CPAN, A HUMAN NUCLEASE REGULATED BY THE CASPASE-SENSITIVE INHIBITOR DFF45

Induction of apoptosis by death receptors such as Fas or tumour necros is factor (TNF) R1 leads to distinct changes in cell morphology, activ ation of the caspase protease cascade, and the degradation of nuclear chromatin by activated nucleases, Here, we describe the purification a nd cDNA cloning of a novel 40 kDa endonuclease from Jurkat cells that is activated by caspases, This protein, designated caspase-activated n uclease (CPAN), is sufficient to degrade naked DNA and to induce apopt otic morphology and DNA fragmentation in naive nuclei. CPAN is highly homologous to a recently described mouse nuclease, CAD [1], and may re present the human homologue, Our data on the human cDNA as well as add itional data on the mouse homologue suggest that a 30 amino-acid porti on of the recently published misuse sequence [1] is incorrect. We show that the activity of human CPAN is regulated by DFF45 [2], an inhibit or necessary for CPAN expression and stabilization in an inactive stat e in living cells. Proteolytic cleavage of DFF45 by caspases in vitro leads to dissociation of DFF45 fragments from CPAN and activation of C PAN as an endonuclease. CPAN is a tightly regulated endonuclease with unique characteristics that might represent a distinctive family of en donucleases.