Function of mammalian LKB1 and Ca2+/calmodulin-dependent protein kinase kinase alpha as Snf1-activating kinases in yeast.
The Snf1/AMP-activated protein kinase (AMPK) family is important for metabolic regulation in response to stress. In the yeast Saccharomyces cerevisiae, the Snf1 kinase cascade comprises three Snf1-activating kinases, Pak1, Tos3, and Elm1. The only established mammalian AMPK kinase is LKB1. We show that LKB1 functions heterologously in yeast. In pak1Delta tos3Delta elm1Delta cells, LKB1 activated Snf1 catalytic activity and conferred a Snf(+) growth phenotype. Coexpression of STRADalpha and MO25alpha, which form a complex with LKB1, enhanced LKB1 function. Thus, the Snf1/AMPK kinase cascade is functionally conserved between yeast and mammals. Ca(2+)/calmodulin-dependent kinase kinase (CaMKK) shows more sequence similarity to Pak1, Tos3, and Elm1 than does LKB1. When expressed in pak1Delta tos3Delta elm1Delta cells, CaMKKalpha activated Snf1 catalytic activity, restored the Snf(+) phenotype, and also phosphorylated the activation loop threonine of Snf1 in vitro. These findings indicate that CaMKKalpha is a functional member of the Snf1/AMPK kinase family and support CaMKKalpha as a likely candidate for an AMPK kinase in mammalian cells. Analysis of the function of these heterologous kinases in yeast provided insight into the regulation of Snf1. When activated by LKB1 or CaMKKalpha, Snf1 activity was significantly inhibited by glucose, suggesting that a mechanism independent of the activating kinases can mediate glucose signaling in yeast. Finally, this analysis provided evidence that Pak1 functions in another capacity, besides activating Snf1, to regulate the nuclear enrichment of Snf1 protein kinase in response to carbon stress.
Hong
Seung-Pyo
SP
Department of Genetics and Development, Columbia University, 701 W. 168th Street, New York, NY 10032, USA.
Momcilovic
Milica
M
Carlson
Marian
M
D055372:AMP-Activated Protein Kinases; D000818:Animals; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase; D002244:Carbon / Q000737:chemistry; D002384:Catalysis; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D005982:Glutathione Transferase / Q000378:metabolism; D005990:Glycerol / Q000737:chemistry; D049452:Green Fluorescent Proteins / Q000378:metabolism; D015151:Immunoblotting; D051379:Mice; D008954:Models, Biological; D008957:Models, Genetic; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D010641:Phenotype; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D011887:Raffinose / Q000737:chemistry; D051381:Rats; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D015398:Signal Transduction; D013912:Threonine / Q000737:chemistry
D018076:DNA, Complementary; D010455:Peptides; D029701:Saccharomyces cerevisiae Proteins; D049452:Green Fluorescent Proteins; D013912:Threonine; D002244:Carbon; D005982:Glutathione Transferase; D011494:Protein Kinases; C411302:ELM1 protein, S cerevisiae; C071570:SNF1-related protein kinases; C094326:PRK1 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; C491654:Stk11 protein, mouse; C502450:TOS3 protein, S cerevisiae; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase; C517701:Camkk1 protein, rat; D055372:AMP-Activated Protein Kinases; D005947:Glucose; D011887:Raffinose; D005990:Glycerol