Recombinant mink cell focus-inducing virus and long terminal repeat alterations accompany the increased leukemogenicity of the Mo+PyF101 variant of Moloney murine leukemia virus after intraperitoneal inoculation.
We recently showed that different routes of inoculation affect the leukemogenicity of the Mo+PyF101 variant of Moloney murine leukemia virus (M-MuLV). Intraperitoneal (i.p.) inoculation of neonatal mice with Mo+PyF101 M-MuLV greatly enhanced its leukemogenicity compared with subcutaneous (s.c.) inoculation. We previously also suggested that the leukemogenicity defect of Mo+PyF101 M-MuLV when inoculated s.c. may result from the inability of this virus to form env gene recombinant (mink cell focus-inducing [MCF]) virus. In this study, virus present in end-stage tumors and in preleukemic animals inoculated i.p. by Mo+PyF101 M-MuLV was characterized. In contrast to s.c. inoculation, all tumors from i.p.-inoculated mice contained high levels of recombinant MCF virus. Furthermore, Southern blot analyses demonstrated that the majority of the tumors contained altered Mo+PyF101 M-MuLV long terminal repeats. The U3 regions from several tumors with altered long terminal repeats were cloned by PCR amplification. Sequence analyses indicated that the M-MuLV 75-bp tandem repeat in the enhancer region was triplicated. This amplification was also previously observed in mice infected s.c. with a pseudotypic mixture of Mo+PyF101 M-MuLV and Mo+PyF101 MCF virus. The enhancer triplication was an early event, and it occurred within 2 weeks postinfection. Recombinant MCF viruses were not detected by Southern blot analyses until 4 weeks postinfection. Thus, the M-MuLV enhancer triplication event was initially important for efficient propagation of ecotropic Mo+PyF101 M-MuLV. The increased leukemogenicity following i.p. inoculation could be explained if the triplication enhances Mo+PyF101 M-MuLV replication in the bone marrow and bone marrow infection is required for recombinant MCF virus formation.
Belli
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Department of Molecular Biology and Biochemistry, University of California, Irvine 92717.
Patel
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Fan
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D016475:3T3 Cells; D000818:Animals; D003001:Cloning, Molecular; D004742:Enhancer Elements, Genetic; D015972:Gene Expression Regulation, Neoplastic; D007942:Leukemia, Experimental / Q000821:virology*; D051379:Mice; D008908:Mink Cell Focus-Inducing Viruses / Q000235:genetics / Q000302:isolation & purification*; D008979:Moloney murine leukemia virus / Q000235:genetics*; D011120:Polyomavirus / Q000235:genetics*; D011289:Preleukemia / Q000821:virology; D011519:Proto-Oncogenes; D011533:Proviruses / Q000302:isolation & purification; D012091:Repetitive Sequences, Nucleic Acid; D012192:Retroviridae Infections / Q000821:virology*; D014412:Tumor Virus Infections / Q000821:virology*