SERUM INCREASES THE CD13 RECEPTOR EXPRESSION, REDUCES THE TRANSDUCTION OF FLUID-MECHANICAL FORCES, AND ALTERS THE METABOLISM OF HL60 CELLS CULTURED IN AGITATED BIOREACTORS

The effects of serum medium concentration on the CD13 receptor surface content and mRNA levels of HL60 (human promyelocytic leukemia) cells were examined using flow cytometry and Northern blotting. Increasing t he serum concentration from 2.5% to 10% and from 5% to 10% increased t he CD13 receptor surface content of HL60 cells by 100% and 25%, respec tively, in spinner flasks agitated at 60 rpm. In bioreactors at 80 rpm , increasing the serum concentration from 2.5% to 10% and from 5% to 1 0% increased the CD13 receptor surface content by 60% and 35%, respect ively. This increase in CD13 receptor surface content was correlated w ith a 30% and a 20% increase in CD13 mRNA levels. Increasing serum con centrations also increased the average HL60 cell size under non-damagi ng conditions (60 rpm in spinner flasks, 80 rpm in bioreactors). Under conditions of agitation at 300 rpm in 2 L bioreactors, increasing ser um concentrations (2.5% vs. 10%, 5% vs. 10%) allowed for higher HL60 a pparent growth rates, but decreased the CD13 receptor surface content and mRNA levels. In view of our earlier findings on the effects of agi tation on the CD43 antigen, these data suggest that serum reduces the transduction of mechanical forces that affect CD13 expression. At 300 rpm, HL60 cells cultured in 10% serum exhibited glucose consumption an d lactate production rates that were approximately 50% and 60% lower t han the values of cells cultured in 5% and 2.5% serum, respectively. ( C) 1998 John Wiley & Sons, Inc.