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. 2022 Sep 2;13:912279. doi: 10.3389/fimmu.2022.912279

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Copyright © 2022 Lian, Liang, Zhang, Lan, Ye, Lin, Qiu and Zeng

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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The polyamine metabolic pathway and transport way. Polyamine biosynthesis involves the conversion of ornithine to putrescine by ornithine decarboxylase (ODC), followed by the formation of spermidine via spermidine synthase (SRM) and decarboxylated s-adenosylmethionine (dcSAM, formed by AMD1). The aminopropyl fragment required for putrescine to produce spermidine was provided by dcSAM. In a similar manner, spermine is produced from the conversion of spermidine by spermine synthase (SMS) and AMD1. The polyamine catabolism process occurs through the action of amine oxidase, mainly polyamine oxidase (PAOX) and spermine oxidase (SMOX). PAOX and SMOX can generate a large amount of reactive oxygen species (ROS) during the process of decomposing polyamines, causing oxidative damage. Currently, three models of polyamine transport systems have been proposed. Although the molecules involved in the polyamine transport system have not been fully recognized, it is known that the polyamine transport system is energy dependent and substrate selective. ODC antienzymes (AZs) and antizyme inhibitors (AZINs) also play important roles in polyamine transport. ODC monomers have a higher affinity for AZs. When the intracellular polyamine concentration is high, AZs binds to ODC monomers, preventing ODC activity and promoting the binding of ODC monomers to the 26S proteasome for degradation in a ubiquitin (Ub)-independent manner (only AZ1 induces ODC degradation). However, the binding of AZs to ODC can be blocked by AZINs.