A framework for fibrolamellar carcinoma research and clinical trials

Fibrolamellar carcinoma (FLC), a rare, lethal hepatic cancer, occurs primarily in adolescents and young adults. Unlike hepatocellular carcinoma, FLC has no known association with viral, metabolic or chemical agents that cause cirrhosis. Currently, surgical resection is the only treatment demonstrated to achieve cure, and no standard of care exists for systemic therapy. Progress in FLC research illuminates a transition from an obscure cancer to one for which an interactive community seems poised to uncover fundamental mechanisms and initiate translation towards novel therapies. In this Roadmap, we review advances since the seminal discovery in 2014 that nearly all FLC tumours express a signature oncogene (DNAJB1-PRKACA) encoding a fusion protein (DNAJ-PKAc) in which the J-domain of a heat shock protein 40 (HSP40) co-chaperone replaces an amino-terminal segment of the catalytic subunit of the cyclic AMP-dependent protein kinase (PKA). Important gains include increased understanding of oncogenic pathways driven by DNAJ-PKAc; identification of potential therapeutic targets; development of research models; elucidation of immune mechanisms with potential for the development of immunotherapies; and completion of the first multicentre clinical trials of targeted therapy for FLC. In each of these key areas we propose a Roadmap for future progress.

SIRPγ-expressing cancer stem-like cells promote immune escape of lung cancer via Hippo signaling

Cancer stem-like cells (CSLCs) acquire enhanced immune checkpoint responses to evade immune cell killing and promote tumor progression. Here we showed that signal regulatory protein γ (SIRPγ) determined CSLC properties and immune evasiveness in a small population of lung adenocarcinoma (LUAD) cancer cells. A SIRPγ^hi population displayed CSLC properties and transmitted the immune escape signal through sustaining CD47 expression in both SIRPγ^hi and SIRPγ^lo/– tumor cells. SIRPγ bridged MST1 and PP2A to facilitate MST1 dephosphorylation, resulting in Hippo/YAP activation and leading to cytokine release by CSLCs, which stimulated CD47 expression in LUAD cells and consequently inhibited tumor cell phagocytosis. SIRPγ promoted tumor growth and metastasis in vivo through YAP signaling. Notably, SIRPγ targeting with genetic SIRPγ knockdown or a SIRPγ-neutralizing antibody inhibited CSLC phenotypes and elicited phagocytosis that suppressed tumor growth in vivo. SIRPG was upregulated in human LUAD and its overexpression predicted poor survival outcome. Thus, SIRPγ^hi cells serve as CSLCs and tumor immune checkpoint–initiating cells, propagating the immune escape signal to the entire cancer cell population. Our study identifies Hippo/YAP signaling as the first mechanism by which SIRPγ is engaged and reveals that targeting SIRPγ represents an immune- and CSLC-targeting strategy for lung cancer therapy.

Atad3a suppresses Pink1-dependent mitophagy to maintain homeostasis of hematopoietic progenitor cells

Although deletion of certain autophagy-related genes has been associated with defects in hematopoiesis, it remains unclear whether hyperactivated mitophagy affects the maintenance and differentiation of hematopoietic stem cells (HSCs) and committed progenitor cells. Here we report that targeted deletion of the gene encoding the AAA+-ATPase Atad3a hyperactivated mitophagy in mouse hematopoietic cells. Affected mice showed reduced survival, severely decreased bone-marrow cellularity, erythroid anemia and B cell lymphopenia. Those phenotypes were associated with skewed differentiation of stem and progenitor cells and an enlarged HSC pool. Mechanistically, Atad3a interacted with the mitochondrial channel components Tom40 and Tim23 and served as a bridging factor to facilitate appropriate transportation and processing of the mitophagy protein Pink1. Loss of Atad3a caused accumulation of Pink1 and activated mitophagy. Notably, deletion of Pink1 in Atad3a-deficient mice significantly 'rescued' the mitophagy defect, which resulted in restoration of the progenitor and HSC pools. Our data indicate that Atad3a suppresses Pink1-dependent mitophagy and thereby serves a key role in hematopoietic homeostasis.

Gene therapy prolongs survival and restores function in murine and canine models of myotubular myopathy

Loss-of-function mutations in the myotubularin gene (MTM1) cause X-linked myotubular myopathy (XLMTM), a fatal, congenital pediatric disease that affects the entire skeletal musculature. Systemic administration of a single dose of a recombinant serotype 8 adeno-associated virus (AAV8) vector expressing murine myotubularin to Mtm1-deficient knockout mice at the onset or at late stages of the disease resulted in robust improvement in motor activity and contractile force, corrected muscle pathology, and prolonged survival throughout a 6-month study. Similarly, single-dose intravascular delivery of a canine AAV8-MTM1 vector in XLMTM dogs markedly improved severe muscle weakness and respiratory impairment, and prolonged life span to more than 1 year in the absence of toxicity or a humoral or cell-mediated immune response. These results demonstrate the therapeutic efficacy of AAV-mediated gene therapy for myotubular myopathy in small- and large-animal models, and provide proof of concept for future clinical trials in XLMTM patients.

Biliary tree stem cells, precursors to pancreatic committed progenitors: evidence for possible life-long pancreatic organogenesis

Peribiliary glands (PBGs) in bile duct walls, and pancreatic duct glands (PDGs) associated with pancreatic ducts, in humans of all ages, contain a continuous, ramifying network of cells in overlapping maturational lineages. We show that proximal (PBGs)-to-distal (PDGs) maturational lineages start near the duodenum with cells expressing markers of pluripotency (NANOG, OCT4, and SOX2), proliferation (Ki67), self-replication (SALL4), and early hepato-pancreatic commitment (SOX9, SOX17, PDX1, and LGR5), transitioning to PDG cells with no expression of pluripotency or self-replication markers, maintenance of pancreatic genes (PDX1), and expression of markers of pancreatic endocrine maturation (NGN3, MUC6, and insulin). Radial-axis lineages start in PBGs near the ducts' fibromuscular layers with stem cells and end at the ducts' lumens with cells devoid of stem cell traits and positive for pancreatic endocrine genes. Biliary tree-derived cells behaved as stem cells in culture under expansion conditions, culture plastic and serum-free Kubota's Medium, proliferating for months as undifferentiated cells, whereas pancreas-derived cells underwent only approximately 8-10 divisions, then partially differentiated towards an islet fate. Biliary tree-derived cells proved precursors of pancreas' committed progenitors. Both could be driven by three-dimensional conditions, islet-derived matrix components and a serum-free, hormonally defined medium for an islet fate (HDM-P), to form spheroids with ultrastructural, electrophysiological and functional characteristics of neoislets, including glucose regulatability. Implantation of these neoislets into epididymal fat pads of immunocompromised mice, chemically rendered diabetic, resulted in secretion of human C-peptide, regulatable by glucose, and able to alleviate hyperglycemia in hosts. The biliary tree-derived stem cells and their connections to pancreatic committed progenitors constitute a biological framework for life-long pancreatic organogenesis.

Concise review: clinical programs of stem cell therapies for liver and pancreas

Regenerative medicine is transitioning into clinical programs using stem/progenitor cell therapies for repair of damaged organs. We summarize those for liver and pancreas, organs that share endodermal stem cell populations, biliary tree stem cells (hBTSCs), located in peribiliary glands. They are precursors to hepatic stem/progenitors in canals of Hering and to committed progenitors in pancreatic duct glands. They give rise to maturational lineages along a radial axis within bile duct walls and a proximal-to-distal axis starting at the duodenum and ending with mature cells in the liver or pancreas. Clinical trials have been ongoing for years assessing effects of determined stem cells (fetal-liver-derived hepatic stem/progenitors) transplanted into the hepatic artery of patients with various liver diseases. Immunosuppression was not required. Control subjects, those given standard of care for a given condition, all died within a year or deteriorated in their liver functions. Subjects transplanted with 100-150 million hepatic stem/progenitor cells had improved liver functions and survival extending for several years. Full evaluations of safety and efficacy of transplants are still in progress. Determined stem cell therapies for diabetes using hBTSCs remain to be explored but are likely to occur following ongoing preclinical studies. In addition, mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs) are being used for patients with chronic liver conditions or with diabetes. MSCs have demonstrated significant effects through paracrine signaling of trophic and immunomodulatory factors, and there is limited evidence for inefficient lineage restriction into mature parenchymal or islet cells. HSCs' effects are primarily via modulation of immune mechanisms.

The pharmacology of regenerative medicine

Regenerative medicine is a rapidly evolving multidisciplinary, translational research enterprise whose explicit purpose is to advance technologies for the repair and replacement of damaged cells, tissues, and organs. Scientific progress in the field has been steady and expectations for its robust clinical application continue to rise. The major thesis of this review is that the pharmacological sciences will contribute critically to the accelerated translational progress and clinical utility of regenerative medicine technologies. In 2007, we coined the phrase "regenerative pharmacology" to describe the enormous possibilities that could occur at the interface between pharmacology, regenerative medicine, and tissue engineering. The operational definition of regenerative pharmacology is "the application of pharmacological sciences to accelerate, optimize, and characterize (either in vitro or in vivo) the development, maturation, and function of bioengineered and regenerating tissues." As such, regenerative pharmacology seeks to cure disease through restoration of tissue/organ function. This strategy is distinct from standard pharmacotherapy, which is often limited to the amelioration of symptoms. Our goal here is to get pharmacologists more involved in this field of research by exposing them to the tools, opportunities, challenges, and interdisciplinary expertise that will be required to ensure awareness and galvanize involvement. To this end, we illustrate ways in which the pharmacological sciences can drive future innovations in regenerative medicine and tissue engineering and thus help to revolutionize the discovery of curative therapeutics. Hopefully, the broad foundational knowledge provided herein will spark sustained conversations among experts in diverse fields of scientific research to the benefit of all.

The neurotrophin family of NGF-related neurotrophic factors

The recent molecular cloning of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) has established the existence of an NGF-related family of neurotrophic factors - the neurotrophins. Purification and recombinant production of BDNF and NT-3 has allowed the initiation or extension of in vitro studies of the neuronal specificity of each of these factors. We have found that NT-3, like NGF and BDNF, promotes survival and neurite outgrowth from certain populations of sensory neurons. There appear to be both distinct and overlapping specificities of the 3 neurotrophins towards peripheral neurons - sympathetic neurons and subpopulations of neural crest and neural placode-derived sensory neurons. Using cultures of central nervous system neurons, we have recently established that BDNF: (i) promotes the survival and phenotypic differentiation of rat septal cholinergic neurons, a property consistent with the discovery of high levels of BDNF mRNA expression within the hippocampus; (ii) promotes the survival of rat nigral dopaminergic neurons and furthermore protects these neurons from two dopaminergic neurotoxins, 6-hydroxydopamine (6-OHDA) and MPTP. Thus the neurotrophic effects of these factors towards peripheral neurons and neuronal populations known to degenerate in two of the major human neurodegenerative diseases - Alzheimer's and Parkinson's disease - provokes the question of whether neurotrophic factors may have therapeutic potential in halting the progression and ameliorating the symptoms of devastating neurological disorders of the CNS or PNS, or improving regeneration of neurons of CNS or PNS after traumatic injury.

Multipotent stem/progenitor cells in human biliary tree give rise to hepatocytes, cholangiocytes, and pancreatic islets

Multipotent stem/progenitors are present in peribiliary glands of extrahepatic biliary trees from humans of all ages and in high numbers in hepato-pancreatic common duct, cystic duct, and hilum. They express endodermal transcription factors (e.g., Sox9, SOX17, FOXA2, PDX1, HES1, NGN3, PROX1) intranuclearly, stem/progenitor surface markers (EpCAM, NCAM, CD133, CXCR4), and sometimes weakly adult liver, bile duct, and pancreatic genes (albumin, cystic fibrosis transmembrane conductance regulator [CFTR], and insulin). They clonogenically expand on plastic and in serum-free medium, tailored for endodermal progenitors, remaining phenotypically stable as undifferentiated cells for months with a cell division initially every ≈36 hours and slowing to one every 2-3 days. Transfer into distinct culture conditions, each comprised of a specific mix of hormones and matrix components, yields either cords of hepatocytes (express albumin, CYP3A4, and transferrin), branching ducts of cholangiocytes (expressing anion exchanger-2-AE2 and CFTR), or regulatable C-peptide secreting neoislet-like clusters (expressing glucagon, insulin) and accompanied by changes in gene expression correlating with the adult fate. Transplantation into quiescent livers of immunocompromised mice results in functional human hepatocytes and cholangiocytes, whereas if into fat pads of streptozocin-induced diabetic mice, results in functional islets secreting glucose-regulatable human C-peptide.

CONCLUSION

The phenotypes and availability from all age donors suggest that these stem/progenitors have considerable potential for regenerative therapies of liver, bile duct, and pancreatic diseases including diabetes.

Cloned, CD117 selected human amniotic fluid stem cells are capable of modulating the immune response

Amniotic fluid stem (AFS) cells are broadly multipotent, can be expanded extensively in culture, are not tumorigenic and can be readily cryopreserved for cell banking. Mesenchymal stem cells (MSC) show immunomodulatory activity and secrete a wide spectrum of cytokines and chemokines that suppress inflammatory responses, block mixed lymphocyte reactions (MLR) and other immune reactions, and have proven therapeutic against conditions such as graft-versus-host disease. AFS cells resemble MSCs in many respects including surface marker expression and differentiation potential. We therefore hypothesized that AFS cells may exhibit similar immunomodulatory capabilities. We present data to demonstrate that direct contact with AFS cells inhibits lymphocyte activation. In addition, we show that cell-free supernatants derived from AFS cells primed with total blood monocytes or IL-1β, a cytokine released by monocytes and essential in mediation of the inflammatory response, also inhibited lymphocyte activation. Further investigation of AFS cell-free supernatants by protein array revealed secretion of multiple factors in common with MSCs that are known to be involved in immune regulation including growth related oncogene (GRO) and monocyte chemotactic protein (MCP) family members as well as interleukin-6 (IL-6). AFS cells activated by PBMCs released several additional cytokines as compared to BM-MSCs, including macrophage inflammatory protein-3α (MIP-3α), MIP-1α and Activin. AFS cells also released higher levels of MCP-1 and lower levels of MCP-2 compared to BM-MSCs in response to IL-1β activation. This suggests that there may be some AFS-specific mechanisms of inhibition of lymphocyte activation. Our results indicate that AFS cells are able to suppress inflammatory responses in vitro and that soluble factors are an essential component in the communication between lymphocytes and AFS cells. Their extensive self-renewal capacity, possibility for banking and absence of tumorigenicity may make AFS cells a superior source of stable, well characterized “off the shelf” immunomodulatory cells for a variety of immunotherapies.

Stem cell use in musculoskeletal disorders

Human stem cells derived from bone marrow are currently used in clinical medicine for bone and cartilage repair for injuries such as meniscal tears. New clinical stem cell studies underway include the treatment of patients with spinal cord injuries. Rapid advances in stem cell science are opening new avenues for drug discovery and may lead to new uses of stem cells for other musculoskeletal disorders.

Stem cell sources to treat diabetes

We review progress towards the goal of utilizing stem cells as a source of engineered pancreatic beta-cells for therapy of diabetes. Protocols for the in vitro differentiation of embryonic stem (ES) cells based on normal developmental cues have generated beta-like cells that produce high levels of insulin, albeit at low efficiency and without full responsiveness to extracellular levels of glucose. Induced pluripotent stem (iPS) cells also can yield insulin-producing cells following similar approaches. An important recent report shows that when transplanted into mice, human ES-derived cells with a phenotype corresponding to pancreatic endoderm matured to yield cells capable of maintaining near-normal regulation of blood sugar [Kroon et al., 2008]. Major hurdles that must be overcome to enable the broad clinical translation of these advances include teratoma formation by ES and iPS cells, and the need for immunosuppressive drugs. Classes of stem cells that can be expanded extensively in culture but do not form teratomas, such as amniotic fluid-derived stem cells and hepatic stem cells, offer possible alternatives for the production of beta-like cells, but further evidence is required to document this potential. Generation of autologous iPS cells should prevent transplant rejection, but may prove prohibitively expensive. Banking strategies to identify small numbers of stem cell lines homozygous for major histocompatibility loci have been proposed to enable beneficial genetic matching that would decrease the need for immunosuppression.

Smart biomaterials design for tissue engineering and regenerative medicine

As a prominent tool in regenerative medicine, tissue engineering (TE) has been an active field of scientific research for nearly three decades. Clinical application of TE technologies has been relatively restricted, however, owing in part to the limited number of biomaterials that are approved for human use. While many excellent biomaterials have been developed in recent years, their translation into clinical practice has been slow. As a consequence, many investigators still employ biodegradable polymers that were first approved for use in humans over 30 years ago. During normal development tissue morphogenesis is heavily influenced by the interaction of cells with the extracellular matrix (ECM). Yet simple polymers, while providing architectural support for neo-tissue development, do not adequately mimic the complex interactions between adult stem and progenitor cells and the ECM that promote functional tissue regeneration. Future advances in TE and regenerative medicine will depend on the development of "smart" biomaterials that actively participate in the formation of functional tissue. Clinical translation of these new classes of biomaterials will be supported by many of the same evaluation tools as those developed and described by Professor David F. Williams and colleagues over the past 30 years.

Human hepatic stem cells from fetal and postnatal donors

Human hepatic stem cells (hHpSCs), which are pluripotent precursors of hepatoblasts and thence of hepatocytic and biliary epithelia, are located in ductal plates in fetal livers and in Canals of Hering in adult livers. They can be isolated by immunoselection for epithelial cell adhesion molecule–positive (EpCAM+) cells, and they constitute ∼0.5–2.5% of liver parenchyma of all donor ages. The self-renewal capacity of hHpSCs is indicated by phenotypic stability after expansion for >150 population doublings in a serum-free, defined medium and with a doubling time of ∼36 h. Survival and proliferation of hHpSCs require paracrine signaling by hepatic stellate cells and/or angioblasts that coisolate with them. The hHpSCs are ∼9 μm in diameter, express cytokeratins 8, 18, and 19, CD133/1, telomerase, CD44H, claudin 3, and albumin (weakly). They are negative for α-fetoprotein (AFP), intercellular adhesion molecule (ICAM) 1, and for markers of adult liver cells (cytochrome P450s), hemopoietic cells (CD45), and mesenchymal cells (vascular endothelial growth factor receptor and desmin). If transferred to STO feeders, hHpSCs give rise to hepatoblasts, which are recognizable by cordlike colony morphology and up-regulation of AFP, P4503A7, and ICAM1. Transplantation of freshly isolated EpCAM+ cells or of hHpSCs expanded in culture into NOD/SCID mice results in mature liver tissue expressing human-specific proteins. The hHpSCs are candidates for liver cell therapies.

Isolation of amniotic stem cell lines with potential for therapy

Stem cells capable of differentiating to multiple lineages may be valuable for therapy. We report the isolation of human and rodent amniotic fluid-derived stem (AFS) cells that express embryonic and adult stem cell markers. Undifferentiated AFS cells expand extensively without feeders, double in 36 h and are not tumorigenic. Lines maintained for over 250 population doublings retained long telomeres and a normal karyotype. AFS cells are broadly multipotent. Clonal human lines verified by retroviral marking were induced to differentiate into cell types representing each embryonic germ layer, including cells of adipogenic, osteogenic, myogenic, endothelial, neuronal and hepatic lineages. Examples of differentiated cells derived from human AFS cells and displaying specialized functions include neuronal lineage cells secreting the neurotransmitter L-glutamate or expressing G-protein-gated inwardly rectifying potassium channels, hepatic lineage cells producing urea, and osteogenic lineage cells forming tissue-engineered bone.

Analysis of the functional integrity of cryopreserved human liver cells including xenografting in immunodeficient mice to address suitability for clinical applications

BACKGROUND

The availability of well-characterized human liver cell populations that can be frozen and thawed will be critical for cell therapy. We addressed whether human hepatocytes can recover after cryopreservation and engraft in immunodeficient mice.

METHODS

We isolated cells from discarded human livers and studied the properties of cryopreserved cells. The viability of thawed cells was established with multiple in vitro assays, including analysis of liver gene expression, ureagenesis, cytochrome P450 activity, and growth factor-induced cell proliferation. The fate of transplanted cells was analysed in immunodeficient NOD-SCID mice.

RESULTS

After thawing, the viability of human hepatocytes exceeded 60%. Cells attached to culture dishes, proliferated following growth factor stimulation and exhibited liver-specific functions. After transplantation in NOD-SCID mice, cells engrafted in the peritoneal cavity, a heterologous site, as well as the liver itself, retained hepatic function and proliferated in response to liver injury. Transplanted hepatocytes were integrated in the liver parenchyma. Occasionally, transplanted cells were integrated in bile ducts.

CONCLUSIONS

Cryopreserved human liver cell showed the ability to retain functional integrity and to reconstitute both hepatic and biliary lineages in mice. These studies offer suitable paradigms aimed at characterizing liver cells prior to transplantation in people.

Regulation of ciliary neurotrophic factor expression in myelin-related Schwann cells in vivo

Adult rat sciatic nerve is known to express high levels of ciliary neurotrophic factor (CNTF) mRNA and protein. Here we examine the cellular localization of CNTF protein and mRNA in peripheral nerve and the regulation of CNTF expression by peripheral axons. In intact nerve, CNTF immunoreactivity is found predominantly in the cytoplasm of myelin-related Schwann cells. After axotomy, CNTF immunoreactivity and mRNA levels fall dramatically and do not recover unless axons regenerate. This behavior is similar to the pattern of myelin gene expression in these nerves. We conclude that the expression of CNTF in Schwann cells depends on axon-Schwann cell interactions.

Recombinant human and rat ciliary neurotrophic factors

The human ciliary neurotrophic factor (CNTF) gene was identified and cloned, based on homology with the recently cloned rat cDNA. The gene encodes a protein of 200 amino acids, which shares about 80% sequence identity with rat and rabbit CNTF and, like these homologues, lacks an apparent secretion signal sequence. The human CNTF gene, like the rat gene, appears to contain a single intron separating two protein coding exons. An intronless human CNTF gene was constructed by the use of polymerase chain reactions and introduced into vectors designed for expression of foreign proteins in E. coli. The rat CNTF gene was also introduced into similar vectors. Both the human and rat proteins were expressed at exceptionally high levels, at 20-40% and 60-70% of total protein, respectively. Extraction of the recombinant proteins from inclusion bodies by guanidinium chloride, followed by two column chromatography steps, produced high yields of pure CNTF that supported survival and neurite outgrowth from embryonic chick ciliary neurons in culture. The biological activity of both recombinant proteins was comparable to that of native rat CNTF.

The receptor for ciliary neurotrophic factor

Although neurotrophic factors were originally isolated on the basis of their ability to support the survival of neurons, these molecules are now thought to influence many aspects of the development and maintenance of the nervous system. Identifying the receptors for these neurotrophic factors should aid in identifying the cells on which these factors act and in understanding their precise mechanisms of action. A "tagged-ligand panning" procedure was used to clone a receptor for ciliary neurotrophic factor (CNTF). This receptor is expressed exclusively within the nervous system and skeletal muscle. The CNTF receptor has a structure unrelated to the receptors utilized by the nerve growth factor family of neurotrophic molecules, but instead is most homologous to the receptor for a cytokine, interleukin-6. This similarity suggestes that the CNTF receptor, like the interleukin-6 receptor, requires a second, signal-transducing component. In contrast to all known receptors, the CNTF receptor is anchored to cell membranes by a glycosyl-phosphatidylinositol linkage.

Human and rat brain-derived neurotrophic factor and neurotrophin-3: gene structures, distributions, and chromosomal localizations

The development and maintenance of the vertebrate nervous system depends upon neuronal survival proteins known as neurotrophic factors. Nerve growth factor (NGF) remains the best characterized neurotrophic molecule. Brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) are two recently cloned neurotrophic factors that are homologous to NGF. Here we describe the molecular cloning of the human and rat genes encoding BDNF, as well as the isolation of the human NT-3 gene. On the basis of comparison of our genomic and cDNA clones with those of previously isolated BDNF and NT-3 genes and cDNAs, we make inferences about the structures of processed transcripts derived from the neurotrophin genes and the protein precursors they encode. We demonstrate that the mature form of BDNF is identical in all mammals examined, and that the same is true of the mature form of NT-3. Furthermore, the respective tissue-distributions and neuronal specificities of NT-3 and BDNF are also conserved among mammals. Finally, we localize the gene encoding human BDNF (gene symbol designated BDNF) to chromosome 11, band p13, and the gene encoding human NT-3 (gene symbol designated NTF3) to chromosome 12, band p13.

trkB encodes a functional receptor for brain-derived neurotrophic factor and neurotrophin-3 but not nerve growth factor

A variety of findings seem to functionally link brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), while distinguishing both of these factors from the third member of the neurotrophin family, nerve growth factor (NGF). Here we demonstrate that all three of these neuronal survival molecules bind similarly to the low affinity NGF receptor, but that BDNF and NT-3, unlike NGF, do not act via the high affinity NGF receptor. However, both BDNF and NT-3, but not NGF, bind to full-length and truncated forms of a receptor-like tyrosine kinase, trkB, for which no ligand had previously been identified. In addition to binding BDNF and NT-3, trkB can mediate functional responses to both of these neurotrophins when it is expressed in PC12 cells, although BDNF appears to be the more effective ligand. Thus trkB encodes an essential component of a functional receptor for BDNF and NT-3, but not for NGF. Further evidence predicts the existence of additional functional receptors for the neurotrophins.

Identification of functional receptors for ciliary neurotrophic factor on neuronal cell lines and primary neurons

The lack of reagents or molecular probes specific for the ciliary neurotrophic factor (CNTF) receptor has hindered characterization of the molecular mechanism(s) by which CNTF influences the proliferation, survival, and differentiation of cells of the vertebrate nervous system. We have developed methods for the detection and separation of cells expressing CNTF receptors by using a variety of binding assays based on a genetically engineered CNTF molecule containing an "epitope tag" at its C-terminus. These assays have allowed us to identify several neuronal cell lines, as well as embryonic and adult neurons in primary cultures, that bind CNTF and functionally respond to CNTF by rapidly activating the transcription of immediate early primary response genes.

NT-3, BDNF, and NGF in the developing rat nervous system: parallel as well as reciprocal patterns of expression

To obtain insight into the site and stage specificity of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) action in vivo, we compared the expression patterns of the genes for these three related neurotrophic factors as well as for the NGF receptor in developing and adult rats. Initial embryonic expression of these related neurotrophic factors approximately coincides with the onset of neurogenesis. However, the levels at which the three factors are expressed at this time and throughout the developing nervous system are dramatically different. NT-3 is by far the most highly expressed in immature regions of the CNS in which proliferation, migration, and differentiation of neuronal precursors is ongoing. NT-3 expression dramatically decreases with maturation of these regions. By contrast, BDNF expression is low in developing regions of the CNS and increases as these regions mature. NGF expression varies during the development of discrete CNS regions, but not in any consistent manner compared with NT-3 and BDNF. Despite the dramatic variations, NT-3, BDNF, and NGF do share one striking similarity--high level expression in the adult hippocampus. Our observations are consistent with the idea that NT-3, BDNF, and NGF have paralleled as well as reciprocal roles in vivo.

Neurotrophin-3: a neurotrophic factor related to NGF and BDNF

The development and maintenance of the nervous system depends on proteins known as neurotrophic factors. Although the prototypical neurotrophic factor, nerve growth factor (NGF), has been intensively studied for decades, the discovery and characterization of additional such factors has been impeded by their low abundance. Sequence homologies between NGF and the recently cloned brain-derived neurotrophic factor (BDNF) were used to design a strategy that has now resulted in the cloning of a gene encoding a novel neurotrophic factor, termed neurotrophin-3 (NT-3). The distribution of NT-3 messenger RNA and its biological activity on a variety of neuronal populations clearly distinguish NT-3 from NGF and BDNF, and provide compelling evidence that NT-3 is an authentic neurotrophic factor that has its own characteristic role in vivo.

Neurotrophin-3: a neurotrophic factor related to NGF and BDNF

The development and maintenance of the nervous system depends on proteins known as neurotrophic factors. Although the prototypical neurotrophic factor, nerve growth factor (NGF), has been intensively studied for decades, the discovery and characterization of additional such factors has been impeded by their low abundance. Sequence homologies between NGF and the recently cloned brain-derived neurotrophic factor (BDNF) were used to design a strategy that has now resulted in the cloning of a gene encoding a novel neurotrophic factor, termed neurotrophin-3 (NT-3). The distribution of NT-3 messenger RNA and its biological activity on a variety of neuronal populations clearly distinguish NT-3 from NGF and BDNF, and provide compelling evidence that NT-3 is an authentic neurotrophic factor that has its own characteristic role in vivo.

Neurotrophic factors, their receptors, and the signal transduction pathways they activate

Our studies of the spatiotemporal availability of neurotrophic factors, coupled with tagged ligand binding assays that identify cell bearing receptors for these factors, should lead toward defining the physiological roles of these molecules in the animal. The use of the tagged ligands to identify factor-responsive cell lines has also provided new model systems for the examination of ligand-receptor interactions, as well as for the study of the subsequent induction of intracellular response pathways. To obtain insights into such intracellular pathways, we have molecularly cloned genes encoding a family of serine-threonine protein kinases, most closely related to kinases involved in the yeast response to pheromones. These kinases may be crucial regulators of early steps in the response of mammalian cells to neurotrophic factors as well as other extracellular signals.

Clinical evaluation of a DNA probe assay for the Philadelphia (Ph1) translocation in chronic myelogenous leukemia

We report the clinical evaluation of an improved DNA probe assay for the characteristic genetic marker of human CML, observed by cytogenetics and designated the Philadelphia chromosome (Ph1). The Ph1 chromosome results from the fusion of c-abl proto-oncogene sequences from chromosome 9 to phl gene sequence on chromosome 22. (The phl gene is often referred to as bcr. However, for clarity we prefer to reserve the designation "bcr" for the region within the phl gene in which translocation breakpoints have been found to occur. We also find it useful to distinguish between two such regions in phl, bcr-210 and bcr-190, named after the 210- and 190-kDa phl/abl fusion proteins resulting from translocations with breakpoints in the respective regions. We refer to the corresponding chromosomal translocations as Ph1(bcr-210) and Ph1(bcr-190).) DNA, extracted from peripheral blood (PB) or bone marrow (BM) and digested with restriction endonuclease BglII, is hybridized with a probe (phl/bcr-3) spanning a breakpoint cluster region within phl. Rearrangements are revealed by the presence of one or two novel junction fragments. Clinical specimens from leukemic patients with active disease were compared by cytogenetic and DNA probe analysis at seven centers in the United States and Europe. The probe assay identified the phl rearrangement in 190 of 191 cases of Ph1-positive CML, as well as in 12 of 27 clinically diagnosed CML specimens lacking a typical Ph1 chromosome. DNA rearrangements also were seen in two of six cases of Ph1-positive ALL. No false positive results were obtained among 93 non-leukemic controls. Mixing experiments showed that the DNA probe assay can detect as few as 1% leukemic cells in a specimen. A preliminary study of CML patients in remission after allogeneic BM transplantation revealed a small fraction of residual Ph1-positive leukemic cells in a significant number of such patients.

Increased epidermal growth factor receptor in multidrug-resistant human neuroblastoma cells

Multidrug-resistant human neuroblastoma cell lines obtained by selection with vincristine or actinomycin D from two independent clonal lines, SH-SY5Y and MC-IXC, have 3- to 30-fold more cell surface epidermal growth factor (EGF) receptors than the drug-sensitive parental cells as indicated by EGF binding assays and immunoprecipitation, affinity-labeling, and phosphorylation studies. Reversion to drug sensitivity in one line was accompanied by a return to the parental level of EGF receptor. SH-EP cells, a clone derived from the same neuroblastoma cell line as SH-SY5Y but which displays melanocyte rather than neuronal lineage markers, also express significantly more EGF receptor than SH-SY5Y cells. By nucleic acid hybridization analysis with a molecularly cloned probe, increased receptor level in multidrug-resistant cells was shown to be the result of higher levels of EGF receptor mRNA in drug-resistant than in drug-sensitive cells. The increased steady state amount of specific RNA did not result from amplification of receptor-encoding genes. A small difference was observed in the electrophoretic mobility under denaturing conditions of EGF receptor immunoprecipitated from drug-resistant and drug-sensitive cells. Quantitative and qualitative modulation of the EGF receptor might reflect alterations in the transformation and/or differentiation phenotype of the resistant cells or might result from unknown selective pressures associated with the development of multidrug resistance.

Biological effects of a murine retrovirus carrying an activated N-ras gene of human origin

We have introduced a genomic DNA clone of a mutated human N-ras gene from a T-cell leukemia cell line into a retroviral vector equipped with a neo resistance gene and with SV40 and pBR322 origins of replication. The helper free N-ras virus, which was recovered after transfection of the construction in the psi 2 packaging cell line, contained a correctly spliced N-ras gene. Proviral DNA was amplified in cos cells and subsequently cloned in bacteria. Nucleic acid sequence analysis of the activated N-ras gene revealed a point mutation at codon 12 resulting in a glycine to aspartic acid substitution. The N-ras virus was able to transform mouse fibroblastic cell lines, but failed to fully transform mouse primary embryo fibroblasts. MoMuLV or amphotropic 4070A pseudotypes of the virus were injected intraperitoneally into newborn mice. The MoMuLV pseudotype produced only helper-virus-induced leukemias. The amphotropic pseudotype caused fibrosarcomas after a long latent period. The results of these and other in vivo experiments are discussed in relation to known pathogenic effects of other retroviruses carrying H-ras or K-ras genes.

Expression of normal and mutant ras proteins in human acute leukemia

The expression of normal and mutant ras genes in human acute leukemias was assessed by the direct analysis of p21ras polypeptides, using immunoprecipitation with monoclonal antibodies. High-resolution two-dimensional gel electrophoresis permits the identification of a wide array of activated ras alleles encoding proteins with single amino acid substitutions at any of several positions. The products of three ras genes, H-ras, N-ras, and K-ras, were detected in each of 33 specimens of fresh leukemic cells. The normal K-ras and N-ras polypeptides were substantially more abundant than H-ras p21 in all samples. In over three-fourths of the cases the total amount of p21ras exceeded that seen in control hematopoietic cell lines. The level of ras expression did not correlate simply with clinical parameters, although the two samples with the most abundant p21ras were obtained from patients with relapsed T-cell acute lymphocytic leukemia (ALL). Abnormal p21ras, consistent with oncogenic activation, was found in eight patients. Six of 11 samples from acute myelocytic leukemia (AML) patients displayed a mutant N-ras p21, while only one of 20 ALL specimens had abnormal N-ras, and one had a mutant H-ras. In every case the mutant protein comprised a minority of total p21ras. In two T-cell ALL cell lines both normal and activated N-ras gene products were expressed at equal levels. By contrast, in five fresh AML samples the abnormal N-ras protein was several-fold less abundant than the normal N-ras p21. This finding implies that only a proportion of leukemic cells in an individual patient may carry the mutant ras oncogene.

Antisera to the variable region of ras oncogene proteins, and specific detection of H-ras expression in an experimental model of chemical carcinogenesis

Antisera were prepared in mice, rats and rabbits by immunization with peptides corresponding to regions of highest variability, located near the C-termini of four ras proteins. Two of these, H-ras (171-189) and K-rasB (171-186), react uniquely with H-ras and K-rasB gene products in immunoblots and immunoprecipitation reactions. Affinity-purified rabbit H-ras (171-189) antibody detects H-ras p21 in tissue culture cells and in tissue sections. Epithelial cells in normal mouse skin and cells in papillomas and carcinomas, in a mouse model system of chemical carcinogenesis in which mutational activation of H-ras occurs with high frequency, express high levels of H-ras p21 protein. These results suggest an hypothesis to explain the mechanism and preferential activation of particular ras loci in certain neoplasia.

Expression of ras proto-oncogene proteins in normal human tissues

The expression of ras proto-oncogenes in normal human tissues was studied by immunohistochemical staining and by immunoblotting using monoclonal antibodies. We detected p21ras protein in almost every fetal and adult tissue, but the level varied significantly among cell types. In some cell lineages, immature cells capable of proliferation contain more p21ras than do mature cells. By contrast, certain fully differentiated cells, such as neurons and the epithelial cells of endocrine glands, express abundant p21ras. Among mammalian tissues the highest level of ras protein was detected in brain. Crude synaptosomal membrane preparations from rat brain contain substantially more p21ras than do plasma membranes from rat liver. The observed distribution of p21ras suggests a role for these proteins both in cellular proliferation and in certain specialized cellular functions.

Phorbol ester- and protein kinase C-mediated phosphorylation of the cellular Kirsten ras gene product

The effect of phorbol 12-myristate 13-acetate on the phosphorylation of the ras p21 protein was studied by metabolically labeling cultured cells with [32P]orthophosphate and using a monoclonal antibody to immunoprecipitate the protein. Phorbol 12-myristate 13-acetate (100 nM) induced phosphorylation of cKi-ras p21 in a mouse adrenocortical cell line (Yl) expressing high levels of cKi-ras with exon 4B. Phosphorylation was detected at 10 min and was maximal at 2 h. The ras protein was not phosphorylated in response to phorbol 12-myristate 13-acetate in NIH 3T3 cells expressing activated cHa-ras or vHa-ras. In vitro, protein kinase C phosphorylated cKi-ras in a phosphatidylserine and diolein-dependent manner. Both in intact cells and in vitro the amino acid phosphorylated was serine. Analysis of p21 from NIH 3T3 cells expressing a variety of ras proteins indicated that phosphorylation occurs within a domain encoded by exon 4B of cKi-ras. Phosphorylation affected neither the binding nor the GTPase activity of the ras protein. We conclude that cKi-ras is a substrate for protein kinase C and that the site of phosphorylation is likely to be serine 181 encoded by exon 4B.

Abundant expression of ras proteins in Aplysia neurons

We have cloned a DNA fragment from the marine mollusc Aplysia californica, which contains sequences homologous to mammalian ras genes, by screening a genomic library with a viral Ha-ras oncogene probe under conditions of low stringency hybridization. Nucleotide sequencing revealed a putative exon that encodes amino acids sharing 68% homology with residues 5 to 54 of mammalian p21ras polypeptides, and which therefore is likely to encode a ras-like Aplysia protein. The cloned locus, designated Apl-ras, is distinct from the Aplysia rho (ras-homologue) gene and appears to be more closely related to mammalian ras. We used a panel of monoclonal antibodies raised against v-Ha-ras p21 to precipitate an Mr 21,000 protein from extracts of Aplysia nervous tissue, ovotestis, and, to a much lesser degree, buccal muscle. Fluorescence immunocytochemistry revealed that ras-like protein is most abundant in neuronal cell bodies and axon processes, with staining most prominent at plasma membranes. Much less was present in other tissues. The prominence of ras protein in neurons, which are terminally differentiated and non-proliferating, indicates that the control of cell division is not the sole function of this proto-oncogene. The large identified neurons of Aplysia offer the opportunity to examine how ras protein might function in mature nerve cells.

Cellular ras oncogene expression and cell cycle measured by flow cytometry in hematopoietic cell lines

Human hematopoietic malignancies provide an excellent model for the study of the activity of cellular oncogenes in a context of known defects in cell proliferation and differentiation. A flow cytometric immunofluorescence assay was developed to quantitate the expression of the cellular ras oncogenes in relation to the cell cycle in individual leukemic cells. Specific binding of a monoclonal antibody to the 21-kd protein (p21ras) encoded by the Ha-ras, Ki-ras, and N-ras genes was measured by flow cytometry and confirmed by fluorescence microscopy. P21ras was detected in 416B, a murine hematopoietic precursor cell characterized by a high level of Ki-ras expression, and in the human leukemic cell lines P-12 and KG-1. The presence of p21ras in the cell lines was also shown by immunoprecipitation. Cellular DNA content was determined simultaneously to define cell cycle phases. There was an equal distribution of p21ras in G1, S, and G2M, with considerable heterogeneity of ras gene expression in the G1 compartment. The assay allows oncogene expression to be studied in populations of intact single cells in which cell heterogeneity is maintained, requires very few cells per sample, and directly correlates oncogene expression to cell kinetic data.

Transforming ras genes from human melanoma: a manifestation of tumour heterogeneity?

Variability in the phenotype of cells comprising individual tumours is a striking feature of animal and human cancer and is generally referred to as tumour heterogeneity. Studies of clonally derived cell populations from tumours that originated presumably from a single transformed cell have shown that tumours are made up of cells that differ in a variety of traits, including drug resistance, antigen expression and metastatic potential. The origin and maintenance of tumour heterogeneity are unclear, but mutational and epigenetic mechanisms are thought to be involved. Here we report the results of a search for transforming genes in human melanoma which have raised the possibility that ras gene activation follows the same variable pattern as other traits involved in tumour heterogeneity. DNA from 4 of 30 melanoma cell lines yielded transforming ras genes in the NIH/3T3 assay. Of five cell lines originating from separate metastatic deposits of a single patient, only one contained activated ras, indicating heterogeneity in ras activation in this case and suggesting that ras activation was not involved in tumour initiation or maintenance in this patient.

Mouse cells contain two distinct ras gene mRNA species that can be translated into a p21 onc protein

The Kirsten (Ki) and Harvey (Ha) strains of murine sarcoma virus encode a 21,000-dalton protein (p21 ras) which is the product of the transforming gene of these viruses. Normal cells express low levels of p21 ras encoded by cellular genes (Ki-ras and Ha-ras) homologous to the Ki and Ha murine sarcoma virus transformation genes. A bone marrow-derived mouse cell line, 416B, has been shown to express unusually high levels of p21 ras. In this manuscript, we investigated the molecular biology of p21 ras gene expression in 416B and other normal mouse cells. We identified four distinct polyadenylated and polysome-associated RNAs, two related to Ki-ras and two to Ha-ras. The levels in 416B cells of the two Ki-ras RNAs, sized 5.2 and 2.0 kilobases, were both elevated approximately 25-fold over levels found in normal mouse cells; there was no corresponding change in 416B cells in the levels of the two Ha-ras RNAs. We partially purified the two Ki-ras mRNAs and separated them by velocity sedimentation in sucrose density gradients. Both the 5.2- and 2.0-kilobase mRNAs could be translated in vitro into p21 ras. These results show that a cellular onc protein can be translated from two distinct cellular mRNA species.

Monoclonal antibodies to the p21 products of the transforming gene of Harvey murine sarcoma virus and of the cellular ras gene family

We have isolated eight rat lymphocyte-myeloma hybrid cell lines producing monoclonal antibodies that react with the 21,000-dalton transforming protein (p21) encoded by the v-ras gene of Harvey murine sarcoma virus (Ha-MuSV). These antibodies specifically immunoprecipitate both phosphorylated and non-phosphorylated forms of p21 from lysates of cells transformed by Ha-MuSV. All eight react with the products of closely related ras genes expressed in cells transformed by two additional sarcoma viruses (rat sarcoma virus and BALB sarcoma virus) or by a cellular Harvey-ras gene placed under the control of a viral promoter. Three of the antibodies also react strongly with the p21 encoded by the v-ras gene of Kirsten MuSV. These same three antibodies immunoprecipitate the predominant p21 species synthesized normally in a variety of rodent cell lines, including the p21 produced at high levels in 416B murine hemopoietic cells. This suggests that an endogenous gene closely related to Kirsten-ras is expressed in these cells. The monoclonal antibodies have been used to confirm two properties associated with p21; localization at the inner surface of the membrane of Ha-MuSV-transformed cells, assayed by immunofluorescence microscopy, and binding of guanine nucleotides.

Tumorigenic transformation of mammalian cells induced by a normal human gene homologous to the oncogene of Harvey murine sarcoma virus

A normal human gene homologous to the p21 ras oncogene of Harvey murine sarcoma virus induced oncogenic transformation and high p21 ras levels in murine fibroblasts when this gene was ligated to a control element (the long terminal repeat) from a murine or feline retrovirus. These results indicate that high levels of a gene product encoded by a normal human oncogene can induce tumorigenic transformation.

Preparation of rat monoclonal antibodies to epitopes encoded by the viral oncogene (v-fms) of McDonough feline sarcoma virus

The McDonough strain of feline sarcoma virus (SM-FeSV) contains a viral oncogene, v-fms, transduced from cat cellular genetic sequences designated c-fms. Monoclonal antibodies reactive to antigenic determinants encoded by v-fms were prepared by immunizing rats with live, syngeneic SM-FeSV-transformed cells, and fusing splenic lymphocytes from a tumor-bearing animal with cultured rat myeloma cells. Culture supernatants from hybrids producing antibodies to epitopes encoded by v-fms were identified by immunoprecipitation of radiolabeled polypeptides from SM-FeSV-transformed mink cells. Four positive hybrids were cloned twice in soft agar, established as stable lines, and grown in defined serum-free medium to facilitate purification of homogeneous antibodies. The monoclonal antibodies were used to assay SM-FeSV-specific products by "immunoblotting" of electrophoretically separated proteins, and by fixed-cell immunofluorescence.

Genetic structure of the replication origin of bacteriophage lambda

A fragment of bacteriophage lambda DNA produced by the restriction endonuclease Eco RI and extending from the immunity region to a point inside gene O is found to have a fully functional origin of replication. Seven ori- mutations of lambda cluster in a small region just to the left of the Eco RI cleavage site which defines the right end of this fragment. These mutations lie within gene O.

Physical structure of the replication origin of bacteriophage lambda

The nucleotide sequence of part of the replication region of wild-type bacteriophage lambda and of four mutants defective in the origin of DNA replication (ori-) has been determined. Three of the ori- mutations are small deletions, and one is a transversion. The sequence of the origin region, defined by these mutations, contains a number of unusual features.

Construction of chimeric phages and plasmids containing the origin of replication of bacteriophage lambda

Segments of the replication control region of bacteriophage lambda (lambda) and lambda mutants defective in replication were attached in vitro to the phi80 phage vector Charon 3 and to the plasmid vector mini Col El (pVH51). The chimeric phages and plasmids have been used to localize the origin of lambda DNA replication and to facilitate a structural analysis of the lambda replicator.