Mitochondrial antisense RNA for cytochrome C oxidase (MARCO) can induce morphologic changes and cell death in human hematopoietic cell lines.

To identify essential molecules capable of inducing terminal morphologic maturation and cell death of myeloid progenitor cells, we isolated cDNA clones by functional expression cloning using a library constructed from all-trans retinoic acid (ATRA)-treated human promyelocytic HL-60 cells. Clones which induced morphologic changes in HL-60 cells from blastic cells to mature neutrophilic granulocytes were selected. The isolated positive cDNA clone was demonstrated to encode an antisense RNA for cytochrome c oxidase/serine tRNA derived from a mitochondrial gene (MARCO). When MARCO was expressed in HL-60 cells with the lac switch system, blastic cell morphology became neutrophilic after 48-hour incubation with IPTG, and cell death was observed after 3 days. Also, high molecular weight DNA fragmentation was observed after 36 hours in culture. Similar results were observed using transformants from human K562 cells and CMK cells. RT-PCR analysis revealed that MARCO was transcribed in both ATRA and TNF-alpha systems, and also in human blood neutrophilic granulocytes. Following transfection with cytochrome c oxidase expression plasmids, TNF-alpha-induced high molecular weight DNA fragmentation in U937 cells and HL-60 cells was inhibited in these transformants. These results indicate that maturational changes in hematopoietic cells and the process of cell death may be induced by mitochondrial respiratory insufficiency, and also that the mitochondrial gene MARCO may be used as one of the candidates for gene supplementation therapy for the acute leukemias.