The proteome of prostate cancer-derived exosomes: Exosomes as biomarker treasure chests
EMSL Project ID
30455
Abstract
Prostate cancer (PCa) is the most common cancer and the second leading cause of cancer death in men. Although considerable progress in the clinical setting has been made in the past decades, early detection, reliable prognosis, and more and improved treatment options are needed to significantly decrease mortality and morbidity from this disease. In the past three years, we developed and applied a novel method to identify tumor-secreted serum markers for PCa. Using human prostate cancers grafted in immune-incompetent mice, we sequenced as many serum proteins as possible to identify human-specific proteins. These human proteins are by definition cancer-derived and may be potential markers for tumor characteristics such as growth, size, location and aggressiveness. These experiments revealed that besides the well known secreted proteins such as PSA (prostate specific antigen), many of the cancer-derived proteins are cytoplasmic proteins secreted by the cancer cells in small vesicles, so-called exosomes. These 50-150 nm vesicles do not contain proteins secreted by the Golgi secretory pathway (such as PSA), but represent a snap-shot of the cellular interior. In addition, exosomes contain transmembrane proteins of which some are predominantly or uniquely expressed in the prostate, providing us with the opportunity to specifically isolate and visualise prostate-derived exosomes. Exosomes are truly biomarker treasure chests that finally give us the ability to easily fish out the needle in the haystack, thereby strongly enriching for cancer-derived proteins in complex fluids such as serum.
In order to identify the proteome of exosomes, we have isolated and peptide-sequenced a purified exosome protein fraction by nanoLC-LTQ-FTMS (7 Tesla). In total, 48 proteins were identified by two or more peptides. Indeed, mainly cytoplasmic proteins were found, but also prostate-specific transmembrane proteins were uncovered. The number of proteins identified in this setup was somewhat limited and no reliable information is present on the posttranslational modification status of the proteins. This latter part is of high interest since particularly the phosphorylation status of the cytoplasmic proteins encapsulated by exosomes might disclose protein activity, kinase pathways activity and the overall state of the cell from which the vesicles were derived. Clearly features we need to know in case of cancer.
The goals of this proposal are to identify as many proteins as possible present in and on prostate cancer-derived exosomes, identify posttranslational modifications and isoforms, and validate expression of the most promising candidate biomarkers. The integrated top-down and bottom-up strategy developed by Dr. Pasa-Tolic will be utilized since this protocol is exceedingly suitable for identification and characterization of purified exosome proteins.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2008-12-29
End Date
2011-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Duijvesz D, KE Burnum, MA Gritsenko, M Hoogland, MS Vredenbregt-van den Berg, GJ van Leenders, R Willemsen, TN Luider, L Pasa-Tolic, and G Jenster. 2013. "Proteomic Profiling of Exosomes Leads to the Identification of Novel Biomarkers for Prostate Cancer ." PLoS One 8(12):e82589. doi:10.1371/journal.pone.0082589