EFFECT OF 5637-CONDITIONED MEDIUM AND RECOMBINANT CYTOKINES ON P-GLYCOPROTEIN EXPRESSION IN A HUMAN GM-CSF-DEPENDENT LEUKEMIC MYELOID CELL-LINE

This study was aimed at evaluating the influence of 5637-conditioned m edium (5637-CM) and human recombinant cytokines on both expression and function of P-glycoprotein (P-gp) in TF-1, a GM-CSF/IL-3-dependent ac ute myeloid leukemia cell line which constitutively expresses function al P-gp. P-gp expression was measured by flow cytometry using MRKI6 mo noclonal antibody. P-gp function was measured by rhodamine 123 (Rh 123 ) efflux kinetics. When TF-1 cells were cultured with 5637-CM (50% v/v ), both P-gp expression and P-gp efflux capacity were increased in a t ime-dependent manner with a 4-fold increase in P-gp expression level a t day 6 whereas TF-1 cell differentiation status remained unchanged as assessed by morphological studies, phenotypical and cytochemistry ana lysis. Recombinant cytokines including GM-CSF, G-CSF, IL-1 beta, IL-6, stem cell factor, LIF, erythropoietin, and IL-3 had no effect on P-gp expression whereas TNF alpha induced dose- and time-dependent P-gp an d mdr-1 gene overexpression. However, TNF alpha-induced P-gp overexpre ssion had no influence on P-gp efflux capacity. Furthermore, when TF-1 cells were exposed to IL-3 for periods longer than 1 month, we found that P-gp efflux capacity was increased as compared to cells cultured with GM-CSF whereas P-gp expression was unchanged. Both TNF alpha and IL-3 did not induce TF-1 differentiation. Collectively, these results suggest that cytokines may influence both expression and function of P -gp in TF-1 cells without interfering with their differentiation statu s. In contrast to cytokines, phorbol esters enhanced expression and ef flux capacity of P-gp in parallel with TF-1 cell monocytic differentia tion. Finally, our study suggests that paracrine and/or autocrine secr etion of cytokines may interfere with P-gp activity in some acute myel oid leukemia cells.