Proteobacteria impair anti-tumor immunity in the omentum by consuming arginine.

Gut microbiota influence anti-tumor immunity, often by producing immune-modulating metabolites. However, microbes consume a variety of metabolites that may also impact host immune responses. We show that tumors grow unchecked in the omenta of microbe-replete mice due to immunosuppressive Tregs. By contrast, omental tumors in germ-free, neomycin-treated mice or mice colonized with altered Schaedler's flora (ASF) are spontaneously eliminated by CD8+ T cells. These mice lack Proteobacteria capable of arginine catabolism, causing increases in serum arginine that activate the mammalian target of the rapamycin (mTOR) pathway in Tregs to reduce their suppressive capacity. Transfer of the Proteobacteria, Escherichia coli (E. coli), but not a mutant unable to catabolize arginine, to ASF mice reduces arginine levels, restores Treg suppression, and prevents tumor clearance. Supplementary arginine similarly decreases Treg suppressive capacity, increases CD8+ T cell effectiveness, and reduces tumor burden. Thus, microbial consumption of arginine alters anti-tumor immunity, offering potential therapeutic strategies for tumors in visceral adipose tissue.

tRNA isoacceptor preference prior to retrovirus Gag-Pol junction links primer selection and viral translation.

An essential step in the replication of all retroviruses is the capture of a cellular tRNA that is used as the primer for reverse transcription. The 3'-terminal 18 nucleotides of the tRNA are complementary to the primer binding site (PBS). Moloney murine leukemia virus (MuLV) preferentially captures tRNA(Pro). To investigate the specificity of primer selection, the PBS of MuLV was altered to be complementary to different tRNAs. Analysis of the infectivity of the virus and stability of the PBS following in vitro replication revealed that MuLV prefers to select tRNA(Pro), tRNA(Gly), or tRNA(Arg). Previous studies from our laboratory have suggested that tRNA primer capture is coordinated with translation. Coincidentally, a cluster of proline, arginine, and glycine precedes the Gag-Pol junction of MuLV. Human immunodeficiency virus type 1 (HIV-1), which prefers tRNA(3)(Lys) as the primer, can be forced to utilize tRNA(Met), tRNA(1,2)(Lys), tRNA(His), or tRNA(Glu), although these viruses replicate poorly. Codons for methionine, lysine, histidine, or glutamic acid are found prior to the Gag-Pol frameshift site. HIV-1 was mutated so that the 5 lysine codons prior to the Gag-Pol frameshift region were specific for tRNA(1,2)(Lys). HIV-1 forced to use tRNA(1,2)(Lys) as the primer, with the mutation of codons specific for tRNA(1,2)(Lys) prior to the Gag-Pol junction, had enhanced infectivity and replicated similarly to the wild-type virus. The results demonstrate that codon preference prior to the Gag-Pol junction influences primer selection and suggest a coordination of Gag-Pol synthesis and acquisition of the tRNA primer required for retrovirus replication.