Dual Differential Roles of Cancerous Immunoglobulins as Suggested by Interactions with Human Serum Proteins

Abstract

In search of functional roles of immunoglobulins expressed by cancer cells, molecular interactions between cancerous immunoglobulins and human serum proteins or protein fragments were investigated by using RP215 monoclonal antibody as the unique probe. RP215 was initially generated against OC-3-VGH ovarian cancer cell extract and shown to react with carbohydrate-associated epitope located mainly on the variable regions of immunoglobulin heavy chains and others expressed by cancer cells which are designated in general as CA215. CA215 and cancerous immunoglobulins (cIgG) were affinity isolated from the shed medium of cultured cancer cells. Furthermore, by using purified CA215 and cIgG as the respective affinity ligands, the serum proteins or components were affinity isolated and subject to analysis by LCMS/MS methods. The results of such analysis suggest that as many as 80-86% of the isolated human serum proteins were identical in those purified by either affinity column. They are generally classified as pro-cancer and anti-cancer protein components. Among the known pro-cancer protein components recognized by cancerous immunoglobulins are C4 binding proteins α-chain, complement C3, complement factor H, serotransferrin and vitronectin, etc. On the other hand, inter-α-trypsin inhibitor heavy chain 4, anastellin, apolipoprotein A1, fibrinogen β-chain and keratin type 1 cytoskeletal 9 or autoimmune IgG were considered to be anti-cancer proteins from human serum. Based on these observations, dual functional roles of cancerous immunoglobulins are hypothesized. It has been demonstrated in this study that cancerous immunoglobulins are capable of serving as specific binding protein-like immunoglobulins to capture serum proteins to promote growth of cancer cells. At the same time, they can neutralize those with anti-cancer properties in human circulations.