PHORBOL ESTERS INDUCE DIFFERENTIATION IN A PRE-LYMPHOCYTE-B CELL-LINE BY ENHANCING NA+/H+ EXCHANGE

Abstract

The murine pre-B-lymphocyte cell line 70Z/3 may be induced to differentiate to a surface Ig-positive phenotype by the polyclonal B-cell mitogen, lipopolysaccharide. This is accomplished via activation of an amiloride-sensitive Na+-uptake system. The active tumor promoter 12-O-tetradecanoylphorobol 13-acetate (TPA) also induces surface IgM expression in 70Z/3 cells. TPA also appears to work by activating a plasma membrane Na+/H+ exchange system. A significant increase in cellular Na+ was detected within 10 min after TPA addition and by 2 h an 80% increase was observed. Amiloride blocked both the induction of surface IgM and the increase in cellular Na+. Both TPA and lipopolysaccharide activate Na+/H+ exchange, as demonstrated by measurements of intracellular pH with carboxyfluorescein. Both TPA and lipopolysaccharide caused a 0.15 U increase in cytoplasmic pH within 5 min after addition to the cells at 37.degree. C. The pH change required high extracellular Na+ and was inhibited by amiloride. A mechanism is suggested by which phorbol esters affect cellular growth and differentiation.