title: Role of the phosphatase PP4 in the activation of JNK-1 in prostate carcinoma cell lines PC-3 and LNCaP resulting in increased AP-1 and EGR-1 activity.
abstract: The specific signaling connections between the mitogen-activated protein kinases (MAPK) such as c-Jun N-terminal kinase (JNK-1) and phosphatases PP4 and M3/6, affecting the family of early nuclear factors, is complex and remains poorly understood. JNK-1 regulates cellular differentiation, apoptosis and stress responsiveness by up-regulating early nuclear factors such as c-Jun, a member of the activating protein (AP-1) family, and the Early Growth Factor (EGR-1). C-Jun, when phosphorylated by c-Jun N-terminal kinase (JNK-1) associates with c-Fos to form the AP-1 transcription factor that activates gene expression. We have investigated the regulation of the JNK-1 kinase by co-transfecting phosphatases PP4 and M3/6 in prostate cancer cell lines PC-3 and LNCaP, which have been previously stimulated with human EGF or cisplatin. Co-transfections of plasmids expressing the JNK-1 and the serine/threonine phosphatases PP4 resulted in a significant increase in JNK-1 activity in both PC3 and LNCaP cells. In contrast, co-transfection of JNK-1 with the dual specific phosphatase serine/threonine M3/6 showed only a marginal effect in JNK-1 activity. The phosphatase M3/6 also failed in blocking the induction of JNK-1 activity observed in presence of PP4. The higher activity of JNK-1 was associated with increased activities of the factors c-Jun/AP-1 and EGR-1. This suggests that JNK-1 activity in PC-3 and LNCaP cells requires not only active PP4 for stable maintenance but also suggests that the relative degree of phosphorylation of multiple cellular components is the determinant of JNK-1 stability.
authors.affiliation: Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile.
authors.forename: Juan
authors.initials: J
authors.lastname: Inostroza
authors.forename: Leonardo
authors.initials: L
authors.lastname: Sáenz
authors.forename: Gloria
authors.initials: G
authors.lastname: Calaf
authors.forename: Gertrudis
authors.initials: G
authors.lastname: Cabello
authors.forename: Eduardo
authors.initials: E
authors.lastname: Parra
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D045744:Cell Line, Tumor / Q000187:drug effects / Q000201:enzymology; D002945:Cisplatin / Q000494:pharmacology; D051766:Early Growth Response Protein 1 / Q000187:drug effects / Q000378:metabolism*; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008297:Male; D048055:Mitogen-Activated Protein Kinase 8 / Q000235:genetics / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000502:physiology*; D011471:Prostatic Neoplasms / Q000201:enzymology*; D018808:Transcription Factor AP-1 / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D018808:Transcription Factor AP-1; D004815:Epidermal Growth Factor; D048031:JNK Mitogen-Activated Protein Kinases; D048055:Mitogen-Activated Protein Kinase 8; D010749:Phosphoprotein Phosphatases; C080406:protein phosphatase 4; D002945:Cisplatin