Caspase-mediated cleavage of syntaxin 5 and giantin accompanies inhibition of secretory traffic during apoptosis.

We report the caspase-dependent cleavage of two Golgi-associated transport factors during apoptosis. The tethering factor giantin is rapidly cleaved both in vitro and in vivo at a conserved site, to generate a stable membrane-anchored domain and a soluble domain that is subject to further caspase-dependent cleavage. The t-SNARE syntaxin 5 is also cleaved rapidly, resulting in the separation of the catalytic membrane-proximal domain from an N-terminal regulatory domain. Cleavage of giantin and syntaxin 5 is accompanied by a cessation of vesicular transport between the ER and the Golgi complex, which first manifests itself as a block in ER exit. The contribution that such an inhibition of trafficking may make towards the generation of an apoptotic phenotype is discussed.