Responses of protein phosphatases and cAMP-dependent
protein kinase in a freeze-avoiding insect, Epiblema
scudderiana.
Thomas D. Pfister and
Kenneth B. Storey
Abstract
Larvae of the goldenrod gall moth, Epiblema scudderiana, use the freeze avoidance strategy of winter cold hardiness and show multiple metabolic adaptations for subzero survival including accumulation of large amounts of glycerol as a colligative antifreeze. Induction and regulation of cold hardiness adaptations requires the intermediary action of signal transduction enzymes. Changes in the activities of several signaling enzymes including cAMP-dependent protein kinase (PKA), protein phosphatases 1 (PP1), 2A, 2C, and protein tyrosine phosphatases (PTPs) were monitored over the winter and during experimental exposures of larvae to subzero temperatures (‑4°C, a temperature that triggers rapid glycerol synthesis or ‑20°C, a common midwinter ambient temperature) or anoxia. A strong increase in the amount of active PP1 in the latter part of the winter may be responsible for shutting off glycogenolysis once glycerol levels are maximized. There appears to be a limited role for PKA in overwintering but PP2A and PP2C activities rose when larvae were exposed to -20°C and PTP activities rose significantly over the winter months and also in response to laboratory subzero (-20°C) and anoxia exposure. The strong responses by PTPs suggest that these may be involved in cell cycle and growth arrest during winter diapause.