Extracellular signal-regulated protein kinases (ERKs) and ERK kinase (MEK) in brain: regional distribution and regulation by chronic morphine

Abstract

Quantitative blot immunolabeling techniques were used to determine the concentrations of ERK1 (M(r) 44 kDa) and ERK2 (M(r) 42 kDa), the two major extracellular signal-regulated protein kinases, in different regions of rat brain. The aggregate ERK concentrations (ERK1 and ERK2) were relatively high in each of the brain regions studied, ranging from approximately 0.35 ng/microgram protein in cerebellum to approximately 1.2 ng/microgram protein in nucleus accumbens. However, differences in the regional distributions of ERK1 and ERK2 resulted in ratios of their relative abundance that differed by close to 10-fold among the regions studied. The ratios of ERK1 protein to ERK2 protein varied along a rostral-caudal gradient from a low of 0.16 in frontal cortex to a high of 1.5 in pons/medulla. In hypotonic homogenates from regions at either extreme of the gradient, ERK1 and ERK2 were both found to be predominantly (> 80%) soluble. In subcellular fractions prepared from sucrose homogenates of frontal cortex and pons/medulla, both ERK1 and ERK2 were enriched in the synaptosomal and cytosolic fractions, whereas ERK2 was also enriched in the microsomal fraction. By contrast, in subfractions containing purified nuclei, levels of ERK1 and ERK2 were about one-third of those seen in homogenates and, in subfractions enriched in mitochondria, both ERK1 and ERK2 were barely detectable. The catalytic activity of the ERKs paralleled their protein levels in all of the brain regions except the hippocampus, in which the activity and phosphotyrosine content were disproportionately high. As a possible explanation for this apparent disparity, the regional distribution of ERK kinase (MEK), which phosphorylates and activates the ERKs, was also investigated. The levels of immunoreactivity of the M(r) 45 kDa ERK kinase band differed by about threefold among the brain regions, with the highest levels being present in nucleus accumbens, hippocampus, substantia nigra, and caudate/putamen. Therefore, a higher concentration of ERK kinase immunoreactivity did not appear to account for the disproportionate levels of ERK activity and phosphotyrosine content in the hippocampus. Potential regulation of ERK and ERK kinase levels was also investigated in rats subjected to chronic morphine treatment. ERK1 and ERK2 levels were increased selectively in locus coeruleus and caudate/putamen after chronic morphine treatment, whereas ERK kinase immunoreactivity remained unchanged in all of the brain regions analyzed. In summary, the regional differences in ERK and ERK kinase expression and the region-specific regulation of ERK expression suggest that ERK-related signaling may play an important role in CNS function and its adaptive responses.

Striatal Dopaminergic and Serotonergic Markers in Human Heroin Users

“…Animal data suggest that ERK might be involved in regulation by opiate drugs of tyrosine hydroxylase, with protein levels increased in rat "striatum" (the rodent counterpart of the human caudate and putamen) following chronic morphine administration (Ortiz et al 1995;Berhow et al 1996). Our data suggest, however, that any regulation by ERK of tyrosine hydroxylase in the human does not involve changes in actual striatal levels of ERK.…”

“…Wakabayashi et al 1995, we measured levels of dopamine metabolites (homovanillic acid, 3-methoxytyramine, dihdroxyphenylacetic acid), serotonin and metabolite 5-hydroxyindoleacetic acid, and noradrenaline. Finally, as experimental animal data show that chronic opiate administration can upregulate striatal concentrations of extracellular signal-regulated kinases (ERKs), signaling molecules that may be involved in the regulation of levels of tyrosine hydroxylase (Ortiz et al 1995;Berhow et al 1996), we also determined striatal concentration of ERK2 in the heroin users. Our biochemical findings suggest that chronic heroin exposure might modestly decrease both dopaminergic and serotonergic function in the human.…”

“…Levels of monoamine neurotransmitters and metabolites (HPLC with electrochemical detection; Wilson et al 1994 (Ordway et al 1994;Zhong et al 1995), VMAT2 protein by quantitative blot immunolabeling using an affinity-purified antibody (Chemicon) raised against a previously described peptide (Erickson et al 1996), and ERK1/2 protein by quantitative blot immunolabeling (Ortiz et al 1995) were conducted as previously described.…”

Differential and Region-Specific Activation of Mitogen-Activated Protein Kinases Following Chronic Administration of Phencyclidine in Rat Brain

“…Ortiz and coworkers (Ortiz et al 1995) have reported that chronic morphine treatment selectively increased the levels of ERK1 and ERK2 in locus coeruleus and caudate/putamen. In contrast, they did not find any changes in ERK levels in the other brain regions examined, such as substantia nigra, ventral tegmental area, nucleus accumbens and frontal cortex.…”

Genistein ameliorates learning and memory deficits in amyloid β(1–40) rat model of Alzheimer’s disease

“…Among different brain regions, hippocampus and some other brain areas have the highest level of ERKs (Ortiz et al, 1995). Borras and colleagues (2006) showed that genistein acts via interaction with estrogen receptors leading to activation of MAP kinases and nuclear translocation of NFĸB, and overexpression of manganese superoxide dismutase (MnSOD) which acts as antioxidant.…”