Osmotic regulation of betaine homocysteine-S-methyltransferase expression in H4IIE rat hepatoma cells.
Cell hydration changes critically affect liver metabolism and gene expression. In the course of gene expression studies using nylon cDNA-arrays we found that hyperosmolarity (405 mosmol/l) suppressed the betaine-homocysteine methyltransferase (Bhmt) mRNA expression in H4IIE rat hepatoma cells. This was confirmed by Northern blot and real-time quantitative RT-PCR analysis, which in addition unraveled a pronounced induction of Bhmt mRNA expression by hypoosmotic (205 mosmol/l) swelling. Osmotic regulation of Bhmt mRNA expression was largely paralleled at the levels of Bhmt protein and enzymatic activity. Like hyperosmotic NaCl, hyperosmotic raffinose but not hyperosmotic urea suppressed Bhmt mRNA expression, suggesting that cell shrinkage rather than increased ionic strength or hyperosmolarity per se is the trigger. Hypoosmolarity increased the expression of a reporter gene driven by the entire human BHMT promoter, whereas destabilization of BHMT mRNA was observed under hyperosmotic conditions. Osmosensitivity of Bhmt mRNA expression was impaired by inhibitors of tyrosine kinases and cyclic nucleotide-dependent kinases. The osmotic regulation of BHMT may be part of a cell volume-regulatory response and additionally lead to metabolic alterations that depend on the availability of betaine-derived methyl groups.
Schäfer
Christine
C
Clinic for Gastroenterology, Hepatology, and Infectiology, Düsseldorf, Germany.
Hoffmann
Lars
L
Heldt
Katrin
K
Lornejad-Schäfer
Mohammad Reza
MR
Brauers
Gernot
G
Gehrmann
Thor
T
Garrow
Timothy A
TA
Häussinger
Dieter
D
Mayatepek
Ertan
E
Schwahn
Bernd C
BC
Schliess
Freimut
F
D000818:Animals; D001622:Betaine / Q000378:metabolism; D050940:Betaine-Homocysteine S-Methyltransferase / Q000235:genetics / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000201:enzymology* / Q000235:genetics / Q000473:pathology / Q000503:physiopathology; D045744:Cell Line, Tumor; D048429:Cell Size; D017867:Cyclic Nucleotide-Regulated Protein Kinases / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D008113:Liver Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology / Q000503:physiopathology; D009994:Osmolar Concentration; D009995:Osmosis; D011401:Promoter Regions, Genetic; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011887:Raffinose / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D012462:Saline Solution, Hypertonic / Q000378:metabolism; D012521:Sarcosine / Q000031:analogs & derivatives / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014158:Transcription, Genetic; D014162:Transfection; D014508:Urea / Q000737:chemistry / Q000378:metabolism; D014882:Water-Electrolyte Balance
D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D012462:Saline Solution, Hypertonic; D001622:Betaine; C025138:dimethylglycine; D014508:Urea; D050940:Betaine-Homocysteine S-Methyltransferase; C494550:Bhmt protein, rat; D011505:Protein-Tyrosine Kinases; D017867:Cyclic Nucleotide-Regulated Protein Kinases; D011887:Raffinose; D012521:Sarcosine