Myeloproliferative Sarcoma Virus Research Articles

Action of temperature-sensitive mutants of myeloproliferative sarcoma virus suggests that fibroblast-transforming and hematopoietic transforming viral properties are related.

The myeloproliferative sarcoma virus is molecularly related to the Moloney sarcoma virus (Pragnell et al., J. Virol. 38:952-957, 1981), but causes both fibroblast transformation in vitro and leukemic changes--including spleen focus formation--in adult mice. The fibroblast transforming properties of myeloproliferative sarcoma virus were used to select viral temperature-sensitive mutants at 39.5 degrees C, the nonpermissive temperature. These mutants are temperature sensitive in the maintenance of the transformed state. This was also shown by cytoskeletal changes of the infected cells at permissive and nonpermissive temperatures. Viruses released from cells maintained at both the permissive and nonpermissive temperature are temperature sensitive in fibroblast transformation functions. All temperature-sensitive mutants show only a low reversion rate to wild-type transforming function. The myeloproliferative sarcoma virus temperature-sensitive mutants are inefficient in causing leukemic transformation (spleen enlargement, focus formation) in mice at the normal temperature. A method to maintain a low body temperature (33 to 34 degrees C) in mice is described. One temperature-sensitive mutant was checked at low body temperature and did not induce leukemia. These data thus indicate that the same or related viral functions are responsible for hematopoietic and fibroblast transformation.

Hematopoietic precursors in disease induced by the myeloproliferative sarcoma virus

Granulocyte and macrophage precursors (GM-CFU-C-), which differentiate in vitro without added granulocyte and macrophage colony stimulating factor (GM-CSF), can be detected in the hematopoietic organs of mice infected with myeloproliferative sarcoma virus (MPSV). Retransplantation experiments have shown that the GM-CFU-C- are incapable of autonomous growth and depend on a factor present in medium conditioned by MPSV spleen cells (MPSV-CM). This factor is not MPSV and is not produced by spleen cells of noninfected mice. Two classical sources of GM-CSF, lung GM-CSF and GM-CSF contained in the plasma of endotoxin-treated mice, cannot replace the MPSV factor. Inversely, MPSV- CM does not stimulate the growth of retransplanted clusters induced in normal bone marrow with lung GM-CSF, whereas lung GM-CSF does. Two conditioned media containing activity promoting the in vitro proliferation and differentiation of hematopoietic stem cells in the mixed colony assay stimulate the growth of MPSV clusters: one medium was conditioned by pokeweed-mitogen-stimulated spleen cells, the other by the WEHI 3 cell line. The implication of the results in the comprehension of MPSV disease is discussed.

Hematopoietic Precursors in Disease Induced by the Myeloproliferative Sarcoma Virus

AbstractGranulocyte and macrophage precursors (GM-CFU-C−), which differentiate in vitro without added granulocyte and macrophage colony stimulating factor (GM-CSF), can be detected in the hematopoietic organs of mice infected with myeloproliferative sarcoma virus (MPSV). Retransplantation experiments have shown that the GM-CFU-C− are incapable of autonomous growth and depend on a factor present in medium conditioned by MPSV spleen cells (MPSV-CM). This factor is not MPSV and is not produced by spleen cells of noninfected mice. Two classical sources of GM-CSF, lung GM-CSF and GM-CSF contained in the plasma of endotoxin-treated mice, cannot replace the MPSV factor. Inversely, MPSV-CM does not stimulate the growth of retransplanted clusters induced in normal bone marrow with lung GM-CSF, whereas lung GM-CSF does. Two conditioned media containing activity promoting the in vitro proliferation and differentiation of hematopoietic stem cells in the mixed colony assay stimulate the growth of MPSV clusters: one medium was conditioned by poke-weed-mitogen-stimulated spleen cells, the other by the WEHI 3 cell line. The implication of the results in the comprehension of MPSV disease is discussed.

Myeloproliferative sarcoma virus: its effects on erythropoiesis in adult DBA/2J mice.

Adult susceptible mice (DBA/2J) infected with MPSV (myeloproliferative sarcoma virus), a defective RNA tumour virus, develop splenomegaly and progressive disruption of the haematologic system culminating in death. The present study was specifically directed toward determining the effects of the virus on erythroid differentiation. Early and late precursor cells (erythroid burst-forming units; BFU-E and colony-forming units; CFU-E, respectively) were evaluated by the ability of bone marrow and spleen cells to form colonies of fully differentiated erythroid cells in vitro. MPSV caused substantial modification of both the BFU-E and CFU-E populations in the bone marrow and spleen of infected animals. Changes were detected in the CFU-E population preceding any significant increase in spleen weight. In the bone marrow, the proportion of CFU-E cells increased almost twofold by days 5-10 after virus infection but decreased by day 15. In the spleen, CFU-E frequency rose 40-fold by days 10-15 and then declined steadily prior to death. At the peak of CFU-E expansion, a small proportion of the population appeared to be erythropoietin (Ep) independent, although there was no evidence of a complete switch to Ep-independence which occurs in Friend virus-induced erythroleukemia. Dose-response curves showed that none of these data could be explained in terms of a changing responsiveness to Ep. However, evidence is presented that indicates that BFU-E from MPSV-infected animals lose or have a reduced requirement for burst-promoting activity (BPA) relative to normal cells although their progeny still need Ep for terminal erythroid differentiation.

Myeloproliferative syndrome induced by MPSV in DBA/2 mice: presence of a mixed-colonies promoting activity (MPA) in the spleen

The myeloproliferative syndrome induced by the myeloproliferative sarcoma virus (MPSV) in DBA/2 mice stimulates the proliferation of pluripotent hemopoietic stem cells (HSC) and of progenitors committed toward granulomacrophagic and erythroid cell lines. This stimulation may result from a direct effect of the MPSV on HSC or from an indirect effect via locally secreted factors. Normal isogenic bone marrow cells were incubated in the mixed colony-forming unit system in semisolid medium supplemented with conditioned media obtained after incubating neoplastic spleen cells for 3 days at 37 degrees C. These spleen conditioned media contain an activity that is physically separable from MPSV by ultracentrifugation and which, in the presence of a very low quantity of erythropoietin, can induce in vitro the proliferation and differentiation of pluripotent HSC, detected by this Mix-CFU technique. We termed this activity mixed-colonies promoting activity (MPA). These results suggest that the hyperplasia of the nonlymphoid hematopoietic system in the neoplastic spleen results from an indirect effect of the MPSV on pluripotent HSC via locally secreted factors.

Myeloproliferative Syndrome Induced by MPSV in DBA/2 Mice: Presence of a Mixed-Colonies Promoting Activity (MPA) in the Spleen

The myeloproliferative syndrome induced by the myeloproliferative sarcoma virus (MPSV) in DBA/2 mice stimulates the proliferation of pluripotent hemopoietic stem cells (HSC) and of progenitors committed toward granulomacrophagic and erythroid cell lines. This stimulation may result from a direct effect of the MPSV on HSC or from an indirect effect via locally secreted factors. Normal isogenic bone marrow cells were incubated in the mixed colony-forming unit system in semisolid medium supplemented with conditioned media obtained after incubating neoplastic spleen cells for 3 days at 37 degrees C. These spleen conditioned media contain an activity that is physically separable from MPSV by ultracentrifugation and which, in the presence of a very low quantity of erythropoietin, can induce in vitro the proliferation and differentiation of pluripotent HSC, detected by this Mix-CFU technique. We termed this activity mixed-colonies promoting activity (MPA). These results suggest that the hyperplasia of the nonlymphoid hematopoietic system in the neoplastic spleen results from an indirect effect of the MPSV on pluripotent HSC via locally secreted factors.

Myeloproliferative sarcoma virus stimulates pluripotent hematopoietic stem cells and provokes tumoral transformation of the hematopoietic microenvironment in vitro

The Myeloproliferative Sarcoma Virus (MPSV) induces an increase in the number and concentration of pluripotent stem cells in long-term murine bone marrow cultures. This is followed by an increased number of precursor cells of the granulocyte and macrophage lines (GM-CFC). This increase is comparable to that observed in DBA/2 mouse spleens in vivo two to three weeks after viral infection. Proliferation of CFU S and GM-CFC decreases five weeks after infection with MPSV, in parallel to the gradual decline of reverse transcriptase activity in the culture medium. GM-CFC which can proliferate in the absence of added colony stimulating factor (CSF) were detected at week 6 post MPSV infection. Adherent tumor cells were observed nine weeks after infection. These fibroblast type cells gave rise to a permanent line which produced a CSF-like activity. Our results show that MPSV causes the tumoral transformation of fibroblast-like cells of the bone-marrow hematopoietic microenvironment. In addition, MPSV also strongly stimulates the proliferation of hematopoietic stem cells. MPSV is, until now, the first murine retrovirus which exhibits such properties.

Characterization of a large genomic size Moloney murine sarcoma virus produced by a transformed rat cell line.

A rat cell line (78A1) transformed by the Moloney murine sarcoma virus-Moloney murine leukaemia virus (Mo-MuSV-MuLV) complex was found to produce a sarcoma virus different from the isolates previously described. Analysis of intracellular RNA of the 78A1 cell line by electrophoresis on agarose gel, and hybridization with DNA probes specific to M1-Mo-MuSV and v-mosMo sequences revealed a size of 6.7 kilobases (kb) for the RNA of this sarcoma virus. This genome is larger than those of m1, m3, HT1 and 124 isolates and slightly smaller than the myeloproliferative sarcoma virus genome (7.0 kb).

The Myeloproliferative Sarcoma Virus Causes Transformation of Erythroid Progenitor Cells In Vitro

The myeloproliferative sarcoma virus induces spleen focus formation in vivo and transforms fibroblasts in vitro. We showed in this study that in vitro infection of spleen or bone marrow cells from susceptible mice with the myeloproliferative sarcoma virus leads to the formation of erythroid bursts. Under optimal conditions erythroid bursts formed in the absence of added erythropoietin, but the addition of as little as 0.05 U of erythropoietin per ml to infected cultures resulted in a significant increase in numbers of erythroid bursts and the proportion of hemoglobinized cells. A comparison of the kinetics of burst formation and the size of the induced bursts with those induced with Friend virus suggested that either sarcoma virus such as the myeloproliferative sarcoma virus or the target cells for the two viruses were not the same. Density characterization and heat lability studies indicated that the increased erythroid proliferation in vitro was a virus-induced event, but the possibility that the induced erythroid burst formation is mediated via interaction with a nonerythroid target cell and subsequent release of a soluble factor cannot be ruled out.

The myeloproliferative sarcoma virus causes transformation or erythroid progenitor cells in vitro.

The myeloproliferative sarcoma virus induces spleen focus formation in vivo and transforms fibroblasts in vitro. We showed in this study that in vitro infection of spleen or bone marrow cells from susceptible mice with the myeloproliferative sarcoma virus leads to the formation of erythroid bursts. Under optimal conditions erythroid bursts formed in the absence of added erythropoietin, but the addition of as little as 0.05 U of erythropoietin per ml to infected cultures resulted in a significant increase in numbers of erythroid bursts and the proportion of hemoglobinized cells. A comparison of the kinetics of burst formation and the size of the induced bursts with those induced with Friend virus suggested that either sarcoma virus such as the myeloproliferative sarcoma virus or the target cells for the two viruses were not the same. Density characterization and heat lability studies indicated that the increased erythroid proliferation in vitro was a virus-induced event, but the possibility that the induced erythroid burst formation is mediated via interaction with a nonerythroid target cell and subsequent release of a soluble factor cannot be ruled out.

Inheritance of susceptibility to the myeloproliferative sarcoma virus: effect of the Fv-2 locus and evidence for a myeloproliferative sarcoma virus resistance locus.

Myeloproliferative sarcoma virus (MPSV) causes a generalized stem cell leukemia with erythroid and myeloid hyperplasia in adult mice. MPSV also transforms fibroblasts. Mice congenic for the Fv-2 locus showed marked differences in susceptibility to MPSV according to the Fv-2 genotype. MPSV was injected into C57BL/6 Fvs and C57BL/6 Fv-2r mice congenic except for the Fv-2 locus. C57BL/6 mice with the Fvs genotype were much more susceptible to MPSV than were those with the Fvr genotype. Both DDD Fv-2r mice congenic with DDD Fv-2s mice except for the Fv-2 locus and DDD Fv-2s mice, however, were sensitive to spleen focus formation by MPSV. These data indicate that at least one additional resistance locus to MPSV is present in C57BL/6 mice but not in DDD mice. Both the Fv-2 locus and the putative MSPV resistance locus (loci) Mpsvr appear to be epistatic to either of the sensitivity loci. Fibroblast focus formation by MPSV was obtained well in C57BL/6 Fv-2r and C57BL/6 Fvs fibroblasts, indicating that the genes for MPSV resistance (Fv-2r and Mpsvr) were not operating in fibroblast cells. A model is proposed which may account for the differences in response of genetically different mice to MPSV and Friend spleen focus-forming virus.

Study of a virus-induced myeloproliferative syndrome associated with tumor formation in mice

In 1968, Chirigos et al. showed that the PP-SV strain (plasma passage of Moloney sarcoma virus) induced the appearance of tumor nodules in the spleen and then in other hemopoietic and non-hemopoietic organs; these nodules were constituted mainly of large fusiform cells, undifferentiated mesenchyme cells and fibrosarcoma-like cells and destroyed the normal architecture of the affected organs. In this paper, we show that this tumoral phase is preceded and accompanied by important alterations of all hemopoietic organs such as spleen, thymus, liver, bone marrow as well as peripheral blood. The granulocytic and erythroid lines are the most involved by the pathological process, which is characterized by a hyperplasia of the splenic red pulp, a hematopoietic metaplasia in the liver, invasion of the blood by young cells and fibrosis of the bone marrow. All this suggests that the neoplasia is a malignant hemopathy, or a mesenchymal sarcoma characterized by its association with significant hemopoietic alterations. As the original strain of Chirigos' virus has been passaged in vivo for 2 yr before its use in this study, we have called our strain MPSV (myeloproliferative sarcoma virus). MPSV may constitute a unique murine virus which can transform in vivo hemopoietic and non-hemopoietic cells. It may be used to study the relationship between fibroblastic cells and hemopoiesis. It appears also to induce a myeloproliferative sarcoma.