Figure 1.

PRMT5 is essential for growth of PHGG and other CNS cancer cells. A, shRNA KD screen of epigenetic regulators identified those that are important for cell growth. The Venn diagram shows numbers of genes important for tumor cell survival in DIPG4 (H3K27M DMG cell line), DIPG10 (H3-wt pontine PHGG), and overlap between the two cell types. B, shRNA screen results showing genes important for cell growth in DIPG4 (left) and DIPG10 (right); significance thresholds in A and B are FC < 0.6, P < 0.025 for DIPG4 cells and FC < 0.75, P < 0.025 for DIPG10 cells. C, In RNAi KD screens, CNS cancer and glioma cell lines depend on PRMT5 to proliferate, validating PRMT5 as a potential therapeutic target in these cancer types. D, Scatter plot of PRMT5 expression vs. CRISPR and RNAi gene effects for individual cell lines assayed by the Broad Institute, both CRISPR and RNAi gene effects are independent of endogenous PRMT5 expression level (trend line slope is not significantly different from 0). E, Summary of Broad Institute CRISPR and RNAi screening data for PRMT5; shaded areas represent the proportion of cell lines for each measured gene effect; DepMap CRISPR KO screening shows that PRMT5 is essential for cell survival at a level similar to housekeeping genes in 97.5% (1,001/1,027) of cell lines tested, suggesting that PRMT5 KO is lethal to cancerous and noncancerous cell types; in the RNAi KD screen, PRMT5 KD is “strongly selective” among different cell types, suggesting that it may slow tumor growth without adversely affecting normal tissue. F,PRMT5 KD effect on PRMT5 expression in cell models of PHGG. Table 1 describes the cell lines. G, Rescue experiment in BT245 cells shows that PRMT5 KD targeting 3′-untranslated region is rescued by transfection of PRMT5 cDNA. H, Western blots in DMG (DIPG7) and PHGG (GBM1) cell lines illustrate effect on PRMT5 protein levels of PRMT5 KD. Densitometry results representing PRMT5/H3 (top) and PRMT5/β-tubulin (bottom) are annotated onto blots to facilitate comparison of expression levels. I, Left: Western blot of symmetric dimethylation of arginine residues throughout the proteome (SDMA, multiple bands) illustrates in BT245 cells the effect of PRMT5 KD on PRMT5 enzymatic activity; right: Western blot of SDMA after LLY283 treatment illustrates the effect of PRMT5 inhibition on SDMA; 15 kD bands of SDMA are histone proteins, densitometry-annotated as in H. NS, not significant; SDMA, symmetric dimethyl arginine.