Induction of Human T Cell Leukemia Virus Type I Receptors on Quiescent Naive T Lymphocytes by TGF-β

Abstract

The retrovirus human T cell leukemia virus (HTLV) type I (HTLV-I) is primarily transmitted by breast-feeding or sexual contact, by cell-to-cell contact between T cells. TGF-beta, which has been shown to enhance transmission of HTLV-I in vitro, is found at high levels in breast milk and semen. In this study, the ability of TGF-beta to regulate expression of molecules involved in HTLV-I binding and entry was examined. Previous studies using a soluble form of the HTLV-I envelope protein SU have shown that quiescent human T cells do not express cell surface molecules that specifically bind SU. After T cell activation, HTLV SU binding proteins are rapidly induced. In this study, we report that TGF-beta induces expression of proteins that bind soluble HTLV SU and HTLV virions on naive CD4(+) T lymphocytes. The induction of these proteins occurred without cell cycle entry or expression of activation markers, involved TGF-beta-induced intracellular signaling, and required de novo transcription and translation. Treatment of naive CD4(+) T lymphocytes with TGF-beta induced expression of GLUT-1, which has recently been reported to function as a receptor for HTLV. Treatment of a TGF-beta-sensitive human myeloid cell line increased the titer of both HTLV-I- and HTLV-II-pseudotyped viruses. Although earlier studies suggested that HTLV SU binding proteins might be an early marker of T cell activation and/or cell proliferation, we report in this study that TGF-beta induces binding of HTLV virions and expression of glucose transporter type 1 in primary CD4(+) T lymphocytes that remain quiescent.