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DAP kinase links the control of apoptosis to metastasis
B Inbal1, O Cohen, S Polak-Charcon
1Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel.
Abstract:
DAP kinase is a new type of calcium/calmodulin-dependent enzyme that phosphorylates serine/threonine residues on proteins. Its structure contains ankyrin repeats and the 'death' domain, and it is associated with the cell cytoskeleton. The gene encoding DAP kinase was initially isolated as a positive mediator of apoptosis induced by interferon-gamma, by using a strategy of functional cloning. We have now tested whether this gene has tumour-suppressive activity. We found that lung carcinoma clones, characterized by their highly aggressive metastatic behaviour and originating from two independent murine lung tumours, did not express DAP kinase, in contrast to their low-metastatic counterparts. Restoration of DAP kinase to physiological levels in high-metastatic Lewis carcinoma cells suppressed their ability to form lung metastases after intravenous injection into syngeneic mice, and delayed local tumour growth in a foreign 'microenvironment' Conversely, in vivo selection of rare lung lesions following injection into syngeneic mice of low-metastatic Lewis carcinoma cells or of DAP kinase transfectants, was associated with loss of DAP kinase expression. In situ TUNEL staining of tumour sections revealed that DAP kinase expression from the transgene raised the incidence of apoptosis in vivo. DAP-kinase transfectants also showed increased sensitivity in vitro to apoptotic stimuli, of the sort encountered by metastasizing cells at different stages of malignancy. We propose that loss of DAP kinase expression provides a unique mechanism that links suppression of apoptosis to metastasis.
Insights
Death-associated protein (DAP) kinase suppresses tumor metastasis by promoting apoptosis. Loss of DAP kinase expression correlates with aggressive lung cancer and metastasis, suggesting its role in tumor suppression.
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Biology
Background:
- DAP kinase is a calcium/calmodulin-dependent serine/threonine kinase.
- Its structure includes ankyrin repeats and a death domain, and it associates with the cytoskeleton.
- Initially identified as a mediator of interferon-gamma-induced apoptosis.
Purpose of the Study:
- To investigate the potential tumor-suppressive activity of DAP kinase.
- To determine the relationship between DAP kinase expression and lung carcinoma metastasis.
Main Methods:
- Functional cloning to isolate the DAP kinase gene.
- Comparison of DAP kinase expression in high-metastatic versus low-metastatic lung carcinoma clones.
- Restoration of DAP kinase in high-metastatic cells and assessment of metastatic potential.
- In vivo and in vitro apoptosis assays.
Main Results:
- High-metastatic lung carcinoma clones lacked DAP kinase expression, unlike their low-metastatic counterparts.
- Restoring DAP kinase in highly metastatic cells reduced lung metastasis and delayed local tumor growth.
- Loss of DAP kinase expression occurred in vivo during the selection of metastatic lesions.
- DAP kinase expression increased apoptosis in tumors and enhanced sensitivity to apoptotic stimuli.
Conclusions:
- Loss of DAP kinase expression is linked to enhanced metastasis in lung carcinoma.
- DAP kinase functions as a tumor suppressor by promoting apoptosis.
- Suppression of apoptosis due to loss of DAP kinase is a mechanism contributing to cancer metastasis.