Fig. 4

Virus infections of cells expressing the FuTraP-ASCT2 variants. a Scheme of the pMCAS(Sync1-MSC16)dsRed vector used for virus production. The envelope of the virus consisted of the signal peptide of Env(A) (sigPE(A)) followed in-frame by Syncytin-1 SU and TM. The first six amino acids before the splicing donor (SD) are shared by Gag and sigPE(A). The mutated cryptic splice acceptor of Syncytin-1 is depicted by an asterisk in the cytoplasmic tail (C), which was truncated to 16 amino acids. Dashed lines indicate alternative splicing generating Syncytin-1 mRNA and dsRed mRNA. Numbering corresponds to original protein sequences. b Infection of cells expressing variants of FuTraP with viruses enveloped by Syncytin-1 (black) or Env(E) (gray). Infected cells were identified by flow cytometry as dsRed-positive. Sensitivity to viral infection was normalised to the wild-type FuTraP-hASCT2-wt (Y-axis). Results of three independent experiments in biological triplicates are plotted. See Additional File 3: Fig. S3 for representative dot plots. c FuTraP sensitivity depends on the receptor expression. The data from b (Y-axis) were plotted against the ASCT2 protein level from Fig. 1f (X-axis). d Inhibition of infection by preincubation of FuTraP cells with sS1-containing supernatant (dark green). Preincubation with supernatant containing RCASBP(B)GFP was used as a mock control (light green). Following preincubation, the cells were infected with Syncytin-1-enveloped virus and fraction of dsRed-positive cells was analysed by flow cytometry. Sensitivity to viral infection was normalised to the wild-type FuTraP-hASCT2-wt (Y-axis). Results of three independent experiments in biological triplicates are plotted. DF-1/LgBiT cells expressing the S1 allele of chicken Tvb (ggTvb^S1) or human EAAT1 (hEAAT1) represent the negative controls (NC). Data is shown as means ± standard errors, *p < 0.05, ****p < 0.0001, Mann–Whitney two-tailed test