Dominant expression of a novel splice variant of caspase-8 in human peripheral blood lymphocytes.

Caspase-8 is an apical and critical proteolytic enzyme in the cascade of apoptosis. As a result of alternative splicing, the generation of at least 7 isoforms of caspase-8 has been reported. The existence of multiple isoforms that lack the essential domains for apoptosis suggests the possible role of these isoforms on the regulation of apoptosis. Here we report a novel longer isoform of caspase-8 (caspase-8L) that was generated by alternative splicing of intron 8, thereby carrying a 136-bp insertion and frame shift of the transcript. The transcript encoded N-terminal two repeats of death effector domain (DED) of caspase-8, but lacking the C-terminal half of the proteolytic domain. Reverse transcriptase (RT)-polymerase chain reaction (PCR) analysis revealed the dominant expression of caspase-8L transcript compared to the intact form of caspase-8 in human peripheral blood lymphocyte (PBL) and T cells. In patients with systemic lupus erythematosus (SLE), imbalanced expression of caspase-8L transcript was identified. These results suggest the important role of caspase-8L in the modulation of apoptosis. Copyright 2000 Academic Press.