Activation of mitogen-activated protein kinases during natural freezing and thawing in the wood frog

The responses of mitogen-activated protein kinase (MAPK) family members, in cluding ERK (extracellular signal-regulated kinase), JNK (c-Jun NH2-termina l kinase), and p38, in the metabolic responses to whole animal freezing (up to 24 h frozen at -2.5 degrees C) and thawing (up to 4 h at 5 degrees C af ter a 12 h freeze) were examined in four organs (liver, kidney, heart, brai n) of the freeze-tolerant wood frog Rana sylvatica. Levels of the active ph osphorylated form of p38 increased within 20 min as an early response to fr eezing in liver and kidney but rose later (after 12 h) in heart. Both JNK a nd p38 were activated during thawing in liver, kidney and heart with tempor ally-distinct patterns in each organ. The only MAPK response to freeze/thaw in frog brain was a transient elevation of p38 after 90 min thawing. ERK a ctivity did not respond to freeze/thaw in any organ. The levels of c-Fos in creased during freezing in kidney and brain whereas c-Jun was unaffected by freeze/thaw. Organ-specific responses by MAPKs, particularly p38, suggest that these may have roles in regulating metabolic or gene expression respon ses that may be adaptive in dealing with freezing stress or metabolic recov ery during thawing.