Optimized SGE approach improves experiment quality <\/p>\n
We developed a HAP1 DNA ligase 4 (LIG4)-knockout (KO) line with genomic integration of a clonally derived Cas9 (HAP1-A5) and confirmed BAP1 essentiality in this line (Figs. 1 and 2a), high Cas9 activity (Fig. 2b and Extended Data Fig. 1a) and robust maintenance of haploidy (Extended Data Fig. 1b). We also optimized plasmids and transfection protocols, increasing transfection efficiency in HAP1 cells from <5% to >60% compared to other12 SGE experiments (Extended Data Fig. 1c and Methods). To screen all coding exons of BAP1, we used five time points: day (D)4, D7, D10, D14 and D21. Our optimized SGE protocol led to increased editing by homology-directed repair (HDR), with ~1% unedited reads (Fig. 2c and Supplementary Table 1). <\/p>\n
a, Target regions of 245 bp were designed for all coding exons of the canonical BAP1 transcript: ENST00000460680.6 (ref. 52). Target regions were processed in separate experiments to sequentially cover all regions. For each region, LIG4-KO, Cas9-expressing HAP1-A5 cells were transfected in triplicate with an sgRNA-expressing plasmid and a corresponding variant library; homologous recombination with this template library at the Cas9 lesion\/cut site results in the introduction of variants into the genome, generating populations of edited cells. This allows for assessment of variant function, because only benign variants will rescue cell fitness following CRISPRCas9-mediated disruption of BAP1, an essential gene. Each region was edited separately using two independent template librarysgRNA pairs; each variant library (library A or library B) contained saturating mutations (colored squares) and library-specific synonymous PPEs (dark red line) to prevent sgRNACas9-mediated recutting of incorporated genomic tracts. dsDNA, double-stranded DNA. b, Cells were cultured over time with pellets collected at D4, D7, D10, D14 and D21. gDNA, genomic DNA. c, Sequencing was used to assess the population dynamics of genomic DNA libraries, generating counts for each variant using the QUANTS pipeline. DESeq2 was used to convert counts into an LFC of variant abundance over time. LFCs were then median scaled and a single functional score was computed through the aggregation of library A and library B data. Functional scores were categorized on the basis of a significance threshold and assessed for accuracy against variants with known pathogenic or benign classifications. <\/p>\n
a, A targeted CRISPRCas9 screen in HAP1-A5 cells confirmed BAP1 essentiality and permitted selection of sgRNAs with favorable depletion kinetics for use in SGE (Methods). b, FACS analysis counts (green fluorescent protein (GFP)-positive cells) demonstrated that the HAP1-A5 clone has very high Cas9 activity (arrow), measured at 48 and 72 h after transduction with a GFP\/blue fluorescent protein (BFP) activity construct (Methods: Ploidy and FACS analysis), compared to the parental Polyclonal (Cas9+ LIG4) line. A total of 10,00020,000 cells were analyzed for each line. Cell count percentages derived from negative-control lines with no Cas9 showed expected low levels of Cas9 activity (see Extended Data Fig. 1a and Supplementary Fig. 1a for representative FACS data). c, Editing using pilot SGE conditions: a template library (496 variants) coupled with sgRNA-A targeting exon 5 of BAP1 was transfected into the polyclonal (Cas9+ LIG4) line and cells were sampled at D5 and D11 (time points previously10 used in SGE). More than 10% of the counts were unedited (wild type), which decreased to <1% when the clonal (Cas9+ LIG4) cell line (HAP1-A5) was edited using the same sgRNA and HDR homology arms with optimized SGE conditions, including a high-complexity template library (1,040 variants) sampled over five time points. d, Count abundance for variants that resulted in synonymous changes or edited intronic regions did not change significantly over a 21-day SGE screen (two-sided MannWhitneyWilcoxon test; D4 versus D21 counts, P=0.3; NS, not significant), whereas variants resulting in stop-gained and frameshift consequences were significantly depleted (****P<2.21016; n=8,707 synonymous and intronic variants; n=5,628 frameshift and stop-gained variants; mean z-score counts of three biological replicates at each time point). Boxes show the interquartile range, the horizontal lines show the median z-score count and whiskers show the maximum and minimum values that are not outliers. e, Density plot showing functional scores colored by Ensembl Variant Effect Predictor (VEP)53 mutational consequence. Black tick marks represent single variant values. f, Jitter plot showing VEP mutational consequence categories versus functional score. Data points that have FDR0.01 are semitransparent and the median synonymous functional score differs significantly from that for all other categories except UTR (KruskalWallis test: P<2.21016, H=6,692.2; two-sided Dunns BH FDR ****q<2.21016). <\/p>\n
Source data <\/p>\n
Of note, the canonical BAP1 transcript (ENST00000460680.6) has 17 exons (Fig. 1a), and because oligonucleotide synthesis lengths are limited, 22 SGE target regions of 245 bp were designed to saturate all of the coding sequence, with 20- to 90-bp exon-flanking sequences also saturated (intron, 5 UTR, 3 UTR). For larger exons, partially overlapping regions were designed. All HDR template libraries were designed using VaLiAnT13. These libraries contained two different synonymous protospacer adjacent motif (PAM)\/protospacer protection edits (PPEs) that were refractory to single guide RNA (sgRNA)Cas9 cutting, preventing cleavage of incorporated tracts. Each SGE region was targeted in two separate experiments; HDR template library A contained a PPE for one sgRNA (A) and library B contained a different PPE for a different sgRNA (B) within the same target region. Transfections were performed in triplicate for both library A and library B for all 22 regions, with samples collected at the five time points mentioned above (Fig. 1b). <\/p>\n
In total, data from 598 genomic DNA time point-replicate libraries progressed to data analysis (Fig. 1c), with an average variant coverage of 535 generated on the Illumina platform (Supplementary Table 2). <\/p>\n
We used cell fitness as a biological readout of BAP1 function, first rigorously reconfirming BAP1 essentiality (Extended Data Fig. 2ac) and SGE efficacy (Extended Data Fig. 2d) in HAP1 cells. To aid the selection of appropriate sgRNAs for experimentation, we performed a targeted CRISPRCas9 screen with 193 sgRNAs tiled across all 17 BAP1 exons (Fig. 2a). sgRNAs for SGE were selected based principally on design parameters (as previously described13), with depletion kinetics also considered (Methods). We deployed these sgRNAs and variant libraries across all 22 BAP1 target regions and confirmed editing (Extended Data Fig. 3). As expected for an essential gene amenable to SGE, scaled counts between D4 and D21 for stop-gained and frameshift variants were reduced, suggesting the depletion of cells with these variants, whereas synonymous and intron variant counts remained unchanged (Fig. 2d). By combining library A and library B, we calculated a single functional score for each variant (Methods). This is the apparent growth rate across D4, D7, D10, D14 and D21 computed by log-linear regression in DESeq2 (ref. 14) and represents log2-transformed fold change (LFC) per unit time (Methods). Stop-gained, frameshift and splice donor\/acceptor variants exhibited predominantly negative functional scores, whereas synonymous, intron and UTR variants had a unimodal distribution centered at 0 (Fig. 2e). Missense variants exhibited a continuum of functional scores with a negatively skewed unimodal distribution (Fig. 2e). <\/p>\n
We next used functional scores and standard errors computed using DESeq2 to accurately define variant effects. For each variant tested, a z-score distribution of functional score divided by standard error was used to calculate P values using a two-tailed z-test (Methods). All unique variants were collated and the false discovery rate (FDR) was derived from the P value using the BenjaminiHochberg (BH) procedure15 to correct for multiple testing. The behavior of individual variants within this spectrum was intriguing, with, for example, specific synonymous alterations appearing disruptive and specific stop-gained and frameshift alleles, particularly those in the terminal exon, appearing nondisruptive. Codon deletions (in-frame, sequentially deleted codons) also exhibited a spectrum of scores with a bimodal distribution, which allowed us to refine key residues\/domains within the BAP1 protein. Individual variant functional scores relative to the FDR threshold are shown in Fig. 2f. All mutational consequence categories, except UTR variants, had a significantly different median functional score from synonymous variants as measured by Dunns nonparametric pairwise multiple-comparisons procedure (q<0.0001; Supplementary Table 3). <\/p>\n
Functional scores and FDR values were used to categorize variants into functional classes, following the integration and validation of data as described below. Variants with an FDR0.01 were categorized as unchanged, those with an FDR<0.01 and a negative functional score were categorized as depleted and those with an FDR<0.01 and a positive functional score were categorized as enriched. Data for 18,108 unique variants were collected after filtering steps with variants categorized as follows: 11,912 unchanged, 5,665 depleted and 531 enriched (Supplementary Table 2). Unchanged variants centered tightly around a zero functional score (median=0.00; range=0.09) and enriched variants had modestly increased scores (median=0.01; range=0.03), while depleted variants exhibited a wider score distribution (median=0.13; range=0.27; Fig. 3a). As above, stop-gained variants were depleted consistently across all exons, except exon 17, suggesting an escape of nonsense-mediated decay. No enriched variants were observed for stop-gained alleles (Fig. 3b). Functional scores for missense variants were significantly different between exons as measured by KruskalWallis rank sum test (P<0.0001, H=1,093.3). Interestingly, while missense variants were depleted in all exons, we noted that proportionally more of these variants were depleted in exons 19 and 1517, and that fewer missense variants were depleted in exons 1014. Exons 19 and 1517 encode conserved UCH and protein interaction motifs, respectively. Indeed, we found a significant positive correlation between the depleted missense functional classification and conservation as measured by ortholog identity at each amino acid position in the protein (Spearmans rank: rs=0.45, P<0.0001). This relationship was also observed for codon deletions (Spearmans rank: rs=0.44, P<0.0001). <\/p>\n
a, Histogram showing all 18,108 unique variants assayed, grouped into 75 intervals and colored according to functional classification. Inset shows a magnified section of functional score intervals with 500 variants. b, Composition of functional classes by exon and mutational consequence (color key as in a). c, EVE scores for functional classes (n variants in class shown). Both depleted and enriched classes have significantly different median values from the unchanged class (KurskalWallis, P<2.21016; two-sided Dunns BH FDR, ****q<0.0001; depleted q<2.21016 and enriched q=3.4105), demonstrating that depleted and enriched variants are less represented over evolution compared to unchanged variants and are therefore more likely to be disruptive. Boxes show the interquartile range, horizontal lines show the median EVE score, whiskers show maximum and minimum values that are not outliers, and outliers are shown as points. d, The bar chart shows the number of variants in each class that are in gnomAD and not ClinVar (n shown) divided by the number of variants in each class assayed. Fewer depleted and enriched variants than unchanged variants were observed in gnomAD (two-sided chi-squared test: 2=49.1, P<2.141011). e, Heat map showing amino acid-level substitutions (A:stop) created by nucleotide-level saturation across 730 codons (single nucleotide variants (SNVs) only), colored by functional classification (SNV missense changes with discordant functional classifications between alternative codons were excluded; n=158). Of note, codon deletion, alanine scan and stop scan changes were designed to be incorporated at each of the 720 nonsplit codons (of 730 total codons). Bar chart shows the percentage identity calculated from Geneious alignment of the eight species shown in Fig. 6d. Key protein regions are shown (UCH, ubiquitin C-terminal hydrolase; HBM, HCF1 binding motif; BRCA1, BRCA1 binding domain; ASXL, additional sex combs like 1\/2\/3 interaction; YY1, Ying Yang 1 binding domain; NLS, nuclear localization signal). f,g, AlphaFold54 BAP1 model with SGE-depleted codon deletions colored dark blue (f). Depleted codon deletions accurately delineate the UCH domain (purple) and protein interaction region (cyan), as highlighted in g. Depletion also occurs in uncharacterized regions, including the -helix C terminal to the UCH domain, proximal to the protein interaction region (arrow, f). <\/p>\n
Source data <\/p>\n
Because Evolutionary model of Variant Effect (EVE)16 scores can be used as a measure of conservation for missense variants, we compared this metric to our SGE results and found that depleted and enriched variants were under more evolutionary constraint (8,525 of 8,822 total unique missense variant assessed; Fig. 3c). Variants under more evolutionary constraint are expected to be observed less frequently in population-ascertained cohorts of healthy controls from the gnomAD database, which was the case for both depleted and enriched variants compared to unchanged variants (chi-squared test; 2=49.1, P<0.0001; Fig. 3d). We also observed that the conserved N-terminal UCH domain of BAP1 showed greater intolerance to missense changes and codon deletions compared to the more central regions of the protein (Fig. 3e), in keeping with its amino acid conservation. The conserved C-terminal protein interaction motifs also demonstrated intolerance to change. Of note, codon deletions precisely delineated critical domains with high accuracy and highlight uncharacterized regions (Fig. 3f,g). <\/p>\n
Before making comparisons to clinical data, we examined the reproducibility of the functional scores and functional classifications for each variant by comparing LFCs from separate genome editing experiments. Overall, 81% of variants (14,624\/18,108) were separately examined using library A and library B HDR templates, with close to linear LFC value correlations (Pearsons R=0.95, P<0.0001; Fig. 4a). When functional classifications were computed using library A or library B LFCs and FDRs, a 90% concordance of variant classification was observed (13,106\/14,624; Fig. 4a). As LFCs and functional classifications were found to be highly correlated, to increase robustness, library A and library B LFCs for each variant were combined into a single combined LFC and termed the abovementioned functional score (Methods). As expected, variant LFCs within PPE codons differed between libraries (Extended Data Fig. 4a,b). Therefore, variants in PPE codons examined by only library A or library B were excluded from downstream analyses (n=140). As above, our functional score was calculated as the apparent growth rate over five time points, an analysis previously used in SGE17. This approach is appropriate for our data, as LFCs between later time points were linearly related (Extended Data Fig. 4cf). The functional scores, functional classifications (depleted, unchanged and enriched) and downstream comparisons used throughout this study were derived from these combined LFC values. <\/p>\n
a, Independent SGE libraries (A and B) were used to edit most target regions with 13,106 of 14,624 variants showing a concordant functional classification (dark blue) and 1,518 variants discordant between libraries (light blue). Of note, the degrees of LFC for each independent variant measurement were highly concordant based on Pearsons correlation coefficient (R) and two-tailed t-test P<2.21016. b, ROC curve for SGE functional score, with AUC value shown. Also shown is the ideal threshold for maximum diagnostic sensitivity and specificity (plotted as 1 specificity). Calculated using pROC (version 1.18.4)55 in R. c, Top, a histogram showing the 18,108 unique variants grouped within 75 intervals of functional score, colored by ClinVar clinical significance. Bottom, a magnified region highlights that pathogenic\/likely pathogenic (dark blue) variants are depleted. The arrow shows the x-axis position of the ideal threshold. d, Top, functional classification by ClinVar clinical significance (1*, 4 September 2023). Bottom, functional classification by observation in ClinVar and gnomAD (n variants shown). e, Depleted variants (n=5,665) categorized into strongly depleted (lower 50%, dark blue) and weakly depleted (upper 50%, light blue) variants, either side of the median functional score (0.1260642). f, More frameshift and stop-gained variants and fewer missense variants were strongly depleted compared to weakly depleted variants (two-sided chi-squared test, 2 = 10,759, P<2.21016). g, Strongly and weakly depleted missense variants have significantly different EVE scores (two-sided MannWhitneyWilcoxon test, ****P<2.21016). Boxes show the interquartile range, horizontal lines show the median EVE score, whiskers show maximum and minimum values that are not outliers, and outliers are shown as points. h, Concordance of SGE functional classification and orthogonal functional assays for VUS in patients with cancer and developmental disorders9,25. Color indicates SGE classification and shape corresponds to orthogonal assay classification. Control variants (from a casecontrol study25) are shown in green text. SGE variants that were strongly depleted (dark blue) and not tolerated in orthogonal assays (triangles) are completely concordant. P12A, which was partially tolerated in an orthogonal assay, was weakly depleted in SGE. All tolerated variants (white squares) in assays were unchanged in SGE (gray), except for E406V, which was enriched (red). <\/p>\n
Source data <\/p>\n
Full nucleotide and protein-level variant effect maps are provided in Extended Data Figs. 5 and 6, respectively. The full dataset with annotations and scores is also available for download at https:\/\/github.com\/team113sanger\/Waters_BAP1_SGE<\/a> and as Supplementary Data 1 and 2. Variant scores and classifications can also be searched on the BAP1 Viewer: https:\/\/bap1-viewer.shinyapps.io\/bap1viewer\/<\/a>. <\/p>\n To further examine functional scores, we first identified variants with strong clinical\/functional data in support of their classification, curating 851 benign (true negative) and 199 pathogenic (true positive) variants that had at least one star (1*) in ClinVar (downloaded 4 September 2023). We used the functional scores for these variants to generate a receiver operating characteristic (ROC) curve, with the area under the curve (AUC) computed (Fig. 4b). We found that our functional score was highly accurate at classifying these variants with a sensitivity of >99%, a specificity of >98%, a classification error rate close to 0 (<0.002%) and a precision-recall AUC of >0.999 (Supplementary Table 4). We also used our data to explore the relationship between functional score\/classification and reported clinical classifications and found high concordance (Fig. 4c,d). <\/p>\n Of note, many clinically used in silico classifiers, including EVE16, SIFT18 and PolyPhen-219, use protein-level information to predict function, whereas SGE assesses function at the nucleotide level, capturing variant effects on splicing, RNA folding, codon usage and other non-protein-level processes. We observed that few synonymous variants were depleted in our screen (Figs. 2e,f and 3b). Importantly, synonymous variants that were classified as depleted had significantly higher SpliceAI scores than unchanged synonymous variants (P<0.0001, two-sided MannWhitneyWilcoxon test; Extended Data Fig. 7a), suggesting functional relevance. In the absence of functional or in silico data, synonymous variants are routinely classified as VUS20, suggesting that these variants could be misclassified without SGE. Importantly, we found that variants (missense, stop-gained and synonymous) created by SGE through different nucleotide-level changes had highly correlated LFCs, as expected (Pearsons R=0.91, P<0.0001; Extended Data Fig. 7b). Missense changes alone also showed a high correlation in LFCs between alternative codons (Pearsons R=0.89, P<0.0001). Of note, 8,822 unique nucleotide-level changes in our screen resulted in 4,619 unique missense changes at the protein level, of which 3,993 could be examined using alternative codon generation, with 16.7% (667\/3,993) showing different functional classifications. Thus, not all missense changes have equal effects when encoded by alternative codons, further highlighting the importance and richness of SGE functional assessment at the nucleotide level. <\/p>\n Because very few BAP1 missense variants have been ascribed to be pathogenic or benign, a direct comparison of sensitivity and specificity using an AUC summary metric between in silico tools and SGE functional scores for missense variants alone is not possible. However, when we compared experimental data with in silico tools, we found that EVE, PolyPhen-2 and CADD21 predicted SGE classifications of non-splice region missense variants with 7779% accuracy (Extended Data Fig. 7c). With per-variant examination, it is notable that EVE, PolyPhen-2 and CADD classify proportionally more missense variants as pathogenic, probably damaging and likely pathogenic, respectively, suggesting that SGE may have a relatively higher specificity (Extended Data Fig. 7dg). <\/p>\n Next, we sought to quantify the evidence strength at which predictions from our assay could be applied using the American College of Medical Genetics and Genomics (ACMG) framework for variant interpretation20. To this end, we generated further truth sets of high-confidence pathogenic and benign variants (Methods and Supplementary Table 4) against which to evaluate assay performance using the established framework from Brnich et al.22. We aimed to evaluate assay performance in predicting the impact of missense variants, which are challenging to classify. <\/p>\n We observed that 99.8% (2,419\/2,423) of variants in our pathogenicity truth set exhibited the expected depletion in the assay output, whereas 97.1% (134\/138) of variants in our benignity truth set were unchanged or enriched in the assay (Table 1). These observations equate to likelihood ratios toward pathogenicity of 27.6 and benignity of 470.6, which correspond to strong and very strong evidence strengths, respectively22,23. Notably, when using truth sets constructed using ClinVar-classified missense variants only (1* review status), there was full concordance with assay results; however, due to small sample numbers, these truth sets yielded likelihood ratios toward pathogenicity and benignity of 6.0 and 7.0, respectively, both equating to a moderate strength of evidence. Further limiting truth sets by restriction to ClinVar variants of 2* did not allow the generation of evidence strengths due to the absence of pathogenic variants. <\/p>\n We were intrigued by the observation that some patients with germline BAP1 variants have been reported as being predisposed to tumors, whereas others have a neurodevelopmental disorder. SGE allows us to test whether these variants have different functional outcomes. <\/p>\n To this end, we ranked the 5,665 depleted variants (we excluded enriched variants) by categorizing them on either side of the median, defining them as strongly depleted (n=2,833) or weakly depleted (n=2,832) (Fig. 4e). We observed that the proportions of mutational consequences seen in strongly and weakly depleted categories were significantly different from one another (chi-squared test; 2=10,759, P<0.0001), with more missense and fewer stop-gained and frameshift mutations weakly depleted (Fig. 4f). We also observed that weakly depleted missense variants were less conserved (P<0.0001, two-sided MannWhitneyWilcoxon test; Fig. 4g). Strongly depleted variants were also depleted at an earlier time point (D10) in the screen compared to most weakly depleted variants (Extended Data Fig. 7h). Taking these findings together, it appears that a subset of missense variants (n=426; strongly depleted) behave similarly to stop-gained\/frameshift variants and a larger number of missense variants (n=1,548; weakly depleted) have a less extreme LFC and slower change in variant abundance. <\/p>\n Sixteen BAP1 germline variants have been associated with developmental disorders9,24. In our screen, we assayed 15 of these 16 variants and found that 13 of 15 were classified as depleted (Supplementary Note 1 and Extended Data Fig. 7i). Functional studies have previously been performed on variants associated with development9 and cancer25, with perfect concordance observed between these orthogonal assays and SGE to the degree that a putative hypomorphic allele can be distinguished (Supplementary Note 1 and Fig. 4h). <\/p>\n Next, we analyzed data from a comprehensive clinical analysis of families with BAP1-tumor predisposition syndrome (TPDS)26 (Supplementary Note 1 and Supplementary Table 5). Interestingly, we found that carriers of depleted variants had a significantly earlier age of onset than carriers of unchanged variants (P<0.01, two-sided MannWhitneyWilcoxon test; Extended Data Fig. 7j). However, we saw no differences between strongly and weakly depleted classifications for age of onset or cancer type (Supplementary Note 1 and Extended Data Fig. 7j,k). Moreover, while there was a difference in molecular consequences (Fig. 4f), conservation (Fig. 4g) and effect sizes, germline cancer-associated variants did not have different functional score effect sizes compared to development-associated variants (Extended Data Fig. 7i,k). <\/p>\n Next, we used whole-exome sequencing data from 454,787 individuals in UK Biobank to explore the phenotypic consequences of BAP1-disruptive alleles27. We identified 57 SGE-depleted, 80 SGE-enriched and 754 SGE-unchanged variants in the exomes of 297, 1,960 and 61,333 carriers, respectively (Supplementary Table 6). We performed a phenome-wide association study (PheWAS) analysis (Supplementary Method 14), focusing on depleted variants only. To evaluate the association of these variants with overall cancer risk, we generated cancer-type phenotypic variables and rare variant burden test masks (variant sets) (Fig. 5a, Extended Data Fig. 8a and Supplementary Table 7). We found that SGE-depleted nonsynonymous variants were significantly associated with all-site cancer predisposition (P=7.85 1003; n=82) with this variant set\/mask composed of missense and high-confidence protein-truncating variants (PTVs), which were classified as depleted by SGE. <\/p>\n a, PheWAS forest plot for all-site cancers using SGE-depleted variants and controls; regression model effect is shown by data points and effect standard error is shown by bars (Supplementary Table 7). Rare variant burden test masks (and CADD, EVE and REVEL56 predictors) are shown by color for BAP1 variants in UK Biobank (n carriers shown in key). Significance, according to the corrected P value determined by generalized linear modeling (Supplementary Method 14), is indicated by a triangle (significant) or a circle (not significant). SGE-depleted nonsynonymous variants (yellow) showed a significant effect and are therefore associated with increased cancer risk. SGE-depleted high-confidence (HC) protein-truncating variants (PTVs; orange) demonstrated a significant effect, as did HC PTVs (red). b, UK Biobank SGE-depleted nonsynonymous variant carriers (n=69) had a significantly higher median blood concentration of IGF-1 compared to noncarriers (n=398,505); P<0.005 (P=0.0033, two-sided MannWhitneyWilcoxon test). Violin plots are colored by BAP1 variant status, boxes show the interquartile range, horizontal lines show the median IGF-1 blood concentration (nmol l1), whiskers show maximum and minimum values that are not outliers, and outliers are shown as points. c, IGF1 mRNA expression levels in transcripts per million (TPM) obtained from TCGA for 80 uveal melanoma tumors28. BAP1-mutant tumors (n=35) have higher IGF1 expression than those with wild-type BAP1 (n=45). Colors, outliers and box description are as in b, except the horizontal line is the median IGF1 expression in tumors. P<0.001 (P=0.00029, two-sided MannWhitneyWilcoxon test). d, The 80 samples from patients with uveal melanoma were ranked by TCGA IGF1 expression level, with tumors with the top 50% highest expression levels classified as having high expression and the bottom 50% classified as having low expression. Top, KaplanMeier estimates, with deceased status (overall survival) shown by vertical tick marks and the model for survival probability based on the overall survival time (in days) shown by lines colored to indicate IGF1 expression level. The P value was calculated using the log-rank test and indicates a significant difference between the overall survival probability for tumors with high and low IGF1 expression from patients in the cohort. Bottom, number at-risk table shows a higher number of patients alive at each time increment for patients whose tumor expressed low versus high levels of IGF-1. <\/p>\n Source data <\/p>\n Beyond cancer, we also examined the association between UK Biobank BAP1 variants and quantitative traits (Supplementary Table 8). As a result, we identified that circulating IGF-1 levels were significantly increased in carriers of SGE-depleted nonsynonymous BAP1 variants compared to noncarriers (Fig. 5b; P<0.005, two-sided MannWhitneyWilcoxon test). Importantly, IGF-1 levels in carriers with and without a cancer diagnosis did not differ, indicating that significantly increased IGF-1 levels are specific to individuals with SGE-depleted nonsynonymous BAP1 variants rather than a cancer diagnosis, and suggests a possible mechanism of BAP1-mediated pathogenicity (Supplementary Note 2). <\/p>\n To further investigate the association of SGE-depleted alleles with increased IGF-1 levels, we obtained The Cancer Genome Atlas (TCGA) RNA-seq data28 for uveal melanomas and found a strong association of loss-of-function BAP1 alleles with IGF1 mRNA expression (P<0.001, two-sided MannWhitneyWilcoxon test) and poor prognosis by KaplanMeier estimate (P=0.004) (Fig. 5c,d). <\/p>\n As a further exemplar of the value of our BAP1 SGE data, we identified a family whose proband presented at the age of 26 years with uveal melanoma. A review of the family history revealed other BAP1-associated tumors segregating over three generations (Fig. 6a,b), with sequencing revealing a germline c.535C>T (R179W) variant in the BAP1 gene. c.535C>T was depleted in our SGE experiment, with a functional score of 0.122 and an FDR of<0.01 (Fig. 6c). This variant had been classified in the clinic as a VUS, but together with our SGE data it has been reclassified as likely pathogenic (ACMG, class IV), a result that will contribute to the clinical management of this kindred. Of note, R179W falls in a highly conserved region of BAP1, which includes the proton donor residue at H169. At codon R179, the only SGE-tolerated substitution is R179Q, with glutamine being the conserved residue in the Drosophila melanogaster BAP1 ortholog Calypso (Fig. 6d,e). <\/p>\n a, Pedigree with a proband carrying a c.535C>T variant (HGVSc, ENST00000460680.6:c.535C>T; HGVSp, ENSP00000417132.1:p.Arg179Trp; R179W) in exon 7 of BAP1. The proband was a 33-year-old male presenting with uveal melanoma (UM) at 26 years (arrow) whose father, uncle and grandmother presented with melanoma (ME), basal cell carcinoma (BCC) and renal cell carcinoma (RCC), respectively. The probands mother was not known to be a carrier and died of metastatic (M) cancer, possibly cholangiocarcinoma (CCA). The pedigree follows established nomenclature: black, clinically confirmed disease (malignant tumor); square, male; circle, female; diagonal line, deceased; d., age at death; number, age at disease presentation. An asterisk indicates the patient for whom samples are shown in b. b, Pathology of the primary cutaneous melanoma in the patient from a. Top, micrograph showing hematoxylin and eosin (H&E) staining. Bottom, micrograph showing BAP1 immunohistochemical staining; staining is absent in tumor tissue (black arrow) but is present (purple cells) in immune infiltrate (red arrow). Scale bars, 100m. Micrographs are representative of three histological sections. c, Functional scores across exon 7. Exonic\/intronic ranges within the target region are shown, with points colored by VEP consequence. Transparency based on FDR. Shape denotes functional classification. The variant in a is labeled. d, Multiple-sequence alignment of exon 7 created by global alignment of BAP1 orthologs from eight species (gap open\/extension penalty=12\/3); numbers are protein positions of human BAP1 (ENSP00000417132.1) and residues are colored by identity (black, 100%; dark gray, 80100%; light gray, 6080%; white, <60%). R179 (and the highly conserved H169 proton donor) is highlighted by a red arrow. Note that the glutamine residue in Drosophila aligns at human position R179, the only missense variant at this position tolerated in SGE. e, Heat map (see Extended Data Fig. 6 for the full heat map) of amino acid substitutions for two key positions, H169 and R179, colored by functional classification. White space results from SNV saturation not producing all amino acid substitutions. c.535C>T produces R179W, which is depleted. R179R, a synonymous change, is unchanged, other missense changes (R179P\/L\/G\/A\/*) and R179 codon deletion are depleted and only R179Q is tolerated. H169 in the catalytic core is intolerant to all observed changes, except for a synonymous change. Black circle, key synonymous changes; white triangle, key missense changes. <\/p>\n Source data <\/p>\n Finally, to further explore the use of SGE data and identify novel BAP1 variants, we queried tumor sequence data for a cohort of 394,756 patient samples in the Foundation Medicine database29 and found 12,172 (3.1%) unique BAP1-altered specimens harboring 13,283 BAP1 alterations, including all possible changes at codon R146 (Extended Data Fig. 9ad). Because these variants were derived from tumor-only sequencing, germline DNA was obtained30 and sequenced from a patient with breast\/cholangiocarcinoma whose sister was diagnosed with renal carcinoma (Extended Data Fig. 9ad). Both patients were confirmed to carry a germline R146K (c.437G>A) variant identified as disruptive by SGE (Extended Data Fig. 9ae), providing another example of how SGE data can help improve diagnostic precision. <\/p>\n <\/p>\n Read more: Optimized SGE approach improves experiment quality We developed a HAP1 DNA ligase 4 (LIG4)-knockout (KO) line with genomic integration of a clonally derived Cas9 (HAP1-A5) and confirmed BAP1 essentiality in this line (Figs. 1 and 2a), high Cas9 activity (Fig. 2b and Extended Data Fig Continue reading
\nSaturation genome editing of BAP1 functionally classifies somatic and germline variants - Nature.com<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"