Structures of disease-specific serum alpha-fetoprotein isoforms

Abstract

Alpha-fetoprotein (AFP) is widely used as a serological marker in the diagnosis of hepatocellular carcinoma (HCC) and non-seminomatous germ cell tumours (NSGCT). By application of isoelectric focusing (IEF) disease-specific AFP isoforms can be identified. Three major bands are apparent: + l (associated with ‘benign’ liver disease), + II (associated with HCC) and +III (associated with NSGCT). Recently, we have characterized the predominant glycans of human serum AFP and now report the application of these findings and electrospray ionization-mass spectrometry (ESI-MS) to the determination of the glycan composition of the isoforms present in the sera of 12 patients with HCC and of one patient with NSGCT. ESI-MS allowed simultaneous identification of various AFP glycoforms in purified serum AFP. Seven glycoforms were identified, but with different abundance in the sera of the HCC patients, whereas six glycoforms were identified in the serum from the NSGCT patient. The glycan structures of these glycoforms were deduced from their observed masses. AFP glycoforms carrying a single biantennary complex-type N-glycan appeared as the predominant glycoforms, whereas those carrying both N-glycan and O-glycan appeared as minor glycoforms. Correlation between the abundance of the AFP glycoforms and the IEF band intensity suggested that different degrees in sialylation cause the formation of isoforms. This contention was subsequently supported by the ESI-MS and kinetic in vitro desialylation studies on purified Bands + l and + lI AFPs. Our findings indicate that HCC-associated isoforms (Band + II) represent a group of glycoproteins whose carbohydrate structures are all characterized by being mono-sialylated, whereas those associated with benign liver disease and NSGCT are di- and a-sialo species, respectively. Knowledge of the structure of the tumour-specific isoforms should form an important basis for clinically useful assays. © 2000 Cancer ResearchCampaign

Mapping of Structure-Function Peptide Sites on the Human Alpha-fetoprotein Amino Acid Sequence

“…A well-characterized activation signal for regulated secretion by T-cells (cytokines, granzymes, etc.) is engagement of the Tcell receptor (TCR) by peptides bound to MHCs on the surface of APCs during T-cells activation (Johnson et al, 2000) (Figures 3, 4). In a similar fashion, the MHC class II proteins encompass a great variety of proteins that serve to present antigenic peptides to CD4(+) helper T-cells (Kawai, 2007).…”

Lectin Capture Strategies Combined with Mass Spectrometry for the Discovery of Serum Glycoprotein Biomarkers

“…In HCC and in testicular cancer, the glycosylation of AFP shifts from a simple biantennary glycan to an ␣-1,6-linked core fucosylated biantennary glycan. These changes have been observed by both direct glycan sequencing of AFP and by increased reactivity of AFP with a variety of lectins that preferentially bind to fucose-containing glycan (41). The glycoform of AFP that reacts preferentially with the lectin Lens culinaris hemagglutinin (LCH) is referred to as AFP-L3, and it has been characterized as being a more specific marker of HCC than total AFP protein levels (68 -70).…”

Role of sialyltransferases involved in the biosynthesis of Lewis antigens in human pancreatic tumour cells

“…Changes in sialic acid content can also be observed in tumour-secreted glycoproteins. This is the case for α-fetoprotein [4], human pancreatic ribonuclease [5] or prostate specific antigen [6].…”