Bone marrow cells carrying the env-pX transgene play a role in the severity but not prolongation of arthritis in human T-cell leukaemia virus type-I transgenic rats: a possible role of articular tissues carrying the transgene in the prolongation of arthritis

Characterizing the protonation states of the catalytic residues in apo and substrate-bound human T-cell leukemia virus type 1 protease

Human T-cell leukemia virus type 1 (HTLV-1) protease is an attractive target when developing inhibitors to treat HTLV-1 associated diseases. To study the catalytic mechanism and design novel HTLV-1 protease inhibitors, the protonation states of the two catalytic aspartic acid residues must be determined. Free energy simulations have been conducted to study the proton transfer reaction between the catalytic residues of HTLV-1 protease using a combined quantum mechanical and molecular mechanical (QM/MM) molecular dynamics simulation. The free energy profiles for the reaction in the apo-enzyme and in an enzyme - substrate complex have been obtained. In the apo-enzyme, the two catalytic residues are chemically equivalent and are expected to be both unprotonated. Upon substrate binding, the catalytic residues of HTLV-1 protease evolve to a singly protonated state, in which the OD1 of Asp32 is protonated and forms a hydrogen bond with the OD1 of Asp32', which is unprotonated. The HTLV-1 protease-substrate complex structure obtained from this simulation can serve as the Michaelis complex structure for further mechanistic studies of HTLV-1 protease while providing a receptor structure with the correct protonation states for the active site residues toward the design of novel HTLV-1 protease inhibitors through virtual screening.

Pathogenesis of Vasculitis in env-pX Rats

Transgenic rats carrying the env-pX gene of human T-cell leukemia virus type I (env-pX rats) develop necrotizing angiitis resembling human polyarteritis nodosa (PN). In the development of vasculitis in these rats, the thymus plays an important role. In this review, we provide an outline of the pathogenesis of vasculitis observed in env-pX rats, and discuss the developmental mechanism of human necrotizing angiitis such as PN with an unknown cause. (*English Translation of J Jpn Coll Angiol 2009; 49: 17-20.).

Cyclic AMP response element-binding protein is implicated in IL-6 production from arthritic synovial cells

Overproduction of interleukin (IL)-6 from synovial cells is critically involved in the pathogenesis of rheumatoid arthritis (RA). Cyclic adenosine monophosphate (AMP) response element-binding protein (CREB), a leucine zipper transcription factor, is expressed at a high level in synovial cells of patients with RA. Although CREB transactivates IL-6 expression in vascular smooth muscle cells, the relation between CREB expression and IL-6 production from arthritic synovial cells remains unclear. In this study, to determine whether CREB is implicated in IL-6 production from arthritic synovial cells, a dominant negative molecule of activation transcription factor 1 (ATF-1) was transfected into synovial cells obtained from arthritic joints of env-pX rats. These transgenic rats carrying the env-pX gene of human T-cell leukemia virus type-1 develop destructive arthritis with high titers of serum rheumatoid factor and are thus regarded as a suitable model of RA. The dominant negative ATF-1 (ATF-1DN) constitutes a heterodimer with CREB and inhibits CREB function, as CREB/ATF-1DN heterodimers no longer bind to the target sequence of CREB. We showed that transfection of ATF-1DN significantly reduced IL-6 production from arthritic synovial cells. These findings suggest that CREB is implicated in IL-6 production from synovial cells and plays an important role in RA pathogenesis.

Human endogenous retrovirus-R Env glycoprotein as possible autoantigen in autoimmune disease

It has long been discussed whether endogenous retroviruses (ERVs) are involved in the pathogenesis of autoimmune diseases. Among various human endogenous retroviruses (HERVs), we have focused on HERV-R. To investigate the biological roles of HERV-R, we earlier established transgenic rats carrying the full sequence of the viral genome. In these HERV-R rats, however, no disease occurred. Another trigger that induces autoimmunity may be essential for the recognition of HERV-R products by the immune system. Thus, in this study, we mated HERV-R rats with env-pX rats (transgenic rats carrying the env-pX gene of human T cell leukemia virus type I) that develop autoimmune diseases, and generated double transgenic (DTG) rats. In DTG rats, autoimmune diseases occurred similarly in env-pX rats. Interestingly, deposition of rat IgM but not IgG was observed on the glomerular endothelial cells. Such IgM deposition was never seen in the parental HERV-R or env-pX rats. We considered that in situ formation of immune complexes consisted of the HERV-R env glycoprotein and anti-HERV-R env IgM antibodies (Abs) in DTG rats, according to the following evidence: (1) No dense deposit, representing deposition of circulating immune complexes, was seen on glomerular endothelial cells. (2) IgM Abs reactive with HERV-R env glycoprotein were generated in the serum. (3) HERV-R env glycoprotein was expressed in the kidney, specifically on glomerular endothelial cells. (4) IgM deposition was partly colocalized with the HERV-R env glycoprotein on the glomeruli. These findings strongly suggest that the HERV-R env glycoprotein is recognized as an autoantigen in the host with autoimmune diseases.

Malignant transformation of thymoma in recipient rats by heterotopic thymus transplantation from HTLV-I transgenic rats

Transgenic rats expressing the pX gene of human T lymphocyte virus type-I (HTLV-I) under control of the rat lymphocyte-specific protein tyrosine kinase type-I promoter (lck-pX rats) developed benign epithelial thymomas. When the thymuses of newborn lck-pX rats were transplanted into the subcapsular space of the kidney in other thymectomized lck-pX rats, similar tumors developed in the transplanted thymuses. Following the tumor growth, dissemination in the abdominal cavity and distant metastasis occurred. The tumors were histopathologically similar to the original thymomas, but prominent nuclear atypia and high mitotic activity were present. The Ki-67 index was twice as high as that in the originals. The tumors were transplantable into the subcutis of lck-pX rats, although transplantation of the originals never succeeded. All evidence indicated that malignant transformation of thymoma was induced by the heterotopic transplantation. Expression of the pX transgene in the transformed tumors were significantly reduced. Among host genes, the expression of p16ink4a/ARF, which was significantly upregulated in the originals, was never detected in the transformed tumors. Genomic Southern blots and PCR suggest that homozygous deletion of the p16ink4a/ARF gene may play important roles in malignant transformation in this model. Our model described here is a useful unique model for in vivo malignant transformation.