P-252: Critical roles of LILRB4 in promoting STAT3/PIM1 mediated metabolism in multiple myeloma

Introduction: Multiple myeloma (MM) is the second most common hematologic malignancy. Although multiple targets on MM cells are discovered and applied in clinical treatment, relapse is almost inevitable in MM patients. In our previous study, a high-risk cell cluster was found from MM patients with overall survival less than 2 years by single-cell RNA sequencing (scRNA seq). In this specific cluster, LILRB4 was highly expressed, indicating the critical role of LILRB4 in myelomagenesis and drug resistance. However, the mechanisms of LILRB4 in MM development has not been fully understood. Here, we investigated the role of LILRB4 in tumorigenesis and MM cell proliferation.

Methods: N/A

Results: Methods and results
Our clinical data showed that MM patients with LILRB4 overexpression had poor prognosis and decreased overall survival. Compared with newly-diagnosed MM patients, expression of LILRB4 was higher in the MM patients relapsed after treatment, indicating the critical role of LILRB4 in MM progression and drug resistance. In vitro experiment showed that MM cells with LILRB4 overexpression enhanced the cell colony-forming ability and promoted cell proliferation. Conversely, knocking-out LILRB4 induced cell apoptosis. We used MM cells that overexpressed LILRB4 to establish myeloma xenograft model and results showed that compared with LILRB4^neg MM cells, mice injected with LILRB4^high MM cells displayed higher tumor formation rate and lower survival rate. Then, we analyzed RNA-seq data to investigate the mechanisms of LILRB4 in MM proliferation. Transcriptome analysis indicated that overexpression of LILRB4 in MM cell lines activated NF-kB, glycolysis, hypoxia and MTORC1 signaling pathways. Among these, NF-kB pathway has been proved in previous studies. More important, RNA-seq data suggested the upregulation of PIM1 in MM cells with LILRB4 overexpression, which has been confirmed in our in vitro experiments. We also found that LILRB4 upregulated the expression of PIM1 through activating SHP2 and STAT3, indicating the underlying mechanism of MM cell proliferation. In addition, in our RNA-seq data, MM cells with LILRB4 overexpression exhibited the enrichment of fatty acid metabolism genes. Interestingly, we found that the amount of lipid droplet increased significantly in LILRB4 overexpressed MM cells as well as the uptake of fatty acid, indicating the correlation between LILRB4 and fatty acid metabolism reprogramming.

Conclusions: In conclusion, LILRB4 is highly associated with poor prognosis of MM patients and has the ability of tumorigenesis. LILRB4 promotes MM cell proliferation by activating SHP2 and STAT3 to upregulate the expression of PIM1, which plays critical roles in MM pathogenesis.