Apoptotic signaling at the Golgi complex: Insights from a caspase-resistant Golgi protein

Golgin-160 is a coiled-coil protein that peripherally associates with the cytoplasmic face of the Golgi complex. Its N-terminal, non-coiled-coil domain contains three caspase cleavage sites. Mutation of these sites from aspartic acids to glutamic acids to make golgin-160(3DE), prevents its caspase cleavage.{09}Cell lines expressing golgin-160(3DE) were found to be remarkably resistant to apoptosis induced by ligation of death receptors and drugs that cause endoplasmic reticulum (ER) stress, but not by other pro-apoptotic stimuli. In cells expressing golgin-160(3DE), cleavage of endogenous (wild type) golgin-160 was also prevented following ligation of death receptors or treatment with drugs that induce ER stress, but not other stimuli. This appears to be due to failure to activate caspases to measurable levels in cells expressing golgin-I60(3DE), suggesting that expression of golgin-160(3DE) disrupts an early step in the initiation of apoptosis in response to specific stimuli.; Expression of constructs mimicking individual caspase cleavage products of golgin-160, artificial disassembly of the Golgi with drugs, and overexpression of tumor necrosis factor receptor (TNFR)-1 were unable to sensitize cells expressing golgin-160(3DE) to apoptosis following ligation of TNFR-1. Further experiments focused on the impact of golgin-160(3DE) expression on tumor necrosis factor receptor (TNFR)-1, and showed that this death receptor was mislocalized in cells expressing golgin-160(3DE). While constituitive membrane trafficking pathways were normal in cells expressing golgin-160(3DE), specialized trafficking of TNFR-1 appeared to be disrupted by expression of golgin-160(3DE). TNFR-1 primarily localized to the Golgi region of cells expressing golgin-160(wt), while it was primarily found in dispersed puncta in cells expressing golgin-160(3DE). These findings suggest that proper trafficking of TNFR-1 is important for its ability to initiate apoptosis in response to TNFalpha, and that golgin-160 is important for this trafficking.; Our observations have uncovered a novel role for golgin-160 in regulation of TNFR-1 trafficking and apoptosis initiation. Further characterization of this role may provide us with a paradigm for signal transduction occurring at the Golgi complex, and help us to better understand regulation of specialized cargo trafficking by Golgi resident proteins.