Regulation of the p53 expression profile by hnRNP K under stress conditions

ABSTRACT

The p53 protein is one of the transcription factors responsible for cell cycle regulation and prevention of cancer development. Its expression is regulated at the transcriptional, translational and post-translational levels. Recent years of research have shown that the 5ʹ terminus of p53 mRNA plays an important role in this regulation. This region seems to be a docking platform for proteins involved in p53 expression, particularly under stress conditions. Here, we applied RNA-centric affinity chromatography to search for proteins that bind to the 5ʹ terminus of p53 mRNA and thus may be able to regulate the p53 expression profile. We found heterogeneous nuclear ribonucleoprotein K, hnRNP K, to be one of the top candidates. Binding of hnRNP K to the 5ʹ-terminal region of p53 mRNA was confirmed in vitro. We demonstrated that changes in the hnRNP K level in the cell strongly affected the p53 expression profile under various stress conditions. Downregulation or overexpression of hnRNP K caused a decrease or an increase in the p53 mRNA amount, respectively, pointing to the transcriptional mode of expression regulation. However, when hnRNP K was overexpressed under endoplasmic reticulum stress and the p53 amount has elevated no changes in the p53 mRNA level were detected suggesting translational regulation of p53 expression. Our findings have shown that hnRNP K is not only a mutual partner of p53 in the transcriptional activation of target genes under stress conditions but it also acts as a regulator of p53 expression at the transcriptional and potentially translational levels.

KEYWORDS:

• P53 expression
• hnRNP K
• transcription
• translation
• cellular stress
• RNA-affinity chromatography

Acknowledgments

We thank Dr Anna Urbanowicz from The Laboratory of Protein Engineering of our Institute for help in overexpression of hnRNA K in a bacterial system and the protein purification. We also thank mgr Agata Malinowska from Laboratory of Mass Spectrometry (IBB PAS, Warsaw) for help in MS analysis.

Disclosure statement

The authors report no conflict of interest.

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Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

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Funding

This work was supported by the Polish National Centre of Science under Grant [2016/21/B/NZ1/02832].