Truncation of cytoplasmic tail of EIAV Env increases the pathogenic necrosis

Equine Infectious Anemia Virus (EIAV), like other lentiviruses, has a transmembrane glycoprotein with an unusually long cytoplasmic tail (CT). Viral envelope (Env) proteins having CT truncations just downstream the putative membrane-spanning domain (PMSD) are assumed to exist among all wild-type budded virions, and also in some cell-adapted strains. To determine whether CT-truncated Env proteins can cause particularly deleterious effects on the Env expressing cells and/or their neighboring cells, plasmids encoding codon-optimized env gene including full-length (pE863) or CT-truncated (pE686* and pE676*) were transiently transfected into 293T cells, respectively. Data from intracellular protein expression and cell death assays revealed that CT-truncated Env, compared to full-length Env, not only induced comparable apoptosis, but also caused much more intensive mitochondria-mediated necrosis that could simultaneously induce significant decrease of intracellular protein expression in the Env expressing cells. Moreover, results from flow cytometric analysis showed that mitochondrial depolarization preceded the caspase activation in cells no matter which env construct was delivered, and indicated that both full-length and CT-truncated Env proteins share a common intrinsic mitochondrial pathway to induce apoptosis. Our results partially elucidate the mechanisms underlying cell death resulting from EIAV pathogenesis.