Abstract
Ribosomal protein RPL26 enhances p53 translation after DNA damage, and this regulation depends upon interactions between the 5'- and 3'-UTRs of human p53 mRNA (Takagi, M., Absalon, M. J., McLure, K. G., and Kastan, M. B. (2005) Cell 123, 49-63; Chen, J., and Kastan, M. B. (2010) Genes Dev. 24, 2146-2156). In contrast, nucleolin (NCL) suppresses the translation of p53 mRNA and its induction after DNA damage. We confirmed reports that RPL26 and NCL interact with each other and then explored the potential role of this interaction in the translational control of p53 after stress. NCL repression of p53 translation utilizes both the 5'- and 3'-UTRs of p53 mRNA, and NCL binds to the same 5'-3'-UTR interaction region that is critical for the recruitment of RPL26 to p53 mRNA after DNA damage. We also found that NCL is able to oligomerize, consistent with a model in which NCL stabilizes this double-stranded RNA structure. We found that the RNA-binding domain of NCL participates in binding to p53 mRNA, is required for both NCL dimerization and NCL-mediated translational repression, and is the domain of NCL that interacts with RPL26. Excessive RPL26 disrupts NCL dimerization, and point mutations in the NCL-interacting region of RPL26 reduce NCL-RPL26 interactions and attenuate both RPL26 binding to human p53 mRNA and p53 induction by RPL26. These observations suggest a model in which the base pairings in the p53 UTR interaction regions are critical for both translational repression and stress induction of p53 by NCL and RPL26, respectively, and that disruption of a NCL-NCL homodimer by RPL26 may be the switch between translational repression and activation after stress.
Highlights
Increased translation of p53 mRNA is important for stress induction of p53 protein
We demonstrated that RPL26 protein binds to a double-stranded RNA structure containing complementary sequences of the 5Ј- and 3Ј-UTRs of p53 mRNA after DNA damage [2]
We explored the mechanisms of p53 translational repression by NCL in both an in vitro translation system and a cell-based reporter system
Summary
Results: RPL26 and nucleolin proteins interact with each other and with a double-stranded RNA structure in p53 mRNA to regulate p53 translation after stress. Ribosomal protein RPL26 enhances p53 translation after DNA damage, and this regulation depends upon interactions between the 5- and 3-UTRs of human p53 mRNA We demonstrated that RPL26 protein binds to a double-stranded RNA structure containing complementary sequences of the 5Ј- and 3Ј-UTRs of p53 mRNA after DNA damage [2]. Nucleolin has been reported to function as a stress-responsive mRNA-binding protein, binding to UTRs of mRNA in a sequence-nonspecific manner to either stabilize the mRNAs (16 –18) or regulate their translation [19]. Nucleolin simultaneously and independently binds to both of the RNA sequences of the base pairing interaction region that is critical for the translational regulation of p53 by RPL26 after DNA damage. Control of p53 Translation by Nucleolin and RPL26 tionship between NCL and RPL26 in this translational regulation
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