Comparison of myeloproliferative sarcoma virus with Moloney murine sarcoma virus variants by nucleotide sequencing and heteroduplex analysis

Abstract

The myeloproliferative sarcoma virus (MPSV) was derived by passage of Moloney sarcoma virus (Mo-MuSV) in adult mice. Mo-MuSV variants transform fibroblasts. However, MPSV also affects erythroid, myeloid, and hematopoietic stem cells. The MPSV proviral genome, two temperature-sensitive mutants derived from it, Mo-MuSV variant M1, and Moloney murine leukemia virus (Mo-MuLV) were compared by heteroduplex mapping. MPSV wild type was found to have 1 kilobase pair deleted from the pol gene and to contain v-mos-related sequences. The 3' end of MPSV, including the oncogene-helper junctions, the v-mos gene, and the 3' long terminal repeat, was sequenced and compared with sequences of Mo-MuLV, MSV-124, and the mouse oncogene c-mos. From these data, MPSV appears to be either closely related to the original Mo-MuSV or an independent recombinant of Mo-MuLV and c-mos. Five possible explanations of the altered specificity of MPSV are considered. (i) The MPSV mos protein has properties inherent in c-mos but lost by other Mo-MuSV mos proteins. (ii) The MPSV mos protein has altered characteristics due to amino acid changes. (iii) Due to a frameshift, MPSV codes for a mos protein truncated at the amino terminal and also a novel peptide. (iv) A second novel peptide may be encoded from the 3' env region. (v) MPSV has long terminal repeats and an enhancer sequence more like Mo-MuLV than Mo-MuSV, with a consequently altered target cell specificity.

A temperature-sensitive mutant of the myeloproliferative sarcoma virus, altered by a point mutation in the mos oncogene, has been modified as a selectable retroviral vector

“…Recombinants between WT and ts mutants. Restriction analysis and heteroduplex analysis of the molecularly cloned ts159 and WT MPSV revealed no obvious explanation for the ts phenotype (25,45). Although ts159 carries a second deletion of 1.5 kilobases in the pol gene compared with WT a Helper-free viruses neor-MPSV and neor_ts159 were obtained from transfected psi-2 clones and used for infection of RAT1 cells.…”

“…Nucleotide sequence of the ts159 mos region. The cloned tslS9 provirus was sequenced from the BglII site at position 226 in the published WT MPSV sequence (45), 668 bases upstream from the pollc-mos junction, to the EcoRV site at position 2154, 154 base pairs downstream from the v-mos stop codon, to define the potential mutation(s) conferring the conditional phenotype (Fig. 3).…”

“…The gene product responsible for Mo-MuSV transformation has been identified as p37mos in Mo-MuSV 124-infected cells (37). There is evidence that MPSV may produce a protein, p34mos, which is slightly shorter at the N terminus due to initiation from a downstream start codon that also corresponds to the first in-frame AUG in the c-mos gene (45). However, no differences have been detected in transforming properties between the MPSV and Mo-MuSV mos proteins or the c-mos protein that reflect this or other slight differences in the coding region between the proteins (46).…”

“…It should be possible to select for neor-ts159-infected cell lines that produce larger quantities of mos protein at the nonpermissive temperatures to facilitate these studies. Analysis of MPSV ts mos has the additional advantage of other mos proteins studied so far (e.g., p859a'm's [1], p37gag-mos [37], and p40mOS [44]) in that it more closely resembles the proposed c-mos amino acid sequence with conserved N atnd C termini (45).…”

“…MPSV is closely related to the replicationdefective family of Mo-MuSV, comprising sequences derived from the Moloney murine leukemia virus (Mo-MuLV) and c-mos. Infection of adult mice with either MPSV or Mo-MuSV strains results in tumor production attributed to enhanced expression of v-mos by the viral long terminal repeats (LTRs); however, the v-mos (or c-mos) oncogene under transcriptional control of the MPSV LTR also induces transformation of epithelial cells (17), embryonic cell lines (43), and hematopoietic cells (45,46), the latter resulting in increased proliferation of hematopoietic stem cells, late erythroid precursor cells and granulocyte-macrophage eosinophil, and megakaryocyte precursors (13, 22, 33, 33a).…”