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Functional roles for granzymes in murine epidermal gamma(delta) T-cell-mediated killing of tumor targets
M Mohamadzadeh1, M J McGuire, D J Smith
1Department of Dermatology, University of Texas Southwestern Medical Center, Dallas, USA.
Abstract:
Granzymes, a family of serine proteases contained in cytoplasmic granules of cytotoxic T lymphocytes and natural killer cells, play a critical role in killing tumor targets by triggering rapid breakdown of DNA and subsequent apoptosis. We have reported previously that dendritic epidermal T cells, which are skin-specific members of the tissue-type gamma(delta) T-cell family in mice, are capable of killing selected tumor cell lines. Here we report that short-term cultured dendritic epidermal T-cell lines contain significant N-alpha-benzyloxycarbonyl-L-Lys-thiobenzyl esterase activity, produce granzyme A protein, and express constitutively mRNA for granzymes A and B. Messenger RNA expression for granzyme B was also confirmed in freshly procured Thy-1+ epidermal cells (i.e., dendritic epidermal T cells). Finally, preincubation of dendritic epidermal T cell lines with a granzyme inhibitor, dichloroisocoumarin, but not with a cysteine protease inhibitor, E-64, abrogated completely their capacity to trigger DNA breakdown in YAC-1 target cells. These results reinforce the concept that dendritic epidermal T cells represent skin-resident killer cells that share several functional properties with conventional killer leukocytes, thereby playing a local immunosurveillance role against tumor development.
Insights
Dendritic epidermal T cells, skin-resident killer cells, utilize granzymes A and B to induce tumor cell apoptosis. Inhibiting granzymes abrogates their tumor-killing ability, confirming their role in skin immunosurveillance.
Area of Science:
- Immunology
- Cell Biology
- Dermatology
Background:
- Granzymes are serine proteases crucial for cytotoxic T lymphocyte and natural killer cell tumor killing.
- Dendritic epidermal T cells (DETCs) are skin-specific gamma(delta) T cells with known tumor-killing capabilities.
- The specific mechanisms and molecules involved in DETC-mediated tumor cytotoxicity require further elucidation.
Purpose of the Study:
- To investigate the expression and function of granzymes in dendritic epidermal T cells.
- To determine if granzymes are responsible for the tumoricidal activity of DETCs.
- To confirm the role of DETCs in local immunosurveillance against skin tumors.
Main Methods:
- Assessing N-alpha-benzyloxycarbonyl-L-Lys-thiobenzyl esterase activity in cultured DETC lines.
- Detecting granzyme A protein and mRNA expression (granzymes A and B) in DETCs.
- Evaluating the effect of granzyme and cysteine protease inhibitors on DETC-mediated DNA breakdown in YAC-1 target cells.
Main Results:
- Short-term cultured DETC lines exhibited significant esterase activity and produced granzyme A.
- Constitutive mRNA expression for granzymes A and B was detected in cultured DETCs and freshly isolated epidermal cells.
- A granzyme inhibitor, but not a cysteine protease inhibitor, completely abolished DETC-induced DNA breakdown in target cells.
Conclusions:
- Dendritic epidermal T cells express and utilize granzymes A and B for tumor cell killing.
- Granzymes are essential for the cytotoxic function of DETCs against tumor targets.
- DETCs function as skin-resident killer cells, contributing to local immunosurveillance and potentially preventing tumor development.