Golgi Protein Fragment Promotes Apoptosis

Science's STKE  03 Dec 2002:
Vol. 2002, Issue 161, pp. tw452
DOI: 10.1126/stke.2002.161.tw452

Chiu et al. investigated the role of the Golgi vesicle-tethering protein p115 in mediating Golgi fragmentation during apoptosis and demonstrated that caspase-dependent p115 cleavage not only contributed to Golgi fragmentation but also to the activation of downstream apoptotic signals. The Golgi apparatus undergoes fragmentation during apoptosis. Chiu et al. used immunofluorescent and Western analysis to show that the vesicle-tethering protein p115 was cleaved in response to pharmacologically induced apoptosis in COS7 cells and Fas receptor activation in HeLa cells. Experiments with caspase inhibitors in vivo and purified caspases in vitro indicated that p115 was cleaved by caspases 3 and 8. The authors used site-directed mutagenesis in combination with Western analysis to identify caspase cleavage sites. Cells expressing a cleavage-resistant p115 mutant exhibited delayed Golgi fragmentation during apoptosis, whereas cells expressing a truncation mutant corresponding to the COOH-terminal p115 cleavage fragment exhibited Golgi fragmentation and underwent apoptosis. Unexpectedly, the COOH-terminal p115 fragment, but not full-length p115 or the NH2-terminal cleavage product, localized to the nucleus when expressed in COS7 cells. By transfecting the cells with the p115 fragment in the presence of a caspase inhibitor, or in combination with the cleavage-resistant mutant (which delayed Golgi fragmentation), the authors determined that the COOH-fragment promoted apoptosis independently of its role in stimulating Golgi fragmentation.

R. Chiu, L. Novikov, S. Mukherjee, D. Shields, A caspase cleavage fragment of p115 induces fragmentation of the Golgi apparatus and apoptosis. J. Cell Biol. 159, 637-648 (2002). [Abstract] [Full Text]