Immunodetection of squamous cell carcinoma-associated variant of nuclear protein

A new monoclonal antibody, MAb C63.3, was developed by immunizing mice with the high molecular weight fraction of the cytoplasmic proteins from the cervical squamous cell carcinoma. In Western blotting, MAb C63.3 reacted with cytoplasmic and chromatin antigens expressed by cervical and vulvar squamous cell carcinomas and much weaker with normal cervical tissue and skin cells. Different molecular variants of C63.3 chromatin antigens were found in normal tissues (heavy variants, M(r) 65,000 and 59,000) compared to squamous cell carcinomas (light variant, M(r) 48,000). Diagnostic value of the cancer-associated M(r) 48,000 antigen is discussed. MAb C63.3 was internalized by cells and bound to the chromatin which suggests that antigen(s) C63.3 might represent a receptor for a yet unknown ligand (growth factor). It is suggested that the high molecular weight C63.3 antigens play a role in maintaining the nonmalignant phenotype.