CELL-CYCLE-DEPENDENT PROTEIN ACCUMULATION BY PRODUCER AND NONPRODUCER MURINE HYBRIDOMA CELL-LINES - A POPULATION ANALYSIS

Single-cells rates of accumulation of cellular protein have been determined as a function of total protein content using flow cytometry and population balance equations for exponentially growing murine hybridoma cells in the individual G1, S, and G2 + M cell cycle phases. A novel flow cytometric technique for the identification of hybridoma cells in mitosis was developed and implemented. The data were obtained from a producer cell line which synthesizes and secretes high levels of monoclonal antibodies, and from a nonproducer clone which does not synthesize and secrete substantial amounts of antibody. The results indicate that the kinetics of single-cell protein accumulation in these two cell lines are considerably different. In particular, low protein content G1 phase producer cells were characterized by a rate of protein accumulation which was approximately five times higher than the mean rate observed for higher protein content producer cells in this cell cycle phase. In contrast, the rate of accumulation of protein increased continuously with total protein content for the G1 phase nonproducer cells. S phase hybridoma cell were characterized by a considerably lower rate of protein accumulation which did not vary much with protein content for either cell line. Finally, G2 + M phase producer cells demonstrated a negative rate of protein accumulation which indicates that the rates of protein secretion and degradation exceed the rate of protein synthesis. It was hypothesized that these differences in total protein accumulation are caused by differences in monoclonal antibody accumulation. The distribution of rates suggests the need for a segregated approach to the modeling of the kinetics of antibody production in hybridomas.