Extracellular interaction between Neurotrophic factor-α1 and HTR1E serotonin receptor promotes cell survival

Abstract

Neurotrophic factor α1 (NFα1), classically known as carboxypeptidase E (CPE) has a non‐enzymatic role in the survival of neurons and cancer cells via binding to a putative receptor. We have identified 5‐Hydroxy tryptamine receptor 1E (HTR1E), a serotonin receptor with unknown function, as a binding partner that interacts with NFα1/CPE extracellularly to mediate cell survival. Co‐immunoprecipitation using a human LN18 cells and pull‐down assay with NFα1/CPE and HTR1E expressed in HEK293 cells confirmed interaction of these two molecules. ¹²⁵I NFα1/CPE binding studies demonstrated saturable, high affinity binding to HTR1E. Molecular docking studies revealed the surface interaction between NFa1/CPE and HTR1E via 3 salt bridges, further stabilized by hydrogen bonding. We also found that HTR1E was able to activate ERK/CREB signaling upon treatment with NFα1/CPE. Pretreatment of HTR1E stable cells with NFα1/CPE followed by H₂O₂‐induced oxidative stress prevented a decrease in pro‐survival protein BCL2 and reduced cytotoxicity. SiRNA knock‐down of HTR1E in U118 glioblastoma cells resulted in significant inhibition of these cancer cells survival. Immunocytochemical analysis of human hippocampus indicated co‐expression of HTR1E with NFα1/CPE in CA1‐3 and dentate gyrus, and cellular co‐localization at the cell membrane in CA3 neurons. This study has uncovered a novel role for HTR1E as a binding partner for NFα1/CPE, and their interaction activates the ERK‐CREB‐BCL2 pathway to promote cell survival.