Creation of lysine-deficient mutant lymphotoxin-α with receptor selectivity by using a phage display system

The cytokine lymphotoxin-α (LTα) activates various biological functions through its three receptor subtypes, tumor necrosis factor receptor 1 (TNFR1), TNFR2 and herpes virus entry mediator (HVEM), but the relative contribution of each receptor to each function is unclear. Therefore it is important to create mutant LTα with receptor selectivity for optimized cancer therapy and the analysis of receptor function. Here, we attempted to create a lysine-deficient mutant LTα with TNFR1-selective bioactivity using a phage display technique. We obtained the TNFR1-selective mutant LTα R1selLT, which contained the mutations K19N, K28Q, K39S, K84Q, K89V, and K119H. Compared with wild-type LTα (wtLTα), R1selLT showed several-fold higher bioactivity via TNFR1 but 40-fold lower bioactivity via TNFR2. Kinetic association–dissociation parameters of R1selLT with TNFR2 were higher than those of wtLTα, whereas these parameters of R1selLT with TNFR1 were lower than those of wtLTα, suggesting that destabilization of the R1selLT–TNFR2 complex causes the decreased bioactivity of R1selLT on TNFR2. We also showed that the K84Q mutation contributed to the enhanced activity via TNFR1, and K39S lowered activity via TNFR2. R1selLT likely will be useful in cancer therapy and in analysis of the LTα structure–function relationship.