A sheep retrovirus envelope protein is enough to trigger tumour formation in the lungs of immunodeficient mice, according to a letter in the 14 April 2005 issue of Nature (Vol. 434, No. 7035, pp. 904-907). This is the first example of a retroviral structural protein that induces tumorigenesis.
Jaagsiekte sheep retrovirus, which killed Dolly, the famous cloned sheep, causes a contagious lung cancer in sheep and goats that can lead to a significant loss of livestock. Although it has previously been shown that the viral envelope protein can transform cells in culture, the mechanism for tumour formation remains unknown. Now, Dusty Miller and colleagues report that expression of the retrovirus envelope protein in the lungs of mice causes tumorigenesis. Interaction of this protein with the sheep viral entry receptor, hyaluronidase 2, is not required, although it may facilitate tumour formation in other species.
Interestingly, the virus protein caused lethal disease in immunodeficient mice, but tumour development was almost entirely blocked in immunocompetent mice. The authors suggest that immune responses to the envelope protein may protect against the formation of tumours.
Dusty Miller (Fred Hutchinson Cancer Research Center, Seattle, WA, USA)
(C) Nature press release
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