EXPERIMENTAL PROCEDURES Yeast

Golgin-160, a ubiquitous protein in vertebrates, localizes to the cytoplasmic face of the Golgi complex. Golgin-160 has a large coiled-coil C-terminal domain and a non-coiled-coil N-terminal (“head”) domain. The head domain contains important motifs, including a nuclear localization signal, a Golgi targeting domain, and three aspartates that are recognized by caspases during apoptosis. Some of the caspase cleavage products accumulate in the nucleus when overexpressed. Expression of anon-cleavable formof golgin-160 impairs apoptosis induced by some pro-apoptotic stimuli; thus cleavage of golgin-160 appears to play a role in apoptotic signaling. We used a yeast two-hybrid assay to screen for interactors of the golgin-160head and identified GCP60 (Golgi complex-associated protein of 60 kDa). Further analysis demonstrated that GCP60 interacts preferentially with one of the golgin-160 caspase cleavage fragments (residues 140–311). This strong interaction prevented the golgin-160 fragment from accumulating in the nucleus when this fragment and GCP60 were overexpressed. In addition, cells overexpressing GCP60 were more sensitive to apoptosis induced by staurosporine, suggesting that nuclear-localized golgin-160-(140–311) might promote cell survival. Our results suggest a potential mechanism for regulating the nuclear translocation and potential functions of golgin-160 fragments.