Although several conserved signaling pathways such as TOR-S6K, AC-PKA-Ras/Raf/MAPkinase, and IGF-1 are known to regulate stress resistance and longevity in various organisms, the mechanism of how RGS (regulator of G-protein signaling) protein affects aging process through G-protein signaling pathway is not understood yet. Our preliminary data exhibited that 1) reduced expression of a RGS protein, Loco, resulted in a longer lifespan of flies with stronger resistances to stressors, higher MnSOD activity, and increased fat contents. 2) In contrast, overexpression of the loco gene shortened lifespan significantly with lower stress resistance and reduced fat contents, also indicating that its RGS domain is related to the regulation of longevity. 3) Interestingly, expressional changes of yeast RGS2 and rat RGS14, homologues of the fly Loco, also affected oxidative stress resistance and longevity in the respective species, suggesting that Loco/RGS14 signaling pathway is evolutionarily conserved in various organisms for the regulation of longevity. It is known that Loco inactivates inhibitory G?i?GTP protein which reduces activity of adenylate cyclase (AC) and RGS14 interacts with activated H-Ras and Raf-1 kinases, which subsequently inhibits ERK phosphorylation. The specific hypothesis for this research is that Loco/RGS14 protein regulates stress resistance and longevity as an activator in AC-cAMP-PKA pathway and/or as a molecular scaffold that sequesters active Ras and Raf from Ras?GTP-Raf-MEK-ERK signaling pathway. Consistently, our preliminary data showed that down-regulation of Loco significantly diminishes cAMP amounts and increases p-ERK levels with higher resistance to the oxidative stress. In addition, proteomic iTRAQ and 2D-gel analyses using loco mutant and overexpression revealed that Loco signaling increases phosphorylation levels of Rpd3 protein (HDAC1, histone deacetylase 1). Reduced expression of Rpd3 protein is reported to extend lifespan in Drosophila. However, it is not characterized how Rpd3/HDAC1 activity is regulated for longevity mechanism. Based on our preliminary data, the specific aims are to examine I) if Loco protein regulates the Ras/Raf/MAPkinase signaling pathway through direct interaction between them, II) if Loco/RGS14 signaling modulates phosphorylation levels of Rpd3/HDAC1 protein in both of fruitfly and mammal, III) if phosphorylation level of HDAC1 protein determines stress resistance and lifespan with regulating subcellular localization and/or activity of HDAC1 protein. Our approaches will find how the Loco/RGS14 protein regulates longevity with new and/or known longevity signaling pathway(s). We believe that the information obtained from our studies will advance our general understanding of the mechanisms of eukaryotic aging process and help us find ways to cure or delay aging-related diseases such as Alzheimer's disease.
The mechanisms of eukaryotic aging process are regulated by the longevity signaling pathways. Using fruit fly as a model system, we will find a longevity signaling pathway affecting stress resistance and/or longevity. The outcomes from this proposal will help us understand mechanisms of aging process and provide some options to cure aging/stress-related diseases.