Oncoviral Bovine Leukemia Virus G4 and Human T-Cell Leukemia Virus Type 1 p13 ^II Accessory Proteins Interact with Farnesyl Pyrophosphate Synthetase

Abstract

G4 and p13II are accessory proteins encoded by the X region of bovine leukemia virus and human T-cell leukemia virus type 1 (HTLV-1), respectively. Disruption of the G4 and p13 II open reading frames interferes with viral spread in animal model systems, indicating that the corresponding proteins play a key role in viral replication. In addition, G4 is oncogenic in primary cell cultures and is absolutely required for efficient onset of leukemogenesis in sheep. To gain insight into the function of these proteins, we utilized the yeast two-hybrid system to identify protein partners of G4. Results revealed that G4 interacts with farnesyl pyrophosphate synthetase (FPPS), a protein involved in the mevalonate/squalene pathway and in synthesis of FPP, a substrate required for prenylation of Ras. The specificity of the interaction was verified by glutathione S-transferase (GST) pull-down assays and by coimmunoprecipitation experiments. Furthermore, confocal microscopy showed that the subcellular localization of G4 was profoundly affected by FPPS. The G4 protein itself was not prenylated, at least in rabbit reticulocyte lysate-based assays. The domain of G4 required for binding to FPPS was restricted to an amphipathic ␣-helix rich in arginine residues. Subtle mutation of this ␣-helix abrogated G4 oncogenic potential in vitro, providing a biological relevance for FPPS-G4 complex formation in cells. Finally, HTLV-1 p13 II was also found to specifically interact with FPPS (in yeast as well as in GST pull-down assays) and to colocalize with G4 in mitochondria, suggesting a functional analogy between these oncoviral accessory proteins. Identification of FPPS as a molecular partner for p13 II and G4 accessory proteins opens new prospects for treatment of retrovirus-induced leukemia.Bovine leukemia virus (BLV), a naturally occurring B-lymphotropic retrovirus, is a member of the Oncovirinae subfamily and belongs to the Deltaretrovirus genus, which also includes the human T-cell leukemia virus types 1 and 2 (HTLV-1 and -2) and the simian T-cell leukemia viruses. All these viruses share a similar genomic organization and induce related pathologies in their respective host species (reviewed in references 44 and 54). In addition to the gag, pol, and env genes, deltaretroviruses contain an X region, located between the env sequences and the 3Ј long terminal repeat. At least four proteins are encoded by this genomic region; perhaps the bestcharacterized ones are the Tax transactivator and the Rex posttranscriptional regulator. These two proteins are expressed from a single double-spliced RNA and are considered to be essential since their mutation abrogates viral infectivity or pathogenicity (39,40,52). Two additional open reading frames are transcribed from the X region, and the corresponding mRNAs potentially encode accessory proteins: R3 and G4 for BLV, p12 I /p13 II /p30 II for HTLV-1, and p10

Mitochondrial Alterations Induced by the p13II Protein of Human T-cell Leukemia Virus Type 1

“…Although the significance of these interactions is unclear, it is noteworthy that eukaryotic adenylate kinase, a probable evolutionary descendent of archaeal adenylate kinases, is a mitochondrial protein involved in energy metabolism. A more recent study demonstrated that p13 II also binds to farnesyl pyrophosphate synthetase, an enzyme involved in the mevalonate/squalene pathway, and in the synthesis of farnesyl pyrophosphate, a substrate required for prenylation of Ras (34). This property is shared by G4, a mitochondrially targeted accessory protein expressed by bovine leukemia virus, another complex retrovirus that is classified with HTLV-1 in the Deltaretrovirus genus.…”

Human T-cell leukemia/lymphoma virus type 1 nonstructural genes and their functions

“…Consistent with this model, response to FasL and the effects of p13 II are antagonized by a farnesyl transferase inhibitor . These observations are particularly interesting in light of the fact that p13 II was shown to bind to farnesyl pyrophosphate synthase, an enzyme required for the synthesis of isoprenoid precursors necessary for the farnesylation of Ras and other substrates (Lefebvre et al, 2002).…”

Mechanisms of HTLV-1 persistence and transformation

“…On the other hand, p13 binds to farnesyl pyrophosphate synthase (FPPS), an enzyme required for the prenylation of Ras (Lefebvre et al, 2002).…”