Identification and partial characterization of a nucleolar antigen with a molecular weight of 145,000 found in a broad range of human cancers

Previous studies in our laboratory have indicated the presence of nucleolar antigens in tumors which were not detected in normal tissues. Some of the polyclonal antisera produced in these studies were shown to identify a Mr, 145,000 nucleolar antigen on immunoblots of tumor nucleoli but not in normal human liver nucleoli. A monoclonal antibody to a Mr 145,000 nucleolar protein (p145) was produced by immunization of mice with a nucleolar extract of HeLa cells which is enriched with this antigen. The monoclonal antibody showed bright nucleolar immunofluorescence localization in a broad range of human tumors including cancers of the gastrointestinal tract, genitourinary tract, lung, liver, muscle, cartilage, and blood. The p145 nucleolar antigen was not detected in most normal human tissues or in benign tumors, with only weak nucleolar staining observed in spermatogonia of the testes and in ductal regions of some hypertrophied prostates. Nucleolar antigen p145 was extracted from HeLa cell nucleoli by homogenization in a 0.01 M Tris buffer containing 0.2% deoxycholate. On sucrose density gradient centrifugation, the antigen remained sedimented with the nucleolar ribonucleoprotein fraction. Nucleolar antigen p145 was released from ribonucleoproteins following treatment with 4 M guanidinium hydrochloride or RNase. Peptide mapping of nucleolar antigen p145 showed that it was distinct from other known nucleolar antigens. Although it remains to be determined if the p145 antigen plays a role in cell transformation, maintenance of the malignant phenotype, or in cell division, it may have value as a tumor marker or as a therapeutic target.