Abstract
RP215 monoclonal antibody (Mab) was shown to recognize a carbohydrate-associated epitope of cancer cell-expressed glycoproteins, known as CA215. Extensive MALDI-TOF MS analysis was performed to search for the molecular identity of CA215. Besides immunoglobulin (Ig) heavy chains, homology to human T-cell receptors (TCR) and Ig-like cell adhesion molecules was also detected. By using RT-PCR and cDNA sequencing, it was observed that as many as 80% of cancer cell lines showed significant levels of gene expressions of TCR-α and TCR-β. Selected Ig-like cell adhesion molecules such as CD47, CD54, CD58 and CD 147 were also highly expressed among all the cell lines tested. In contrast, co-receptors and co-stimulators of TCR such as CD3, CD4 and CD8 were rarely expressed demonstrating the non-functional nature of TCR in cancer cells. Results of immunohistochemical staining and Western blot assays of cancer cell lines as well as cancerous tissue sections were consistent with these observations. Anti-TCR and anti-human IgG antibodies were shown to induce complement-dependent cytotoxicity and apoptosis of cultured cancer cells indicating the surface nature of Ig-like proteins. Based on these experimental observations, it was hypothesized that the expressions of these immunoglobulin superfamily (IgSF) proteins may be relevant to the immune protection and proliferations of cancer cells during carcinogenesis or cancer progression. Surface-bound TCR-like proteins as well as immunoglobulins may be the potential targets for RP215-based anti-cancer drugs.