A protein tyrosine kinase p56lck is really a normal low receptor PTK of the Src family and is expressed almost exclusively in T cells. The p56lck not just plays an important function in transducing TCR mediated activation signal via interaction with cytoplasmic regions of CD4 and CD8 coreceptor elements but inaddition it relays the G1/S transition signal from the IL 2 receptor, showing essential roles of p56lck for T cell activation and proliferation. The importance of p56lck for T cell reproduction was initially indicated CAL-101 870281-82-6 by virtue of its overexpression, producing from retroviral insertion to the lck locus in two Moloney murine leukemia virus induced lymphoid tumors. As well as the function of p56lck in Tcell reproduction, p56lck is famous to be concerned in FasL expression throughout activation activated T cell apoptosis and Fas mediated death signaling pathway leading to Bid bosom and mitochondrial cytochrome c release. Although these previous studies claim that p56lck is associated with service induced T cell apoptosis mainly via its function in upregulating FasL expression and its contribution to Fas signaling pathway, a few recent studies have Endosymbiotic theory suggested a primary dependence on p56lck for many types of apoptosis induced by ionizing radiation, ceramide, rosmarinic acid, doxorubicin, paclitaxel, or 5 fluorouracil, through modulating the mitochondria dependent apoptotic signaling pathway. On another hand, a p56lck bad murine helper T cell clone caused by p56lck specific antisense RNA expression was hypersusceptible to apoptosis when activated through TCR. The phenylalanine analog para fluorophenylalanine induced apoptosis was more significant in p56lck inferior Jurkat T cells than in p56lck positive Jurkat T cells by increasing mitochondrial cytochrome c release and resultant activation of caspase cascade. These previous data have suggested that p56lck plays a job in T cell apoptosis as a pro apoptotic or anti apoptotic modulator MAPK assay and might be differential based on initial causes provoking apoptosis, but the exact mechanism has not been completely understood. In today’s study, to understand the process underlying the apoptosis induced by the proteasome inhibitor and its modulation by protein tyrosine kinase p56lck, we examined the apoptotic signaling pathway triggered by MG132 in human acute leukemia Jurkat T cells, with focusing on ER stressmediated activation of JNK, p38MAPK, and caspase 12, and mitochondria dependent caspase pathway. In addition, we examined the result of anti apoptotic protein Bcl xL on MG132 induced apoptosis.