Arrayed Genome-Wide Perturbation Screen Identifies Hnrnpk As Rate-Limiting for Prion Propagation (2022)
Figure 4

Figure 4. Hnrnpk and PSA limits prion levels in chronically infected cells.

A: Western blot showing Hnrnpk siRNA transfection (96 hrs.) decreases Hnrnpk protein levels while increases PrPSc in RML prion infected GT-1/7. Prnp siRNAs suppressed both PrPC and PrPSc as expected. ⍺: anti Quantifications are reported as normalized to Actin and in comparison, to NT. PK-western blot is quantified relative to NT.

B: Western Blot of PSA-treated uninfected and infected GT-1/7 cells. Increasing concentration of PSA leads to a more prominent reduction of PrPSc in mouse cells. PK-western blot is quantified relative to DMSO.

C: mRNA levels of Hnrnpk and Prnp following siRNA and PSA treatment. FPKM: Fragments per kilobase of transcript per million mapped reads. Hnrnpk siRNAs lead to a decrease in Hnrnpk mRNA levels as well as an increase in Prnp mRNA levels. No difference is seen between DMSO treated and PSA treated cells for either Hnrnpk levels of Prnp levels. n = 2 per treatment group.

D: Quantification of PrPSc levels in RML GT-1/7 cells following treatment with 1 µM PSA in comparison to DMSO. Each dot represents an experiment. Shown are mean ± SD.

E: Brightfield microscopy images of the effect of siRNA mediated HNRNPK downregulation on prion-induced vacuolation in PG127 hovS cells. Downregulation of HNRNPK leads to an enhanced cytopathological vacuolation phenotype when compared to NT siRNA. ovPRNP siRNA transfected, as well as uninfected cells were used as controls (see Fig 4B). Downregulation of ovPRNP in the infected hovS eliminates the vacuoles; Right panel: Quantification of vacuoles of NT, HNRNPK and ovPRNP siRNA treated PG127 hovS. Cells from pictures at three different positions in the well were manually counted and the amount of vacuolated cells was normalized to the total amount of cells. Values represent mean ± SD. * p = 0.0113, **** p = <0.0001 (Dunnett's multiple comparisons test). Scale bar = 100 µm. n = 3 technical replicates.

F: Quantification of PrPSc levels in PG127 hovS cells following treatment with 1 µM PSA in comparison to DMSO. Each dot represents an experiment. Shown are mean ± SD.

G: Same as in E, using shRNAs instead of siRNA. Downregulation of HNRNPK leads to an enhanced cytopathological vacuolation phenotype when compared to NT shRNA. Uninfected cells were used as controls (Figure EV4E). Right panel: Quantification of vacuoles of NT and HNRNPK shRNA treated PG127 hovS. Cells from pictures at three different positions in the well were manually counted and the amount of vacuolated cells was normalized to the total amount of cells. Values represent mean ± SD. *** p = <0.0009 (Dunnett's multiple comparisons test). Scale bar = 100 µm. n = 3 technical replicates.

H: Quantification of PrPSc levels in PG127 hovS cells following treatment with shRNA against HNRNPK and 1 µM PSA in comparison to DMSO and NT. Each dot represents an experiment. *= p-value < 0.027 (Student's t-test). Shown are mean ± SD.

I: Gene set overrepresentation analysis of differentially expressed genes (log2FC -0.25 ≥ or 0.25 ≤ and FDR ≤ 0.05) for siRNA mediated Hnrnpk downregulation or PSA treatment in RML GT-1/7 cells analyzed by RNAseq. Differentially regulated genes (up in siRNA treatment and down in PSA or vice versa) were overlapped and used for pathway analysis. No significantly enriched pathways are detected for upregulated genes in Hnrnpk and downregulated in PSA treatment. For the opposing direction, an enrichment of genes involved in glucose metabolism was detected.