hnRNP K Supports High-Amplitude D Site-Binding Protein mRNA (Dbp mRNA) Oscillation To Sustain Circadian Rhythms

ABSTRACT

Circadian gene expression is defined by the gene-specific phase and amplitude of daily oscillations in mRNA and protein levels. D site-binding protein mRNA (Dbp mRNA) shows high-amplitude oscillation; however, the underlying mechanism remains elusive. Here, we demonstrate that heterogeneous nuclear ribonucleoprotein K (hnRNP K) is a key regulator that activates Dbp transcription via the poly(C) motif within its proximal promoter. Biochemical analyses identified hnRNP K as a specific protein that directly associates with the poly(C) motif in vitro. Interestingly, we further confirmed the rhythmic binding of endogenous hnRNP K within the Dbp promoter through chromatin immunoprecipitation as well as the cycling expression of hnRNP K. Finally, knockdown of hnRNP K decreased mRNA oscillation in both Dbp and Dbp-dependent clock genes. Taken together, our results show rhythmic protein expression of hnRNP K and provide new insights into its function as a transcriptional amplifier of Dbp.

KEYWORDS:

• circadian rhythm
• Dbp
• hnRNP K
• mRNA oscillation

SUPPLEMENTAL MATERIAL

Supplemental material is available online only.

ACKNOWLEDGMENTS

We thank Ze’ev Ronai (Sanford Burnham Prebys Medical Discovery Institute) for providing HA-hnRNP K WT and Sung-Hoon Kim (McGill University) for providing the GST-hnRNP K plasmid.

This work was supported by the Bio & Medical Technology Development Program of the National Research Foundation (NRF) funded by the Korean government (MSIT) (no. 2017M3C7A1023478), by the National Research Foundation of Korea (NRF) funded by the Korean government (MEST) (no. 2019R1A2C2009440), by the Cooperative Research Program for Agriculture Science & Technology Development (project no. PJ01324801) of the Rural Development Administration, and by BK21 Plus funded by the Ministry of Education, Republic of Korea (10Z20130012243).

We declare no conflict of interest.