Evolutionarily conserved primary TNF sequences relate to its primitive functions in cell death induction

Abstract

TNF is a primitive protein that has emerged from more than 550 million years of evolution. Our bioinformatics study of TNF from nine different taxa in vertebrates revealed several conserved regions in the TNF sequence. By screening overlapping peptides derived from human TNF to determine their role in three different TNF-induced processes -apoptosis, necrosis and NF-κB stimulation -we found that TNF conserved regions are mostly related to cell death rather than NF-κB stimulation. Among the most conserved regions, peptides (P)12, P13 and P1213 (comprising P12 and P13) induced apoptosis, whereas P14, P15, P16 and P1516 (comprising P15 and P16) induced necrosis. Cell death induced by these peptides was not through binding to the TNF receptor. P16-induced necrosis was mainly through disruption of the cell membrane, whereas P1213-induced apoptosis involved activation of TRADD followed by formation of complex II. Finally, using a monoclonal antibody and a mutant TNF protein, we show that TNF-induced apoptosis is determined by a conserved linear sequence that corresponds to that within P1213. Our results reveal the determinant sequence that is key to the TNF primitive function of inducing apoptosis.

TNF-derived peptides inhibit tumour growth and metastasis through cytolytic effects on tumour lymphatics

“…a–f). This direct cytolytic effect is consistent with the ability of P16 to lyse erythrocytes we have reported previously .…”

“…Finally, evidence from transcription electron microscopy (TEM) imaging, TNF protein structural analysis and liposome leakage experiments suggested that a unique β-barrel/β-hairpin secondary structure embedded in these necrosis-inducing peptides may be responsible for their cytolytic property, thereby providing an explanation for their tumour-suppressive properties. This is consistent with our previous circular dichroism evidence that P16 contains elements of β-sheet, and undergoes a shift to a more α-helical conformation in the presence of lipid vesicles [5].…”

“…protegrin-1 (PG-1)], both of which act as a potent defence mechanisms [25][26][27]. These structural features of P15 and P16 are consistent with our previous circular dichroism data on these peptides [5].…”

“…We have previously shown that biologically functioning TNF trimers activate the nuclear factor (NF)‐κB signalling pathway and promote cell activation without necessarily inducing cell death in Jurkat A3 cells. In contrast, some conserved peptides derived from TNF could induce apoptosis and/or necrosis . This mode of cell killing seemed to be direct, in that it was independent of TNF receptor binding.…”

Viruses and the origin of microbiome selection and immunity

“…However, metazoan apoptosis appears to be unique through its use of TNF receptors (Quistad and Traylor-Knowles, 2016), which are activated by TNF ligands (Aggarwal, 2003). Many of the domains involved with apoptotic signaling via TNF receptors are also present and functional in cnidarians, considered to be among the oldest animal phyla (Lasi et al, 2010;Quistad et al, 2014;Sakamaki et al, 2014Sakamaki et al, , 2015Lu et al, 2016;Moya et al, 2016).…”