Differential N-glycosylation of Kallikrein 6 Derived from Ovarian Cancer Cells or the Central Nervous System

Uros Kuzmanov,Nianxin Jiang,Christopher R Smith,Antoninus Soosaipillai,Eleftherios P Diamandis

doi:10.1074/mcp.m800516-mcp200

Uros Kuzmanov, Nianxin Jiang + Show 3 more

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https://doi.org/10.1074/mcp.m800516-mcp200

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Abstract

Ovarian cancer causes more deaths than any other gynecological disorder. Perturbed glycosylation is one of the hallmarks of this malignancy. Kallikrein 6 (KLK6) elevation in serum is a diagnostic and prognostic indicator in ovarian cancer. The majority of ovarian carcinomas express high levels of KLK6, which diffuses into the circulation. Under physiological conditions, KLK6 is expressed highly in the central nervous system and found at high levels in cerebrospinal fluid from where it enters the circulation. Our aim was to characterize and compare the N-glycosylation status of this protein in ovarian cancer ascites fluid and cerebrospinal fluid. Anion-exchange chromatography was used to reveal different post-translational modifications on the two isoforms. Mobility gel shift Western blot analysis coupled with glycosidase digestion showed that the molecular weight difference between the two isoforms was because of differential glycosylation patterns. The presence of a single N-glycosylation site on KLK6 was confirmed by site-directed mutagenesis. Using a Sambucus nigra agglutinin-monoclonal antibody sandwich enzyme-linked immunosorbent assay approach, it was shown that ovarian cancer-derived KLK6 was modified with alpha2-6-linked sialic acid. The structure and composition of glycans of both KLK6 isoforms was elucidated by glycopeptide monitoring with electrospray ionization-Orbitrap tandem mass spectrometry. Therefore, the extensive and almost exclusive sialylation of KLK6 from ovarian cancer cells could lead to the development of an improved biomarker for the early diagnosis of ovarian carcinoma.

Highlights

Ovarian cancer causes more deaths than any other gynecological disorder
Immunohistochemical and ELISA studies have shown that the major site of kallikrein 6 (KLK6) expression is the central nervous system (CNS), with very high levels of the protein detected in cerebrospinal fluid (CSF) [33,34,35]
Following the chromatography step, eluted fractions were analyzed for the presence of KLK6 by sandwich ELISA methodology

Summary

Introduction

Ovarian cancer causes more deaths than any other gynecological disorder. Perturbed glycosylation is one of the hallmarks of this malignancy. Altered sialylation of proteins in this disease is indicated by increased levels of the sialyl LewisX and sialyl-Tn antigens in ovarian carcinoma, even at early stages of progression [15, 17, 18]. This coincides with the findings showing disrupted sialyltransferase protein expression (19 –21) and altered mRNA expression of several sialyltransferases in ovarian cancer cells [22]. Immunohistochemical and ELISA studies have shown that the major site of KLK6 expression is the central nervous system (CNS), with very high (mg/liter) levels of the protein detected in cerebrospinal fluid (CSF) [33,34,35]. Kallikrein 6 N-glycosylation in Ovarian Cancer the major source of KLK6 in the circulation of normal individuals is the CNS

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