The variations in human orphan G protein-coupled receptor QRFPR affect PI3K-AKT-mTOR signaling

QRFPR is a recently identified member of the G protein-coupled receptor and is an orphan receptor for 26Rfa, which plays important role in the regulation of many physiological functions.

Here, we employed whole exome sequencing (WES) to examine the patients with intellectual disability (ID) and difficulty in feeding. We performed SIFT and PolyPhen2 predictions for the variants. The structure model was built from scratch by I-TASSER. Here, results derived from a number of cell-based functional assays, including shRNA experiment, intracellular Ca²⁺ measurement, the expression of PI3 K-AKT-mTOR, and phosphorylation. The functional effect of QRFPR variants on PI3K-AKT-mTOR signaling was evaluated in vitro transfection experiments.

Here, we identified two QRFPR variants at c.202 T>C (p.Y68H) and c.1111C>T (p.R371W) in 2 unrelated individuals. Structural analysis revealed that p.Y68H and p.R371W variants may affect the side chain structure of adjacent amino acids causing reduced binding of QRFPR to 26Rfa. The results show that QRFPR stimulated by 26Rfa leading to the transient rise of intracellular Ca²⁺ . The QRFPR variations p.Y68H and p.R371 W can reduce the mobilization of intracellular Ca²⁺ . The phosphorylation levels of the PI3K, Akt, and mTOR were significantly up- or downregulated by QRFPR overexpression or silencing, respectively. The QRFPR variations inhibited PI3K-AKT-mTOR signaling, resulting in downregulation of p-mTOR.

Our findings suggest that QRFPR acts as important role in neurodevelopment, and the effects of QRFPR are likely to be mediated by the Ca²⁺ -dependent PI3K-AKT-mTOR pathways. Importantly, these findings provide a foundation for future elucidation of GPCR-mediated signaling and the physiological implications.