Sera from 25 metastatic
breast cancer patients and 25 healthy controls were subjected to affinity chromatography using immobilized
galectin-1. Serum from the healthy subjects contained on average 1.2 mg per ml (range 0.7-2.2)
galectin-1 binding
glycoproteins, whereas serum from the
breast cancer patients contained on average 2.2 mg/ml (range 0.8-3.9), with a higher average for large primary tumours. The major bound
glycoproteins were α-2-macroglobulin,
IgM and
haptoglobin. Both the
IgM and
haptoglobin concentrations were similar in
cancer compared to control sera, but the percentage bound to
galectin-1 was lower for
IgM and higher for
haptoglobin: about 50% (range 20-80) in
cancer sera and about 30% (range 25-50) in healthy sera.
Galectin-1 binding and non-binding fractions were separated by affinity chromatography from pooled
haptoglobin from healthy sera. The N-
glycans of each fraction were analyzed by mass spectrometry, and the structural differences and
galectin-1 mutants were used to identify possible
galectin-1 binding sites.
Galectin-1 binding and non-binding fractions were also analyzed regarding their
haptoglobin function. Both were similar in forming complex with haemoglobin and mediate its uptake into alternatively activated macrophages. However, after uptake there was a dramatic difference in intracellular targeting, with the
galectin-1 non-binding fraction going to a LAMP-2 positive compartment (lysosomes), while the
galectin-1 binding fraction went to larger
galectin-1 positive granules. In conclusion,
galectin-1 detects a new type of functional
biomarker for
cancer: a specific type of glycoform of
haptoglobin, and possibly other serum
glycoproteins, with a different function after uptake into tissue cells.