Depletion of Ric-8B leads to reduced mTORC2 activity

Abstract

mTOR, a serine/threonine protein kinase that is involved in a series of critical cellular processes, can be found in two functionally distinct complexes, mTORC1 and mTORC2. In contrast to mTORC1, little is known about the mechanisms that regulate mTORC2. Here we show that mTORC2 activity is reduced in mice with a hypomorphic mutation of the Ric-8B gene. Ric-8B is a highly conserved protein that acts as a non-canonical guanine nucleotide exchange factor (GEF) for heterotrimeric Gαs/olf type subunits. We found that Ric-8B hypomorph embryos are smaller than their wild type littermates, fail to close the neural tube in the cephalic region and die during mid-embryogenesis. Comparative transcriptome analysis revealed that signaling pathways involving GPCRs and G proteins are dysregulated in the Ric-8B mutant embryos. Interestingly, this analysis also revealed an unexpected impairment of the mTOR signaling pathway. Phosphorylation of Akt at Ser473 is downregulated in the Ric-8B mutant embryos, indicating a decreased activity of mTORC2. Knockdown of the endogenous Ric-8B gene in cultured cell lines leads to reduced phosphorylation levels of Akt (Ser473), further supporting the involvement of Ric-8B in mTORC2 activity. Our results reveal a crucial role for Ric-8B in development and provide novel insights into the signals that regulate mTORC2.

Elp3‐mediated codon‐dependent translation promotes mTORC2 activation and regulates macrophage polarization

“…As Elp3 and mTORC2 deficiencies share overlapping phenotypes (Hallowell et al , 2017 ), we next looked for any positive regulator of mTORC2 activation whose translation may require Elp3. In this context, we got interested in Ric8b, a noncanonical guanine nucleotide exchange factor (GEF) whose deficiency impairs Akt phosphorylation on Serine 473 (Nagai et al , 2020 ). Ric8b mRNA levels were induced by IL‐4 in BMDMs from both Elp3 Control and Elp3 ΔMye mice, suggesting that Elp3 does not control Ric8b transcription (Fig EV4A ).…”

“…As Ctu2, a tRNA-modifying enzyme acting in the same cascade as Elp3, also promotes mTORC2 activation, it is likely that these enzymes are required for the translation of mRNA candidates acting as activators of mTORC2. In this context, we identified Ric8b, a candidate known to promote mTORC2 activation (Nagai et al, 2020), as a direct target of Elp3. Ric8b expression is induced by IL-4 in macrophages, similarly to Elp3.…”

“…Mechanistically, Elp3 deficiency impairs mTORC2 activation. Ric8b, a noncanonical guanine nucleotide exchange factor (GEF) acting as a positive regulator of mTORC2 (Nagai et al , 2020 ), relies on Elp3 to be properly translated in a codon‐dependent manner. Both transcriptomic signature and metabolic reprogramming triggered by IL‐4 is defective upon Elp3 deficiency.…”

Methylome-wide association studies of traumatic injury identifies differential DNA methylation of synaptic plasticity and GABAergic-signalling

“…It is expressed in neural crest cells, astrocytes, Purkinje cells, the cerebellum, hippocampus and adrenal gland, is associated with neurodevelopment, cortical surface area, cortical thickness, and may regulate synapse formation. 62, 63 The second genome-wide significant CpG site, cg02101279 (rMDD P = 8.60 x 10 -8 ), is also associated with a distal enhancer-like sequence with NR3C1-binding potential (EH38E2155469). However, the CpG site is six base-pairs from the enhancer and there is no gene linked to this sequence in the ENCODE SCREEN database.…”

“…It is expressed in neural crest cells, astrocytes, Purkinje cells, the cerebellum, hippocampus and adrenal gland, is associated with neurodevelopment, cortical surface area, cortical thickness, and may regulate synapse formation. 62,63 The second genome-wide significant CpG site, cg02101279 (rMDD P = 8.60 x 10 -8 ), is also associated with a distal enhancer-like sequence with NR3C1-binding potential (EH38E2155469).…”