Molecular mechanisms of impaired stimulation of DNA synthesis in cultured hepatocytes of aged rats.
We examined epidermal growth factor (EGF)- and epinephrine-stimulated mitogen-activated protein kinase kinase (MEK) 1 and MEK2 activities, DNA polymerase alpha activity, and EGF-stimulated E2F DNA binding activity in primary cultured hepatocytes from 6- and 24-mo-old rats. MEK stimulation by either EGF or epinephrine was not altered with aging. However, stimulation of DNA polymerase alpha activity by these agents was 70% and 50% lower, respectively, in cells of aged compared with cells of young rats, consistent with a lesser increase in [3H]thymidine incorporation. EGF-stimulated E2F (a transcription factor that regulates expression of the DNA polymerase alpha gene) binding to DNA was reduced with age. PD-098059, a specific inhibitor of MEK, inhibited EGF-stimulated MEK1 and MEK2 activities in hepatocytes from 6- and 24-mo-old rats. Although PD-098059 inhibited EGF-stimulated DNA synthesis in hepatocytes from 6-mo-old rats, it had no effect in 24-mo-old rats. Thus the age-related impairment appears to occur before E2F activation, and signal transduction sequences other than the mitogen-activated protein kinase pathway may be involved in stimulated DNA synthesis in hepatocytes from old rats.
Molecular Physiology and Genetics Section, Laboratory of Cellular and Molecular Biology, Gerontology Research Center, Baltimore, Maryland 21224, USA.
S
S
Kitano
T W
TW
Fawcett
Y
Y
Yo
G S
GS
Roth
D000375:Aging / Q000502:physiology*; D000818:Animals; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis*; D004256:DNA Polymerase I / Q000378:metabolism; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D004815:Epidermal Growth Factor / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D008297:Male; D020929:Mitogen-Activated Protein Kinase Kinases; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D056465:Retinoblastoma-Binding Protein 1; D013936:Thymidine / Q000378:metabolism; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000378:metabolism
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D004815:Epidermal Growth Factor; D004247:DNA; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D020929:Mitogen-Activated Protein Kinase Kinases; D004256:DNA Polymerase I; D013936:Thymidine; D004837:Epinephrine