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.

hnRNP K supports the maintenance of RORγ circadian rhythm through ERK signaling

“…Previously, we reported that the protein oscillation of hnRNP K drives Dbp and its downstream mRNA oscillation. 7 Furthermore, we demonstrated that RORγ and its downstream metabolic genes such as GluT2 and Elovl3 are also supported by hnRNP K. Taken together, we propose that hnRNP K is a key factor to elicit the transcriptional activation of Dbp and RORγ, which contribute to the maintenance of robust circadian rhythms. Interestingly, it was previously reported that hnRNP K functions as an mRNA stabilizer of Per3, which maintains its mRNA oscillation in a post-transcriptional way.…”

“…Treatment with glycine (0.125 M) was performed for 10 minutes to stop the reaction of fixation following the treatment of 1% formaldehyde in NIH3T3 cells. Chromatin immunoprecipitation (ChIP) assays were performed as previously described 7,28 . Anti‐hnRNP K antibody (Abcam, ab70492) and anti‐RNAPII (Abcam, 8WG16) were added to the lysate to immunoprecipitate hnRNP K and RNAPII.…”

“…28 We also demonstrated that hnRNP K could act as a trans-acting factor of the poly(C) motif within the Dbp proximal promoter. 7 This led us to wonder whether there was any other poly(C) motif within the proximal promoter regions (promoter region of 1 kb from the TSS) of other clock genes. First, we scanned the whole mouse genome (22 296 genes) to detect genes that have the poly(C) motif in their promoters and play roles in the circadian rhythm based on the GO database ( Figure S1A).…”

“…[3][4][5] Recently, it was reported that heterogeneous nuclear ribonucleoprotein K (hnRNP K) controls the expressions of clock genes such as Dbp and Per3. 6,7 Here, we investigate transcriptional activation of RORγ by hnRNP K, which interacts with the poly(C) motif of RORγ.hnRNP K is known as a durable poly(C)-binding protein 7-11 that controls multiple gene expression processes such…”

Daytime Restricted Feeding Affects Day–Night Variations in Mouse Cerebellar Proteome

“…In the cerebellar cortex, Dbp is rhythmically expressed with an acrophase at the onset of the active period in rats fed ad libitum (Rath et al, 2012). Interestingly, Hnrnpk activates the transcription of Dbp and possibly of clock proteins (Kwon et al, 2020). Therefore, it is tempting to speculate that the elevated expression of given isoforms of Hnrnpk in the cerebellum of daytime food-restricted mice prior to meal time (i.e., spot 554) participates to some extent to feeding-induced shift of the cerebellar clockwork.…”