title: Potential upstream regulators and downstream targets of AMP-activated kinase signaling during oocyte maturation in a marine worm.
abstract: Unlike in mice, where the onset of oocyte maturation (germinal vesicle breakdown, GVBD) is blocked by cAMP and triggered by AMP-activated kinase (AMPK), oocytes of the marine nemertean worm Cerebratulus undergo GVBD in response to cAMP elevations and AMPK deactivation. Since the pathways underlying AMPK's effects on mammalian or nemertean GVBD have not been fully defined, follicle-free nemertean oocytes were treated with pharmacological modulators and subsequently analyzed via immunoblotting methods using phospho-specific antibodies to potential regulators and targets of AMPK. Based on such phosphorylation patterns, immature oocytes possessed an active LKB1-like kinase that phosphorylated AMPK's T172 site to activate AMPK, whereas during oocyte maturation, AMPK and LKB1-like activities declined. In addition, given that MAPK can deactivate AMPK in somatic cells, oocytes were treated with inhibitors of ERK1/2 MAPK activation. However, these assays indicated that T172 dephosphorylation during maturation-associated AMPK deactivation did not require MAPK and that an observed inhibition of GVBD elicited by the MAPK kinase blocker U0126 was actually due to ectopic AMPK activation rather than MAPK inactivation. Similarly, based on tests using an inhibitor of maturation-promoting factor (MPF), T172 dephosphorylation occurred upstream to, and independently of, MPF activation. Alternatively, active MPF and MAPK were necessary for fully phosphorylating a presumably inhibitory S485/491 site on AMPK. Furthermore, in assessing signals possibly linking AMPK deactivation to MPF activation, evidence was obtained for maturing oocytes upregulating target-of-rapamycin activity and downregulating the cyclin-dependent kinase inhibitor Kip1. Collectively, these findings are discussed relative to multiple pathways potentially mediating AMPK signaling during GVBD.
authors.affiliation: Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA. sstr@unm.edu
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Stricker
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D045163:Antibodies, Phospho-Specific; D059001:Aquatic Organisms / Q000166:cytology / Q000502:physiology*; D002070:Butadienes / Q000494:pharmacology; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D020536:Enzyme Activators / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors; D005260:Female; D007448:Invertebrates / Q000166:cytology / Q000502:physiology*; D016200:Maturation-Promoting Factor / Q000037:antagonists & inhibitors; D000090204:Mesothelin; D009570:Nitriles / Q000494:pharmacology; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009866:Oogenesis / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
chemical_list: D045163:Antibodies, Phospho-Specific; D002070:Butadienes; D020536:Enzyme Activators; C000715528:Msln protein, mouse; D009570:Nitriles; D047428:Protein Kinase Inhibitors; C113580:U 0126; D050760:Cyclin-Dependent Kinase Inhibitor p27; D011494:Protein Kinases; D058570:TOR Serine-Threonine Kinases; D016200:Maturation-Promoting Factor; D048049:Extracellular Signal-Regulated MAP Kinases; D055372:AMP-Activated Protein Kinases; D000090204:Mesothelin