A COOH-terminal fragment (right) but not full-length (left) p115 induces apoptosis.

The Golgi apparatus breaks down temporarily to segregate into daughter cells during mitosis, but during apoptosis the organelle fragments irreversibly. On page 637, Chiu et al. report that cleavage of a critical tethering protein during apoptosis not only drives the fragmentation of the Golgi apparatus, but also appears to help propagate the apoptotic signal. The work adds to mounting evidence that the Golgi apparatus is a perpetrator as well as a victim of apoptosis.

The authors found that the tethering protein p115, which is essential for maintaining normal Golgi apparatus architecture, is selectively cleaved during apoptosis. The apoptotic proteases caspase-3 and caspase-8 cleave the protein in vitro, and a stable cell line expressing a cleavage-resistant form of p115 exhibits a delay in Golgi fragmentation during apoptosis. Expressing the COOH-terminal cleavage fragment of p115 in cells is sufficient to induce fragmentation, and, surprisingly, this fragment also translocates to the nucleus, where it induces apoptosis. The data suggest that the p115 COOH-terminal fragment serves two functions during apoptosis, both disrupting the Golgi apparatus as a dominant–negative inhibitor of p115, and sending a signal to the nucleus to induce other apoptotic processes. ▪