Mapping the Melanoma Plasma Proteome (MPP) Using Single-Shot Proteomics Interfaced with the WiMT Database

SIMPLE SUMMARY: We developed a clinical proteomics methodology, known as Wise MS Transfer (WiMT), for deep identification of blood proteins in undepleted plasma samples. We applied it to the analysis of undepleted melanoma plasma samples as a proof of principle. Malignant melanoma is the most aggressive type of skin cancer, and early diagnostic and prognostic predictors are essential to establish the most suitable treatment tailored to the patient. Our results showed the greatest identification of proteins and biological processes to date reported for a “dilute and shoot” approach within plasma samples from melanoma patients. More than 1200 proteins related to key biological processes in melanoma progression were mapped, including signaling (the PI3K–Akt signaling pathway), immune system processes (complement and coagulation cascade), and secretion (exosome proteins). These proteins and related biological processes constitute the core of blood components that could be monitored by mass spectrometry in clinical proteomic studies from undepleted plasma samples in melanoma. ABSTRACT: Plasma analysis by mass spectrometry-based proteomics remains a challenge due to its large dynamic range of 10 orders in magnitude. We created a methodology for protein identification known as Wise MS Transfer (WiMT). Melanoma plasma samples from biobank archives were directly analyzed using simple sample preparation. WiMT is based on MS1 features between several MS runs together with custom protein databases for ID generation. This entails a multi-level dynamic protein database with different immunodepletion strategies by applying single-shot proteomics. The highest number of melanoma plasma proteins from undepleted and unfractionated plasma was reported, mapping >1200 proteins from >10,000 protein sequences with confirmed significance scoring. Of these, more than 660 proteins were annotated by WiMT from the resulting ~5800 protein sequences. We could verify 4000 proteins by MS1t analysis from HeLA extracts. The WiMT platform provided an output in which 12 previously well-known candidate markers were identified. We also identified low-abundant proteins with functions related to (i) cell signaling, (ii) immune system regulators, and (iii) proteins regulating folding, sorting, and degradation, as well as (iv) vesicular transport proteins. WiMT holds the potential for use in large-scale screening studies with simple sample preparation, and can lead to the discovery of novel proteins with key melanoma disease functions.