Selective cooperation of HTLV-1-encoded p40(tax-1) with cellular oncoproteins in the induction of hematopoietic cell proliferation

Human T cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T cell leukemia (ATL). The virus-encoded p40(tax-1), a nuclear oncoprotein, is known to promote transcription of its own as well as a variety of cellular genes. However, the mechanism by which p40(tax-1) promotes lymphocyte transformation is not fully understood. In the present study, we examined whether p40(tax-1) can induce hematopoietic cell proliferation by cooperating with the products of cellular proto-oncogenes; i.e. an activated form of the src-family protein tyrosine kinase p56(lck) (lck F505), c-Myc or Bcl-2. These oncoproteins are critical mediators of interleukin 2 (IL-2)-induced proliferative signals. We show that p40(tax-1) alone cannot render the hematopoietic cell line, BAF-B03, able to proliferate in the absence of cytokines, but it can do so in cooperation with lckF505, or c-Myc but not with Bcl-2.