title: The mechanism by which MEK/ERK regulates JNK and p38 activity in polyamine depleted IEC-6 cells during apoptosis.
abstract: Polyamine-depletion inhibited apoptosis by activating ERK1/2, while, preventing JNK1/2 activation. MKP-1 knockdown by SiRNA increased ERK1/2, JNK1/2, and p38 phosphorylation and apoptosis. Therefore, we predicted that polyamines might regulate MKP1 via MEK/ERK and thereby apoptosis. We examined the role of MEK/ERK in the regulation of MKP1 and JNK, and p38 activities and apoptosis. Inhibition of MKP-1 activity with a pharmacological inhibitor, sanguinarine (SA), increased JNK1/2, p38, and ERK1/2 activities without causing apoptosis. However, pre-activation of these kinases by SA significantly increased camptothecin (CPT)-induced apoptosis suggesting different roles for MAPKs during survival and apoptosis. Inhibition of MEK1 activity prevented the expression of MKP-1 protein and augmented CPT-induced apoptosis, which correlated with increased activities of JNK1/2, caspases, and DNA fragmentation. Polyamine depleted cells had higher levels of MKP-1 protein and decreased JNK1/2 activity and apoptosis. Inhibition of MEK1 prevented MKP-1 expression and increased JNK1/2 and apoptosis. Phospho-JNK1/2, phospho-ERK2, MKP-1, and the catalytic subunit of PP2Ac formed a complex in response to TNF/CPT. Inactivation of PP2Ac had no effect on the association of MKP-1 and JNK1. However, inhibition of MKP-1 activity decreased the formation of the MKP-1, PP2Ac and JNK complex. Following inhibition by SA, MKP-1 localized in the cytoplasm, while basal and CPT-induced MKP-1 remained in the nuclear fraction. These results suggest that nuclear MKP-1 translocates to the cytoplasm, binds phosphorylated JNK and p38 resulting in dephosphorylation and decreased activity. Thus, MEK/ERK activity controls the levels of MKP-1 and, thereby, regulates JNK activity in polyamine-depleted cells.
authors.affiliation: Department of Physiology, University of Tennessee Health Science Center, 894 Union Avenue, Memphis, TN, 38163, USA.
authors.forename: Mitul N
authors.initials: MN
authors.lastname: Bavaria
authors.forename: Shi
authors.initials: S
authors.lastname: Jin
authors.forename: Ramesh M
authors.initials: RM
authors.lastname: Ray
authors.forename: Leonard R
authors.initials: LR
authors.lastname: Johnson
mesh_terms: D000818:Animals; D017209:Apoptosis; D002166:Camptothecin / Q000494:pharmacology; D002460:Cell Line; D054638:Dual Specificity Phosphatase 1 / Q000378:metabolism; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D007422:Intestines / Q000166:cytology* / Q000201:enzymology; D048670:MAP Kinase Kinase 4 / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D011073:Polyamines / Q000378:metabolism*; D054648:Protein Phosphatase 2 / Q000378:metabolism; D051381:Rats; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: D011073:Polyamines; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D054648:Protein Phosphatase 2; D054638:Dual Specificity Phosphatase 1; D002166:Camptothecin