title: Phosphorylation of protein phosphatase 1 by cyclin-dependent protein kinase 5 during nerve growth factor-induced PC12 cell differentiation.
abstract: The transcription factor Egr-1 activates cyclin-dependent protein kinase 5 (Cdk5) during nerve growth factor (NGF)-induced differentiation of PC12 cells into neurons (Harada, T. Morooka, T., Ogawa, S., and Nishida, E. (2001) Nat. Cell Biol. 3, 453-459). The downstream target of Cdk5 in the Egr-1/Cdk5 pathway is not clear. In this study, we observed that phosphorylation of protein phosphatase 1 (PP1) on Thr(320) is reduced in brain extracts from Egr-1(-/-) mice, indicating that a kinase downstream of Egr-1 phosphorylates PP1. In HEK 293 cells co-transfected with PP1 and Cdk5, Cdk5 phosphorylates PP1. In vitro, Cdk5 purified from bovine brain phosphorylates bacterially expressed recombinant PP1. In NGF-treated PC12 cells, inhibition of Cdk5 by olomoucine or silencing Cdk5 expression by small interfering RNA strategy, suppresses PP1 phosphorylation. Silencing Cdk5 expression by small interfering RNA also blocks NGF-induced neurite outgrowth. Overexpression of PP1 (wild type) promotes NGF-induced differentiation of PC12 cells, whereas that of PP1 (T320A) has no effect. Our data indicate that PP1 is a downstream target of the NGF/Egr-1/Cdk5 pathway during NGF-induced differentiation of PC12 cells and suggest that PP1 phosphorylation promotes neuronal differentiation.
authors.affiliation: Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Canada.
authors.forename: Tong
authors.initials: T
authors.lastname: Li
authors.forename: Lorraine E
authors.initials: LE
authors.lastname: Chalifour
authors.forename: Hemant K
authors.initials: HK
authors.lastname: Paudel
mesh_terms: D000818:Animals; D002417:Cattle; D002454:Cell Differentiation / Q000187:drug effects*; D051360:Cyclin-Dependent Kinase 5 / Q000378:metabolism*; D051766:Early Growth Response Protein 1 / Q000378:metabolism; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D020932:Nerve Growth Factor / Q000494:pharmacology*; D009474:Neurons / Q000166:cytology; D016716:PC12 Cells; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D051381:Rats
chemical_list: D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; D020932:Nerve Growth Factor; D051360:Cyclin-Dependent Kinase 5; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1