Abstract
The product of the proliferating cell nuclear antigen (PCNA) gene is the co-factor of DNA polymerase delta, which is required for cellular and viral DNA replication. Its steady-state mRNA levels are growth-regulated in young human diploid fibroblasts (HDF) as well as in many other cell types. In senescent HDF, PCNA mRNA is not detectable. However, the PCNA gene is transcribed in senescent HDF as efficiently as in young cells. Furthermore, PCNA hnRNA is easily detectable by reverse transcriptase-polymerase chain reaction in both senescent and young HDF, and the levels are essentially similar. These results indicate that in senescent HDF which are incapable of synthesizing cellular DNA, one of the genes coding for a protein of the DNA-synthesizing apparatus is still transcribed, but the product fails to be processed into mature mRNA.
Highlights
From the $Department of Pathology and Fels Institute for Cancer Research and Molecular Biology, Temple University Medical School,Philadelphia, Pennsylvania previously reported [10]
Its steady-state mRNA levels are growth-regulated in young human diploid fibroblasts (HDF)as well as in many other cell types
The proliferating cell nuclear antigen (PCNA) gene is more recently, Seshadri and Campisi [14], using WI-38 cells, whileconfirmingthatc-mycandornithinedecarboxylase mRNAs were expressed in young and senescent cells, reported that c-fos was not expressed in the latter cells and that the failureof expression wasat the transcriptional level
Summary
In young WI-38 cells as in many other cell types, same for both young and senescent cells (10 X lo6 nuclei/assay), and steady-state levels of several growth-regulated mRNAs (for the same number of counts was hybridized to the filter (8 X lo6cpm) containing the probes (2 fig of DNA/slot). PCR, reverse transcriptase-polymerase chain reaction; PCNA, prolif- RNA (1 pg) and the number of cycles [40] were kept constant for erating cell nuclear antigen; PDL, population doubling level; EGF, young and senescent cells.
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