Monoclonal antibodies to desmosomal glycoprotein I : their contribution to cancer diagnosis and protein structure studies

Vilela, Marcelo Jose (1989) Monoclonal antibodies to desmosomal glycoprotein I : their contribution to cancer diagnosis and protein structure studies. University of Southampton, Doctoral Thesis.

Abstract

Desmosomes are adhesive intercellular junctions present in almost all epithelia. Epithelial tissues can give rise to carcinomas which constitute 90% of all human cancers. The primary aim of this study was to raise a monoclonal antibody against desmosomal components, more specifically the desmosomal glycoprotein 1 (dg1), and to develop an epithelial marker for use in cancer diagnosis. This aim has been achieved with the production of 32-2B, a monoclonal antibody against dg1 which satisfies criteria for use as a pan-epithelial marker. The antibody works in paraffin embedded human tissues and might be useful in cancer diagnosis. It was shown that the epitope recognized by the antibody is present in a wide variety of tumours and is complementary to a widely used anti-keratin antibody, CAM-5.2 as, for example, it reacts strongly with squamous cell carcinomas. One of the main uses for 32-2B is in distinguishing poorly differentiated carcinomas from lymphomas. This antibody has been tested in a large number of tumours and normal tissues. It has now become commercially available and is being used in the histopathology departments of several hospitals. In experiments to investigate the localization of the epitope recognized by 32-2B monoclonal antibody using trypsinisation of live MDCK cells, it was found that the epitope is membrane protected and is presumably cytoplasmic. The size of the fragment bearing the epitope was found to be of 50 kD. Because of the discrepancy with previous data from other laboratories which propose a 90 kD for the cytoplasmic domain of dg1, another monoclonal antibody, 33-3D, was produced, and used in the present study. 33-3D showed the same specificity as 32-2B for dg1 isolated from bovine epidermal desmosomes, using one and two dimensional gel electrophoresis. However, 33-3D identified different bands in canine kidney cells and also a different sized cytoplasmic fragment. 32-2B and 33-3D also identified different bands in human keratinocytes and HN-5 cells, indicating that dg1 is heterogeneous in different species. There is currently controversy about this point in the literature but the results presented in this thesis support the view that dg1 is heterogeneous. In conclusion, there seems to be more than one molecular form of the desmosomal glycoprotein 1 with the same immunological characteristics, but the nature of this heterogeneity is not understood. Hypotheses concerning the structure of the molecule and the causes for its heterogeneity are discussed.

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