CDK1 IS A MARKER OF PROLIFERATION IN HUMAN LYMPHOID-CELLS

To better understand the relationship between the proliferation of hum an lymphoid cells and the expression of cdk1, a catalytic subunit of t he histone HI kinase (HIK), we examined its mRNA and protein content i n 3 B-cell lines: Ramos, Reh-6 and IARC 963. Cells were elutriated acc ording to their position in the cell cycle. Cell fractions were analyz ed for cdk1 mRNA and protein cellular content by Northern blot and imm unoblot, respectively, as well as for HIK activity, Both mRNA and prot ein amounts and HIK activity varied according to cell cycle phase, the lowest values being observed in G(1)-enriched fractions. par comparis on, elutriated fractions were also tested for the expression of cdk2 a nd cdk4 proteins. Both showed some variations among fractions, but the y were less clear than those of cdk1. We also tested 29 samples of lym phoid neoplastic and non-neoplastic tissues far proliferative activity (percentage of S and G(2)/M cells estimated by flow cytometry) and ex pression of cdk1, cdk2 and cdk4 proteins, We found a significant corre lation between the percentage of cells in S or S + G(2)/M phases and c dk1 protein content but not cdk2 or cdk4 content. We conclude that cdk 1 expression in human lymphoid cells varies during the cell cycle at b oth mRNA and protein levels. (C) 1995 Wiley-Liss, Inc.