Restored expression of vitamin D receptor and sensitivity to 1,25-dihydroxyvitamin D3 in response to disrupted fusion FOP2-FGFR1 gene in acute myeloid leukemia cells

Background: Acute myeloid leukemia (AML) cells can be induced to undergo terminal differentiation with subsequent loss of tumorigenicity using 1,25-dihydroxyvitamin D-3 (1,25D) alone or in combination with hematopoietic cytokines. KG1 cells are resistant to 1,25D-induced cell differentiation. These cells have the aberrant signal transduction resulting from a constitutively active fusion protein FOP2-FGFR1, a constitutively active STAT1 and a high level of interferon (IFN) stimulated genes (ISGs). Methods: In this paper we report that in KG1 cells with constitutively activated protein FOP2-FGFR1 delivery of plasmid DNA disrupted FOP2-FGFR1 fusion gene. Results: As a consequence, STAT1 signal transduction pathway became switched off, the expression of vitamin D receptor (VDR) gene was increased and sensitivity to 1,25D-induced differentiation was restored. The activation of ISGs in KG1 cells resulted in resistance to externally added IFNs, and also this effect was reversed in cells with disrupted FOP2-FGFR1 fusion gene. Discussion: In this paper we have documented for the first time a link between constitutively active STAT1 signal transduction pathway, high level of ISGs and low expression of VDR gene. Conclusions: We show in this paper that delivery of plasmid DNA to the cells may disrupt fusion gene FOP2-FGFR1 which occurs in a disease entity called 8p11 myeloproliferative syndrome. Inhibition of the FOP2-FGFR1 signal transduction pathway restored sensitivity of the cells to 1,25D-induced cell differentiation.