title: Role of protein turnover in the activation of p38 mitogen-activated protein kinase in rat pinealocytes.
abstract: Differences in the time profiles of activation between p38MAPK and p42/44MAPK by norepinephrine (NE) in rat pinealocytes suggest involvement of mechanisms other than the phosphorylation cascades in their activation. In the present study we investigated whether protein turnover played a role in regulating p38MAPK activation in the rat pineal gland. NE stimulation caused an increase in MAPK kinase3/6 (MKK 3/6) and p38MAPK phosphorylation that occurred in the absence of changes in the mRNA or protein levels of p38MAPK or MKK3/6. The stimulatory effect of NE on phosphorylated MKK3/6 and p38MAPK, but not phosphorylated p42/44MAPK, was blocked by treatment with actinomycin or cycloheximide, indicating a requirement of transcription and translation in activation of the p38MAPK but not the p42/44MAPK pathway. Moreover, inhibition of proteasomes by clasto-lactacystin beta-lactone or Z-Leu-Leu-Leu-CHO (MG132) selectively increased basal and NE-stimulated phosphorylated MKK3/6 and p38MAPK levels without affecting the mRNA or protein levels of MKK3 or p38MAPK. In contrast, the effect of proteasomal inhibition on NE-stimulated p42/44MAPK phosphorylation was inhibitory. Treatment with MG132 also reduced the decline in the phosphorylated levels of NE-stimulated MKK3/6 and p38MAPK that normally follows beta-adrenergic blockade. Together, our results indicate that p38MAPK but not p42/44MAPK activation in the rat pineal gland is tightly coupled to protein synthesis and degradation. The synthesis of an activator upstream of MKK3/6 is required for the NE-activation of p38MAPK.
authors.affiliation: Department of Physiology, University of Alberta, Edmonton, Alta., Canada T6G 2H7. anho@ualberta.ca
authors.forename: A K
authors.initials: AK
authors.lastname: Ho
authors.forename: L
authors.initials: L
authors.lastname: McNeil
authors.forename: D
authors.initials: D
authors.lastname: Terriff
authors.forename: D M
authors.initials: DM
authors.lastname: Price
authors.forename: C L
authors.initials: CL
authors.lastname: Chik
mesh_terms: D000818:Animals; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004789:Enzyme Activation; D007976:Leupeptins / Q000494:pharmacology; D048371:MAP Kinase Kinase 3 / Q000378:metabolism; D020935:MAP Kinase Signaling System; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D010766:Phosphorylation; D010870:Pineal Gland / Q000166:cytology / Q000201:enzymology*; D046988:Proteasome Endopeptidase Complex / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: D007976:Leupeptins; D003609:Dactinomycin; D003513:Cycloheximide; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D048371:MAP Kinase Kinase 3; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D009638:Norepinephrine