Protein Phosphatase 1, Regulatory Subunit 3E (PPP1R3E)

PPP1R3E encodes a novel glycogen-targeting subunit of PP1 that is expressed in rodent liver. The phosphatase activity associated with R3E is slightly higher than that associated with R5/PTG and it is downregulated in streptozotocin-induced diabetes by 60–70% and restored by insulin treatment. Surprisingly, although mRNA for R3E is most highly expressed in rat liver and heart muscle, with only low levels in skeletal muscle, R3E mRNA is most abundant in human skeletal muscle and heart tissues with barely detectable levels in human liver. This species-specific difference in R3E mRNA expression has similarities to the high level of expression of G_L mRNA in human but not rodent skeletal muscle. The observations imply that the mechanisms by which insulin regulates glycogen synthesis in liver and skeletal muscle are different in rodents and humans.