Succinate in the cancer-immune cycle.

Succinate is an important intermediate of the tricarboxylic acid (TCA) cycle. In mitochondria, it plays a crucial role in generating adenosine triphosphate. Succinate metabolism is also intertwined with the metabolism of other metabolites and with the "GABA shunt" of the glutamine pathway. Recently, it has become increasingly apparent that the roles of succinate extend into the realms of immunity and cancer. Succinate is a key modulator of the hypoxic response, an important player in tumorigenesis; succinate is also involved in protein succinylation, a novel posttranslational modification pathway. This expanding repertoire of succinate functions suggests that it has broad roles in cellular contexts. Mutations in enzymes such as succinate dehydrogenase (SDH) that participate in succinate-related pathways lead to various pathologies, including tumor formation and innate inflammatory processes. Succinate can have both pro- or anti-tumor effectiveness. Therefore, investigation of succinate as an inflammatory signal may increase our understanding of the cancer-immunity cycle involved in both inflammatory diseases and cancer. Here, we briefly review the emerging roles of succinate, extending beyond metabolism, into anti-cancer immunity. This expansion of succinate roles suggests that it may represent a novel class of regulators in inflammation, which act as key signals in human cancers.