title: Inhibition of protein phosphatase-1 is linked to phosphorylation of p53 and apoptosis.
abstract: p53 is a multifunctional protein and its activity can be modulated by phosphorylation and dephosphorylation. In this study, we sought to examine the notion that serine/threonine phosphatases (PP-1 and PP-2A) are active modulators of the p53-dependent apoptotic pathway. Exposure of neonatal rat cardiomyocytes to the established apoptotic agents, bafilomycin A1 (BAF) or staurosporine (STAU) induced apoptosis and caused a decrease in PP-1 activity of 35%. This response was restricted to apoptotic stimuli as treatment with phenylephrine neither decreased PP-1 and PP-2A activity nor induced DNA fragmentation in cardiomyocytes. The level of phosphorylated p53 was increased as a result of BAF or STAU-treatment. We further examined the effect of PP-1 inhibition on cardiomyocytes by the use of the phosphatase inhibitor, okadaic acid, and an antisense strategy. Okadaic acid (100 nM) resulted in a decrease in PP-1 activity of 45%, enhanced phosphorylation of p53, and stimulated apoptosis. Furthermore, overexpression of the antisense PP-1 catalytic subunit transcript caused a 44% decrease in expression of PP-1, with no change in the levels of the PP-2A catalytic subunit, and also evoked DNA fragmentation. Our data support the view that decreased activity of PP-1 is an important signaling event in the apoptotic process.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA. xlong001@umaryland.edu
authors.forename: X
authors.initials: X
authors.lastname: Long
authors.forename: G
authors.initials: G
authors.lastname: Wu
authors.forename: S T
authors.initials: ST
authors.lastname: Gaa
authors.forename: T B
authors.initials: TB
authors.lastname: Rogers
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D017209:Apoptosis; D015153:Blotting, Western; D020134:Catalytic Domain; D004247:DNA / Q000378:metabolism; D015536:Down-Regulation; D004797:Enzyme-Linked Immunosorbent Assay; D018942:Macrolides; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D054645:Protein Phosphatase 1; D021122:Protein Subunits; D051381:Rats; D017208:Rats, Wistar; D019311:Staurosporine / Q000494:pharmacology; D014357:Trypsin / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D018942:Macrolides; D021122:Protein Subunits; D016159:Tumor Suppressor Protein p53; D010768:Phosphoserine; D019319:Okadaic Acid; C040929:bafilomycin A1; D004247:DNA; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D014357:Trypsin; D019311:Staurosporine