Kitano S, Fawcett T W, Yo Y, Roth G S
Molecular Physiology and Genetics Section, Laboratory of Cellular and Molecular Biology, Gerontology Research Center, Baltimore, Maryland 21224, USA.
Am J Physiol. 1998 Jul;275(1):C146-54. doi: 10.1152/ajpcell.1998.275.1.C146.
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.
我们检测了来自6月龄和24月龄大鼠的原代培养肝细胞中表皮生长因子（EGF）和肾上腺素刺激的丝裂原活化蛋白激酶激酶（MEK）1及MEK2活性、DNA聚合酶α活性，以及EGF刺激的E2F DNA结合活性。EGF或肾上腺素对MEK的刺激作用不会随衰老而改变。然而，与年轻大鼠的细胞相比，这些因子对老年大鼠细胞中DNA聚合酶α活性的刺激作用分别降低了70%和50%，这与[3H]胸苷掺入量增加较少一致。EGF刺激的E2F（一种调节DNA聚合酶α基因表达的转录因子）与DNA的结合随年龄增长而减少。MEK的特异性抑制剂PD - 098059可抑制来自6月龄和24月龄大鼠肝细胞中EGF刺激的MEK1和MEK2活性。尽管PD - 098059抑制了6月龄大鼠肝细胞中EGF刺激的DNA合成，但对24月龄大鼠却没有作用。因此，与年龄相关的损伤似乎发生在E2F激活之前，并且除丝裂原活化蛋白激酶途径之外的信号转导序列可能参与了老年大鼠肝细胞中受刺激的DNA合成。
