1851del leading to S566_E571delinsR. However, 1835_1852delinsCGC leading to the same S566_E571delinsR, were found in two tumors. Three inflammatory fibroid polyps had 1836_1850del leading to S566_E571delinsK. A complex deletion-insertion affecting a similar region (1837_1856delinsGATTGATGATC) and leading to S566_I573delinsRIDDL was identified once. In addition, duplication and single nucleotide substitution were found 5' to the common inflammatory fibroid polyp mutational 'hot spot'. These mutations consist of 1808_1828dup leading to I557_E563dup, and 1821T>A resulting in 561V>D substitution. A 2664A>T and 2663_2674del leading to 842D>V and D842_H845del, respectively, were identified in exon 18. Similar gain-of-function PDGFRA mutations reported in gastrointestinal stromal tumors have been considered to be a driving pathogenetic force. This study showed consistent expression and common mutational activation of PDGFRA in small intestinal inflammatory fibroid polyps as in their gastric counterparts, and these lesions should be considered PDGFRA-driven benign neoplasms. We also suggest that these polyps may develop from earlier described PDGFRA-positive mesenchymal cells distributed along the villus membrane after oncogenic PDGFRA activation.

Clinical significance of oncogenic KIT and PDGFRA mutations in gastrointestinal stromal tumours

Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. Despite clinicopathological differences, GISTs share oncogenic KIT or platelet-derived growth factor-alpha (PDGFRA) mutations. Imatinib, KIT and PDGFRA inhibitor, has been successfully used in the treatment of metastatic GISTs. There are primary KIT or PDGFRA mutations diagnosed before imatinib treatment, linked to GIST pathogenesis, and secondary mutations detected during treatment, causing drug resistance. KIT exon 11 mutations are the most common. Gastric GISTs with exon 11 deletions are more aggressive than those with substitutions. KIT exon 11 mutants respond well to imatinib. Less common KIT exon 9 Ala502_Tyr503dup mutants occur predominantly in intestinal GISTs and are less sensitive to imatinib. An Asp842Val substitution in exon 18 is the most common PDGFRA mutation. GISTs with such mutation are resistant to imatinib. PDGFRA mutations are associated with gastric GISTs, epithelioid morphology and a less malignant course of disease. GISTs in neurofibromatosis 1, Carney triad and paediatric tumours generally lack KIT and PDGFRA mutations. Secondary KIT mutations affect exons 13-17. GISTs with secondary mutations in exon 13 and 14 are sensitive to sunitinib, another tyrosine kinase inhibitor. KIT and PDGFRA genotyping is important for GIST diagnosis and assessment of sensitivity to tyrosine kinase inhibitors.

Signal-response coupling mediated by the transduced colony-stimulating factor-1 receptor and its oncogenic fms variants in naive cells

Colony-stimulating factor-1 (CSF-1 or M-CSF) supports the proliferation and survival of mononuclear phagocytes by binding to a receptor (CSF-1R) encoded by the c-fms proto-oncogene. Whereas the CSF-1R kinase is normally regulated by ligand, receptors bearing 'activating mutations' act constitutively as enzymes and can transform fibroblasts and haemopoietic cells of different lineages. Introduction of human CSF-1R enables mouse NIH-3T3 cells to form colonies in agar in response to human CSF-1 and to proliferate in serum-free medium supplemented with CSF-1, albumin, transferrin and insulin. Similarly, expression of human CSF-1R in interleukin 3-dependent mouse FDC-P1 myeloid cells enables them to grow in CSF-1. High levels of CSF-1R expression in FDC-P1 cells can induce factor-independent growth which is abrogated by a 'neutralizing' monoclonal antibody to the receptor. Therefore, critical mutations in the c-fms gene or overexpression of CSF-1R in immature myeloid precursors might each contribute to leukaemia.

Role of c-kit/SCF in cause and treatment of gastrointestinal stromal tumors (GIST)

c-Kit encodes for the receptor tyrosine kinase (RTK) and belongs to type III receptor family. This includes platelet derived growth factor (PDGF) alpha and beta and macrophage colony stimulating factor (mCSF) apart from others. Their characteristic features are the presence of five immunologlobulin like domains in the extracellular region and 70-100 residues long kinase insert domain in the cytoplasmic region. The RTKs activate several signaling pathways within the cells leading to cell proliferation, differentiation, migration or metabolic changes. The Kit ligand-stem cell factor (SCF) induces a rapid and complete receptor dimerization resulting in activation by autophosphorylation of the catalytic tyrosine kinase and generation of signal transduction leading to regulation of cell growth. Various mutations in c-kit such as insertions and deletions (without affecting reading frame) and point mutations in the inhibitory juxtamembrane (JM) domain encoded by exon 11 have been reported in gastrointestinal stromal tumors (GISTs). Thus, c-kit signaling is believed to play a role in tumorigenesis. Efforts are being made to control and treat these tumors by blocking kit signaling using Imatinib with varying degrees of success. This review deals with the features of c-kit, its ligand and roles in gastrointestinal stromal tumors.

KIT and PDGFRA mutations in gastrointestinal stromal tumors (GISTs)

Mutually exclusive KIT and PDGFRA mutations are central events in GIST pathogenesis, and their understanding is becoming increasingly important, because specific treatment targeting oncogenic KIT and PDGFRA activation (especially imatinib mesylate) has become available. KIT mutations in GIST are clustered in four exons. Most common are exon 11 (juxtamembrane domain) mutations that include deletions, point mutations (affecting a few codons), and duplications (mostly in the 3' region). The latter mutations most often occur in gastric GISTs. Among gastric GISTs, tumors with deletions are more aggressive than those with point mutations; this does not seem to hold true in small intestinal GISTs. Exon 9 mutations (5-10%) usually are 2-codon 502-503 duplications, and these occur predominantly in intestinal versus gastric GISTs. Lesser imatinib sensitivity of these tumors has been noted. Kinase domain mutations are very rare; GISTs with such mutations are variably sensitive to imatinib. PDGFRA mutations usually occur in gastric GISTs, especially in the epithelioid variants; their overall frequency is approximately 30% to 40% of KIT mutation negative GISTs. Most common is exon 18 mutation leading Asp842Val at the protein level. This mutation causes imatinib resistance. Exon 12 and 14 mutations are rare. Most mutations are somatic (in tumor tissue only), but patients with familial GIST syndrome have consitutitonal KIT/PDGFRA mutations; >10 families have been reported worldwide with mutations generally similar to those in sporadic GISTs. GISTs in neurofibromatosis 1 patients, children, and Carney triad seem to lack GIST-specific KIT and PDGFRA mutations and may have a different disease mechanism. Secondary mutations usually occur in KIT kinase domains in patients after imatinib treatment resulting in resistance to this drug. Mutation genotyping is a tool in GIST diagnosis and in assessment of sensitivity to kinase inhibitors. This is a US government work. There are no restrictions on its use.

Development of goldfish macrophages in vitro

Over 100 years after the first description of macrophages by Metchnikoff, there are still questions as to the mechanisms leading to the heterogeneity of their lineage. Current views are based on the mononuclear phagocyte system (MPS) theory, where all mammalian macrophages are derived from circulating blood monocytes and ultimately from hematopoietic stem cells in the bone marrow. Our studies on the regulation of fish macrophage development, suggested that teleosts have alternate pathways of monopoiesis, which undoubtedly contribute to macrophage heterogeneity in the goldfish. Macrophage heterogeneity has been attributed to a network of positive and negative regulators of macrophage development, including soluble mediators known as colony-stimulating factors of which two (M-CSF and GM-CSF) promote formation and growth of mature macrophages. In contrast to our knowledge of CSFs and their receptors in mammals, there is no published information about fish macrophage CSFs. Since fish macrophages generate their own growth factors, it is reasonable to assume that pathways of fish macrophage development and hematopoiesis may be distinct from those of mammalian macrophages. More importantly, the presence of fish progenitor/stem cells and developing macrophages in long-term cultures, allowed us to address pathways of macrophage differentiation, which could not be addressed in mammalian macrophage culture systems. Characterization of primary kidney macrophage (PKM) cultures from goldfish hematopoietic tissues (kidney) indicated that three distinct subpopulations developed in response to endogenous macrophage growth factors. These macrophage subpopulations expressed several differentiation markers, including the hematopoietic stem cell antigen AC133, c-kit, granulin, CD63, macrosialin, c/EBPbeta, legumain, and the colony-stimulating factor receptor-1 (CSF-1R). In the goldfish, there appeared to be a stringent control between those early progenitors that self-renewed, and those that were recruited into the maturation pathways. We report that upon commitment, goldfish macrophages developed through two distinct differentiation pathways: one consistent with the "classical" pathway (MPS) of macrophage development (progenitors-->monocytes-->mature macrophages), and an "alternate" pathway (AP-macrophages) where mature macrophages appeared to rapidly develop from early progenitors in the absence of an intermediate monocyte stage. AP-macrophages represent a unique subset of spontaneously growing cells. Their self-renewal was promoted by endogenous macrophage growth factors (MGF), and effectively controlled by a novel soluble form of the CSF-1R (sCSF-1R). The discovery of sCSF-1R in the goldfish highlights the inherent complexity in the hematopoietic regulatory machinery of teleosts.

Functions and mechanisms of receptor tyrosine kinase Torso signaling: lessons from Drosophila embryonic terminal development

The Torso receptor tyrosine kinase (RTK) is required for cell fate specification in the terminal regions (head and tail) of the early Drosophila embryo. Torso contains a split tyrosine kinase domain and belongs to the type III subgroup of the RTK superfamily that also includes the platelet-derived growth factor receptors, stem cell or steel factor receptor c-Kit proto-oncoprotein, colony-stimulating factor-1 receptor, and vascular endothelial growth factor receptor. The Torso pathway has been a model system for studying RTK signal transduction. Genetic and biochemical studies of Torso signaling have provided valuable insights into the biological functions and mechanisms of RTK signaling during early Drosophila embryogenesis.

SHIP2 Is Recruited to the Cell Membrane upon Macrophage Colony-Stimulating Factor (M-CSF) Stimulation and Regulates M-CSF-Induced Signaling

The Src homology 2-containing inositol phosphatase SHIP1 functions in hemopoietic cells to limit activation events mediated by PI3K products, including Akt activation and cell survival. In contrast to the limited cellular expression of SHIP1, the related isoform SHIP2, is widely expressed in both parenchymal and hemopoietic cells. The goal of this study was to determine how SHIP2 functions to regulate M-CSF signaling. We report that 1) SHIP2 was tyrosine-phosphorylated in M-CSF-stimulated human alveolar macrophages, human THP-1 cells, murine macrophages, and the murine macrophage cell line RAW264; 2) SHIP2 associated with the M-CSF receptor after M-CSF stimulation; and 3) SHIP2 associated with the actin-binding protein filamin and localization to the cell membrane, requiring the proline-rich domain, but not on the Src homology 2 domain of SHIP2. Analyzing the function of SHIP2 in M-CSF-stimulated cells by expressing either wild-type SHIP2 or an Src homology 2 domain mutant of SHIP2 reduced Akt activation in response to M-CSF stimulation. In contrast, the expression of a catalytically deficient mutant of SHIP2 or the proline-rich domain of SHIP2 enhanced Akt activation. Similarly, the expression of wild-type SHIP2 inhibited NF-kappaB-mediated gene transcription. Finally, fetal liver-derived macrophages from SHIP2 gene knockout mice enhanced activation of Akt in response to M-CSF treatment. These data suggest a novel regulatory role for SHIP2 in M-CSF-stimulated myeloid cells.

Identification and analysis of additional copies of the platelet-derived growth factor receptor and colony stimulating factor 1 receptor genes in fugu

The receptors for the platelet-derived growth factor (PDGFRalpha and PDGFRbeta) belong to a subfamily of protein tyrosine kinase receptors that also includes kit and the colony stimulating factor-1 receptor (CSF1R). In mammals, the genes encoding PDGFRalpha and PDGFRbeta are tandemly linked to the kit and CSF1R genes, respectively. Based on the structural similarity and genomic organization of these four genes, it has been suggested that they arose from an ancestral protein tyrosine kinase receptor gene by two rounds of duplication. We have previously cloned the PDGFRbeta and CSF1R genes from the pufferfish, Fugu rubripes, and shown that they are tandemly linked like the mammalian genes [Genome Res. 6 (1996) 1185]. We have now cloned two additional members of this gene family, fPDGFRbeta2 and fCSF1R2 from the fugu and shown that these two genes are also tandemly linked. This indicates that the PDGFRbeta-CSF1R locus has been duplicated in the lineage leading to fugu. The fugu fPDGFRbeta2 and fCSF1R2 genes contain three and one extra introns, respectively, compared with other members of this family. Polymerase chain reaction cloning of a conserved region of PDGFRbeta gene from other ray-finned fishes identified two copies in the zebrafish (order Cypriniformes) and sunfish (order Tetraodontiformes). These results are discussed in the context of the proposed teleost lineage-specific whole genome duplication hypothesis.

Expression profile of protein tyrosine kinase genes in human osteoarthritis chondrocytes

OBJECTIVE

To determine the expression profile of protein kinase (PK) and protein tyrosine kinase (PTK) genes in human primary osteoarthritis (OA) chondrocytes and to compare it with that of immortalized human chondrocytes T/C 28a4 with a view to learning whether T/C 28a4 cells can be used for elucidating signal transduction pathways in human chondrocytes.

DESIGN

We used the Atlas Human cDNA Array and a method based on PCR with degenerate primers to analyse the expression profile of protein kinase genes in primary human OA chondrocytes and compared it with that of immortalized human chondrocyte cell line T/C 28a4 using RT-PCR and Western blotting.

RESULTS

A total of 21 PTK genes were identified and several of these have never been shown to be expressed in human OA chondrocytes. Comparative expression analysis of some selected kinase genes showed that the mRNA expression pattern of many protein kinase genes in OA chondrocytes was identical to that of T/C 28a4 cells. However, there were differences in the level of protein expression of selected protein kinases in these cells. For example, mRNA expression of the novel kinase HCK was detected in OA chondrocytes and in the cell lines analysed but by Western blotting HCK protein was not detected in OA chondrocytes. In these studies, we also identified a novel mutant form of the discoidin domain receptor 2 (DDR2) transcript from chondrocyte-like cell line HTB-94.

CONCLUSIONS

Our results provide novel information about protein kinase gene expression in OA chondrocytes and indicate that the transformed chondrocyte cell line T/C 28a4 may be suitable for elucidating signal transduction pathways in chondrocytes and to investigate how they regulate chondrocyte function in inflammatory and degenerative joint diseases.

Genomic organization of the human cholesterol-responsive ABC transporter ABCA7: tandem linkage with the minor histocompatibility antigen HA-1 gene

We have recently cloned a novel cholesterol-responsive ABC transporter, designated ABCA7, which is predominantly expressed in human leukocytes. Here we report the structure of the human ABCA7 gene. The ABCA7 gene spans a region of approximately 32 kb and comprises 46 exons. Its putative promoter sequence contains potential binding sites for transcription factors with roles in hematopoiesis and cholesterol metabolism. Surprisingly, sequence analysis of the ABCA7 3' gene flanking region revealed that the terminal exon of ABCA7 borders immediately on the 5' end of the coding region of the recently identified human minor histocompatibility antigen HA-1. We demonstrate that the coding regions of ABCA7 and HA-1 are physically separated by a 1.7-kb intergene region. Subsequent genomic structure analysis showed that the HA-1 gene consists of 23 exons which extend across a 16-kb genomic region. Our results provide evidence that the genes for the human minor histocompatibility antigen HA-1 and the ABC transporter ABCA7 are arranged in a head-to-tail array and that both genes localize to a common locus of approximately 48 kb size on chromosome 19p13.3.

An orthologue of the kit-related gene fms is required for development of neural crest-derived xanthophores and a subpopulation of adult melanocytes in the zebrafish, Danio rerio

Developmental mechanisms underlying traits expressed in larval and adult vertebrates remain largely unknown. Pigment patterns of fishes provide an opportunity to identify genes and cell behaviors required for postembryonic morphogenesis and differentiation. In the zebrafish, Danio rerio, pigment patterns reflect the spatial arrangements of three classes of neural crest-derived pigment cells: black melanocytes, yellow xanthophores and silver iridophores. We show that the D. rerio pigment pattern mutant panther ablates xanthophores in embryos and adults and has defects in the development of the adult pattern of melanocyte stripes. We find that panther corresponds to an orthologue of the c-fms gene, which encodes a type III receptor tyrosine kinase and is the closest known homologue of the previously identified pigment pattern gene, kit. In mouse, fms is essential for the development of macrophage and osteoclast lineages and has not been implicated in neural crest or pigment cell development. In contrast, our analyses demonstrate that fms is expressed and required by D. rerio xanthophore precursors and that fms promotes the normal patterning of melanocyte death and migration during adult stripe formation. Finally, we show that fms is required for the appearance of a late developing, kit-independent subpopulation of adult melanocytes. These findings reveal an unexpected role for fms in pigment pattern development and demonstrate that parallel neural crest-derived pigment cell populations depend on the activities of two essentially paralogous genes, kit and fms.

Mechanism of action and in vivo role of platelet-derived growth factor

Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the alpha-receptor and the beta-receptor. Activation of PDGF receptors leads to stimulation of cell growth, but also to changes in cell shape and motility; PDGF induces reorganization of the actin filament system and stimulates chemotaxis, i.e., a directed cell movement toward a gradient of PDGF. In vivo, PDGF has important roles during the embryonic development as well as during wound healing. Moreover, overactivity of PDGF has been implicated in several pathological conditions. The sis oncogene of simian sarcoma virus (SSV) is related to the B-chain of PDGF, and SSV transformation involves autocrine stimulation by a PDGF-like molecule. Similarly, overproduction of PDGF may be involved in autocrine and paracrine growth stimulation of human tumors. Overactivity of PDGF has, in addition, been implicated in nonmalignant conditions characterized by an increased cell proliferation, such as atherosclerosis and fibrotic conditions. This review discusses structural and functional properties of PDGF and PDGF receptors, the mechanism whereby PDGF exerts its cellular effects, and the role of PDGF in normal and diseased tissues.

Macrophage colony-stimulating factor promotes cell survival through Akt/protein kinase B

The signaling pathways activated by the macrophage colony-stimulating factor (M-CSF) to promote survival of monocyte and macrophage lineage cells are not well established. In an effort to elucidate these pathways, we have used two cell types responsive to M-CSF: NIH 3T3 fibroblasts genetically engineered to express human M-CSF receptors (3T3-FMS cells) and human monocytes. M-CSF treatment induced M-CSF receptor tyrosine phosphorylation and recruitment of the p85 subunit of phosphatidylinositol 3-kinase (PI3K) to these receptors. These M-CSF receptor events correlated with activation of the serine/threonine kinase Akt. To clarify that PI3K products activate Akt in response to M-CSF, NIH 3T3 fibroblasts expressing mutant human M-CSF receptors (3T3-FMS(Y809F)) that fail to activate Ras in response to M-CSF also exhibit increased Akt kinase activity in response to M-CSF challenge. Furthermore, Akt appears to be the primary regulator of survival in 3T3-FMS cells, as transfection of genes encoding dominant-negative Akt isoforms into these fibroblasts blocked M-CSF-induced survival. In normal human monocytes, M-CSF increased the levels of tyrosine-phosphorylated proteins and induced Akt activation in a PI3K-dependent manner. The PI3K inhibitor LY294002 blocked M-CSF-mediated monocyte survival, an effect that was partially restored by caspase-9 inhibitors. These data suggest that M-CSF may induce cell survival through Akt-induced suppression of caspase-9 activation.

PDGFB regulates the development of the labyrinthine layer of the mouse fetal placenta

PDGFB is a growth factor which is vital for the completion of normal prenatal development. In this study, we report the phenotypic analysis of placentas from mouse conceptuses that lack a functional PDGFB or PDGFRbeta gene. Placentas of both types of mutant exhibit changes in the labyrinthine layer, including dilated embryonic blood vessels and reduced numbers of both pericytes and trophoblasts. These changes are seen from embryonic day (E) 13.5, which coincides with the upregulation of PDGFB mRNA levels in normal placentas. By E17, modifications in shape, size, and number of the fetal blood vessels in the mutant placentas cause an abnormal ratio of the surface areas between the fetal and the maternal blood vessels in the labyrinthine layer. Our data suggest that PDGFB acts locally to contribute to the development of the labyrinthine layer of the fetal placenta and the formation of a proper nutrient-waste exchange system during fetal development. We point out that the roles of PDGFB/Rbeta signaling in the placenta may be analogous to those in the developing kidney, by controlling pericytes in the labyrinthine layer and mesangial cells in the kidney.

Isolation of yeast artificial chromosomes containing the entire transcriptional unit of the human FGF1 gene: a 720-kb contig spanning human chromosome 5q31.3-->q32

The q31-q33 region of chromosome 5 includes a number of genes encoding growth factors, growth factor receptors, and hormone/neurotransmitter receptors. The human fibroblast growth factor 1 locus (FGF1) resides in this region of chromosome 5, which is frequently lost in myelodysplastic syndromes and acute myeloid leukemia patients. Other disease loci, including the loci for limb-girdle muscular dystrophy and an autosomal dominant deafness, have been mapped on this region, but their genes have not been isolated. It was shown that the critical region lost in two patients with the 5q- syndrome resides between FGF1 and IL12B. We previously reported the construction of a yeast artificial chromosome (YAC) contig spanning 330 kb around the FGF1 gene. Here we report the isolation of additional YAC clones that extend 290 kb from the previous contig. Sequence-tagged sites developed from the outermost YAC ends were utilized in the contig cloning of two P1 clones P1Y2 and P1Y8. Together, these YAC and P1 clones span 720 kb around the FGF1 locus. With the use of fluorescence in situ hybridization, a physical map has been constructed of these P1 and GRL (glucocorticoid receptor locus) probes on metaphase and interphase chromosomes. On the basis of our work and the known orientation of GRL transcription, the determined order of these loci on chromosome 5q31.3-q32 is centromere-P1Y8-3'[FGF1]5'-P1Y2-5'[GRL]3'-telome re. Knowing the transcriptional orientation of the FGF1 gene relative to the centromere will now facilitate the directional cloning of clinically important genes that may reside in this region.

The human hepatocyte growth factor receptor gene: complete structural organization and promoter characterization

The hepatocyte growth factor (HGF) receptor is a tyrosine kinase transmembrane protein encoded by the c-met proto-oncogene. Here, we have isolated and characterized human genomic DNA clones containing the entire coding sequence of the HGF receptor. The gene spans approx. 120kb in length and consists of 21 exons interrupted by 20 introns. Two alternative splice sites corresponding to known mRNA transcripts are located at exon 10 and exon 14, respectively. Structural analysis of the 5'-regulatory region reveals that the c-met promoter lacks TATA or CAAT elements but has an extremely high G-C content and multiple Sp1 binding sites. By transfection of a series of chimeric reporter constructs containing a variable region of the c-met promoter and the coding region for chloramphenicol acetyltransferase, we have identified two positive, and one negative regulatory elements that dictate c-met transcription in renal epithelial mIMCD-3 cells at nucleotide positions -2615 to -1621, -223 to -68, and -1621 to -1093, respectively. Moreover, deletion and mutation of the multiple Sp1 sites in the c-met promoter region markedly reduced c-met promoter activity in mIMCD-3 cells, suggesting that the Sp1 sites are essential for establishing the constitutive expression of the c-met gene. These data provide fundamental information on HGF receptor gene organization, as well as on the genomic origin of different receptor isoforms, and should facilitate further studies on the transcriptional regulation of its expression.

Hematopoietic tissues, as a playground of receptor tyrosine kinases of the PDGF-receptor family

Three receptor tyrosine kinases of the PDGF receptor family (RTKP) that clustered within 1000 Kb of the mouse chromosome 5 constitute an interesting unit that are expressed in three distinct cell lineages essential for constructing hematopoietic tissues. Namely, the c-kit gene that is expressed in hematopoietic stem cells is flanked by pdgfr alpha and flk genes expressed respectively in stromal cells and vascular endothelial cells. In this article, we review our results on their expression in the embryonic hematopoietic tissues. We found that co-expression of Flkl and c-Kit was frequently detected either in vascular endothelial cells or hematopoietic cells in the early hematopoietic tissues. On the other hand, the three RTKPs are expressed in different cell lineages in the fetal liver. On the basis of this finding, we propose two modes of embryonic hematopoiesis; hematogenic angiopoiesis and hematopoiesis.

MIRs are present in coding regions of human genes

By using a weighted function and the method of enlarged similarity a search has been performed to identify mammalian interspersed repeats (MIRs) in DNA sequences from the EMBL data bank. The existence of MIRs is shown in coding regions of human genes and also in chicken and duck genomes. It is possible to conclude from the results obtained that MIRs were established in the coding regions of some genes and may have taken part in gene evolution. Furthermore, MIRs may have been amplified in vertebrate genomes before the origin of mammals.

Genomic organization of the extracellular coding region of the human FGFR4 and FLT4 genes: evolution of the genes encoding receptor tyrosine kinases with immunoglobulin-like domains

Receptor tyrosine kinases with five, seven, and three Ig-like domains in their extracellular region are grouped in subclasses IIIa, IIIb, and IIIc, respectively. Here, we describe the genomic organization of the extracellular coding region of the human FGFR4 (IIIc) and FLT4 (IIIb) genes and compare it to that of the human FGFR1(IIIc), KIT, and FMS (IIIa). The results show that while genes belonging to the same subclass have an identical exon/intron structure in their extracellular coding region-as they do in their intracellular coding region-genes of related subclasses only have a similar exon/intron structure. These results strongly support the hypothesis that the genes of the three subclasses evolved from a common ancestor by duplications involving entire genes, already in pieces. Hypotheses on the origin of introns and on the difference in the number of extracellular Ig-like domains in the three gene subclasses are discussed.

The promoter of macrophage colony-stimulating factor receptor is active in astrocytes

Macrophage colony-stimulating factor (M-CSF) is a hematopoietin whose actions are essential for growth and survival of macrophages, placental development, ramification of microglia and tumor progression. The expression of the receptor for macrophage colony-stimulating factor (c-fms) is regulated by two distinct promoters: distal and proximal. The distal promoter is active in trophoblasts during embryogenesis and the proximal promoter directs expression to the cells of myeloid lineage. Here we report the generation of transgenic mice expressing beta-galactosidase under the control of the human proximal c-fms promoter and demonstrate the promoter activity in astrocytes, cells of neurological origin that partially take over the role of the macrophages in the central nervous system. Enzymatic activity of beta-galactosidase was detected in homogenated spleen, bone marrow and brain and in the cell extracts from peritoneal macrophages of transgenic mice. Immunohistochemical staining of brain showed the presence of beta-galactosidase in astrocytes. We hypothesize that M-CSF released by astrocytes, upon stimulation by lipopolysaccharide (LPS), tumor necrosis factor alpha (TNF alpha) or interleukin-1 (IL-1), regulates the expression of its own receptor.

Conserved linkage between the puffer fish (Fugu rubripes) and human genes for platelet-derived growth factor receptor and macrophage colony-stimulating factor receptor

We have cloned and sequenced the teleost homologs of the human genes encoding platelet-derived growth factor receptor-beta (PDGFR beta) and macrophage colony-stimulating factor 1 receptor (CSFIR) from the puffer fish Fugu rubripes. The Fugu PDGFR beta and CSFIR genes each consist of 21 coding exons similar to the human CSFI gene, but are considerably smaller than their human counterparts because of the smaller introns. Furthermore, the two Fugu genes are linked tandemly in a head-to-tail array similar to their human homologs with 2.2 kb of intergenic sequence. Amino acid sequences of the Fugu and human PDGFR beta and CSFIR genes show an overall homology of 45% and 39%, respectively, with the kinase domains showing a much higher degree of conservation. Dot-matrix analysis revealed several short stretches of conserved sequences in the 3' untranslated regions of the PDGFR beta genes and the adjacent promoter regions of the CSFIR genes. These conserved sequences may have a role in the regulation of expression of either or both of these closely linked genes.

Molecular evolution of the genes encoding receptor tyrosine kinase with immunoglobulinlike domains

Receptor tyrosine kinases (RTK) with five, three, or seven immunoglobulinlike domains in their extracellular regions are classified as subclasses III, IV, and V, respectively. Conservation of the exon/intron structure of the downstream part of the human KIT, FMS, and FLT3 genes that encode RTK of subclass III together with the particular chromosomal localization of these genes suggests that RTKIII genes have evolved from a common ancestor by cis and trans duplications. To strengthen this model of evolution and to determine if it can be extended to RTKIV and V genes, we constructed a phylogenetic tree of RTKIII, IV, and V on the basis of a multiple alignment of their catalytic tyrosine kinase domain sequences and determined the exon/intron structure of PDGFRA (subclass III), FGFR4 (subclass IV), and FLT4 (subclass V) genes in their downstream part. Phylogenetic analyses with amino acid or nucleotide sequences both resulted in one most parsimonious tree. The phylogenetic trees obtained indicate that all three subclasses are well individuated and that RTKIII and RTKV are closer to each other than RTKIV. Furthermore, RTKIII and FLT4 (subclass V) genes possess the same exon/intron structure in their downstream part while the structure of the RTKIV genes is very similar to that of RTKIII and FLT4. Both approaches are in complete agreement and indicate that RTKIII, IV, and V genes most probably evolved from a common ancestor already "in pieces" by successive duplications involving entire genes.

Expression of growth factor receptor-encoded mRNA by colonic epithelial cells is altered in inflammatory bowel disease

A link between inflammation of the colon in inflammatory bowel disease (IBD) and the increased risk of colon cancer in ulcerative colitis (UC) may be provided by growth factor receptor genes. Their expression may be altered in response to growth factors present in the mucosa, and this, in turn, may induce further genetic changes, linked to carcinogenesis, in the cells of the colonic epithelium. To test this hypothesis, we assayed steady-state levels of eight growth factor receptor mRNAs in colonic epithelial cells of IBD patients and controls. Four of these genes (EGF-R, IGFI-R, CSF1-R, and PDGF-R-beta) were expressed in epithelial cells, whereas four (erbB-2, erbB-3, NGF-R, and met) were not. The level of the former in involved or uninvolved IBD was considerably lower than in normal epithelial cells from either sporadic colon cancer or diverticulitis patients. In contrast, expression was much higher in IBD patients with colon tumors than in active chronic IBD. The level of PDGF-R-beta mRNA was two- to fourfold higher in involved than in uninvolved areas of the colons of two UC patients, but not in one Crohn's disease patient. Message abundance of its ligand, PDGF-beta, however, was the same in paired UC samples. The pattern of expression of PDGF-beta and cripto was identical to that of EGF-R, whereas the level of mRNA of amphiregulin was the same in active chronic IBD and IBD patients with tumors. A fourth growth factor, Kfgf, was not expressed. Increased levels of PDGF-R-beta mRNA in involved UC relative to uninvolved UC may be related to the disease process in UC. Decreased expression of growth factor- and growth factor receptor-encoded mRNA in active chronic IBD may be related to the disease process, or it may be an effect of steroid therapy undergone by these patients. Enhanced expression of these genes in IBD patients with tumors compared to those without tumors suggests that this may be a marker for development of colon cancer in IBD.

A 1.8-Mb YAC contig spanning three members of the receptor tyrosine kinase gene family (Pdgfra, Kit, and Flk1) on mouse chromosome 5

We constructed a yeast artificial chromosome (YAC) contig spanning the genes encoding Kit (Kit), the platelet-derived growth factor alpha receptor (Pdgfra), and fetal liver kinase 1 (Flk1), three members of a receptor tyrosine kinase gene family located in the central portion of mouse chromosome 5. The orientation of YAC clones and the extent of their overlap was determined by "probe content mapping," that is, hybridization analysis of YAC clones using the available gene probes and YAC end sequences. For four YAC clones, which constitute a minimal set spanning 1.8 Mb, a detailed restriction map was constructed. This map, in conjunction with the previously published long-range restriction map, indicates the order, the physical distances, and the relative transcriptional orientations of the Pdgfra, Kit, and Flk1 genes. The YAC clones and corresponding YAC end probes presented here provide an important resource for the molecular analysis of a cluster of developmental mutations, namely dominant white spotting (W), patch (Ph), recessive spotting (rs), and rump-white (Rw), associated with this chromosomal region.

The Genomic Structure of the Proto-Oncogene c-kit Encoded at the Murine White Spotting Locus

The proto-oncogene c-kit encodes a transmembrane receptor with tyrosine kinase activity, which transduces signal from kit ligand (KL), and is responsible for hematogenesis, melanogenesis and gametogenesis during fetal development and adult life. Partial or complete loss of c-kit function due to mutation of the c-kit or KL gene accounts for the phenotypes of the murine White-spotting and Steel mutations, respectively. The c-kit protein has the structural features of extracellular immunoglobulin-like domains and intracellular kinase domain with a hydrophilic 'insert'. These features have categorized c-kit along with platelet-derived growth factor receptors, colony-stimulating factor 1 receptor (c-fms) and others to subclass III of the receptor tyrosine kinases. We report the structure of the murine c-kit gene. The c-kit gene consists of 21 exons and spans at least 70 kb. The 5' and 3' flanking exons encode the untranslated sequences as well as part of the coding sequence. The internal exons are typically small with each of them encoding a structurally important subunit of the protein. Comparison of gene structures of members of the subclass III receptor tyrosine kinases has improved our understanding of the structure-functional relationship of the c-kit protein. Copyright 1995 S. Karger AG, Basel

Opposing actions of c-ets/PU.1 and c-myb protooncogene products in regulating the macrophage-specific promoters of the human and mouse colony-stimulating factor-1 receptor (c-fms) genes

The receptor for macrophage colony stimulating factor (CSF-1), the c-fms gene product, is a key determinant in the differentiation of monocytic phagocytes. Dissection of the human and mouse c-fms proximal promoters revealed opposing roles for nuclear protooncogenes in the transcriptional regulation of this gene. On the one hand, c-ets-1, c-ets-2, and the macrophage-specific factor PU.1, but not the ets-factor PEA3, trans-activated the c-fms proximal promoter. On the other hand c-myb repressed proximal promoter activity in macrophages and blocked the action of c-ets-1 and c-ets-2. Basal c-fms promoter activity was almost undetectable in the M1 leukaemia line, which expressed high levels of c-myb, but was activated as cells differentiated in response to leukemia inhibitory factor and expressed c-fms mRNA. The repressor function of c-myb depended on the COOH-terminal domain of the protein. We propose that ets-factors are necessary for the tissue-restricted expression of c-fms and that c-myb acts to ensure correct temporal expression of c-fms during myeloid differentiation.

The diastrophic dysplasia gene encodes a novel sulfate transporter: positional cloning by fine-structure linkage disequilibrium mapping

Diastrophic dysplasia (DTD) is a well-characterized autosomal recessive osteochondrodysplasia with clinical features including dwarfism, spinal deformation, and specific joint abnormalities. The disease occurs in most populations, but is particularly prevalent in Finland owing to an apparent founder effect. DTD maps to distal chromosome 5q and, based on linkage disequilibrium studies in the Finnish population, we had previously predicted that the DTD gene should lie about 64 kb away from the CSF1R locus. Here, we report the positional cloning of the DTD gene by fine-structure linkage disequilibrium mapping. The gene lies in the predicted location, approximately 70 kb proximal to CSF1R, and encodes a novel sulfate transporter. Impaired function of its product is likely to lead to undersulfation of proteoglycans in cartilage matrix and thereby to cause the clinical phenotype of the disease. These results demonstrate the power of linkage disequilibrium mapping in isolated populations for positional cloning.

Genomic structure of the downstream part of the human FLT3 gene: exon/intron structure conservation among genes encoding receptor tyrosine kinases (RTK) of subclass III

The FLT3 gene encodes a subclass-III receptor tyrosine kinase (RTKIII). We have determined the structural organization of the downstream part of the human FLT3 gene (also designated dsp-FLT3) that corresponds to the intracellular region of the protein. The coding region is spread over twelve exons spanning 10 kb of genomic DNA. Exon sizes range from 83 to 154 bp, while intron sizes range from 86 bp to more than 1.9 kb. Comparison with the corresponding domain of other RTKIII genes (KIT and FMS) shows that these genes share the same number of exons, which are highly conserved in size, sequence and exon/intron boundary positions. In addition, the intron phase of equivalent introns of FLT3, KIT and FMS are all identical. Our results reinforce our hypothesis based initially only on the KIT and FMS comparison showing that RTKIII genes share a common structural organization and have evolved from a common ancestor gene by cis and trans duplication. Comparison of the genomic organization of the intracellular-encoding part of RTKIII genes with that of RTKI, II and IV genes shows that subclasses III and IV are the most closely related.

5q- chromosome. Evidence for complex interstitial breaks in a case of refractory anemia with excess blasts

Interstitial loss of the long arm of chromosome 5 (5q-) is an anomaly frequently seen in myelodysplasia (MDS) and acute myelogenous leukemia (AML). Although the limits of the interstitial deletions vary among patients, there is a critical region of overlap at 5q31 that is consistently deleted in most cases. The order of genes in the critical 5q31 region is centromere, interleukin gene cluster, an anonymous polymorphic locus D5S89, early growth response factor, CSF1 receptor, telomere. Fluorescence in situ hybridization of specific 5q31 probes to metaphases with del(5) (q11q31) from a patient with secondary refractory anemia with excess blasts in transformation demonstrates that the interstitial deletion is not contiguous. The 5q- chromosome has lost the D5S89 and CSF1R loci while retaining some of the sequences in between. A probe derived from a 300-kbp yeast artificial chromosome containing the D5S89 locus is interrupted on the normal chromosome 5 of this patient. Data presented in this report are consistent with (i) presence of a critical gene within the YAC and (ii) more than a single interstitial break within the 5q- chromosome. These results, while pinpointing one of the critical 5q31 loci, also provide evidence for a second telomeric locus.

Fusion of PDGF receptor beta to a novel ets-like gene, tel, in chronic myelomonocytic leukemia with t(5;12) chromosomal translocation

Chronic myelomonocytic leukemia (CMML) is a myelodysplastic syndrome characterized by abnormal clonal myeloid proliferation and by progression to acute myelogenous leukemia (AML). CMML thus offers an opportunity to study early genetic events in the transition to AML. A recently recognized subgroup of CMML has a t(5;12)(q33;p13) balanced translocation. We report that the consequence of the t(5;12) translocation is expression of a fusion transcript in which the tyrosine kinase domain of the platelet-derived growth factor receptor beta (PDGFR beta) on chromosome 5 is coupled to a novel ets-like gene, tel, on chromosome 12. The tel-PDGFR beta fusion demonstrates the oncogenic potential of PDGFR beta and may provide a paradigm for early events in the pathogenesis of AML.

The macrophage transcription factor PU.1 directs tissue-specific expression of the macrophage colony-stimulating factor receptor

The macrophage colony-stimulating factor (M-CSF) receptor is expressed in a tissue-specific fashion from two distinct promoters in monocytes/macrophages and the placenta. In order to further understand the transcription factors which play a role in the commitment of multipotential progenitors to the monocyte/macrophage lineage, we have initiated an investigation of the factors which activate the M-CSF receptor very early during the monocyte differentiation process. Here we demonstrate that the human monocytic M-CSF receptor promoter directs reporter gene activity in a tissue-specific fashion. Since one of the few transcription factors which have been implicated in the regulation of monocyte genes is the macrophage- and B-cell-specific PU.1 transcription factor, we investigated whether PU.1 binds and activates the M-CSF receptor promoter. Here we demonstrate that both in vitro-translated PU.1 and PU.1 from nuclear extracts bind to a specific site in the M-CSF receptor promoter just upstream from the major transcription initiation site. Mutations in this site which eliminate PU.1 binding decrease M-CSF receptor promoter activity significantly in macrophage cell lines only. Furthermore, PU.1 transactivates the M-CSF receptor promoter in nonmacrophage cells. These results suggest that PU.1 plays a major role in macrophage gene regulation and development by directing the expression of a receptor for a key macrophage growth factor.

The macrophage transcription factor PU.1 directs tissue-specific expression of the macrophage colony-stimulating factor receptor

The macrophage colony-stimulating factor (M-CSF) receptor is expressed in a tissue-specific fashion from two distinct promoters in monocytes/macrophages and the placenta. In order to further understand the transcription factors which play a role in the commitment of multipotential progenitors to the monocyte/macrophage lineage, we have initiated an investigation of the factors which activate the M-CSF receptor very early during the monocyte differentiation process. Here we demonstrate that the human monocytic M-CSF receptor promoter directs reporter gene activity in a tissue-specific fashion. Since one of the few transcription factors which have been implicated in the regulation of monocyte genes is the macrophage- and B-cell-specific PU.1 transcription factor, we investigated whether PU.1 binds and activates the M-CSF receptor promoter. Here we demonstrate that both in vitro-translated PU.1 and PU.1 from nuclear extracts bind to a specific site in the M-CSF receptor promoter just upstream from the major transcription initiation site. Mutations in this site which eliminate PU.1 binding decrease M-CSF receptor promoter activity significantly in macrophage cell lines only. Furthermore, PU.1 transactivates the M-CSF receptor promoter in nonmacrophage cells. These results suggest that PU.1 plays a major role in macrophage gene regulation and development by directing the expression of a receptor for a key macrophage growth factor.

Expression of c-fms on smooth muscle cells isolated from experimental arteriosclerosis

In the present study, we demonstrated gene transcription of c-fms in smooth muscle cells isolated from an experimental rabbit model of arteriosclerosis (intimal smooth muscle cells), although there was no gene transcription of c-fms detected in medial smooth muscle cells. On immunocytochemical analysis, both types of smooth muscle cells similarly reacted with an antibody specific to muscle cells (HHF 35), but did not react with an antibody specific to rabbit macrophages (RAM 11). Intimal smooth muscle cells bound to acetylated LDL and resulting foam cell formation was observed. In response to M-CSF, an increased rate of cell proliferation was observed in intimal smooth muscle cells, but not in medial smooth muscle cells. These results indicated that intimal smooth muscle cells have monocyte-macrophages characteristics such as the expression of c-fms and scavenger receptor gene.

A single P1 clone bearing three genes from human chromosome 11p15.5: HRC1, HRAS1, and RNH

Molecular genetic alterations of chromosome 11p15.5 are a common finding in human cancer. We previously reported the characterization of two cosmids representing a 55-kilobase (kb) region of DNA surrounding the protooncogene HRAS1. A cluster of genes was identified adjacent to this locus, and one of these genes, HRC1, was divergently transcribed 30 kb upstream from HRAS1. A recent report placed the gene for placental ribonuclease inhibitor (RNH, ribonuclease-angiogenin inhibitor) within 90 kb of HRAS1 by pulsed-field gel electrophoresis (PFGE) mapping. We used recombinant P1 bacteriophage clones for physical mapping to determine the position of RNH relative to the HRAS1 transcription unit and HRC1 on chromosome 11p15.5. PFGE and Southern analysis of genomic DNA suggested the order of the genes (HRC1-HRAS1-RNH). P1 clones confirmed this assignment, and placed RNH within 30-50 kb of the 3' end of HRAS1. Furthermore, a single 80-kb P1 clone that bears all three genes was isolated and clarified the Not I restriction map for the HRAS1-RNH interval. Their close physical association was predicted by simple screening of an arrayed P1 library; the clone containing all three genes was selected from multiple positive signals obtained for each HRC1 and RNH because it mapped to the same library-well address.

Two novel transmembrane protein tyrosine kinases expressed during Caenorhabditis elegans hypodermal development

We describe our characterization of kin-15 and kin-16, a tandem pair of homologous Caenorhabditis elegans genes encoding transmembrane protein tyrosine kinases (PTKs) with an unusual structure: the predicted extracellular domain of each putative gene product is only about 50 amino acids, and there are no potential autophosphorylation sites in the C-terminal domain. Using lacZ fusions, we found that kin-15 and kin-16 both appear to be expressed during postembryonic development in the large hypodermal syncytium (hyp7) around the time that specific hypodermal cells fuse with hyp7. kin-15 and kin-16 were positioned on the genetic and physical maps, but extrachromosomal arrays containing wild-type kin-15 and/or kin-16 genes were unable to complement candidate lethal mutations. The results suggest that kin-15 and kin-16 may be specifically involved in cell-cell interactions regulating cell fusions that generate the hypodermis during postembryonic development.