L233P mutation in the bovine leukemia virus Tax protein depresses endothelial cell recruitment and tumorigenesis in athymic nude mice
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Bovine leukemia virus (BLV) can be divided into two categories based on the amino acid at position 233 in the Tax protein, which probably plays a crucial role in leukemogenesis. We show here that a rat fibroblast cell line stably expressing L233-Tax formed significantly larger tumors than P233-Tax-expressing cells in a murine xenograft study. Although the microvessel density was comparable in both tumors, visible blood vessel invasion was observed only on tumors from L233-Tax-expressing cells. Endothelial cell tube formation assays using human umbilical vein endothelial cells showed no significant difference in angiogenic activity between conditioned medium from L233- and P233-Tax-expressing cells, whereas in vitro chemotaxis assays revealed that only L233-Tax-expressing cells produced a chemoattractant for endothelial cells. Since pathological neovascularization can occur from the recruitment of endothelial progenitor cells, these results suggest that L233-Tax-expressing cells recruit murine endothelial progenitor cells and promote neovascularization to support tumor growth. BLV-infected lymphoma cells may also recruit bovine endothelial progenitor cells to promote neovascularization. The findings of this study are consistent with our previous observation that BLV carrying P233-Tax has a significantly longer incubation period for developing tumors than the virus carrying L233-Tax and provide insight into the function of Tax in leukemogenesis by BLV.
Bovine leukemia virus
Human T-lymphotropic virus
Enzootic bovine leucosis
Long terminal repeat
Adult T-cell leukemia
HTLV-1 basic leucine zipper factor
Human umbilical vein endothelial cell
Dulbecco’s modified Eagle’s medium
Relative firefly luciferase unit
Ham’s F12 medium:DMEM (1:1)
We would like to thank Sapporo General Pathology Laboratory for immunohistochemical staining. We also thank Edanz Group (www.edanzediting.com/ac) for editing a draft of this manuscript.
This work was supported in part by grants from the Project of the NARO Bio-Oriented Technology Research Advancement Institution (the special scheme project on vitalizing management entities of agriculture, forestry and fisheries) [grant number 16930291] and by the Ministry of Education, Culture, Sports, Science and Technology of Japan [grant numbers 24580451, 16K08060] to KO.
Compliance with ethical standards
Conflicts of interest
The authors declare that there are no conflicts of interest.
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