ASC, a novel 22-kDa protein, aggregates during apoptosis of human promyelocytic leukemia HL-60 cells

The cytoskeletal and/or nuclear matrix molecules responsible for morphologi cal changes associated with apoptosis were identified using monoclonal anti bodies (mAbs). We developed mAbs against Triton X-100-insoluble components of HL-60 cells pretreated with all-trans retinoic acid. In particular, one mAb recognized a 22-kDa protein that exhibited intriguing behavior by formi ng an aggregate and appearing as a speck during apoptosis induced by retino ic acid and other anti-tumor drugs. Cloning and sequencing of its cDNA reve aled that this protein comprises 195 amino acids and that its C-terminal ha lf has a caspase recruitment domain (CARD) motif, characteristic of numerou s proteins involved in apoptotic signaling. We referred to this protein as ASC (apoptosis-associated Speck-like protein containing a CARD). The ASC ge ne was mapped on chromosome 16p11.2-12. The antisense oligonucleotides of A SC were found to reduce the expression of ASC, and consequently, etoposide- mediated apoptosis of HL-60 cells was suppressed. Our results indicate that ASC is a novel member of the CARD-containing adaptor protein family.