NUCLEOLIN AND FIBRILLARIN EXPRESSION IN STIMULATED LYMPHOCYTES AND DIFFERENTIATING HL-60 CELLS - A FLOW CYTOMETRIC ASSAY

Nucleolin and fibrillarin are two histone-like major proteins in the n ucleolus that were found to be overexpressed in proliferating cells. U sing specific antibodies to either nucleolin or fibrillarin flow cytom etric, measurements were carried out to demonstrate quantitative chang es of these proteins during lymphocyte mitogenic activation and differ entiation of HL-60 promyelocytic leukaemia cells. The expression of nu cleolin increased during lymphocyte stimulation and decreased slowly b ut constantly in the course of differentiation of HL-60 cells. Express ion of fibrillarin reached a maximum in the first cell cycle and then dropped to a basic level in stimulated lymphocytes. Compared to nucleo lin, the level of fibrillarin decreased more rapidly and more extensiv ely in differentiating HL-60 cells. The data support other observation s that nucleolin is a stabile structural protein at the ribosomal gene s while fibrillarin may have a more specific functional role in nucleo logenesis and ribosome production.