AML-1A and AML-1B regulation of MIP-1 expression in multiple myeloma

Macrophage inflammatory protein-1 (MIP1 ) is produced in high concentration by multiple myeloma (MM) cells in about 70% of patients, and MIP-1 levels correlate with their disease activity. Patients who have high levels of MIP-1 have a poor prognosis. Furthermore, blocking MIP-1 expression in an in vivo model of human MM profoundly decreases both tumor burden and bone destruction, suggesting that MIP-1 is an important mediator of MM bone disease. Therefore, to analyze the regulation of MIP-1 production in MM, we cloned the human MIP-1 promoter and characterized the transcription factor (TF) motifs that control MIP-1 expression in MM cells. The proximal region of MIP-1 promoter was composed of 2 sets of identical transcription regulatory regions consisting of GATA-2 AML-1 C/EBP motifs. Since 2 alternatively spliced variants of the acute myeloid leukemia-1 (AML-1) class of TFs can bind the AML-1 region, AML-1A and AML-1B, the relationship between the expression levels of AML-1A or AML-1B in MM cells and their capacity to express MIP-1 was examined. AML-1A mRNA was relativelyoverexpressedcomparedwithAML-1B in MM cell lines that produced high levels of MIP-1 (> 1 ng/mL per 106 cells per 72 hours), but AML-1A was not increased in MM cell lines that expressed less than 200 pg/mL MIP-1 . More importantly, the ratio of AML-1A to AML-1B mRNA levels was also increased in 3 of 3 highly purified myeloma cells from patients with MM who expressed increased amounts of MIP-1 . The ratio of AML-1A to AML-1B mRNA in patients with MM was 8-fold higher than in healthy controls. Transduction of AML-1B into the MMderived MM.1S and ARH-77 cells totally blocked MIP-1 production, while AML-1A did not further increase the already high levels of MIP-1 produced by these cells. Taken together, these data demonstrate that in patients with MM who produce increased concentrations of MIP-1 , the relative level of AML-1B is significantly decreased compared with healthy controls. The data suggest that strategies that enhance AML-1B expression or decrease AML-1A in MM cells may be beneficial therapeutically. (Blood. 2003;101:3778-3783)