Several alterations in the mechanism of cell cycle control have been observed in human T-lymphotropic virus type I (HTLV-I)-infected cells. Here, it is reported that HTLV-I-infected cells both in their immortalized and transformed phase do not undergo apoptosis following ionizing radiation (IR) treatment. However, when IL-2 withdrawal is combined with genotoxic stress, HTLV-I-infected T-cells in their immortalized phase (IL-2-dependent) undergo apoptosis where as their transformed counterparts (IL-2-independent) do not. These results suggest that, during the transformation process, the HTLV-I-infected T-cells become less sensitive to cell death signals through the acquisition of constitutive activation of the IL-2 receptor pathway. The expression of bcl-2 and bcl-XL proteins, which are known to increase cell survival mediated by IL-2, as well as of p21waf1 and p53, was not substantially different in immortalized and transformed cells following IR. All together, these findings suggest that activation of alternative anti-apoptotic pathways, regulated by IL-2, might be responsible for the differential cell death response observed in immortalized versus transformed HTLV-I-infected T-cells.


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