RESUMO
The obstruction of post-insulin receptor signaling is the main mechanism of insulin-resistant diabetes. Progestin and adipoQ receptor 3 (PAQR3), a key regulator of inflammation and metabolism, can negatively regulate the PI3K/AKT signaling pathway. Here, we report that gentiopicroside (GPS), the main bioactive secoiridoid glycoside of Gentiana manshurica Kitagawa, decreased lipid synthesis and increased glucose utilization in palmitic acid (PA) treated HepG2 cells. Additionally, GPS improved glycolipid metabolism in streptozotocin (STZ) treated high-fat diet (HFD)-induced diabetic mice. Our findings revealed that GPS promoted the activation of the PI3K/AKT axis by facilitating DNA-binding protein 2 (DDB2)-mediated PAQR3 ubiquitinated degradation. Moreover, results of surface plasmon resonance (SPR), microscale thermophoresis (MST) and thermal shift assay (TSA) indicated that GPS directly binds to PAQR3. Results of molecular docking and cellular thermal shift assay (CETSA) revealed that GPS directly bound to the amino acids of the PAQR3 NH2-terminus including Leu40, Asp42, Glu69, Tyr125 and Ser129, and spatially inhibited the interaction between PAQR3 and the PI3K catalytic subunit (P110α) to restore the PI3K/AKT signaling pathway. In summary, our study identified GPS, which inhibits PAQR3 expression and directly targets PAQR3 to restore insulin signaling pathway, as a potential drug candidate for the treatment of diabetes.
RESUMO
Damaged DNA binding (DDB) protein is an important gene in the repair of damaged DNA. DDB is a heterodimer (DDB1 and DDB2) protein, murine DDB2 has 10 exons about 1.5kb in size (Genbank Accession No. AY027937). Here we identified five DDB2 variants (M1-M5) from various mouse tissues that are generated by alternative splicing. We used reverse transcription-PCR (RT-PCR) to identify splicing variants and isolated PCR products using an agarose-gel PCR purification kit. All isolated PCR products were cloned and the structure of splicing variants was confirmed by sequencing. The first splicing variant M1 was generated by omission of exon 4. The second splicing variant M2, by omission of exons 4-5. The third variants M3 was generated by omission from the middle of exon 1 to exon 6 and was expressed in the heart. Fourth variants M4 was generated by omission of exon 2 and exons 4-7. M5, the last splicing variant was generated by omission of exons 4-7. M4 and M5 were expressed in the spleen. Analysis of tissue distribution by RT-PCR indicates that M1 is most highly expressed in the mouse brain. These results indicated that murine DDB2 has five splicing variants and splicing variants expression patterns were different depending on mouse tissue. Further functional studies of each splicing variants will provide more information about the molecular mechanism of DDB2 function and DDB2 gene expression regulation.