title: A mechanism by which the osmotic laxative magnesium sulphate increases the intestinal aquaporin 3 expression in HT-29 cells.
abstract: OBJECTIVE
  We have suggested that an osmotic laxative, magnesium sulphate (MgSO(4)), may act as a cathartic in a very rational manner by increasing the aquaporin 3 (AQP3) expression level and by changing osmotic pressure in the colon. In this study, we examined the mechanism by which MgSO(4) increases the intestinal AQP3 expression level by using the human colon cancer HT-29 cell line.
  
  
  METHODS
  After the addition of MgSO(4) to HT-29 cells, the expression levels of AQP3 mRNA and protein were measured using real-time RT-PCR and western blotting, respectively. The intracellular Mg(2+) concentration, adenylate cyclase (AC) activity and protein kinase A (PKA) activity were also determined. The phosphorylated cAMP response element-binding protein (CREB) expression levels were determined by western blotting.
  
  
  RESULTS
  The AQP3 mRNA expression level started to increase significantly at 1 h after MgSO(4) addition and peaked at 9 h, at a level 3 times as high as the control levels. The AQP3 protein expression level started to increase 6 h after the addition and reached a level almost twice as high as the control levels by hour 12. In the HT-29 cells treated with MgSO(4), there was a 1.4-fold increase in the intracellular Mg(2+) concentration, a 1.5-fold increase in AC activity, a 1.6-fold increase in PKA activity, and a significant increase in phosphorylation of the CREB.
  
  
  CONCLUSIONS
  These results suggest that the AC activation caused by an increase in the intracellular Mg(2+) concentration may trigger CREB phosphorylation through PKA activation and promote AQP3 gene transcription.
authors.forename: Nobutomo
authors.initials: N
authors.lastname: Ikarashi
authors.forename: Toshihide
authors.initials: T
authors.lastname: Mochiduki
authors.forename: Ayaka
authors.initials: A
authors.lastname: Takasaki
authors.forename: Takashi
authors.initials: T
authors.lastname: Ushiki
authors.forename: Kohta
authors.initials: K
authors.lastname: Baba
authors.forename: Makoto
authors.initials: M
authors.lastname: Ishii
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kudo
authors.forename: Kiyomi
authors.initials: K
authors.lastname: Ito
authors.forename: Takahiro
authors.initials: T
authors.lastname: Toda
authors.forename: Wataru
authors.initials: W
authors.lastname: Ochiai
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Sugiyama
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000704:Analysis of Variance; D051400:Aquaporin 3 / Q000378:metabolism*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D004586:Electrophoresis; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000187:drug effects*; D054368:Laxatives / Q000494:pharmacology*; D008274:Magnesium / Q000378:metabolism; D008278:Magnesium Sulfate / Q000494:pharmacology*; D009997:Osmotic Pressure; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: C115163:CREB1 protein, human; D017362:Cyclic AMP Response Element-Binding Protein; D017931:DNA Primers; D054368:Laxatives; D051400:Aquaporin 3; D008278:Magnesium Sulfate; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D008274:Magnesium