The long terminal repeat (LTR) regulates gene expression of HIV-1 by interacting with multiple host and viral factors. Cross-sectional studies in the pre-HAART era demonstrated that single nucleotide polymorphisms (SNPs) in peripheral blood-derived LTRs (a C-to-T change at position 3 of C/EBP site I (3T) and at position 5 of Sp site III (5T)) increased in frequency as disease severity increased. Additionally, the 3T variant correlated with HIV-1-associated dementia. LTR sequences derived by longitudinal sampling of peripheral blood from a single patient in the DrexelMed HIV/AIDS Genetic Analysis Cohort resulted in the detection of the 3T and 5T coselected SNPs before the onset of neurologic impairment, demonstrating that these SNPs may be useful in predicting HIV-associated neurological complications. The relative fitness of the LTRs containing the 3T and/or 5T co-selected SNPs as they evolve in their native patient-derived LTR backbone structure demonstrated a spectrum of basal and Tat-mediated transcriptional activities using the IIIB-derived Tat and colinear Tat derived from the same molecular clone containing the 3T/5T LTR SNP. In silico predictions utilizing colinear envelope sequence suggested that the patient's virus evolved from an X4 to an R5 swarm prior to the development of neurological complications and more advanced HIV disease. These results suggest that the HIV-1 genomic swarm may evolve during the course of disease in response to selective pressures that lead to changes in prevalence of specific polymorphisms in the LTR, env, and/or tat that could predict the onset of neurological disease and result in alterations in viral function.

Human T cell leukemia virus type 1 (HTLV-1)3 is the causative agent of an array of pathologic abnormalities, including the lymphoproliferative disease, adult T cell leukemia (ATL), and the neurologic disorder HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) (reviewed in Ref. 1). Among the proteins encoded by the viral genome, Tax has been identified as a key player in HTLV-1-induced pathogenesis. Functioning as a transcriptional trans-activator, Tax is known to aberrantly regulate cellular genes, prompting the genesis of ATL by interacting with a host of cellular transcription factors and signaling molecules to enhance or repress cellular gene expression (2-4). Tax affects the expression of several factors that may contribute to cellular transformation, including altered regulation of several cytokines and receptors involved in T cell growth and proliferation, such as granulocyte/macrophage colony-stimulating factor, TNF-␣, IL-15, IL-2, and IL-2R␣ (5-7). In addition, in vivo studies have demonstrated that transgenic mice expressing Tax develop a variety of cancers, including neurofibrosarcomas and large granular lymphocytic leukemias, depending on the promoter driving expression of the tax gene (8, 9).Tax has been described as an intracellular protein localizing to the nucleus by virtue of an amino-terminal nuclear localization signal (10) and has also been shown to shuttle between the nucleus and cytoplasm (11), suggesting that cytoplasmic Tax serves additional roles (reviewed in Ref. 12). Supporting this hypothesis, we previously demonstrated that Tax contains a leucine-rich nuclear export signal between amino acids 188 and 202 that facilitates its export from the nucleus to the cytoplasm (13). Tax may localize to the cytoplasm as an intermediary step during the course of its release from HTLV-1-infected cells, as demonstrated by its presence in cytoplasmic secretory-like vesicles (14). Upon its release, secreted Tax may function as an extracellular cytokine. 3 The abbreviations used are: HTLV-1, human T cell leukemia virus type 1; ATL, adult T cell leukemia; HTLV-1-associated myelopathy/tropical spastic para-

Human T cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The HTLV-1 transcriptional transactivator protein Tax plays an integral role in virus replication and disease progression. Traditionally, Tax is described as a nuclear protein where it performs its primary role as a transcriptional transactivator. However, recent studies have clearly shown that Tax can also be localized to the cytoplasm where it has been shown to interact with a number of host transcription factors most notably NF-kappaB, constitutive expression of which is directly related to the T cell transforming properties of Tax in ATL patients. The presence of a functional nuclear export signal (NES) within Tax and the secretion of full-length Tax have also been demonstrated previously. Additionally, release of Tax from HTLV-1-infected cells and the presence of cell-free Tax was demonstrated in the CSF of HAM/TSP patients suggesting that the progression to HAM/TSP might be mediated by the ability of Tax to function as an extracellular cytokine. Therefore, in both ATL and HAM/TSP Tax nuclear export and nucleocytoplasmic shuttling may play a critical role, the mechanism of which remains unknown. In this study, we have demonstrated that the calcium binding protein calreticulin interacts with Tax by co-immunoprecipitation. This interaction was found to localize to a region at or near the nuclear membrane. In addition, differential expression of calreticulin was demonstrated in various cell types that correlated with their ability to retain cytoplasmic Tax, particularly in astrocytes. Finally, a comparison of a number of HTLV-1-infected T cell lines to non-infected T cells revealed higher expression of calreticulin in infected cells implicating a direct role for this protein in HTLV-1 infection.

Human T-cell leukemia virus type 1 (HTLV-1) is etiologically linked to adult T-cell leukemia and a progressive demyelinating disorder termed HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). One of the most striking features of the immune response in HAM/TSP centers on the expansion of HTLV-1-specific CD8(+) cytotoxic T lymphocyte (CTL) compartment in the peripheral blood and cerebrospinal fluid. More than 90% of the HTLV-1-specific CTLs are directed against the viral Tax (11-19) peptide implying that Tax is available for immune recognition by antigen presenting cells, such as dendritic cells (DCs). DCs obtained from HAM/TSP patients have been shown to be infected with HTLV-1 and exhibit rapid maturation. Therefore, we hypothesized that presentation of Tax peptides by activated DCs to naIve CD8(+) T cells may play an important role in the induction of a Tax-specific CTL response and neurologic dysfunction. In this study, a pathway-specific antigen presenting cell gene array was used to study transcriptional changes induced by exposure of monocyte-derived DCs to extracellular HTLV-1 Tax protein. Approximately 100 genes were differentially expressed including genes encoding toll-like receptors, cell surface receptors, proteins involved in antigen uptake and presentation and adhesion molecules. The differential regulation of chemokines and cytokines characteristic of functional DC activation was also observed by the gene array analyses. Furthermore, the expression pattern of signal transduction genes was also significantly altered. These results have suggested that Tax-mediated DC gene regulation might play a critical role in cellular activation and the mechanisms resulting in HTLV-1-induced disease.