1,25-DIHYDROXYVITAMIN D-3 SELECTIVELY INDUCES INCREASED EXPRESSION OFTHE NA,K-ATPASE BETA-1 SUBUNIT IN AVIAN MYELOMONOCYTIC CELLS WITHOUT A CONCOMITANT CHANGE IN NA,K-ATPASE ACTIVITY

Treatment of avian myelomonocytic cells with 1,25-dihydroxyvitamin D-3 (1,25(OH)2D3) results in an approximately two fold increase in levels of Na,K-ATPase beta 1 subunit mRNA and protein (both total and plasma membrane-associated). The changes in beta 1 subunit expression occur in the absence of a detectable increase in expression of any of the th ree alpha subunit isoforms or in Na,K-ATPase activity. The selective i nduction of the expression of the beta subunit in avian myelomonocytic cells by 1,25(OH)2D3 reveals a previously unobserved feature of the r egulation of Na,K-ATPase expression, while the targeting of beta subun it polypeptides to the plasma membrane in the absence of a correspondi ng increase in active Na,K-ATPase suggests that, in these cells, trans port of the beta subunit to the plasma membrane may be independent of its binding to the alpha subunit. (C) 1997 Wiley-Liss, Inc.