High levels of the DNA‐binding activity of E2F in adult T‐cell leukemia and human T‐cell leukemia virus type I‐infected cells: possible enhancement of DNA‐binding of E2F by the human T‐cell leukemia virus I transactivating protein, Tax

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Abstract
Transcription factor E2F binds to cellular promoters of certain growth- and cell cycle-controlling genes and forms distinct heteromeric complexes with other nuclear proteins. It has therefore been proposed that E2F is involved in cellular proliferation control. Human T-cell leukemia virus type I (HTLV-I) is an etiological agent of adult T-cell leukemia (ATL). We show here by mobility-shift assay that E2F-containing DNA-binding complexes were detected in HTLV-I-infected T-cell lines and leukemic cells obtained from ATL patients but not in an uninfected T-cell line, Jurkat, and normal peripheral blood mononuclear cells. The Tax protein, encoded by HTLV-I, is a potent transcription activator of viral and several cellular genes. We demonstrate that expression of Tax can induce the E2F-containing DNA-binding complexes in Jurkat T cells. Thus, Tax, through enhancement of the DNA-binding activity of E2F, may be capable of regulating cellular gene expression implicated in the proliferation and transformation of T cells in ATL. This activity may be relevant to the mechanisms whereby HTLV-I which does not contain oncogenes induces neoplasia.