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Independent regulation of thymidine kinase mRNA and enzyme levels in serum-stimulated cells.

1990; Elsevier BV; Volume: 265; Issue: 12 Linguagem: Inglês

10.1016/s0021-9258(19)39243-9

1083-351X

Moriko Ito, Susan E. Conrad,

PI3K/AKT/mTOR signaling in cancer

We have studied the regulation of thymidine kinase mRNA and protein/enzyme expression in quiescent and serum-stimulated rat cells transfected with a human TK cDNA clone expressed from a number of promoters. Our results indicate that while the pattern of mRNA expression is a function of the promoter used, the pattern of protein/enzyme expression is not. When the gene is expressed from the homologous human TK promoter both mRNA and enzyme levels remain low throughout G1 and increase as the cells enter S phase. When it is expressed from the heterologous SV40 early promoter, mRNA levels are high throughout G1, but enzyme and protein levels remain low until 8-10 h following serum stimulation. Thus, protein levels appear to be uncoupled from mRNA levels in this system, suggesting the presence of translational and/or posttranslational regulation. An analysis of mutant cDNA clones indicates that this regulation is not dependent upon sequences at the 5' or 3' end of the cDNA, including the entire 5'-untranslated region, the authentic AUG and the first 48 nucleotides of the coding region.