THE ASSOCIATION OF EXPRESSION OF A NOVEL CYCLOPHILIN WITH SUPPRESSED GROWTH AND DIFFERENTIATION OF THE MYELOID LEUKEMIA CELL LINE HL-60

Abstract

Using a newly developed anti-peptide monoclonal antibody, the expression of a novel cyclophilin-like molecule, NK-TR1, in the differentiation of HL-60 promyelocytic leukemia cells was characterized. NK-TR1 was identified in peripheral blood monocytes stimulated with lipopolysaccharide (LPS) and interferon gamma (IFN-y). Unstimulated monocytes demonstrated a low but detectable intracellular level of NK-TR1 protein that increased over 3 days of LPS and IFN-y treatment consistent with the kinetics of monocyte differentiation. Similarly, while the intracellular level of NK-TR1 in untreated promyelocytic HL-60 was low, exposure to 1.2% dimethyl sulfoxide (DMSO), an inducer of granulocytic differentiation, resulted in a marked transient increase in expression that returned to basal levels before the development of differentiation-associated biochemical changes. Phorbol myristate acetate, a promoter of monocytic differentiation, also caused a marked increase in NK-TR1 expression over basal levels. Transfection of NK-TR1 antisense cDNA into HL-60 cells suppressed DMSO-mediated growth arrest. In addition, maturation of HL-60 cells to a more mature phenotype as measured by expression of CD16 and the ability to reduce nitroblue tetrazolium dye was clearly diminished in antisense transfectants when compared to controls. These results are consistent with the hypothesis that the NK-TR1 gene product is serving as an important mediator in a signaling pathway initiated by differentiation agents.