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R-Ras2 is required for germinal center formation to aid B cells during energetically demanding processes

ABSTRACT: Upon antigen recognition within peripheral lymphoid organs, B cells interact with T cells and other immune cells to transiently form morphological structures called germinal centers (GCs), which are required for B cells clonal expansion, immunoglobulin class switching, and affinity maturation. This process, known as the GC response, is an energetically demanding process that requires metabolic reprogramming of B cells. Here, we showed that the Ras-related guanosine triphosphate hydrolase (GTPase) R-Ras2 (also known as TC21) plays an essential, nonredundant, and B cell–intrinsic role in the GC response. Both the conversion of B cells into GC B cells and their expansion were impaired in mice lacking R-Ras2, but not in those lacking a highly-related R-Ras subfamily member or both the classic H-Ras and N-Ras GTPases. In the absence of R-Ras2, activated B cells did not increase oxidative phosphorylation or aerobic glycolysis. We showed that R-Ras2 was an effector of both the B cell receptor (BCR) and CD40 and that, in its absence, B cells exhibited impaired activation of the PI3K-Akt-mTORC1 pathway, reduced mitochondrial DNA replication, and decreased expression of genes involved in glucose metabolism. Because most human B cell lymphomas originate from GC B cells or B cells that have undergone the GC response, our data suggests that R-Ras2 may also regulate metabolism in B cell malignancies.

ORGANISM(S): Mus musculus

PROVIDER: GSE113599 | GEO | 2018/04/25

REPOSITORIES: GEO

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Project description:Serum-dependent transcriptional networks identify distinct functional roles for H-ras and N-ras during initial stages of the cell cycle; Using oligonucleotide microarrays, we compared gene expression transcriptional profiles corresponding to the initial cell cycle stages of mouse fibroblasts lacking H-Ras and/or NRas with those of matching, WT controls. The similarity of transcription profiles among serum-starved fibroblasts of all different WT and ras knockout genotypes tested, indicated that H-Ras and N-Ras do not play significant roles in control of transcriptional responses to serum deprivation stress. In contrast, genomic disruption of H-ras or N-ras, individually or in combination, determined highly specific, differential gene expression profiles in response to post-starvation stimulation with serum for 1 hour (G0/G1 transition) or for 8 hours (mid-G1 progression). The absence of N-Ras caused significantly higher changes than the absence of H-Ras on the wave of transcriptional activation linked to G0/G1 transition. In contrast, the absence of H-Ras affected more potently the profile of the transcriptional wave detected during mid-G1 progression. Functional analysis demonstrated a predominant functional association of H-Ras with growth and proliferation, whereas N-Ras exhibited a closer functional link to development or cell cycle regulation as well as immunomodulation and apoptosis. Mechanistic analysis indicated that ERK-dependent activation of Stat1 mediates the regulatory effect of N-Ras on defense and immunity, whereas the pro-apoptotic effects of N-Ras are mediated through ERK and p38 signaling. Our observations support previous reports of an absolute requirement for different peaks of Ras activity during the initial stages of the cell cycle and confirm the notion of functional specificity for the H-Ras and N-Ras isoforms. Experiment Overall Design: Mus musculus cell lines from the appropriate ras genotype were harvested on Dulbeccoâs modified Eagleâs medium (DMEM) supplemented with fetal bovine serum (10% FBS), glutamine (2mM), penicillin (100 U/ml) and streptomycin (100 mg/ml). Cultures were grown in a humidified CO2 (5%) atmosphere at 37Â°C and when subconfluent cells were starved for 24 hours. After starvation cells were either used for RNA isolation, or induced for 1 hour or 8 hours with 20% fetal bovine serum and then RNA extraction and isolation was carried out for hybridization on Affymetrix microarrays.

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R-Ras2 is required for germinal center formation to aid B cells during energetically demanding processes

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