A 39 kDa fragment of endogenous ASK1 suggests specific cleavage not degradation by the proteasome

Transfected human apoptosis signal-regulating kinase 1 (ASK1) produces a 150 kDa protein. However, we have detected endogenous ASK1 predominantly as 39 and 50 kDa C-terminal and 75 and 110 kDa N-terminal fragments in a panel of nontransfected cancer cell lines and HUVEC endothelial cells. This suggests that in nonapoptotic cells, endogenous ASK1 protein is normally cleaved at a number of specific sites, some of which are in the kinase domain. Transfected ASK1 protein is known to be degraded by the proteasome. In contrast, the cleavage of endogenous ASK1 is independent of the proteasome as treatment with the proteasome inhibitor, lactacystin did not inhibit cleavage. Cisplatin treatment decreased the amount of 39 kDa C-terminal ASK1 fragments in mutant p53 cell lines suggesting a decrease in cleavage associated with apoptosis. Transfected ASK1 may, therefore, not accurately reflect the role of endogenous ASK1.

This is the peer reviewed version of the following article: Stordal, B. and Davey, R. (2008), A 39 kDa fragment of endogenous ASK1 suggests specific cleavage not degradation by the proteasome. IUBMB Life, 60: 180-184, which has been published in final form at https://doi.org/10.1002/iub.24 . This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions (https://authorservices.wiley.com/author-resources/Journal-Authors/li...) . This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.