Alteration in cellular RNAs during the in vitro lifespan of cultured human diploid fibroblasts.

An abrupt concommitant increase in total cellular RNA and protein was observed as cultured human diploid fibroblasts entered the senescent phase of their in vitro lifespan. DNA content remained stable from early to final passages. Fractionation of cellular RNAs by polyacrylamide gel electrophoresis demonstrated an increase in both 28S and 18S ribosomal and 4S transfer RNAs in these senescent cells. Separation of poly(A) RNA (mRNA) by oligo(dT)-cellulose chromatography suggests an increase in this group of RNAs. However, the ratios of 28S to 18S rRNAs, tRNA to rRNA, and mRNA to total cellular RNA were not significantly different in cells before and after senescence, indicating that the overall increases in total cellular RNA was not due to an accumulation of a single RNA class.