KBP-1 Supports Acute Myeloid Leukemia Development

Novel targets are needed to develop effective therapeutic approaches to treat acute myeloid leukemia (AML). We have developed a systematic strategy to identify factors important for leukemia development. We first use clinical databases to identify plasma membrane proteins that have correlations with the clinical outcomes of leukemia patients. We then validate the functions of candidate proteins in leukemia models and compare these functions to those in normal cells. The signaling pathways identified provide candidate targets for development of therapeutic approaches. Using this approach, we previously identified several ITIM-containing receptors that support AML development.

Here we performed an in silico analysis of the relationship between gene expression and the overall survival of AML patients using data from three independent databases: the TCGA AML database (https://tcga-data.nci.nih.gov/tcga/; n = 187), the GSE6891 database (n = 520), and the GSE10358 database (n = 91). Expression of genes encoding several factors, including IL2RA, GPR56, ACDY7, and kappa-binding protein -1 (KBP-1), inversely correlated with the overall survival of AML patients. We focused on the potential function of KBP-1 in AML development in this study.

KBP-1 is a transcriptional regulator that was known to inhibit NF-kB signaling and enhance TGF-beta signaling. Previous studies indicated that KBP-1 inhibits teratoma growth. We detected significantly higher kbp-1 mRNA levels in cells from human AML cells than other leukemia cells. To study the potential function of KBP-1 in human leukemia, we inhibited the expression of KBP-1 by introducing lentivirus-encoded shRNAs into MV4-11 and THP-1 cells. The KBP-1 deficiency resulted in significantly decreased in vitro growth of these leukemia cells over time. To determine the underlying mechanism by which KBP-1 supports the growth of leukemia cells, we compared the cell cycle status, migration, and apoptosis of AML cells treated with these shRNAs or scrambled control shRNA. KBP-1-deficient cells had significantly increased levels of apoptosis compared to cells treated with the control shRNA (for example, 68% early apoptosis in KBP-1 knockdown MV4-11 cells vs 15% early apoptosis in control MV4-11 cells at 3 days after shRNA infection). These results indicate that KBP-1 supports leukemia cell growth by suppressing apoptosis.

We further studied the function of KBP-1 in AML development using the KBP-1 knockout mice and retrovirus transplantation mouse models. Consistent with the results of KBP-1 knockdown in human leukemia cells, the knockout of KBP-1 in MLL-AF9 AML cells dramatically delayed AML development in mice, as determined by survival, flow cytometry, immunohistochemistry, and colony forming analyses. Serial transplantation of wild-type and KBP-1 knockout AML cells indicates that KBP-1 deficiency impaired the self-renewal of AML stem cells. We are working on elucidating the underlying mechanism by which KBP-1 supports the activity of AML stem cells. Together, this is the first demonstration of KBP-1 function in hematopoietic maligancies. KBP-1 is highly expressed by AML cells and its expression correlates with AML development. KBP-1 supports the survival of human AML cells and the activity of AML stem cells. The tumor-supportive role of KBP-1 in AML is different from its tumor-suppressive function in teratoma.