The cell surface proteome is the interface where normal cells and cancer cells contact the extracellular space and is a major target for cancer immunotherapy. To survive, cancer cells regulate by boosting nutrient inputs, transmitting growth signals and evading immune surveillance.About 4,000 different membrane proteins are encoded in the human genome, but only 24 antibodies targeting cell surfaces have been approved for therapeutic interventions, prompting the need to find new tumor-specific antigens.
James A. Wells and colleagues from the University of California, San Francisco, published ‘Broad and thematic remodeling of the surfaceome and glycoproteome on isogenic cells transformed with driving proliferative oncogenes’ in the Proceedings of the National Academy of Sciences (PNAS) .The researchers provided a large-scale comparative study to study how 6 adjacent proliferative oncogenes cause large cell self-remodeling in the surface proteome and glycoprotein group.
In the past decade, chemical glycoproteomics has revealed specific examples of changes in glycosylation and heterogeneity of glycans on specific proteins. However, it is still unknown how the expression of different oncogenes changes the glycosylation of a single protein within the proteome. The hybrid electron transfer dissociation method has become a pioneer in glycoproteomic analysis, such as activated ion ETD and assisted activation ETD. Because they can generate sequence information tandem mass spectrometry, connecting peptide backbones and corresponding glycan modifications. These technologies can provide granularity for changes in the glycosylation state of cell surface proteins during oncogene transformation.
The study discussed how a common non-oncogenic epithelial cell with stable expression of adjacent driving oncogenes changes the surface proteome and glycoproteome. Using cell surface capture and AI-ETD glycoproteomics, it was found that each oncogene induced common and unique up-regulated and down-regulated surface proteomes and associated glycan. These oncogene-induced surface proteins highlight targets or combinations that need to be considered for immunotherapy.
The researchers studied six oncogenes (HER2 overexpression, EGFRL858R, KRASG12V, BRAFV600E, MEKDD, AKTmyr), and there are many different differences between them. They are divided into two groups based on growth rate, surface morphology, and related glycan aggregation. Cluster 1, which contains HER2 overexpression, proliferates most actively and has decreased adhesion. Comparison of the incidence of oncogenic mutations of all cancer types shows that BRAF and KRAS have strong mutual exclusion, and slightly mutual exclusion with EGFR.
One of the most significant oncogene-induced changes observed is the proteins involved in solute transport, which are reversed when MEK is inhibited. These include up-regulation of SLC2A1, SLC6A15, SLC7A1, SLCO4A1 and MF12/melanotransferrin, and down-regulation of SLC22A5 and STEAP4 .
Another important finding is the general down-regulation of surface proteins involving receptor tyrosine phosphatase and other tumor suppressors such as PTPRF, PTPRS, UNC5B and BCAM. Especially the expression of PTPRF and PTPRS, through the inactivation of EGFR signaling and tumor metastasis The reduction of cytokine is related to the importance of their role as an oncoprotein in many cancers. For example, UNC5B has recently been shown to prevent tumor progression by inducing cell cycle arrest in G2/M phase in an in vivo model of bladder cancer.
Metastasis is the main cause of death in cancer patients, and tumor cells gain the ability to penetrate surrounding tissues. These functions are achieved by changing the adhesion molecules on the cell surface, which play a role in mediating cell-cell interactions. The researchers identified five targets, LAMC2, LAMA3, LAMB3, PODXL and MME, which play an important role in the metastasis of different types of tumors, and found that they are up-regulated in most oncogene mutations.
Another important reason for cancer development is that they evade immune surveillance. This can be achieved by overexpressing proteins with immunosuppressive effects or by down-regulating proteins that increase immune activation. Researchers have identified three differentially regulated proteins, NT5E and HLA-F And DSE, they play an important role in immune function.
Changes in glycosylation are common to cancer cells and can be caused by a variety of factors, including changes in glycosyltransferase expression, availability of glyconucleotide substrates, changes in substrate protein expression, or changes in protein substrate tertiary structure, which destroy metastatic glycan in tumor cells. We found that glycosyltransferases FUT10, EXT2, GALNT11, GCTN2, and ST6GALNAC2 were highly up-regulated in all cancer cell lines.
In summary, the researchers studied how six common and neighboring oncogenes drive cell proliferation in a simplified cell autologous model. They found that the independent expression of these six oncogenes will cause profound changes in the surface group, including the expressed proteins and modify their glycans. This work helps to understand the similarities and differences between adjacent oncogenes and provides an opportunity to seek antibody tools to adapt to more complex tumor environments.
Kevin K.Leung, Gary M. Wilson,et.al. Broad and thematic remodeling of the surfaceome and glycoproteome on isogenic cells transformed with driving proliferative oncogenes. Proceedings of the National Academy of Sciences Mar 2020, 201917947.