Constitutive active p21ras enhances primary T cell responsiveness to Ca2+ signals without interfering with the...

Chronic engagement of the T cell receptor mediates the induction of T lymphocyte unresponsiveness called clonal anergy. The development of such unresponsiveness has been suggested as one of the mechanisms that regulate peripheral tolerance to self-antigens and hamper the capacity of tumor antigen-specific T cells to eliminate cancerous cells. In the attempt to enhance the effector function of CD4(+) T lymphocytes and their resistance to clonal anergy induction, we have transduced primary T cells with a retroviral vector encoding active p21(ras) (Ras(Leu61)). Here we show that Ras(Leu61) elicited TCR-independent activation of the Ras-Raf-ERK pathway and conferred primary T cells with the ability to secrete IL-2 in response to stimulation with a Ca(2+) ionophore alone, without altering antigen-, CD3/CD28- and PMA/ionomycin-driven IL-2 secretion and T cell proliferation in vitro. However, chronic engagement of the TCR onthe surface of Ras(Leu61) T cells still led to an inability of the cells to produce IL-2 upon restimulation. These results indicate that enforced p21(ras) functionality enhances primary T cells responses to calcium-generated signals, but is insufficient to prevent TCR-driven T cell unresponsiveness and suggest that additional biochemical mechanisms, independent of p21(ras), negatively regulate IL-2 production in unresponsive T cells.