Abstract
During differentiation of human leukemic HL60 cells into granulocytes, sustained increases in intracellular pH and Na^+^/H^+^ antiporter activity have been observed. In the present study we report that retinoic acid (RA)‐induced granulocytic differentiation of HL60 cells causes an ∼18‐fold increase in the steady‐state mRNA levels for the Na^+^/H^+^ antiporter. This was due to an increase in the rate of Na^+^/H^+^ antiporter gene transcription as measured by nuclear run‐on analysis. Antiporter protein synthesis increased by seven‐fold during RA‐induced granulocytic differentiation of HL60 cells as measured by immunoprecipitation of ^35^S‐methionine‐labeled proteins with the RP1‐c28 Na^+^/H^+^ antiporter antibody. No increase in antiporter mRNA was observed in response to etretinate, an analogue of retinoic acid, which did not induce differentiation. Thus, Na^+^/H^+^ antiporter gene expression is associated with RA‐induced granulocytic differentiation of HL60 cells. The present findings and our previous data (Rao et al., 1991) demonstrate that Na^+^/H^+^ antiporter gene expression is a generalized feature of HL60 cell differentiation. © 1992 Wiley‐Liss, Inc.