TIGAR's promiscuity

TIGAR [TP53 (tumour protein 53)-induced glycolysis and apoptosis regulator] protein is known for its ability to inhibit glycolysis, shifting glucose consumption towards the pentose phosphate pathway to promote antioxidant protection of cancer cells. According to sequence homology and activity analyses, TIGAR was initially considered to be a fructose-2,6-bisphosphatase; it has thus received much attention in cancer cell metabolism, given its dependence on p53 and the key role of F26BP (fructose 2,6-bisphosphate) at modulating glycolysis and gluconeogenesis. However, in a rigorous study published in this issue of the Biochemical Journal, Gerin and colleagues report that recombinant TIGAR is a 23BPG (2,3-bisphosphoglycerate) phosphatase, although it also dephosphorylates other carboxylic acid-phosphate esters and, weakly, F26BP. As such, inhibition of endogenous TIGAR leads to a dramatic increase in cellular 23BPG, influencing F26BP to a lower extent that depends on the cellular context. These results challenge the currently held notion that TIGAR modulates glycolysis through decreasing F26BP, and opens a yet unrecognized function(s) for TIGAR-mediated 23BPG control of cellular metabolism in health and disease.