GLYCOSYLATION OF ALPHA-1-PROTEINASE INHIBITOR AND HAPTOGLOBIN IN OVARIAN-CANCER - EVIDENCE FOR 2 DIFFERENT MECHANISMS

The change in glycosylation of the two acute-phase proteins, alpha-1-proteinase inhibitor (API) and haptoglobin (Hp), in progressive ovarian cancer is different. This has been shown by monosaccharide analysis and lectin-binding studies of proteins purified from serum. In the glycan chains of API, there is decreased branching (more biantennary chains), less branches ending in alpha 2-3 sialic acid, more branches ending in alpha 2-6 sialic acid and more fucose, probably linked alpha 1-6 to the core region. On the other hand, Hp shows increased branching (more triantennary chains), more branches ending in alpha 2-3 sialic acid, less branches ending in alpha 2-6 sialic acid, and more fucose, probably in the alpha 1-3 linkage at the end of the chains. This is surprising because API and Hp are thought to be glycosylated by a common pathway in the liver. We have also shown that the fucose-specific lectin, lotus tetragonolobus, extracts abnormal forms of bath Hp and API in ovarian cancer, but the expression of this Hp is related to tumour burden and the expression of this API is related to lack of response to therapy. It is suggested that this difference in the behaviour of API and Hp in ovarian cancer may be associated with the different changes in their glycosylation. Of the many mechanisms that could explain these findings, a likely one is that a pathological process is removing API with triantennary chains from the circulation. In addition to their normal roles (API-enzyme inhibitor and Hp-transport protein) these proteins are reported to have many other effects in biological systems, such as immunosuppression. As correct glycosylation of API and Hp is required for their normal stability/activity, changes in glycosylation could affect their functions in ovarian cancer and these modifications could alter the course of the disease.