T. Kitahara et al., UP-REGULATION OF ERK (MAP KINASE) AND MEM (MAP KINASE KINASE) TRANSCRIPTION AFTER RAT FACIAL-NERVE TRANSECTION, Neuroscience research, 20(3), 1994, pp. 275-280
Up-regulation of ERK (extracellular signal-regulated kinase or MAP kin
ase) and MEK (ERK kinase or MAPK kinase) expression after rat facial n
erve injury was demonstrated by in situ hybridization histochemistry a
nd immunohistochemistry. These two enzymes play roles in one of the ma
jor intracellular signal cascade pathways involving receptor tyrosine
kinase common to growth factor receptors, and transcription factors. S
ignificant increases in ERK1 mRNA levels were observed from day 3 afte
r facial nerve transection, with the highest level of expression from
1 to 2 weeks after the operation. This high level of mRNA expression t
hen decreased gradually to the normal level. ERK1-like immunoreactivit
y showed a similar time course to that of its mRNA expression; however
, the decay profile was more prolonged. The up-regulation of MEK, the
ERK kinase/MAPK kinase, was also detected by immunohistochemistry. The
protein expression profiles were almost equivalent, but the MEK expre
ssion was slightly advanced, suggesting that the observed up-regulatio
n of MEK was not due to that of ERK. The receptor tyrosine kinase sign
al transduction pathway via MEK-ERK located downstream of growth facto
r receptors seems vital as a regulator of the synthesis of molecules t
hat play important roles in the recovery process following injury or/a
nd regeneration.