Identification and Partial Characterization of a Mr 105,000 Nucleolar Antigen Associated with Cell Proliferation1

This study reports the identification and partial characterization of a novel M, 105,000 nucleolar antigen (P105) identified by a monoclonal antibody. This monoclonal antibody was obtained when a nucleolar protein extract separated from the immunodominant protein C23 was used as the immunogen. Nucleolar antigen PI 05 was not detected in normal (resting) human liver, kidney, or peripheral blood lymphocytes but was present in a variety of human malignant cells and tissues. Lymphocyte nucleoli also exhibited specific P105 staining after 72 h of phytohemagglutinin stimulation. Nucleolar antigen P105 was detected in growing and dividing ML 60 cells but was not detected in retinoic acidinduced differentiated HL 60 cells. When I lei .a cells were made quiescent by 48 h of serum starvation, the PI 05 antigen was not detected, but after refeeding with serum-containing medium, the antigen P105 was detected in the lÃ-ela nucleoli within 2 h. These results indicate that nucleolar antigen P105 is a proliferating cell nuclear and nucleolar antigen-like molecule which appears early in the ( ;,-S phase of the cell cycle.