Protection from Endogenous Perforin: Glycans and the C Terminus Regulate Exocytic Trafficking in Cytotoxic Lymphocytes

Cytotoxic lymphocyte-mediated apoptosis is dependent on the delivery of perforin to secretory granules and its ability to form calcium-dependent pores in the target cell after granule exocytosis. It is unclear how cytotoxic lymphocytes synthesize and store perforin without incurring damage or death. We discovered that the extreme C terminus of perforin was essential for rapid trafficking from the endoplasmic reticulum to the Golgi compartment. Substitution of the C-terminal tryptophan residue resulted in retention of perforin in the ER followed by calcium-dependent toxic activity that eliminated host cells. We also found that N-linked glycosylation of perforin was critical for transport from the Golgi to secretory granules. Overall, an intact C terminus and N-linked glycosylation provide accurate and efficient export of perforin from the endoplasmic reticulum to the secretory granules and are critical for cytotoxic lymphocyte survival. ► The final C-terminal residue of perforin regulates export from the ER ► Host cell survival depends on rapid export of perforin from the ER ► Delivery of perforin to secretory granules is regulated by its N-linked glycans ► Loss of the C-terminal glycopeptide is not required for perforin activation