DAP-kinase: from functional gene cloning to establishment of its role in apoptosis and cancer

DAP-kinase is a pro-apoptotic Ca2+ calmodulin-regulated serine/threonine ki nase that participates in a wide array of apoptotic systems initiated by in terferon-gamma, TNF-alpha, activated Fas, and detach ment from extracellula r matrix, It was isolated by an unbiased functional approach to gene clonin g aimed at hitting central mediators of the apoptotic process. This 160 Kd protein kinase is localized to actin microfilaments and carries interesting modules such as ankyrin repeats and the death domain. The death promoting effects of DAP-kinase depend on its intact catalytic activity, the correct intracellular localization, and on the presence of the death domain, A few mechanisms restrain the killing effects of the protein in healthy cells, Th e enzyme's active site is negatively controlled by an adjacent CaM regulato ry domain whose effect is relieved by binding to Ca2+-activated calmodulin. A second mode of autoinhibition engages the serine-rich C-terminal tail, s panning the last 17 amino acids of the protein. A link between DAP-kinase a nd cancer has been established. It was found that the mRNA and protein expr ession is frequently last in various human cancer cell lines. Analysis of t he methylation status of DAP-kinase's 5' UTR in DNA extracted from fresh tu mor samples, showed high incidence of hypermethylation in several human car cinomas and B cell malignancies. The antitumorigenic effect of DAP-kinase w as also studied experimentally in mouse model systems where the re-introduc tion of DAP-kinase into highly metastatic mouse lung carcinoma cells who ha d lost the protein, strongly reduced their metastatic capacity. Thus, it ap pears that loss of DAP-kinase confers a selective advantage to cancer cells and may play a causative role in tumor progression. A few novel kinases sh aring high homology in their catalytic domains with DAP-kinase have been re cently identified constituting altogether a novel family of death promoting serine/threonine kinases.