Cytotoxic T lymphocytes overcome Bcl-2 inhibition: target cells contribute to their own demise.

Cytotoxic T lymphocytes (CTLs) eliminate pathogenic cells in large part through the activity of the serine protease granzyme B (grB). However, while the apoptotic activity of grB is blocked by over-expression of Bcl-2, CTLs can still kill target cells through an ill-defined Bcl-2-independent pathway. In this report, we have identified key modulators of this Bcl-2-independent cell-death pathway, which is induced by CTLs and not purified components.

Identification of {alpha}-tubulin as a granzyme B substrate during CTL-mediated apoptosis.

Cytotoxic lymphocytes induce target cell apoptosis via two major pathways: Fas/FasL and granule exocytosis. The latter pathway has largely been defined by the roles of the pore-forming protein perforin and by the serine proteinases granzymes A and B. Upon entry into target cells, the granzymes cleave substrates that ultimately result in cell death.

Granule-mediated killing by granzyme B and perforin requires a mannose 6-phosphate receptor and is augmented by cell surface heparan sulfate.

During granule-mediated killing by cytotoxic T lymphocytes or natural killer cells, the serine protease granzyme B enters the target cell by endocytosis and induces apoptosis. Previous studies suggested a role for the mannose 6-phosphate receptor, but further experiments with purified granzyme B indicated this was not essential. Additionally, it is now clear that grB is exocytosed from killer cells in a high-molecular-weight complex with the proteoglycan serglycin.

Granzyme B induces endothelial cell apoptosis and contributes to the development of transplant vascular disease.

Endothelial cell death induced by cytotoxic T cells is a key initiating event in the development of transplant vascular disease (TVD), the leading cause of late solid organ transplant failure. We studied the role of the granzyme B (GrB) pathwaye, which is one of the main mechanisms by which T cells induce apoptosis of allogeneic targets, in the pathogenesis of TVD. Granzyme B, in combination with perforin (pfn), induced apoptosis of cultured endothelial cells.

Granzyme B induces smooth muscle cell apoptosis in the absence of perforin: involvement of extracellular matrix degradation.

Objective: T cell-induced cytotoxicity, of which granzyme B is a key mediator, is believed to contribute to the pathogenesis of inflammatory vascular diseases. In this report, we investigate the mechanism of granzyme B-induced smooth muscle cell (SMC) death.

Methods And Results: The addition of purified granzyme B alone to cultured SMCs caused a significant reduction in cell viability.

The granzyme B-serglycin complex from cytotoxic granules requires dynamin for endocytosis.

Cytotoxic T lymphocytes and natural killer cells destroy target cells via the directed exocytosis of lytic effector molecules such as perforin and granzymes. The mechanism by which these proteins enter targets is uncertain. There is ongoing debate over whether the most important endocytic mechanism is nonspecific or is dependent on the cation-independent mannose 6-phosphate receptor.

Granzyme B-induced apoptosis requires both direct caspase activation and relief of caspase inhibition.

Cytotoxic lymphocytes employ Granzyme B as a potent initiator of apoptosis to cleave and activate effector caspases. Unexpectedly, cells transfected with Bcl-2 were resistant to granzyme B-induced killing, suggesting that a mitochondrial pathway was critical. Utilizing cells expressing a dominant-negative caspase 9, the current study demonstrated that caspase activation via the apoptosome was not required.