Abstract
The mRNAs encoding poly (A) binding protein (PABP1), eukaryotic elongation factor 1A (eEF1A) and ribosomal protein S6 (RPS6) belong to the family of terminal oligo pyrimidine tract (TOP) containing mRNAs. Translation of the TOP mRNAs is regulated by growth signals and usually codes for proteins involved in mRNA translation. Previous studies from our laboratory showed that translation of PABP1 mRNA was preferentially enhanced during recovery of HeLa cells from heat shock. Presence of the 5′ TOP cis element was required for the observed increase of PABP1 mRNA translation. In the studies reported here we showed that translation of two additional TOP mRNAs such as, eEF1A and RPS6 was similarly enhanced during recovery. In addition, we showed by in vivo cross-linking experiments that the cellular nucleic acid binding protein ZNF9 binds to all three TOP mRNAs examined in these studies as well as to the β-actin mRNA that lacks a TOP cis element. Binding of ZNF9 to mRNAs was observed in both heat-shocked and non heat- shocked cells. However, depletion of ZNF9 by siRNA prevented the preferred stimulation of PABP1, eEF1A and RPS6 expression during recovery from heat shock. There was no detectable effect of ZNF9 depletion on the basal level of expression of either β-actin or PABP1, eEF1A and RPS6 in HeLa cells following recovery from heat shock.ConclusionAlthough the presence of ZNF9 was required for the translational stimulation of PABP1, eEF1A and RPS6 mRNAs, the mechanistic details of this process are still unclear. Since ZNF9 was shown to bind both TOP and non-TOP mRNAs, it is uncertain whether ZNF9 exerts its stimulatory effect on TOP mRNA translation following recovery from heat shock through the TOP cis-element. Perhaps additional factors or post-translational modification(s) of ZNF9 following heat shock are necessary for the preferred increase of TOP mRNA translation.
Highlights
PABP is a multifunctional and ubiquitous mRNA-binding protein in eukaryotes.PABP is known to play a role in several cellular processes including stimulation of mRNA translation and control of mRNA stability [1] [2]
Conclusion: the presence of ZNF9 was required for the translational stimulation of PABP1, eukaryotic elongation factor 1A (eEF1A) and ribosomal protein S6 (RPS6) mRNAs, the mechanistic details of this process are still unclear
Perhaps additional factors or post-translational modification(s) of ZNF9 following heat shock are necessary for the preferred increase of TOP mRNA translation
Summary
PABP is known to play a role in several cellular processes including stimulation of mRNA translation and control of mRNA stability [1] [2]. All four cytoplasmic PABPs have four RNA binding domains at their N-terminal ends and with the exception of PABP5, have a proline rich linker and a PABPC domain [7]. PABP1 mRNA is a member of the family of mRNAs containing a terminal oligo pyrimidine tract (TOP) at their 59 ends [10]. The activity of TOP is contained within the first 30 nucleotides of TOP mRNAs and is strictly dependent on its integrity adjacent to the cap structure; it fails to have any effect on mRNA translation when it is located internally even when it comes before an A residue [12]
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