The Oncogenic Jaagsiekte Sheep Retrovirus Cytoplasmic Tail Adopts a Unique Conformation on a Phosphocholine Surface

Abstract

Jaagsiekte sheep retrovirus (JSRV) is the etiologic agent of a transmissible lung cancer in sheep, ovine pulmonary adenocarcinoma (OPA). OPA resembles bronchiole-alveolar carcinoma in humans, and it is an excellent animal model for this disease. A unique feature of JSRV is that the viral envelope (Env) protein also functions as an oncogene, in that expression JSRV Env protein causes morphological transformation of fibroblast and epithelial cell lines, and vectored Env expression induces epithelial tumors in several animals. Previous studies showed that the region containing the short 46 amino acid C-terminal cytoplasmic tail (CT) of JSRV Env is essential for the ability of JSRV to transform cells. Residues in the cytoplasmic tail include a tyrosine (Y590), which is present in a consensus motif YXXM, which could potentially bind the regulatory subunit of phosphatidyl inositol 3-kinase (PI3K) if the Y590 is phosphorylated. Alanine scanning mutagenesis on the JSRV TM cytoplasmic tail has been conducted. Mutation of some residues abolished Env transformation potential, while mutation of other residues had not effect or partial effects. To further understand the mechanism of JSRV transformation, structure-function analysis of the TM cytoplasm tail (CT) is important. We have determined the structure of the JSRV CT using NMR spectroscopy. These data allow us to interpret the alanine scanning mutagenesis, and allow better understanding of previous studies. Interestingly, using both CD and NMR, we find that the CT is only structured in the presence of a phosphocholine surface. The results validated some aspects of the predicted structure, and they also provided a basis for evaluating models of transformation.This work was funded by NIH CA94188