PI3K-dependent Reprogramming of Hexokinase Isoforms Regulates B Lymphocyte Metabolism

Abstract

The PI3K signalling pathway is known to regulate B cell metabolic programming upon activation, but the mechanisms involved are not well understood. Here we find that the PI3K pathway controls reprogramming of hexokinases (HKs), the enzymes that convert glucose into glucose-6-phosphate as a key rate-limiting step of glycolysis and other metabolic pathways. In primary mouse B cells, PI3K pathway inhibition substantially impaired the activation-induced increase in extracellular acidification rates (ECAR), a measure of glycolysis. In contrast, B cells isolated from PI3Kdelta gain-of-function mutant mice exhibit elevated ECAR. We find that B cell activation substantially elevates protein levels of HK2 and HK3 isoforms, but not HK1, in a PI3K-dependant manner. PI3K or mTOR inhibition significantly reduced induction of HK2 and HK3 expression, whereas Akt inhibition did not affect HK isoform expression. In human B lymphoma cells, HK isoforms differ significantly in their degree of mitochondrial localization, with HK1 being mitochondrial, HK3 being cytoplasmic and HK2 present in both mitochondria and cytoplasm. To assess whether HK isoforms have unique non-redundant functions, HK2-deficient B lymphoma cells were generated and were found to exhibit decreased ECAR as well as significant changes in metabolomic profile, despite normal expression and localization of HK1 and HK3. Taken together, our study reveals that PI3K-dependant reprogramming of hexokinase isoforms can impact on B cell glycolysis and other metabolic pathways. Studies in progress are examining the functional importance of HK2 in antibody responses using mice with B cell-specific deletion of this enzyme.

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“…Glycolysis is a process that converts glucose to pyruvic acid and generates a small amount of ATP and NADH (Chandel, 2021). HK3 plays a role as a key enzyme in the glycolysis process by catalyzing the conversion of glucose to glucose-6-phosphate (Aaron et al ., 2020), promoting the glycolysis process and increasing the ATP content of the body. ATP transports chemical energy within the cell for metabolism and provides energy for the milk production process (Malloy et al ., 1988).…”