Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of coronavirus disease 2019 (COVID-19). The rapid, sensitive and specific diagnosis of SARS-CoV-2 by fast and unambiguous testing is widely recognized to be critical in responding the current outbreak. Since the current testing capacity by conventional PCR based methods is insufficient because of shortages of supplies such as RNA extraction kits and PCR reagents, alternative and/or complementary testing assays should be developed. Here, we exploit the potential of targeted mass spectrometry based proteomic technologies to solve the current issue of insufficient SARS-CoV-2 diagnostic testing capacity. We have assessed the limit of detection by parallel reaction monitoring (PRM) on an Orbitrap Eclipse mass spectrometer for target tryptic peptides of several SARS-CoV-2 proteins from a sample of virus infected Vero cells. For Nucleocapsid protein the limit of detection was found to be in the mid-attomole range (0.9 × 10−12 g), which would theoretically correspond to approximately 10,000 SARS-CoV-2 particles, under the assumption that all viral proteins are assembled in macromolecular virus particles. Whether or not this sensitivity is sufficient to play a role in SARS-CoV-2 detection in patient material such as swabs or body fluids largely depends on the amount of viral proteins present in such samples and is subject of further research. If yes, mass spectrometry based methods could serve as a complementary protein based diagnostic tool and further steps should be focused on sample preparation protocols and on improvements in sample throughput.

The rapid, sensitive and specific detection of SARS-CoV-2 is critical in responding to the current COVID-19 outbreak. In this proof-of-concept study, we explored the potential of targeted mass spectrometry (MS) based proteomics for the detection of SARS-CoV-2 proteins in both research samples and clinical specimens. First, we assessed the limit of detection for several SARS-CoV-2 proteins by parallel reaction monitoring (PRM) MS in infected Vero E6 cells. For tryptic peptides of Nucleocapsid protein, the limit of detection was estimated to be in the mid-attomole range (9E-13 g). Next, this PRM methodology was applied to the detection of viral proteins in various COVID-19 patient clinical specimens, such as sputum and nasopharyngeal swabs. SARS-CoV-2 proteins were detected in these samples with high sensitivity in all specimens with PCR Ct values <24 and in several samples with higher CT values. A clear relationship was observed between summed MS peak intensities for SARS-CoV-2 proteins and Ct values reflecting the abundance of viral RNA. Taken together, these results suggest that targeted MS based proteomics may have the potential to be used as an additional tool in COVID-19 diagnostics.

Ubiquitin-specific protease 7 (USP7) has been implicated in cancer progression and neurodevelopment. However, its molecular targets remain poorly characterized. We combined quantitative proteomics, transcriptomics, and epigenomics to define the core USP7 network. Our multi-omics analysis reveals USP7 as a control hub that links genome regulation, tumor suppression, and histone H2A ubiquitylation (H2AK119ub1) by noncanonical Polycomb-repressive complexes (ncPRC1s). USP7 strongly stabilizes ncPRC1.6 and, to a lesser extent, ncPRC1.1. Moreover, USP7 represses expression of AUTS2, which suppresses H2A ubiquitylation by ncPRC1.3/5. Collectively, these USP7 activities promote the genomic deposition of H2AK119ub1 by ncPRC1, especially at transcriptionally repressed loci. Notably, USP7-dependent changes in H2AK119ub1 levels are uncoupled from H3K27me3. Even complete loss of the PRC1 catalytic core and H2AK119ub1 has only a limited effect on H3K27me3. Besides defining the USP7 regulome, our results reveal that H2AK119ub1 dosage is largely disconnected from H3K27me3.

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It remains challenging in chronic lymphocytic leukemia (CLL) to distinguish between patients with favorable and unfavorable time to first treatment (TTFT). Additionally, the downstream protein correlates of well-known molecular features of CLL are not always clear. To address this, we selected 40 CLL patients with TTFT ≤ 24 months and compared their B cell intracellular protein expression with 40 age- and sex-matched CLL patients with TTFT > 24 months using mass spectrometry. In total, 3268 proteins were quantified in the cohort. IGHV mutational status and trisomy 12 were most impactful on the CLL proteome. Comparing cases to controls, five proteins were significantly upregulated, whereas three proteins where significantly downregulated. Of these, only THEMIS2, a signaling protein acting downstream of the B cell receptor, was significantly associated with TTFT, independently of IGHV and TP53 mutational status (HR 2.49, [95%CI 1.62–3.84], P < 0.001). This association was validated on the mRNA and protein level by qPCR and ELISA, respectively. Analysis of two independently generated RNA sequencing and mass spectrometry datasets confirmed the association between THEMIS2 expression and clinical outcome. In conclusion, we present a comprehensive characterization of the proteome of untreated CLL and identify THEMIS2 expression as a putative biomarker of TTFT.