Delayed delivery of AAV-GDNF prevents nigral neurodegeneration and promotes functional recovery in a rat model of Parkinson's disease

Glial cell line-derived neurotrophic factor (GDNF) is a strong candidate agent in the neuroprotective treatment of Parkinson's disease (PD). We investigated whether adeno-associated viral (AAV) vector-mediated delivery of a GDNF gene in a delayed manner could prevent progressive degeneration of dopaminergic (DA) neurons, while preserving a functional nigrostriatal pathway. Four weeks after a unilateral intrastriatal injection of 6-hydroxydopamine (6-OHDA), rats received injection of AAV vectors expressing GDNF tagged with FLAG peptide (AAV-GDNFflag) or beta-galactosidase (AAV-LacZ) into the lesioned striatum. Immunostaining for FLAG demonstrated retrograde transport of GDNFflag to the substantia nigra (SN). The density of tyrosine hydroxylase (TH)-positive DA fibers in the striatum and the number of TH-positive or cholera toxin subunit B (CTB, neuronal tracer)-labeled neurons in the SN were significantly greater in the AAV-GDNFflag group than in the AAV-LacZ group. Dopamine levels and those of its metabolites in the striatum were remarkably higher in the AAV-GDNFflag group compared with the control group. Consistent with anatomical and biochemical changes, significant behavioral recovery was observed from 4-20 weeks following AAV-GDNFflag injection. These data indicate that a delayed delivery of GDNF gene using AAV vector is efficacious even 4 weeks after the onset of progressive degeneration in a rat model of PD.

Development and characterization of an antisense-mediated prepackaging cell line for adeno-associated virus vector production

One of the limitations of recombinant adeno-associated virus (rAAV) vector systems for gene therapy applications has been the difficulty in producing the vector in sufficient quantity for adequate evaluation. Since the AAV Rep proteins are cytotoxic, it is not easy to establish stable cell lines that express them constitutively. We describe a novel 293-derived prepackaging cell line which constitutively expresses the antisense rep/cap driven by a loxP-flanked CMV promoter. This cell line was converted into a packaging cell line expressing Rep/Cap for rAAV vector production through adenovirus-mediated introduction of a Cre recombinase gene. Without the introduction of the Cre recombinase gene, the cell line was shown to produce neither Rep nor Cap. rAAV vector was produced (1 x 10(9) genome copies/3.5-cm dish) 4 days after the transduction with Cre-expression adenovirus vector together with transfection of AAV vector plasmid. We further showed that the addition of Cap-expression adenovirus vector caused a 10-fold increase in the yield of rAAV vector. This system is also capable of producing rAAV as a transfection-free system by using a small amount of rAAV instead of vector plasmid.

In vivo persistence of retrovirally transduced murine long-term repopulating cells is not limited by expression of foreign gene products in the fully or minimally myeloablated setting

Many nonmalignant hematologic disorders could potentially be treated by genetic correction of as few as 5-10% of target lineage cells. However, immune system clearance of cells expressing gene products perceived as foreign could be limiting. There is evidence that tolerance to foreign proteins can result when myeloablative conditioning is used, but this limits the overall applicability of such techniques. Therefore, we sought to evaluate the engraftment of hematopoietic stem cells carrying a foreign transgene after low-dose irradiation by comparing in vivo survival of murine long-term repopulating cells (LTRC) transduced with either a retroviral vector expressing the bacterial neomycin phosphotransferase gene (neo) or a vector containing neo gene sequences but modified to prevent protein expression (nonexpression). First, marrow cells from congenic donors were transduced with either vector and transplanted into recipients treated with standard dose irradiation of 800 rads. High-level engraftment and gene marking resulted, without differences in the marking levels or pattern of persistence of the cells between cells transduced with either vector. Low-dose irradiation at 100 rads was tested using higher cell doses. Marking levels as high as 10% overall were obtained, again with no differences between mice receiving cells transduced with the neo versus the nonexpression vectors. To investigate a potentially more immunogenic protein, marrow cells were transduced with a vector containing the green fluorescent protein (GFP) gene, and their persistence was studied in recipient mice receiving 100 rads. Stable GFP expression in 5-10% of circulating cells was observed long term. We conclude that even with very low dose conditioning, engraftment by genetically modified LTRC cells at clinically significant levels can be achieved without evidence for clearance of cells known to be expressing immunogenic proteins.

Reversible integration of the dominant negative retinoid receptor gene for ex vivo expansion of hematopoietic stem/progenitor cells

Since hematopoietic stem cells (HSCs) differentiate readily ex vivo resulting in the loss of self-renewal and engraftment abilities, the transient block of differentiation is essential to maintain those abilities during their ex vivo expansion culture. To this end, we developed a method of reversible integration of the dominant negative retinoic acid receptor (DN-RAR) gene, a differentiation-blocking gene, into cells utilizing the Cre/loxP-dependent gene recombination system. The murine immature hematopoietic 32D cells differentiate into mature neutrophils upon G-CSF treatment. However, 32D cells transduced with a retroviral vector expressing the DN-RAR gene put between two loxP sites continued to proliferate without showing differentiation even in the presence of G-CSF. After the cells were fully amplified, the cells were transduced with the Cre recombinase gene. The cells then restored the ability to differentiate into mature neutrophils upon G-CSF treatment. PCR analysis showed that the DN-RAR gene was efficiently removed from the genome by introduction of the Cre gene. This system may eventually be applicable to the ex vivo expansion of HSCs.

Gene transfer into nonhuman primate hematopoietic stem cells: implications for gene therapy

Hematopoietic stem cells (HSCs) are desirable targets for gene therapy because of their self-renewal and multilineage differentiation abilities. Retroviral vectors are extensively used for HSC gene therapy. However, the initial human trials of HSC gene marking and therapy showed that the gene transfer efficiency into human HSCs with retroviral vectors was very low in contrast to the much higher efficiency observed in murine experiments. The more quiescent nature of human HSCs and the lower density of retroviral receptors on them hindered the efficient gene transfer with retroviral vectors. Since nonhuman primates have marked similarity to humans in all aspects including the HSC biology, their models are considered to be important to evaluate and improve gene transfer into human HSCs. Using these models, clinically relevant levels (around 10% or even more) of gene-modified cells in peripheral blood have recently been achieved after gene transfer into HSCs and their autologous transplantation. This has been made possible by improving ex vivo transduction conditions such as introduction of Flt-3 ligand and specific fibronectin fragment (CH-296) into ex vivo culture during transduction, and the use of retroviral vectors pseudotyped with the gibbon ape leukemia virus or feline endogenous retrovirus envelope. Other strategies including the use of lentiviral vectors and in vivo selective expansion of gene-modified cells with the drug resistance gene or selective amplifier gene (also designated the molecular growth switch) are now being tested to further increase the fraction of gene-modified cells using nonhuman primate models. In addition to the high gene transfer efficiency, high-level and long-term expression of transgenes in human HSCs and their progeny is also required for effective HSC gene therapy. For this purpose, other backbones of retroviral vectors such as the murine stem cell virus and cis-DNA elements, such as the ss-globin locus control region and the chromatin insulator, also need to be tested in nonhuman primate models. Nonhuman primate studies will continue to provide an important framework for human HSC gene therapy. Well-designed nonhuman primate studies will also offer unique insights into the HSCs, immune system, and transplantation biology characteristic of large animals.

Primary T lymphocytes as targets for gene therapy

Peripheral blood T lymphocytes have been considered an attractive target for gene therapy applications. They can be easily harvested and readily expanded ex vivo. The transduction efficiency of primary human lymphocytes with standard retroviral vectors approaches 50% or more using optimized methods of gene transfer. Other methods of gene transfer, including adenoviral, adeno-associated viral, and lentiviral vectors, or nonviral techniques, have also been used for gene transfer into primary lymphocytes. Despite encouraging results in vitro, human clinical trials using retroviral vectors to transduce primary lymphocytes have been hindered by low expression levels of transgenes and immune responses against transgene products. Strategies to overcome these problems need to be developed.

Introduction of a xenogeneic gene via hematopoietic stem cells leads to specific tolerance in a rhesus monkey model

Host immune responses against foreign transgenes may be a major obstacle to successful gene therapy. To clarify the impact of an immune response to foreign transgene products on the survival of genetically modified cells, we studied the in vivo persistence of cells transduced with a vector expressing a foreign transgene compared to cells transduced with a nonexpressing vector in the clinically predictive rhesus macaque model. We constructed retroviral vectors containing the neomycin phosphotransferase gene (neo) sequences modified to prevent protein expression (nonexpressing vectors). Rhesus monkey lymphocytes or hematopoietic stem cells (HSCs) were transduced with nonexpressing and neo-expressing vectors followed by reinfusion, and their in vivo persistence was studied. While lymphocytes transduced with a nonexpressing vector could be detected for more than 1 year, lymphocytes transduced with a neo-expressing vector were no longer detectable within several weeks of infusion. However, five of six animals transplanted with HSCs transduced with nonexpression or neo-expression vectors, and progeny lymphocytes marked with either vector persisted for more than 2 years. Furthermore, in recipients of transduced HSCs, infusion of mature lymphocytes transduced with a second neo-expressing vector did not result in elimination of the transduced lymphocytes. Our data show that introduction of a xenogeneic gene via HSCs induces tolerance to the foreign gene products. HSC gene therapy is therefore suitable for clinical applications where long-term expression of a therapeutic or foreign gene is required.

In vivo marking of rhesus monkey lymphocytes by adeno-associated viral vectors: direct comparison with retroviral vectors

We have compared adeno-associated virus (AAV)-based and retrovirus-based vectors for their ability to transduce primary T lymphocytes in vitro and then tracked the persistence of these genetically marked lymphocytes in vivo, using the rhesus monkey model. To avoid the complication of immune rejection of lymphocytes transduced with xenogeneic genes in tracking studies primarily designed to investigate transduction efficiency and in vivo kinetics, the vectors were designed without expressed genes. All vectors contained identically mutated beta-galactosidase gene (beta-gal) and neomycin resistance gene (neo) DNA sequences separated by different length polylinkers, allowing simple differentiation by polymerase chain reaction (PCR). Each of 2 aliquots of peripheral blood lymphocytes from 4 rhesus monkeys were transduced with either AAV or retroviral vectors. The in vitro transduction efficiency (mean vector copy number/cell) after the ex vivo culture was estimated by PCR at 0.015 to 3.0 for AAV, varying depending on the multiplicity of infection (MOI) used for transduction, and 0.13 to 0.19 for the retroviral transductions. Seven days after transduction, Southern blot analysis of AAV-transduced lymphocytes showed double-stranded and head-to-tail concatemer forms but failed to show integration of the AAV vector. AAV and retroviral aliquots were reinfused concurrently into each animal. Although the retrovirally marked lymphocytes could be detected for much longer after infusion, AAV transduction resulted in higher short-term in vivo marking efficiency compared with retroviral vectors, suggesting possible clinical applications of AAV vectors in lymphocyte gene therapy when long-term vector persistence is not required or desired.

Hematopoietic stem cell gene therapy: a current overview

Retrovirus-mediated gene transfer into murine hematopoietic stem cells and reconstitution of syngeneic mice have demonstrated persistence and functioning of the transgenes over extended periods of time. In contrast, clinically relevant levels of gene transfer into large animal and human stem cells have not been widely achieved. Results of current clinical gene transfer studies have raised fundamental questions about the physiology of primitive human hematopoietic cells and gene therapy vectors. Efforts are being undertaken to answer these problems and to develop more efficient gene therapy strategies.

Expression of interferon-gamma by stromal cells inhibits murine long-term repopulating hematopoietic stem cell activity

Several lines of evidence suggest that overexpression of interferon gamma (IFN-gamma) in the marrow microenvironment may play a role in the pathogenesis of marrow suppression in aplastic anemia. We previously showed that overexpression of IFN-gamma by marrow stromal cells inhibits human long-term culture initiating cell activity assayed in vitro to a much greater degree than the addition of soluble IFN-gamma. The effect of IFN-gamma on true repopulating stem cells assayed in vivo has not been studied previously. We compared the effect of co-culture of murine marrow cells in the presence of stromal cells transduced with a retroviral vector expressing murine IFN-gamma vs stromal cells transduced with a control neo vector. Using a murine congenic competitive repopulation assay, there was significantly less long-term repopulating stem cell activity remaining after culture on mIFN-gamma-expressing stroma as compared to control stroma. We also investigated the effect of directly transducing murine bone marrow cells with the mIFN-gamma or control vector. Marrow cells transduced with either vector were transplanted into W/Wv recipient mice. The percentage of vector-containing cells in the mIFN-gamma mice was significantly lower than in the control mice, suggesting that mIFN-gamma-transduced primitive cells may not have survived culture, or that mIFN-gamma directly decreases gene transfer into repopulating cells. Despite no significant differences in white or red blood cells in the mice transplanted with the mIFN-gamma-transduced cells, the number of bone marrow colony-forming unit-C 16 weeks after transplantation was significantly lower in the IFN-gamma group. These data indicate that ectopic or overexpression of mIFN-gamma, especially by marrow microenvironmental elements, may have a marked effect on primitive hematopoiesis as assayed in vivo.

Abrogation of TGF-beta activity during retroviral transduction improves murine hematopoietic progenitor and repopulating cell gene transfer efficiency

Transforming growth factor-beta has complex activities on hematopoietic cells. We have previously shown that murine long-term repopulating activity is compromised by ex vivo culture in TGF-beta 1 and conversely is increased by abrogating endogenous TGF-beta activity with a neutralizing antibody. In the current study, we investigated the effect of abrogation of autocrine or paracrine TGF-beta present during retroviral transduction on gene transfer efficiency to primitive hematopoietic cells. Murine marrow cells were cultured and retrovirally transduced for 4 days in the presence of interleukin-3, interleukin-6 and stem cell factor, and either a neutralizing anti-TGF-beta antibody or an isotype control. Committed progenitor cells were analyzed for gene transfer efficiency, and cells were also injected into W/Wv recipient mice for analysis of transduction of long-term repopulating cells. The progenitor (CFU-C) transduction efficiency in the presence of anti-TGF-beta was significantly greater. Semiquantitative PCR analysis and Southern blot analysis for the retroviral marker gene in the blood and bone marrow of recipient mice revealed a significant increase in the transduction efficiency of long-term repopulating cells after culture and transduction in the presence of the anti-TGF-beta. Thus neutralization of TGF-beta activity during retroviral transduction allows more efficient gene transfer into primitive murine hematopoietic cells and may prove beneficial in future clinical gene transfer or therapy trials.

Ex vivo expansion of genetically marked rhesus peripheral blood progenitor cells results in diminished long-term repopulating ability

The possibility of primitive hematopoietic cell ex vivo expansion is of interest for both gene therapy and transplantation applications. The engraftment of autologous rhesus peripheral blood (PB) progenitors expanded 10 to 14 days were tracked in vivo using genetic marking. Stem cell factor (SCF)/granulocyte colony-stimulating factor (G-CSF)-mobilized and CD34-enriched PB cells were divided into two equal aliquots and transduced with one of two retroviral vectors carrying the neomycin-resistance gene (neo) for 4 days in the presence of interleukin-3 (IL-3), IL-6, and SCF in the first 5 animals, IL-3/IL-6/SCF/Flt-3 ligand (FLT) in 2 subsequent animals, or IL-3/IL-6/SCF/FLT plus an autologous stromal monolayer (STR) in the final 2. At the end of transduction period, one aliquot (nonexpanded) from each animal was frozen, whereas the other was expanded under the same conditions but without vector for a total of 14 days before freezing. After total body irradiation, both the nonexpanded and expanded transduced cells were reinfused. Despite 5- to 13-fold higher cell and colony-forming unit (CFU) doses from the expanded fraction of marked cells, there was greater short- and long-term marking from the nonexpanded cells in all animals. In animals receiving cells transduced and expanded in the presence of IL-3/IL-6/SCF/FLT, engraftment by the marked expanded cells was further diminished. This discrepancy was even more pronounced in the animals who received cells transduced and expanded in the presence of FLT and autologous stroma, with no marking detectable from the expanded cells. Despite lack of evidence for expansion of engrafting cells, we found that the addition of FLT and especially STR during the initial brief transduction period increased engraftment with marked cells into a clinically relevant range. Levels of marked progeny cells originating from the nonexpanded aliqouts were significantly higher than that seen in previous 4 animals receiving cells transduced in the presence of IL-3/IL-6/SCF, with levels of 10% to 20% confirmed by Southern blotting from the nonexpanded IL-3/IL-6/SCF/FLT/STR graft compared with 0.01% in the original IL-3/IL-6/SCF cohort. These results suggest that, although expansion of PB progenitors is feasible ex vivo, their contribution towards both short- and long-term engraftment is markedly impaired. However, a brief transduction in the presence of specific cytokines and stromal support allows engraftment with an encouraging number of retrovirally modified cells.

Green fluorescent protein retroviral vectors: low titer and high recombination frequency suggest a selective disadvantage

Green fluorescent protein (GFP) has been used as a reporter molecule for gene expression because it fluoresces green after blue-light excitation. Inclusion of this gene in a vector could allow rapid, nontoxic selection of successfully transduced cells. However, many attempts by our laboratory to isolate stable retroviral producer cell clones secreting biologically active vectors containing either the highly fluorescent S65T-GFP mutant or humanized GFP have failed. Vector plasmids containing various forms of GFP and the neomycin resistance gene were transfected into three different packaging cell lines and fluorescence was observed for several days, but stable clones selected with G418 no longer fluoresced. Using confocal microscopy, the brightest cells were observed to contract and die within a matter of days. RNA slot-blot analysis of retroviral producer supernatants showed no viral production from the GFP plasmid-transfected clones, although all clones derived after transfection with an identical retroviral construct not containing GFP produced virus. Genomic Southern analysis of the GFP-transduced clones showed a much higher probability of rearrangement of the priviral sequences than in the control non-GFP clones. Overall, 18/34 S65T-GFP clones and 17/33 humanized-GFP clones had rearrangements, whereas 2/15 control non-GFP clones had rearrangements. Hence, producer cells expressing high levels of these GFP genes seem to be selected against, with stable clones undergoing major rearrangements or other mutations that both abrogate GFP expression and prevent vector production. These observations indicate that GFP may not be an appropriate reporter gene for gene transfer applications in our vector/packaging system.

The signal transduction through Grb2/Ash in hematopoietic cells

Grb2/Ash is composed of one SH2 and two SH3 domains and functions as an adapter linking tyrosine-kinase receptors and Ras in fibroblasts. The SH2 domain binds to tyrosine-phosphorylated proteins and the SH3 domain binds to protein containing proline-rich regions. However, the mechanisms of signal transduction through Grb2/Ash in hematopoietic cells are still unclear. By means of the binding experiments using the GST fusion protein including the full length Grb2/Ash, we have found that Shc and unidentified 130-kDa and 135-kDa proteins are associated with Grb2/Ash and that they are tyrosine-phosphorylated by treatment with granulocyte-macrophage colony-stimulating factor (GM-CSF) and erythropoietin (EPO) in a human leukemia cell line UT-7. We have purified the 130-kDa protein (pp 130) using GST-GRB2/Ash affinity column. The amino-acid sequence analysis showed that the pp130 was identical to the human c-cbl proto-oncogene product (c-Cbl). c-Cbl constitutively binds to the SH3 domain of Grb2/Ash both in vitro and in vivo but not to the SH2 domain of Grb2/Ash. Moreover, c-Cbl (pp 130) becomes tyrosine-phosphorylated rapidly and transiently depending on GM-CSF and EPO stimulation. However, we could not find the homologous regions with guanine nucleotide exchange factors or GTPase-activating proteins in the c-cbl gene. These findings strongly suggest that c-Cbl is implicated in the signal transduction of GM-CSF and EPO in hematopoietic cells, and c-Cbl and Grb2/Ash might also transduce a signal that is different from the signal leading to Ras regulation. Recently, we have shown that the proto-oncogene vav product (Vav) is also tyrosine-phosphorylated by treatment with GM-CSF and EPO and is constitutively associated with the SH3 domain of Grb2/Ash in UT-7. Another guanine nucleotide exchange factor Sos is also associated with Grb2/Ash in UT-7. It has been reported that Vav has guanine nucleotide exchange activity and activates Ras in vitro and in vivo. These data suggest that tyrosine kinases, the adapter Grb2/Ash, and the guanine nucleotide exchange factor Vav and Sos are members of a signaling pathway leading to Ras activation in hematopoietic cells.

Fulminant septicemic syndrome of Bacillus cereus in a leukemic patient

We report a rapidly fatal Bacillus cereus septicemia in a leukemic patient receiving remission-induction therapy. Symptoms resembling food poisoning and fever preceded coma accompanied by neurologic abnormalities. Autopsy revealed necrotizing leptomeningitis with subarachnoid hemorrhage and coagulation necrosis of the liver with bacterial infiltration. These clinicopathologic findings were closely similar to those of reported cases. Because of a rapidly fatal clinical course, suspicion of this syndrome early in the course is important to determine an appropriate treatment. Therefore, we propose that this type of septicemia should be termed as fulminant septicemic syndrome of Bacillus cereus.

Tyrosine phosphorylation of a 94-kDa protein associated with GRB2/ASH is implicated in the signal transduction of hematopoietic survival factors

Grb2/Ash is an adapter molecule that contains Src-homology (SH) 2 and 3 domains. We have examined Grb2/Ash-associated proteins in hematopoietic cells, and have noted a 94-kDa phosphotyrosine-containing protein (pp94) among them. It was shown that the SH2 domain of Grb2/Ash is necessary for the binding of pp94 to Grb2/Ash from the binding experiments using the GST Fusion proteins and the phosphotyrosine analogue phenylphosphate. Tyrosine phosphorylation of pp94 was rapid and transient, and was only observed when the cells were stimulated with factors that were absolutely required for survival of the cells (survival factors). The kinase inhibitors, staurosporine and genistein, inhibit the proliferation UT-7 cells. However, genistein does not inhibit the survival of the cells while staurosporine inhibits both the proliferation and the survival of the cells. Tyrosine phosphorylation of pp94 was sensitive to staurosporine but resistant to genistein. It is possible that tyrosine phosphorylation of pp94 might be related to the survival rather than to the proliferation of the cells.

Proto-oncogene products Vav and c-Cbl are involved in the signal transduction through Grb2/Ash in hematopoietic cells

Grb2/Ash is composed of one SH2 and two SH3 domains and functions as an adapter linking tyrosine kinase receptors and Ras in fibroblasts. We have investigated the nature of proteins interacting with Grb2/Ash in hematopoietic cells. The product of the vav proto-oncogene (Vav) is expressed exclusively in hematopoietic cells and has guanine nucleotide exchange activity. Here we report that granulocyte/macrophage-colony- stimulating factor (GM-CSF), interleukin-3, and erythropoietin (Epo) induce rapid and transient tyrosine phosphorylation of Vav and that Vav is constitutively associated with the SH3 domain of Grb2/Ash in a human leukemia cell line UT-7. These data implicate Vav in a signaling pathway leading to activation of Ras or Ras-related proteins in hematopoietic cells. Furthermore, we have shown that the proto-oncogene c-cbl product (c-Cbl) is also tyrosine-phosphorylated by stimulation with GM-CSF or Epo and is constitutively associated with the SH3 domain of Grb2/Ash in UT-7. However, we could not find the homologous regions with guanine nucleotide exchange factors or GTPase-activating proteins in the c-cbl gene. Therefore, Grb2/Ash might also transduce a signal that is different from the signal leading to the small-G protein regulation.

c-Cbl is inducibly tyrosine-phosphorylated by epidermal growth factor stimulation in fibroblasts, and constitutively tyrosine-phosphorylated and associated with v-Src in v-src-transformed fibroblasts

The c-cbl gene was cloned as the cellular homolog of the v-cbl oncogene that is the transforming component of a murine tumorigenic retrovirus, CAS NS-1, though the biological roles of c-Cbl remain to be elucidated. We have previously reported that c-Cbl is implicated in the signal transduction triggered by granulocyte-macrophage colony-stimulating factor or erythropoietin in hematopoietic cells. Here, we observed tyrosine phosphorylation of C-cbl in cells expressing epidermal growth factor receptor depending on EGF stimulation and in v-src transformed cells. Furthermore, c-Cbl was revealed to associate with v-Src in vivo. By means of binding experiments using glutathione S-transferase fusion proteins, we have found that the SH2 and SH3 domains of many proteins bind to c-Cbl. These findings strongly suggest that c-Cbl is implicated in a wide variety of signal transduction pathways, including those of EGF receptor and Src protein, as well as in the signaling pathways of hematopoietic cells.

TPO/c-mpl ligand induces tyrosine phosphorylation of multiple cellular proteins including proto-oncogene products, Vav and c-Cbl, and Ras signaling molecules

Thrombopoietin (TPO)/c-mpl ligand is a hematopoietic growth factor that stimulates proliferation and maturation of megakaryocytes. To analyze the signaling pathway downstream of the c-mpl product, we used a human megakaryoblastic cell line, Mo7e, that has been proved to be responsive to TPO in terms of DNA synthesis. In this study, we found that TPO treatment resulted in tyrosine phosphorylation of Jak-2 kinase. Moreover, it was revealed that several functional molecules involved in the Ras signaling pathway, Shc and Sos, were phosphorylated by treatment with TPO. Finally, tyrosine phosphorylation of the proto-oncogene products, Vav and c-Cbl, has been proved to be induced by TPO. These results suggest that TPO could activate several signaling pathways including the Jak/Stat pathway, the Ras pathway and possibly another pathway involving the c-Cbl proto-oncogene product.

[Successful treatment of splenomegaly and anemia by VP therapy in idiopathic myelofibrosis complicated with acromegaly: a case report]

Here we report a 65-year-old male patient with idiopathic myelofibrosis (IMF) accompanied with acromegaly. He was admitted because of anemia and splenomegaly. No favorable effects were observed when hydroyurea was administered. However, his symptoms were successfully treated by administration of vincristine and prednisolone (VP therapy), which is usually applied for choronic myelogenous leukemia in the accelerated phase. Therefore, VP therapy might be one possible for IMF. Since there have been several reports suggesting the possible association of hematological malignancies with acromegaly, we speculate that acromegaly was implicated in the initiation or progression of IMF in this case.

Tyrosine phosphorylation of vav protooncogene product in primary human myelogenous leukemic cells stimulated by granulocyte colony-stimulating factor

Granulocyte colony-stimulating factor(G-CSF), but not granulocyte-macrophage CSF(GM-CSF), induced tyrosine phosphorylation of 95-kDa protein in 13 cases of primary human acute myelogenous leukemic cells. Electrophoretic mobility of 95-kDa phosphoprotein and the protooncogene product p95vav was identical. In addition, p95vav was tyrosine-phosphorylated only in G-CSF-stimulated cells. In contrast to primary leukemic cells, amount of p95vav was under detectable level and G-CSF did not induce tyrosine phosphorylation of 90-100-kDa proteins in human neutrophils. These results indicate specific involvement of vav product in signaling pathway of G-CSF in primary human leukemic cells.

Activation of Fes tyrosine kinase by gp130, an interleukin-6 family cytokine signal transducer, and their association

gp130 is a signal-transducing subunit of receptors for the interleukin-6 (IL-6)-related cytokine subfamily including IL-6, leukemia inhibitory factor, oncostatin M, IL-11, and ciliary neurotrophic factor, indicating that gp130-mediated signals are involved in the immune response, hematopoiesis, inflammation, and endocrine and nervous system activity. We previously showed that gp130 stimulation rapidly activates Jak, Btk, and Tec tyrosine kinases, all of which constitutively associate with gp130. To further elucidate intracellular signal transduction through gp130, we examined the possible involvement of another nonreceptor tyrosine kinase, p92c-fes (Fes). We showed that gp130 stimulation rapidly induced tyrosine phosphorylation of Fes and actually activated its kinase activity in hematopoietic lineage cells. Furthermore, Fes associated with gp130 independently of ligand stimulation like Jak, Btk, and Tec tyrosine kinases. These results indicate that multiple nonreceptor tyrosine kinases are involved in the gp130-mediated signal transduction pathway. Because both gp130 and Fes are expressed not only in hematopoietic lineage cells but also in heart and nerve cells, Fes may play a role in signal transduction through gp130 in these tissues.

The proto-oncogene product c-Cbl becomes tyrosine phosphorylated by stimulation with GM-CSF or Epo and constitutively binds to the SH3 domain of Grb2/Ash in human hematopoietic cells

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and erythropoietin (Epo) are hematopoietic growth factors that regulate proliferation and differentiation of hematopoietic cells. They elicit and control a cascade of biochemical events, the earliest of which is tyrosine phosphorylation of several cellular proteins. Grb2/Ash is composed of SH2 and SH3 domains. The SH2 domain binds to tyrosine-phosphorylated proteins, and the SH3 domains bind to proteins containing proline-rich regions. It is considered that Grb2/Ash functions as an adapter protein linking tyrosine kinases and Ras in downstream of receptors for growth factors in fibroblasts. However, the mechanisms of signal transduction through Grb2/Ash and the roles of proteins associated with Grb2/Ash remain to be determined in hematopoietic cells. By means of the binding experiments using the glutathione S-transferase fusion protein including the full-length Grb2/Ash, we have found that Shc and unidentified 130- and 135-kDa proteins are associated with Grb2/Ash and that they are tyrosine phosphorylated by treatment with GM-CSF or Epo in a human leukemia cell line, UT-7. We have purified the 130-kDa protein (pp130) using the glutathione S-transferase-Grb2/Ash affinity column. The amino acid sequence analysis of the three peptides derived from the in situ protease digestion of the purified pp130 showed that the pp130 was identical to the human c-cbl proto-oncogene product (c-Cbl). c-Cbl constitutively binds to the SH3 domain of Grb2/Ash both in vitro and in vivo but not to the SH2 domain of Grb2/Ash, and the binding of Grb2/Ash to c-Cbl or Sos was not altered by GM-CSF stimulation. Moreover, c-Cbl (pp130) becomes tyrosine phosphorylated rapidly and transiently depending on GM-CSF or Epo stimulation. These findings strongly suggest that c-Cbl is implicated in the signal transduction of GM-CSF or Epo in hematopoietic cells and that c-Cbl is involved in another signaling pathway different from the Ras signaling pathway.