Genetic analysis of the short splice variant of the inhibitor of caspase-activated DNase (ICAD-S) in chicken DT40 cells

Alexander V. Ageichik, Kumiko Samejima, Scott H. Kaufmann, William C. Earnshaw

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


We have studied the regulation of the caspase-Activated DNase (CAD) by its inhibitor, ICAD. To study the role of ICAD short and long splice forms ICAD-S and ICAD-L, respectively, in vivo, we constructed chicken DT40 cell lines in which the entire coding regions of ICAD alone or ICAD plus CAD were deleted. ICAD and ICAD/CAD double knockouts lacked both DNA fragmentation and nuclear fragmentation after the induction of apoptosis. We constructed a model humanized system in which human ICAD-L and CAD proteins expressed in DT40 ICAD/CAD double knock-out cells could rescue both DNA fragmentation and stage II chromatin condensation. ICAD-S could not replace ICAD-L as a chaperone for folding active CAD in these cells. However, a modified version of ICAD-S, in which the two caspase-3 cleavage sites were replaced with two tobacco etch virus (TEV) protease cleavage sites (ICAD-S2TEV) and which was therefore resistant to caspase cleavage, did inhibit CAD activation upon induction of apoptosis in vivo. Moreover, ICAD-L2TEV was functional as a chaperone for the production of active CAD in DT40 cells. In extracts prepared from these cells, we were able to activate CAD by cleavage of ICAD-L2TEV with TEV protease under non-apoptotic conditions. Thus, ICAD appears to be the only functional inhibitor of CAD activation in these cell-free extracts. Taken together, these observations indicate that ICAD-S may function together with ICAD-L as a buffer to prevent inappropriate CAD activation, particularly in cells where ICAD-S is the dominant form of ICAD protein.

Original languageEnglish (US)
Pages (from-to)27374-27382
Number of pages9
JournalJournal of Biological Chemistry
Issue number37
StatePublished - Sep 14 2007

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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