title: Activation of ERK by Ca2+ store depletion in rat liver epithelial cells.
abstract: In rat liver epithelial (WB) cells, Ca2+ pool depletion induced by two independent methods resulted in activation of extracellular signal-regulated protein kinase (ERK). In the first method, Ca2+ pool depletion by thapsigargin increased the activity of ERK, even when rise in cytosolic Ca2+ was blocked with the Ca2+ chelator BAPTA-AM. For the second method, addition of extracellular EGTA at a concentration shown to deplete intracellular Ca2+ pools also increased ERK activity. In each instance, ERK activation, as measured by an immunocomplex kinase assay, was greatly reduced by the tyrosine kinase inhibitor genistein, suggesting that Ca2+ store depletion increased ERK activity through a tyrosine kinase pathway. The intracellular Ca2+-releasing agent thapsigargin increased Fyn activity, which was unaffected by BAPTA-AM pretreatment, suggesting that Fyn activity was unaffected by increased cytosolic free Ca2+. Furthermore, depletion of intracellular Ca2+ with EGTA caused inactivation of protein phosphatase 2A and protein tyrosine phosphatases. ANG II-induced activations of Fyn, Raf-1, and ERK were augmented in cells pretreated with BAPTA-AM, but ANG II-induced expression of the dual-specificity phosphatase mitogen-activated protein kinase phosphatase-1 was blocked by BAPTA-AM pretreatment. Together these results indicate that ERK activity is regulated by the balance of phosphorylation vs. dephosphorylation reactions in intact cells and that the amount of Ca2+ stored in intracellular pools plays an important role in this regulation.
authors.affiliation: Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Maloney
authors.forename: O M
authors.initials: OM
authors.lastname: Tsygankova
authors.forename: L
authors.initials: L
authors.lastname: Yang
authors.forename: Q
authors.initials: Q
authors.lastname: Li
authors.forename: A
authors.initials: A
authors.lastname: Szot
authors.forename: K
authors.initials: K
authors.lastname: Baysal
authors.forename: J R
authors.initials: JR
authors.lastname: Williamson
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002460:Cell Line; D002614:Chelating Agents / Q000494:pharmacology; D054638:Dual Specificity Phosphatase 1; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000378:metabolism; D019833:Genistein / Q000494:pharmacology; D017874:Immediate-Early Proteins / Q000037:antagonists & inhibitors; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051076:Proto-Oncogene Proteins c-fyn; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D018797:Cell Cycle Proteins; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D017874:Immediate-Early Proteins; D011518:Proto-Oncogene Proteins; D000804:Angiotensin II; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D019833:Genistein; C494961:Fyn protein, rat; D051076:Proto-Oncogene Proteins c-fyn; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D054638:Dual Specificity Phosphatase 1; C517021:Dusp1 protein, rat; D017027:Protein Tyrosine Phosphatases; D002118:Calcium