No abstract

The I-mfa domain proteins HIC (also known as MDFIC) and I-mfa (also known as MDFI) are candidate tumor suppressor genes that are involved in cellular and viral transcriptional regulation. Here, we show that HIC and I-mfa directly interact with human T-cell leukemia virus type-1 (HTLV-1) Tax protein in vitro. In addition, HIC and I-mfa repress Tax-dependent transactivation of an HTLV-1 long terminal repeat (LTR) reporter construct in COS-1, Jurkat and high-Tax-producing HTLV-1-infected T cells. HIC also interacts with Tax through its I-mfa domain in vivo and represses Tax-dependent transactivation of HTLV-1 LTR and NF-κB reporter constructs in an interaction-dependent manner. Furthermore, we show that HIC decreases the nuclear distribution and stimulates the proteasomal degradation of Tax. These data reveal that HIC specifically interacts with HTLV-1 Tax and negatively regulates Tax transactivational activity by altering its subcellular distribution and stability.

No abstract

Human T-lymphotropic virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia/lymphoma (ATL). Miscellaneous host immune surveillance systems control T-cell growth/leukemogenesis during HTLV-1 infection. We characterized CD70 and CD27 expression on lymphocytes of HTLV-1 carriers and patients with ATL (study approved by the local Medical Ethical Committee). High CD70 expression was observed on CD4 + CD25+ T cells from patients with acute-type ATL, while patients with smoldering- or chronic-type ATL and HTLV-1 carriers exhibited lower expression. Furthermore, significantly higher CD27 expression was observed on HTLV-1-specific CTLs. We found an association between CD70 expression on CD4 + T cells and HTLV-1 infection; increased CD70 expression was observed after exposure to Tax. Moreover, addition of anti-CD70 antibodies enhanced the CD107a surface mobilization of HTLV-1 Tax-specific CTLs following Tax-peptide stimulation in the PBMCs of carriers. These data demonstrate the important role of the CD70/CD27 axis in immune responses in HTLV-1 carriers and ATL patients.

Despite the efficacy of combination chemotherapy with arsenic trioxide (ATO), interferon α (IFN) and zidovudine (AZT) for adult T cell leukemia/lymphoma (ATL), the precise mechanism underlying this combination treatment effect is unknown. In the present study, ATO/IFN/AZT was examined in an ATL leukemic cell line (S1T, non-Tax expressing), a human T-lymphotropic virus 1 (HTLV-1)-infected cell line (MT2, Tax-expressing) and primary ATL cells from patients with acute and chronic ATL. IFN/AZT marginally inhibited MT2 cell proliferation, but substantially inhibited S1T cell proliferation. IFN/AZT increased the cleavage of numerous caspases and PARP in S1T cells, and regulated the signal transducer and activator of transcription 1 and nuclear factor-κB signaling pathway. These effects represent the potential anti-ATL mechanisms of INF/AZT . In addition, the combination of ATO and IFN/AZT demonstrated synergistic effects on S1T cells. Therefore, the Tax-independent mechanism underlying the anti-ATL effect of ATO must be further elucidated.