Protein-Specific Differential Glycosylation of Immunoglobulins in Serum of Ovarian Cancer Patients

Abstract

Previous studies indicated that glycans in serum may serve as biomarkers for diagnosis of ovarian cancer; however, it was unclear to which proteins these glycans belong. We hypothesize that protein-specific glycosylation profiles of the glycans may be more informative of ovarian cancer and can provide insight into biological mechanisms underlying glycan aberration in serum of diseased individuals. Serum samples from women diagnosed with epithelial ovarian cancer (EOC, n = 84) and matched healthy controls (n = 84) were obtained from the Gynecologic Oncology Group. Immunoglobulin (IgG, IgA, and IgM) concentrations and glycosylation profiles were quantified using multiple reaction monitoring mass spectrometry. Differential and classification analyses were performed to identify aberrant protein-specific glycopeptides using a training set. All findings were validated in an independent test set. Multiple glycopeptides from immunoglubins IgA, IgG, and IgM were found to be differentially expressed in serum of EOC patients compared with controls. The protein-specific glycosylation profiles showed their potential in the diagnosis of EOC. In particular, IgG-specific glycosylation profiles are the most powerful in discriminating between EOC case and controls. Additional studies of protein- and site-specific glycosylation profiles of immunoglobulins and other proteins will allow further elaboration on the characteristics of biological functionality and causality of the differential glycosylation in ovarian cancer and thus ultimately lead to increased sensitivity and specificity of diagnosis.

Recent Advances in the Mass Spectrometry Methods for Glycomics and Cancer

“…It has already been applied to rapid-throughput analysis of serum glycopeptides from several cancers. 22, 72–74 …”

“…82 There are limitations to this approach as it covers a subset of the glycome. Changes in non-sialylated glycopeptides of some proteins such as IgG have been shown to accompany cancers, 72 which could be missed by this method.…”

Glycans and glycoproteins as specific biomarkers for cancer

“…Normalizing the glycopeptide to the level of the protein helps to identify the actual glycosylation changes irrespective of the changes in the level of protein expression between samples [137]. This method has been extended to include other glycoproteins in serum[142] and it is currently applied in our laboratory to screen for disease biomarkers for cancer [143] autoimmune conditions and other diseases. A recent study investigated the immunoglobulins in ovarian cancer patients compared to the controls.…”

Prospective applications of ultrahigh resolution proteomics in clinical mass spectrometry

“…These glycosylation patterns are often derived from high abundance proteins, and as such would be well targetable using clinical MS assays. Recently, MRM technology was developed and applied to assess the differential N-glycosylation patterns of serum immunoglobulins in ovarian cancer patients compared to controls [74][75][76]. In addition, a MALDI-FTICR system has been used to map a complex mixture of glycopeptides obtained from immunoglobulin A, exemplified in Figure 2 and showing the benefits of HRAM with regard to resolving overlapping species [63].…”