Fig 2: LRRC15 binds with SARS-CoV-2 spike protein at the receptor-binding domain(A) A375 cells were transduced with indicated activating sgRNAs and incubated with SARS-CoV-2 spike S1-Fc fusion protein. Protein binding was measured by flow cytometry. (B) HeLa cells were transduced with indicated activating sgRNAs and incubated with SARS-CoV-2 spike S1-Fc fusion protein. Protein binding was measured by flow cytometry.(C) Dose-dependent binding of SARS-CoV-2 spike protein (Wuhan-Hu-1) to both ACE2 and LRRC15 with a Fc tag was determined by ELISA. Human IgG1 was included as a negative control. Dots indicate means of duplicates.(D) HeLa cells were transduced with indicated activating sgRNAs and incubated with SARS-CoV-2 spike NTD-Fc or RBD-Fc fusion protein. Protein binding was measured by flow cytometry.(E) The binding of the SARS-CoV-2 RBD and NTD to LRRC15 was measured by ELISA.

Fig 3: A surfaceome-focused CRISPRa screen identified cellular receptors binding with SARS-CoV-2 spike protein.(A) Schematic of a focused CRISPRa screen for surface proteins interacting with SARS-CoV-2 spike S1-Fc fusion protein. (B) Volcano plots showing sgRNAs enriched or depleted in cells binding with SARS-CoV-2 spike S1-Fc or human IgG isotype control. Results from 2 biologically independent replicates are shown. For underlying data, see S1 Data. ACE2, angiotensin-converting enzyme 2; CRISPRa, CRISPR activation; dCas9, “dead” Cas9; IgG, immunoglobulin G; LRRC15, leucin-rich repeat-containing 15; SARS-CoV-2, Severe Acute Respiratory Syndrome Coronavirus 2; sgRNA, single guide RNA.

Fig 4: LRRC15 expression is enriched in the fibroblasts of COVID-19 patients and associated with reduced SARS-CoV-2 viral burden.(A, B) Cell type–specific expression of ACE2 and LRRC15, assessed by scRNA-seq of lungs from deceased COVID-19 patients (A) Delorey and colleagues [44] or (B) Melms and colleagues [43]. (C) Tukey boxplots (IQR boxes with 1.5 × IQR whiskers) of the relative frequencies of fibroblast subtypes among total fibroblasts, comparing COVID-19 patients (blue) to non-COVID-19 controls (red). Statistical significance was assessed by two-tailed unpaired Mann–Whitney test. (D) Volcano plot of differentially expressed genes in the lungs of deceased COVID-19 patients, comparing samples with high vs. low SARS-CoV-2 RNA levels at the time of death [46]. Genes with positive log2 fold changes are associated with high viral burden, while genes with negative log2 fold changes are associated with low viral burden. (E) LRRC15 expression in lung cell lines (A549, A549-ACE2, Calu-3), comparing mock controls vs. SARS-CoV-2-infected samples. Data represent means ± SEM. Statistical significance was assessed by two-tailed unpaired Welch’s t test. For underlying data, see S2 Data. ACE2, angiotensin-converting enzyme 2; COVID-19, Coronavirus Disease 2019; IQR, interquartile range; LRRC15, leucin-rich repeat-containing 15; SARS-CoV-2, Severe Acute Respiratory Syndrome Coronavirus 2; scRNA-seq, single-cell RNA-sequencing.

Fig 5: LRRC15 binds with SARS-CoV-2 spike protein at the RBD.(A) A375 cells were transduced with indicated activating sgRNAs and incubated with SARS-CoV-2 spike S1-Fc fusion protein. Protein binding was measured by flow cytometry with MFI shown. (B) HeLa cells were transduced with indicated activating sgRNAs and incubated with SARS-CoV-2 spike S1-Fc fusion protein. Protein binding was measured by flow cytometry with MFI shown. (C) Dose-dependent binding of SARS-CoV-2 spike protein (Wuhan-Hu-1) to both ACE2 and LRRC15 with an Fc tag was determined by ELISA. Human IgG1 was included as a negative control. Dots indicate means of duplicates. (D) HeLa cells were transduced with indicated activating sgRNAs and incubated with SARS-CoV-2 spike NTD-Fc or RBD-Fc fusion protein. Protein binding was measured by flow cytometry with MFI shown. (E) The binding of the SARS-CoV-2 RBD and NTD to LRRC15 was measured by ELISA. For underlying data, see S3 Data. ACE2, angiotensin-converting enzyme 2; LRRC15, leucin-rich repeat-containing 15; MFI, mean fluorescence intensity; NTD, N-terminal domain; RBD, receptor-binding domain; SARS-CoV-2, Severe Acute Respiratory Syndrome Coronavirus 2; sgRNA, single guide RNA.