20-Hydroxyecdysone counteracts insulin to promote programmed cell death by modifying phosphoglycerate kinase 1

The regulation of glycolysis and autophagy during feeding and metamorphosis in holometabolous insects is a complex process that is not yet fully understood. Insulin regulates glycolysis during the larval feeding stage, allowing the insects to grow and live. However, during metamorphosis, 20-hydroxyecdysone (20E) takes over and regulates programmed cell death (PCD) in larval tissues, leading to degradation and ultimately enabling the insects to transform into adults. The precise mechanism through which these seemingly contradictory processes are coordinated remains unclear and requires further research. To understand the coordination of glycolysis and autophagy during development, we focused our investigation on the role of 20E and insulin in the regulation of phosphoglycerate kinase 1 (PGK1). We examined the glycolytic substrates and products, PGK1 glycolytic activity, and the posttranslational modification of PGK1 during the development of Helicoverpa armigera from feeding to metamorphosis.

Our findings suggest that the coordination of glycolysis and autophagy during holometabolous insect development is regulated by a balance between 20E and insulin signaling pathways. Glycolysis and PGK1 expression levels were decreased during metamorphosis under the regulation of 20E. Insulin promoted glycolysis and cell proliferation via PGK1 phosphorylation, while 20E dephosphorylated PGK1 via phosphatase and tensin homolog (PTEN) to repress glycolysis. The phosphorylation of PGK1 at Y194 by insulin and its subsequent promotion of glycolysis and cell proliferation were important for tissue growth and differentiation during the feeding stage. However, during metamorphosis, the acetylation of PGK1 by 20E was key in initiating PCD. Knockdown of phosphorylated PGK1 by RNA interference (RNAi) at the feeding stage led to glycolysis suppression and small pupae. Insulin via histone deacetylase 3 (HDAC3) deacetylated PGK1, whereas 20E via acetyltransferase arrest-defective protein 1 (ARD1) induced PGK1 acetylation at K386 to stimulate PCD. Knockdown of acetylated-PGK1 by RNAi at the metamorphic stages led to PCD repression and delayed pupation.

The posttranslational modification of PGK1 determines its functions in cell proliferation and PCD. Insulin and 20E counteractively regulate PGK1 phosphorylation and acetylation to give it dual functions in cell proliferation and PCD.