Increase in abundance of a transcript hybridizing to elongation factor I alpha during cellular senescence and...

We have isolated a senescence-specific clone (pSEN) from a cDNA library constructed from late passage WI-38 human diploid fibroblast that accounts for approximately 1% of the recombinants. Nucleotide sequence analysis of the partial cDNA clone has led to the identification of pSEN as elongation factor I alpha. Northern analysis of poly(A)+ RNA from various intermediate population doubling levels shows that a 2.2 kb transcript hybridizes to pSEN but is expressed prior to PDL-40 at very low levels. This transcript begins to accumulate at PDL-40 and is induced approximately 50-fold just prior to senescence. Furthermore, this transcript was shown to be specific to Go of the cell cycle whereas a second, lower molecular weight transcript (1.6 kb) was observed during S phase (Giordano and Foster, unpublished data). The 2.2 kb transcript is also detected in neonatal foreskin cells but very little increase in abundance is observed between early and late passage cells. Sucrose gradient fractionation of RNA from late passage WI-38 cells suggests that the lower molecular weight transcript is associated with the polysome fraction while the 2.2 kb transcript sediments with the nonpolysomal fraction. Thus, the possibility exists that the 1.6 kb transcript is derived from the 2.2 kb transcript.