CircAgtpbp1 Acts as a Molecular Sponge of miR-543-5p to Regulate the Secretion of GH in Rat Pituitary Cells

SIMPLE SUMMARY: Circular RNAs(circRNAs) and microRNAs(miRNAs) are a type of endogenous non-coding RNA that are widely expressed in tissues and play an important role in growth and development. Growth hormone (GH) regulates the growth and apoptosis of cells. However, there are still few reports on the mechanisms involving circRNA and GH. Therefore, this study aimed to explore how circRNAs regulate the secretion of GH. We studied a circRNA named circAgtpbp1 from our previous RNA sequencing, which can target miR-543-5p binding to the 3’UTR of Gh1 messager RNA (mRNA). Our results demonstrate that circAgtpbp1 is a stable, truly circular molecule, which is located on chromosome 17. Moreover, we found that circAgtpbp1 can promote the secretion of GH by attenuating the effect of miR-543-5p. These findings expand our existing knowledge of the mechanisms of hormone regulation and enrich the research involving the regulation of hormones by non-coding RNA. ABSTRACT: CircRNAs have been identified to be expressed differently and stably in numerous species and tissues, but their functions in growth hormone (GH) secretion are still largely unknown. In summary, we have revealed a circRNA-miRNA-mRNA network that may play a biological role in the rat pituitary gland. First, we verified the chromosome location information of circAgtpbp1 according to sequencing analysis. The circAgtpbp1 characteristics were authenticated through PCR, qRT–PCR, treating with RNase and fluorescent in situ hybridization (FISH). Second, we detected the expression pattern of circAgtpbp1 in the rat anterior pituitary by qRT–PCR. We also designed circAgtpbp1 siRNA and constructed overexpression plasmid to evaluate the effect of circAgtpbp1 function on GH secretion by qRT–PCR, ELISA and Western blot. CircAgtpbp1 is a stable, truly circular molecule. We found that circAgtpbp1 interacted with miR-543-5p and can regulate GH secretion in pituitary cells through a circAgtpbp1-miR-543-5p-GH axis. Overall, the evidence generated by our study suggests that circAgtpbp1 can act as a sponge of miR-543-5p to reduce the inhibitory effect of miR-543-5p on Gh1 and further promote GH secretion. These findings expand our existing knowledge on the mechanisms of hormone regulation in the pituitary gland.