DAP KINASE LINKS THE CONTROL OF APOPTOSIS TO METASTASIS

DAP kinase is a new type of calcium/calmodulin-dependent enzyme that p hosphorylates serine/threonine residues on proteins. Its structure con tains ankyrin repeats and the 'death' domain, and it is associated wit h the cell cytoskeleton(1-3). The gene encoding DAP kinase was initial ly isolated as a positive mediator of apoptosis induced by interferon- gamma, by using a strategy of functional cloning(4). We have now teste d 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, d id not express DAP kinase, in contrast to their low-metastatic counter parts. Restoration of DAP kinase to physiological levels in high-metas tatic Lewis carcinoma cells suppressed their ability to form lung meta stases after intravenous injection into syngeneic mice, and delayed lo cal tumour growth in a foreign 'microenvironment'. Conversely, in vivo selection of rare lung lesions following injection into syngeneic mic e of low-metastatic Lewis carcinoma cells or of DAP kinase transfectan ts, was associated with loss of DAP kinase expression. In situ TUNEL s taining of tumour sections revealed that DAP kinase expression from th e transgene raised the incidence of apoptosis in vivo. DAP-kinase tran sfectants also showed increased sensitivity in vitro to apoptotic stim uli, of the sort encountered by metastasizing cells at different stage s of malignancy. We propose that loss of DAP kinase expression provide s a unique mechanism that links suppression of apoptosis to metastasis .