Changes in Na,K-ATPase gene expression during granulocytic differentiation of HL60 cells

During granulocytic differentiation of HL60 cells, immediate reduction of ouabain-sensitive potassium flux is observed within the first 12 hours of addition of dimethyl sulfoxide (DMSO). We show that gene expression of the α3 isoform of Na⁺,K⁺-ATPase, which encodes an ouabain-inhibitable Na⁺,K⁺-ATPase activity, significantly declines during the first 24 hours of granulocytic differentiation by DMSO of HL60 cells. The more common α1 isoform decreases, but more gradually over 72 hours of DMSO induction. Loss of α3 and α1 messenger RNA (mRNA) are due to changes in mRNA decay; their transcription is not altered. α3 mRNA half-life is 3 hours in HL60 cells; upon induction by 16 hours of DMSO, it decreases to approximately 2 hours. α1 transcripts are less sensitive to DMSO induction, with their half-life being 3.5 hours in HL60 cells; upon induction, their half-life decreases to 3 hours. Experiments measuring protein stability confirm that α3 protein is more labile than α1. In uninduced HL60 cells, α3 membrane protein comprises 30% of the total α isoforms, and is less stable than α1, with a protein half-life of only 9 hours. Upon DMSO induction, steady-state α3 protein decreases markedly within 10 hours, whereas α1 protein remains stable. These results show that posttranscriptional changes during induction play a major role in the differential regulation of α1 and α3 isoforms of Na⁺,K⁺-ATPase; regulation of the latter may be important for early granulocytic differentiation, or for one of the differentiated functions of mature granulocytes.