Lineage-specific modulation of calcium pump expression during myeloid differentiation.

Calcium is accumulated from the cytosol into the endoplasmic reticulum by sarco-endoplasmic reticulum calcium transport ATPase (SERCA) enzymes. Because calcium stored in the endoplasmic reticulum is essential for cell growth, differentiation, calcium signaling, and apoptosis and because different SERCA enzymes possess distinct functional characteristics, in the present report we explored SERCA expression during in vitro differentiation of the human myeloid/promyelocytic cell lines HL-60 and NB4 and of freshly isolated acute promyelocytic leukemia cells. Two SERCA species have been found to be coexpressed in these cells: SERCA 2b and another isoform, SERCAPLIM, which is recognized by the PLIM430 monoclonal antibody. Induction of differentiation along the neutrophil granulocytic lineage by all-trans retinoic acid or cyclic AMP analogs led to an increased expression of SERCAPLIM, whereas the expression of the SERCA 2b isoform was decreased. The modulation of SERCA expression was manifest also on the mRNA level. Experiments with retinoic acid receptor isoform-specific retinoids indicated that SERCA expression is modulated by retinoic acid receptor alpha-dependent signaling. SERCA expression of retinoic acid-resistant cell variants was refractory to treatment. Differentiation along the monocyte/macrophage lineage by phorbol ester resulted in an increased expression of both SERCA isoforms. In addition, when cells were treated by phorbol ester in the presence of the glucocorticoid dexamethasone, a known inhibitor of monocyte differentiation, a selective blockage of the induction of SERCAPLIM was observed. Altered SERCA expression modified the functional characteristics of calcium transport into the endoplasmic reticulum. These observations show for the first time that the modulation of calcium pump expression is an integral component of the differentiation program of myeloid precursors and indicate that a lineage-specific remodelling of the endoplasmic reticulum occurs during cell maturation. In addition, these data show that SERCA isoforms may serve as useful markers for the study of myeloid differentiation.