Structure/function analysis of lymphocyte perforin: role as an extrinsic tumour suppressor

Abstract

Listen

Translate article

Cytotoxic T lymphocytes and natural killer cells kill virus-infected or transformed cells through the combined actions of a pore forming protein (perforin) and a family of serine proteases (granzymes). 1 Upon the formation of a stable conjugate between the two cells, the exocytosis of granule toxins from the lymphocyte results in the induction of specific pathways to apoptosis in the target cell. Perforin is both permissive and indispensable for apoptosis, as it enables the granzymes to access their key substrates in the target cell cytoplasm to bring about caspase-dependent and -independent cell death. While considerable progress has been made in our understanding of pro-apoptotic pathways activated by the granzymes, the precise molecular role played by perforin remains poorly understood. Over recent years, we have developed a number of robust expression modalities for mouse and human perforin, in order to characterise its molecular and cellular functions. These have included the capacity to express wild-type and mutated perforin molecules in a cellular context where cytoxicity can be measured, and in baculovirus-based systems where purified protein can be analysed for its cytotoxic activity. By combining these approaches, we have been able to map some of perforin’s functional domains, including a determination of the key residues responsible for calcium binding. 2 In addition, a repository of missense mutations identified in patients with the rare familial immune deficiency syndrome, familial haemophagocytic lymphohistiocytosis (FHL) has proven invaluable in identifying perforin residues that result in either presynaptic protein instability or post-synaptic dysfunction at the level of the target cell membrane. 3 Mutagenesis and modelling have recently allowed us to define the mechanism through which perforin forms transmembrane olgomers. 4 The functional implications of certain common human perforin polymorphisms such as Ala91Val and much rarer mutations will also be discussed, particularly with respect to perforin’s role in human cancer susceptibility. 5