title: Evidence for LKB1/AMP-activated protein kinase/ endothelial nitric oxide synthase cascade regulated by hepatocyte growth factor, S-adenosylmethionine, and nitric oxide in hepatocyte proliferation.
abstract: S-adenosylmethionine (SAMe) is involved in numerous complex hepatic processes such as hepatocyte proliferation, death, inflammatory responses, and antioxidant defense. One of the most relevant actions of SAMe is the inhibition of hepatocyte proliferation during liver regeneration. In hepatocytes, SAMe regulates the levels of cytoplasmic HuR, an RNA-binding protein that increases the half-life of target messenger RNAs such as cyclin D1 and A2 via inhibition of hepatocyte growth factor (HGF)-mediated adenosine monophosphate-activated protein kinase (AMPK) phosphorylation. Because AMPK is activated by the tumor suppressor kinase LKB1, and AMPK activates endothelial nitric oxide (NO) synthase (eNOS), and NO synthesis is of great importance for hepatocyte proliferation, we hypothesized that in hepatocytes HGF may induce the phosphorylation of LKB1, AMPK, and eNOS through a process regulated by SAMe, and that this cascade might be crucial for hepatocyte growth. We demonstrate that the proliferative response of hepatocytes involves eNOS phosphorylation via HGF-mediated LKB1 and AMPK phosphorylation, and that this process is regulated by SAMe and NO. We also show that knockdown of LKB1, AMPK, or eNOS with specific interference RNA (iRNA) inhibits HGF-mediated hepatocyte proliferation. Finally, we found that the LKB1/AMPK/eNOS cascade is activated during liver regeneration after partial hepatectomy and that this process is impaired in mice treated with SAMe before hepatectomy, in knockout mice deficient in hepatic SAMe, and in eNOS knockout mice.
  
  
  CONCLUSIONS
  We have identified an LKB1/AMPK/eNOS cascade regulated by HGF, SAMe, and NO that functions as a critical determinant of hepatocyte proliferation during liver regeneration after partial hepatectomy.
authors.affiliation: CIC bioGUNE, Centro de Investigación Biomédica en Red de Enfermedades Hepaáticas y Digestivas, Technology Park of Bizkaia, Bizkaia, Spain.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Vázquez-Chantada
authors.forename: Usue
authors.initials: U
authors.lastname: Ariz
authors.forename: Marta
authors.initials: M
authors.lastname: Varela-Rey
authors.forename: Nieves
authors.initials: N
authors.lastname: Embade
authors.forename: Nuria
authors.initials: N
authors.lastname: Martínez-Lopez
authors.forename: David
authors.initials: D
authors.lastname: Fernández-Ramos
authors.forename: Laura
authors.initials: L
authors.lastname: Gómez-Santos
authors.forename: Santiago
authors.initials: S
authors.lastname: Lamas
authors.forename: Shelly C
authors.initials: SC
authors.lastname: Lu
authors.forename: M Luz
authors.initials: ML
authors.lastname: Martínez-Chantar
authors.forename: José M
authors.initials: JM
authors.lastname: Mato
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000818:Animals; D002455:Cell Division; D004261:DNA Replication; D020868:Gene Silencing; D006498:Hepatectomy; D022781:Hepatocytes / Q000166:cytology* / Q000201:enzymology*; D006706:Homeostasis; D008115:Liver Regeneration / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D052250:Nitric Oxide Synthase Type III; D017346:Protein Serine-Threonine Kinases; C491654:Stk11 protein, mouse; D055372:AMP-Activated Protein Kinases