A soluble envelope protein of endogenous retrovirus (FeLIX) present in serum of domestic cats mediates infection of a pathogenic variant of feline leukemia virus.
T-lymphotropic feline leukemia virus (FeLV-T), a highly pathogenic variant of FeLV, induces severe immunosuppression in cats. FeLV-T is fusion defective because in its PHQ motif, a gammaretroviral consensus motif in the N terminus of an envelope protein, histidine is replaced with aspartate. Infection by FeLV-T requires FeLIX, a truncated envelope protein encoded by an endogenous FeLV, for transactivation of infectivity and Pit1 for binding FeLIX. Although Pit1 is present in most tissues in cats, the expression of FeLIX is limited to certain cells in lymphoid organs. Therefore, the host cell range of FeLV-T was thought to be restricted to cells expressing FeLIX. However, because FeLIX is a soluble factor and is expressed constitutively in lymphoid organs, we presumed it to be present in blood and evaluated its activities in sera of various mammalian species using a pseudotype assay. We demonstrated that cat serum has FeLIX activity at a functional level, suggesting that FeLIX is present in the blood and that FeLV-T may be able to infect cells expressing Pit1 regardless of the expression of FeLIX in vivo. In addition, FeLIX activities in sera were detected only in domestic cats and not in other feline species tested. To our knowledge, this is the first report to prove that a large amount of truncated envelope protein of endogenous retrovirus is circulating in the blood to facilitate the infection of a pathogenic exogenous retrovirus.
Laboratory of Signal Transduction, Department of Cell Biology, Institute for Virus Research, Kyoto University, 53 Shogoin-Kawaharacho, Sakyo-ku, Kyoto 606-8507, Japan.|Laboratory of Virolution, Experimental Research Center for Infectious Diseases, Institute for Virus Research, Kyoto University, 53 Shogoin-Kawaharacho, Sakyo-ku, Kyoto 606-8507, Japan.
Shoichi
S
Sakaguchi
Laboratory of Signal Transduction, Department of Cell Biology, Institute for Virus Research, Kyoto University, 53 Shogoin-Kawaharacho, Sakyo-ku, Kyoto 606-8507, Japan.
Takayuki
T
Shojima
Asahikawa Municipal Asahiyama Zoological Park and Wildlife Conservation Center, Kuranuma, Higashiasahikawa-cho, Asahikawa, Hokkaido 070-8205, Japan.
Daisuke
D
Fukui
Laboratory of Signal Transduction, Department of Cell Biology, Institute for Virus Research, Kyoto University, 53 Shogoin-Kawaharacho, Sakyo-ku, Kyoto 606-8507, Japan.|Laboratory of Virolution, Experimental Research Center for Infectious Diseases, Institute for Virus Research, Kyoto University, 53 Shogoin-Kawaharacho, Sakyo-ku, Kyoto 606-8507, Japan.
Takayuki
T
Miyazawa
D000818:Animals; D002415:Cats; D002460:Cell Line; D005256:Leukemia Virus, Feline / Q000235:genetics* / Q000472:pathogenicity*; D011991:Receptors, Virus / Q000097:blood* / Q000378:metabolism; D012192:Retroviridae Infections / Q000662:veterinary* / Q000821:virology; D014412:Tumor Virus Infections / Q000662:veterinary* / Q000821:virology; D014774:Virulence
C405955:FeLIX protein, feline leukemia virus; D011991:Receptors, Virus