An altered repertoire of fos/jun (AP-1) at the onset of replicative senescence.

With multiple divisions in culture, normal diploid cells suffer a loss of growth potential that leads to replicative senescence and a finite replicative capacity. Using quantitative RT-PCR, we have monitored mRNA expression levels of c-fos, c-jun, JunB, c-myc, p53, H-ras, and histone H4 during the replicative senescence of human fibroblasts. The earliest and the largest changes in gene expression occurred in c-fos and junB at mid-senescence prior to the first slowing in cell growth rates. The basal level of c-fos mRNA decreased to one-ninth that of the early-passage levels, while junB declined to one-third and c-jun expression remained constant. The decline in the basal c-fos mRNA level in mid-senescence should lead to an increase in Jun/Jun AP-1 homodimers at the expense of Fos/Jun heterodimers and may trigger a cascade of further changes in c-myc, p53, and H-ras expression in late-passage senescent fibroblasts.     

Hydrogen peroxide-induced expression of the proto-oncogenes, c-jun, c-fos and c-myc in rabbit lens epithelial cells

The involvement of H2O2 in cataract development has been established inboth human patients and animal models. At the molecular level H2O2 has beenobserved to cause damage to DNA, protein and lipid. To explore the oxidativestress response of the lens system at the gene expression level, we haveexamined the effects of H2O2 on the mRNA change of the proto-oncogenes,c-jun, c-fos and c-myc in a rabbit lens cell line, N/N1003A. H2O2 treatmentof the rabbit lens epithelial cells for 60 min induces quick up-regulationof both c-jun and c-fos mRNAs. The maximal induction is 38 fold for c-jun at150 µM and 72 fold for c-fos at 250 µM H2O2. Treatment ofN/N1003A cells with 50-250 µM H2O2 for 60 min leads to a 2-5 foldincrease of the c-myc mRNA level. H2O2 also induces an up-regulation intransactivity of the activating protein-1 (AP-1) as shown with a reportergene driven by a prolactin gene promoter with 4 copies of AP-1 binding sitesinserted in the upstream of the promoter. Maximal induction occurs with 150µM H2O2. In the same system, the antioxidants, N-acetyl-cysteine (NAC)and pyrrolidine dithiocarbamate (PDTC) at concentrations shown toup-regulate the mRNAs of both c-jun and c-fos, also enhance thetransactivity of AP-1. NAC and PDTC have different effects in modulating theinduction of AP-1 activity by H2O2 and TPA. These results reveal thatoxidative stress regulates expression of various regulatory genes in lenssystems, which likely affects cell proliferation, differentiation andviability and thus affect normal lens functions.